Venus-Technology-Plan

DRAFT

Venus Technology Plan DRAFT December 2018

Venus Technology Plan DRAFT

The Venus Exploration Analysis Group (VEXAG) resolved to update the scientific priorities and strategies for Venus exploration. To achieve this goal, three major tasks were defined to update: (1) the document prioritizing Goals, Objectives and Investigations for Venus Exploration: (GOI), (2) the Roadmap for Venus Exploration (RVE) that is consistent with VEXAG priorities as well as Planetary Decadal Survey priorities, and (3) the Technology Plan for future Venus missions. Here, we present the 2018 Venus Technology Plan.

Prepared by the VEXAG Focus Group on Technology and Laboratory Instrumentation: Gary Hunter (Chair), Jeffery Balcerski, Samuel Clegg, James Cutts, Candace Gray, Noam Izenberg, Natasha Johnson, Tibor Kremic, Lawrence Matthies, Joseph O'Rourke, and Ethiraj Venkatapathy.

TABLE OF CONTENTS 1.0 Executive Summary ...... 1 2.0 Overview ...... 5 3.0 Venus Exploration Challenges ...... 6 4.0 Technology Plan Overview ...... 8 5.0 System-Level Capabilities ...... 14 6.0 Subsystem Technologies ...... 26 7.0 Instruments ...... 32 8.0 Infrastructure Overview ……………………………………………………………………...36 9.0 Technology Highlights Since 2014…………………………………………………………37 10.0 Findings ...... 39 11.0 Acronyms and Abbreviations ...... 42 12.0 References ...... 46

VEXAG Charter. The Venus Exploration Analysis Group (VEXAG) is NASA's community-based forum designed to provide scientific input and technology development plans for planning and prioritizing the exploration of Venus over the next several decades. VEXAG is chartered by NASA's Planetary Science Division in the Science Mission Directorate (SMD) and reports its findings to NASA. Open to all interested scientists, VEXAG regularly evaluates Venus exploration goals, scientific objectives, investigations, and critical measurement requirements, including especially recommendations in the NRC Decadal Survey and the Solar System Exploration Strategic Roadmap.

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VENUS TECHNOLOGY PLAN

1.0 Executive Summary The planet Venus, with its unique environment, presents unusual challenges for planetary exploration.A number of scientifically important missions could be implemented with existing technology although some may involve engineering development. New mission paradigms and technologies are emerging. More ambitious missions would require significant investments and maturation of new technologies; however, in some cases, these new technologies could leverage recent technology advances and commercial developments. A potential Venus exploration technology program includes a balance of investments in missions for the short term and technology investments enabling new paradigms and more ambitious missions that could be conducted. The following findings are based on the work discussed within this document, studies conducted after the previous Technology Plan, and additional responses from members of the VEXAG community. The findings are grouped into three categories: Technology Development, and Infrastructure Development, and General.

Technology Development 1. Entry Technology for Venus: Successful delivery of HEEET at TRL 6, has eliminated one of the critical technology gap identified in 2014 for in-situ Venus missions. HEEET and PICA are two NASA developed technologies that provide broad cover for a large class of Venus in-situ missions. Given in-situ mission cadence to Venus is bound to remain low and unpredictable, these capabilities must be maintianied. It is critical the SMD-PSD ensure the entry technology capability does not atrophy, and that periodic assessment and small investments be made to ensure both HEEET and PICA continue to be available.

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atmospheric composition, cloud particle size /composition, atmospheric structure, and geophysics. Development of these aerial platform technologies is an enabling capability. 4. In Situ Instruments for Landed Missions: In Situ Instruments for Landed Missions: Advances in capabilities in instrumentation for other planetary applications will continue to have strong impact on the corresponding capabilities for Venus landers. However, in some cases, implementation of these instrument systems for Venus specific applications can be challenging given, e.g., increased complexity in sample handling related to short lived Lander Missions. Further, while leveraging instrument development from other planetary applications has its role, development of specific instruments meeting unique Venus science needs is necessary. The adaptation of flight demonstrated technology to Venus applications and the development of new instrument systems uniquely targeted to the Venus environment should continue to be supported. 5. Venus Communications and Navigation Infrastructure: The establishment of a low cost orbiting communication platform infrastructure at Venus for the support of in situ exploration would be an enabling foundation for future Venus exploration. Such an infrastructure would be based on the advancement of smallsat and cubesat technology and as such can be implemented at much lower cost than the Mars orbital infrastructure. Such orbiters could also aid position estimation for aerial platforms when the aerial platforms are out of sight of Earth- based tracking stations. As with Mars, the orbiters would also conduct independent science measurements. Study of the feasibility of and methods for establishing such a communications and navigation infrastructure is recommended. 6. Advanced Cooling Technology for Long-Duration Surface Operations: Current passively cooled systems are limited to a lifetime of 3 to 5 hours with possible extension to 24 hours. Highly efficient mechanical thermal conversion and cooling devices (typified by the Stirling cycle-engines and capable of operating in a 460oC environment) are required for this purpose. With lifetimes of months, these are enabling for the Venus mobile surface and near-surface laboratory mission concepts. Investments in advanced cooling technology have been limited and are needed to enable future missions. 7. Advanced Descent and Landing: Lander mission proposals have begun to Tessearae regions of Venus, which radar imaging indicates to be extremely rough and irregular topography. In the near term, this uses unguided descent with large landing ellipses and hazard tolerant landing systems to cope with rocks and steep slopes. To enable targeting smaller ellipses or rougher terrain beyond the near term requires developing techniques for improved targeting accuracy, potentially accompanied by hazard avoidance during the terminal descent phase. Probes and sondes with surface imaging capability may also benefit from descent guidance. New concepts are needed for adapting precision descent and landing hazard avoidance technologies to operation in the dense, hot Venus atmosphere. 8. Autonomy and Automation: Increasing capabilities for automation and autonomous decision-making combined with increasing computing power can change the way missions are conducted. Leveraging development in these fields can enhance the science delivered across a range of possible mission scenarios from orbital, aerial, to landed and to exploit synergies between data acquired from the different platforms. Efforts to transition automation and autonomous technologies to Venus specific applications would enhance science delivered and mission success. 9. Small Platforms: SmallSat, CubeSat and other small platform technology can make important contributions to Venus exploration. Orbiters and in situ aerial vehicles using

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this technology can make important scientific contributions, while small platforms lander systems can open new possibilities in Venus explorations. These small platforms can complement the more traditional concepts of Venus mission design with an unique niche in Venus exploration. The development of small platform concepts as an addition to larger missions, as well as a new mission type or mission augmentation, is an integral part of a complete multistage Venus exploration program.

Infrastructure Development 1. Infrastructure Development: As seen in Section 8.0, significant progress has been made in the establishment of a range of facilities and capabilities across multiple organizations to not only develop instrumentation and flight systems, but also conduct Venus science. The type of infrastructure needed will also evolve as new technologies, such as autonomy, begin to have a role in mission planning. Infrastructure is a major resource that should continue to be supported and expanded in a manner that meets the evolving needs of the broad Venus community. 2. Environmental Modelling and Simulation: There is there is a strong need for a system science approach to Venus modeling including coupling of different models, e.g. interior models coupled to surface models. Further, laboratory data is needed to provide improved input to these models. Establishing and maintaining such a broad but interdependent infrastructure is strongly recommended.

General 1. Uniqueness of Venus Technology Needs: Technology development and infrastructure to enable new science capabilities is a foundation for future Venus exploration. The introduction of the High Temperature Operating Technologies (HOTTech) Program targeted toward advances in Venus surface technologies is enabler for such Venus exploration. Further development of targeted component technologies as well as subsystem/system capabilities is encouraged. PSD should continue and expand support for programs such as HOTTech, and identify where joint sponsorship and dual use development can be leveraged in, e.g., the implementation of small platforms and autonomous systems, that would result in new mission capabilities. 2. Maintain Facilities and Capabilities: Since NASA does not maintain, manage, or actively assess availability of critical and NASA unique technologies for future missions, changes to industrial capability has the potential to curtail or limit NASA to plan for and execute Venus in-situ missions. Active awareness of the current and future availability of critical technologies, especially those that NASA has developed and transferred to industry such as ablative TPS for Venus missions, periodic assessment of the risk of atrophy, and plans that might mitigate the risk and ensure future availability are steps that can be taken. It is recommended that NASA take steps to manage the risk of atrophy of needed facilities and capabilities. . 2.0 Overview This is the fourth in a series of three documents prepared by the Venus Exploration Analysis Group (VEXAG) to provide NASA’s Planetary Science Division with the a basis for formulating a

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strategic direction for future Venus exploration. The Venus Goals, Objectives, and Investigation document [1] establishes the scientific goals for Venus exploration, and it prioritizes the objectives and investigations needed to address those goals. The Roadmap for Venus Exploration (RVE) [2] translates these objectives into mission modes that can most effectively address the objectives and implement the investigations. The RVE also re-examines the recommendations in the Planetary Science Decadal Survey [ 3 ] to provide an assessment of the state of technical readiness for implementing missions using these different mission modes. The present document, the Venus Technology Plan, draws information from both of these documents and performs a more detailed assessment of the maturity of the technologies to perform these missions, and an overview of technologies that require NASA investment to meet mission needs.

3.0 Venus Exploration Challenges While there is a long history of Venus exploration, there has been no dedicated United States mission to Venus since Magellan ceased operations in September 1994. To some degree, this is reflective of the challenges associated with Venus exploration.

3.1 Venus Environment The Venus environment poses varied challenges for robotic exploration missions: 1) The orbital thermal environment is stressful as a result of the high solar reflection from the Venus clouds, but it is a much less challenging environment than Mercury orbits. 2) During planetary atmospheric entry, the velocity and thermal conditions are more severe than for entry at Earth or Mars with conventional aeroshells (but less than Jupiter entry). 3) Once in the atmosphere, missions operating high (~55 km) in the atmosphere can experience a benign environment in terms of temperature and pressure but are exposed to the harsh, chemically reactive environment that is maintained in the sulphuric acid clouds. 4) Descent and landing on Venus is helped by the dense atmosphere, which simplifies both the initial descent and the terminal phases relative to comparable phases at Mars. 5) Surface operations using conventional electronics and passive thermal control systems are limited to a few hours. Long-duration missions require components and packaging that will function at Venus ambient pressure and temperature and/or have active thermal-control systems.

3.2 Spaceflight Heritage More than 30 spacecraft have flown to Venus since Mariner 2 flew by the planet 50 years ago (Fig. 3-1). These missions have included flybys, orbiters, probes, short-lived landers, and balloons. All of the in situ missions occurred in the first 25 years. The Magellan orbital radar mission, which was completed in 1994, and the European Space Agency’s (ESA’s) Venus Express in 2015, have ensured that Venus observational science from spacecraft have continued. The absence of recent in- situ missions has resulted atrophy of some of the technical capabilities important in Venus exploration, which must be maintained. However, the early successes provided a proof of principle that orbiters, probes, short-lived landers, and balloons can be successfully deployed at Venus. Several assessments of Venus technology have been conducted expanding on the core concepts of previous missions. In 2006, NASA’s Solar System Exploration Roadmap [4] included a Venus Mobile Explorer mission and an extensive discussion of the required technology for this mission. In 2007, an assessment of extreme environments technologies for planetary exploration was conducted under the leadership of Jet Propulsion Laboratory (JPL) [5]. This was followed by a monograph focused

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specifically on Venus technologies [6]. In April 2009, the Science and Technology Definition Team (STDT) for the Venus Flagship Mission [7] conducted an assessment of not only the new technology requirements for the Design Reference Mission, but also the mission and payload enhancements for a mission with greatly enhanced science return. Members of VEXAG submitted a white paper [8] in September 2009 to the Planetary Science Decadal Survey on technologies for future Venus exploration. A series of studies were conducted in 2017-2018 related to small satellites [9], aerial platforms [10], and “Venus Bridge” approaches [11]. These are all important sources for this present document.

Fig. 3-1. Historical set of Venus missions: Mariner 2 (NASA), Pioneer Venus probe (NASA), Venera X (USSR), VeGA (USSR), Magellan (NASA) and Venus Express (ESA).

3.3 New Mission Modes Based on Recent Technology Advances Advances in multiple fields have suggested the potential for new classes of missions driven by improvements in miniaturization and harsh environment technologies. A common theme is that these technology advancements have allowed the potential for small platform missions of a variety of types to provide valuable science. One such advancement is the introduction of small and cube sat technology enabling orbiter, aerial, or lander systems with significant capabilities, but in smaller packages. Such satellite technology can provide valuable Venus science, but at reduced cost and complexity through, e.g., being initially launched into orbit as an auxiliary payload [9]. A second advancement is in the area of aerial platforms with capabilities beyond those previously flown in larger balloon missions, often leveraging reduced size or alternate methods of exploration of the atmosphere [10]. These aerial platforms include vehicles that are driven around Venus in the superrotating flow but maintain a fixed altitude; vehicles that are able to control altitude; and vehicles with varying degrees of control in all three dimensions. A third technology advancement includes new capabilities in high temperature technologies to enable small, long-lived lander systems with the potential for extended operational lifetimes in situ on the Venus surface. These core harsh

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environments technologies can enable multiple mission such as a science station providing data from the Venus surface for 60 days or more. Other advances in technology, such as increasing capabilities for autonomous decision-making, can change the way new missions, based on heritage mission classes, are conducted. Examples include autonomous decision making in image targeting for orbiters, independent flight vehicle operation in the atmosphere for aerial platforms, or sample handling in drill location, selection, sample acquisition, and handling for short-lived landers [14]. VEXAG’s Venus Exploration Goals, Objectives, and Investigations (GOI) Group has identified broad range of potential science investigations. A number of mission classes, based both on established and new mission modes, and generally involving different types of instrument/sensor- carrying platforms, will be needed to conduct the comprehensive investigation of Venus to address the GOI. These mission modes require different degrees, and types of, technology. Later in this document we describe the technologies that are needed to enable each of the mission modes.

4.0 Technology Plan Overview The Venus Technology Plan is complementary to the VEXAG Goals, Objectives, and Investigations for Venus Exploration and Roadmap for Venus Exploration documents. In effect, the Venus Technology Plan describes the technologies and tools needed to carry out the roadmap towards realizing the goals and objectives of Venus exploration. Given the breadth of what it takes to explore a planet that has as many unanswered fundamental and significant science questions as Venus, the Venus Technology Plan is itself a document covering a vast range of topics. It is composed of multiple components encompassing not only what is necessary for a single complete mission profile, but a broad array of technologies and components to conduct a wide range of missions able to be proposed today, as well as in the near, mid, and far term. Across such a vast array of possible missions, there are common components e.g., instruments, power, operations, and communications. However, each of these components not only significantly depends on the type of mission, but also, given the unique challenges of Venus exploration, can be in strong contrast to corresponding technologies for other planets. A simple summary of the status is Venus technology is: There are a number of important missions that can be performed now with the technologies available. These can enhanced with technology developments from exploration of other planets and other fields. However, in the near, mid, and far term, notable technology developments across a range of fields raises the possibility of new types of missions previously thought unattainable. An energetic Venus exploration program over time may be a pathway of combining well-established technologies and mission concepts with the introduction of new capabilities to address core Venus science questions from a combination of orbital, aerial, and landed platforms. In this section, an overview of the Venus Technology Plan is given, while in the following sections a more discussion is provided on System, Subsystem, and Instrument technologies. A summary assessment of the technologies needed for the Roadmap mission modes appears in Table 4-1 (also see Figs. 4-1 and 4-2).. The time frame in which each of these technologies is needed is indicated in the second column and assumes investments as appropriate. The time frames noted in the Table captions are described as:

N is NearTerm: 2018 to 2022: These missions can be proposed using existing technology with limited development with fully developed Science rationale.

M is Mid Term: 2023 to 2032 - First Decade: The technology is ready with moderate development and missions concepts have been well studied and the Science rationale has been well established. The missions can be proposed and executed in the first decade of the next Decadal

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survey.

F is Far-Term: 2033 to 2042 -Second Decade: Science rationale exist. Mission concept of operation, science instruments and/or associated technology development requires additional development. Moderate to high levels of investment are required and as a result, missions may be executed in second decade or later of the next Decadal survey.

It should be noted that availability of a capabilities and related techologies to conduct a mission does not imply the mission will occur, but only that it could be made ready to occur if such a mission is selected. Table 1 shows a range of Technology Areas and an Assessment of that Technology Area. These Assessments are based on a more detailed description of the technologies needed for individual mission modes appears in Sections 5, 6, and 7 and are the basis of these Assessments. The Technology Areas are organized into three categories: Systems Technologies (Section 5) apply at the scale of the spacecraft; Subsystems Technologies (Section 6) include particularly important components of these systems; Instruments (Section 7) must generally be tailored to the unique conditions at Venus. A brief overview of the infrastructure available for Venus technology advancements is provided in Section 8. Table 4.2 describes a series of possible Generic Missions in the Near, Mid, and Far Term. These are examples of what type of missions might be accomplished in a given time frames, but do not select a specific mission. In particular, a specific mission being proposed will need internally to justify its maturity and viability; this table is meant show a progression of technology maturity and possible mission classes from 2018 to 2043. In Tables 4-3A-C, we have characterized the maturity of each technology with respect to the mission mode with a color code, which is explained in the legend. If a block is not color coded, the technology is not applicable to that mission type. For Immediate missions, technology maturity is very high (green) or high (yellow); for near and mid-term missions the maturity ranges from being ready to needing investment or moderate (orange), and for some far-term missions low (red). Overall, if a technology has seen notable advancement since the last Technology Plan, those are noted with Up arrows. It should be noted that Tables 4.3A-C show a progression from Near to Far-Term of inceasing capablites and increasingly complext missions. There is much that can be done in the Near-Term with technology and missons that in some case have already been proposed. From that baseline, new missions and science can be propsed and flowin in Next Decadal Period assuming technology development. In the Far-Term, Venus Exploration can be more like that of other planets, but there are major technical challenges in achieving such missions. A major message of this report is that, based on recent advances, further technology investment can surmount many of the the previous challenges of Venus exploration and allow new froniters Venus science and exporation.

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Table 4-1. Framework for assessing technologies for Venus exploration.

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Table 4-2A: Mission modes descriptions for Near, Mid, and Far Term Missions

Mission Mode Generic Description

Orbiters An orbiter using radar for surface mapping, and active remote sensing for topography, emissivity, gravity, etc. Aerial Platform Sustained Aerial platforms with ability to operate in the atmosphere for sustained periods, but without flight control Deep Probe A probe characterizing the environment down to the surface Multiple Shallow Probes

Near-Term Shallow probes characterizing the upper-mid atmospheres and Sondes Lander A short lived lander comprised of a conventional electronics instrument suite Highly complex orbiter systems with broad instrument array and limited ability to independently carry out and Advanced Orbiters optimize investigations Subsatelite/ Small Sat Communication and observations systems able to provide a multiple scientific investigations as well as a Platforms communications and navigation instrastructure Aerial Platforms- Upper Aerial platforms with ability to operate in the atmosphere for sustained periods, with limited flight control e.g. Atmosphere altitude control

Mid-Term Small Platform Lander- Small in situ platforms capable of operating at Venus ambient conditions to accomplish focused science Long Duration investigations Multiple Deep Probes and Deep probes and sondes coordinated with aerial platform operations and each other Sondes Advanced Orbiter An orbiter network composed of advanced orbiters and small sats providing coordinated science and mission /Smallsat Networks communications support Aerial Platforms- Near Aerial platforms with ability to operate in the atmosphere for sustained periods including exploration of the deep Surface atmosphere. Lander -Cooled Long A complex long-lived cooled landed systems with a suite of advanced earth-ambient temperature instruments Duration A number of lander systems coordinated and linked in multiple scientific investigations, which are composed of a

Far-term Lander Network mixture of increasingly complex high temperature and actively cooled landers Mobile Surface Mobile laboratory systems able to travel significant distances on the surface Sample Return Clouds Sample recovery and return from the upper atmosphere Sample Return Surface Sample recovery and return from the surface

Table 4-3A: Mission modes and applicable technologies for near-term missions.

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Table 4-3B. Mission Modes and applicable technologies for Mid-Term Missions

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4-3C. Mission Modes and applicable technologies for Far-Term Missions

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Fig. 4-1. Artist’s concepts of the near-term Venera-D and Venus Climate Mission.

Fig 4-2: Artist concepts of future mid-term and far-term Venus missions

5.0 System-Level Capabilities System-level capabilities are typically at the level of enabling the mission modes. It is important to recognize that these capabilities cannot be considered in isolation. These system-level capabilities will generally flow down to one or more of the subsystem technologies described in Section 6.0.

5.1 Aerobraking Aerobraking technology uses atmospheric drag to modify the orbit of a spacecraft incrementally as the spacecraft dips into the upper atmosphere of the planet. Additionally, information about density and winds can be gleaned from spacecraft instruments, like the inertial measurement unit (IMU), obtained during the flight through the atmosphere. Aerobraking was employed on the Magellan mission to lower the spacecraft orbit to a configuration more suitable for radar mapping, and it was used later in the mission to circularize the orbit for gravity observations. ESA’s Venus Express performed a number of aerobraking maneuvers at the end of the mission to characterize variability in

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the upper atmosphere. Measurements from Venus Express during aerobraking maneuvers are relevant to future use of aerobraking at Venus and offers insight to how aggressively the maneuvers can be executed to reduce the time needed to achieve the desired orbit. Aerobraking has also been used successfully at Mars as an enabling technology that significantly reduces the propellant requirements. Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter used aerobraking to obtain proper orbital timing and altitudes for science measurements. The Mars MAVEN mission utilizes aerobraking techniques in a series of “deep dips” into the atmosphere, not to modify the orbit, but for atmosphere sampling purposes. One disadvantage of aerobraking is the operational support required to monitor the spacecraft each aerobraking pass. Recent Mars spacecraft have been equipped with onboard algorithms that use periapsis timing estimation to reduce the operation workload by providing automated orbital sequencing updates. Additional efforts have developed advances in onboard software, which include atmosphere and aerodynamic models as well as guidance and maneuver calculation algorithms, that offer additional automation capabilities and further reduce operational cost while ensuring aerobraking mission constraints are satisfied [15-16].The technology is mature, but the spacecraft design (and particularly that of the solar panels) and orbital mechanics must be compatible with the Venusian heat and stresses generated.

5.2 Aerocapture Aerocapture differs from aerobraking in many respects. While aerobraking reduces the spacecraft velocity through very small drag by dipping slowly into the very upper reaches of the atmosphere in 100’s to 1000’s of orbits without overheating the spacecraft, aerocapture is performed in one single orbit. Properly designed entry system with efficient thermal protection system (TPS) protects the payload from the mechanical and thermal loading associated with single large velocity reduction during entry. Though aerocapture has not yet been employed on any planetary mission, larger payload can be placed in orbit around Venus, especially for missions that require orbits closer to the planet. Novel aerocapture approaches to achieve velocity reduction through drag modulation, could be not only enabler for small spacecraft missions in the near term and scalable design could lead to mid and large class payload that places an orbiter and allows for single or multiple probe or balloon deployment. ADEPT technology (to be discussed in the next section) combined with drag modulated aerocapture could prove to be attractive from the scalability perspective.

Figure 5.2-1 Single event drag modulated aerocapture [17]

5.3 Entry (Upper Atmosphere) Entry technologies are needed for implementation of all mission modes designated in Table 4-1 except for remote sensing missions. Although successful entry at Venus has been accomplished many times by Soviet, and later Russian landers, and by both a large probe and three smaller NASA

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probes, some of the thermal protection technologies used in those NASA missions are no longer available. In addition, limited single or multiple science instruments are being proposed with cubesat small spacecrafts constructs at relatively lower costs. Even orbital missions using small spacecraft could be accomplished using both traditional rigid as well as novel deployable entry systems. Retiring the risks and realizing such potential missions of opportunity using seconday payload may increase the cadence from zero to something better. This has been recognized by SMD, which sponsored VEXAG to conduct Venus Bridge Study. Approaches include:

1. Heritage Carbon Phenolic: This solution requires a descent into Venus at high entry angles to mitigate the cumulative heat load imposing high-g loads on payloads [18]. Attempting to replicate the material used in previous Venus missions is one approach. Its advantage is that it has been proven to work. The shortcoming is that it would be extremely challenging to reproduce a similar family of materials as the manufacturing processes have atrophied. Consequently, raw material is no longer available, and it would be expensive to qualify replacement materials. Thus, this solution is prone to premature obsolescence.

2. 3-D Woven Thermal Protection System: The use of 3-D woven materials infused with resin to withstand a broad range of entry environment to result in mass-efficient ablative TPS has been under development by led by NASA Ames Research Center (ARC) and funded by both SMD and Space Technology Mission Directorate (STMD). Description of how HEEET heat-shield is assembled from flat 3-D Woven preforms can be found in reference [19].

NASA ARC working together with Bally Ribbon Mills (BRM) [20] developed the weaving technology for HEEET. BRM built a specialized loom for weaving 2” thick by 24” wide preform needed to make scalable parts. As part of the development, NASA ARC developed and transferred the molding and resin infusion technology to Fiber Materials Inc (FMI). The two companies have been certified to produce flight ready components and thus can support future Venus missions. The fully assembled heat-shield shown in Figure 5.3.2 is the engineering test unit that has undergone comprehensive structural, thermal-vac and point load tests successfully for load conditions that bound Venus aerocapture and entry missions. The HEEET dual layer approach results in a robust and mass efficient heat-shield compared to the Carbon-Phenolic system. HEEET dual layer material has been tested at the NASA ARC arc jet Interacting Heating Facility (IHF), using the 3” nozzle to obtain highest stagnation test conditions. Figure 5-3.3 shows the HEEET acreage and seam material joint with the adhesive undergoing testing at ~ 6500 W/cm2 and at ~ 5.5 atm.

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Figure 5-3.2. The HEEET woven preforms are molded, resin infused and machined. The figure shows the integrated 1m heat-shield prior to final machining.

Figure 5-3.3 HEEET arcjet testing at the NASA ARC IHF arcjet with the 3” nozzle configuration (right) and the post-test article (left). The test article is made of one-half acreage material and the other half, the seam material with the bonding with adhesive between them. The test article is very similar to the heat-shield configuration and this test represents the highest condition achievable in the ground test facilities (6500 W/cm2 and 5.5 atm).

The mass efficiency is close to 50% and as a result permits Venus entry at shallow flight path angle not feasible with Carbon Phenolic TPS. Thus, HEEET can enable sensitive optical instruments as part of the entry g-load can be tailored to 10’s of gs rather than 100s of gs with Carbon Phenolic. HEEET project began in 2014 and is nearly complete as a fully matured technology. As a result of investments by STMD and SMD, HEEET not only closes a critical technology gap for Venus missions but it is enabling by science community to consider instruments that were not feasible until now.

3. Adaptable Deployable Entry and Placement Technology ADEPT: ADEPT (Fig. 5-3.4) is an innovative approach involves protecting the payload during entry with a large deployed entry system that also reduces the ballistic coefficient due to larger deployed surface. ADEPT technology development has been funded by STMD and the project is nearing completion with the sounding rocket flight test.

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Figure 5-3.4. The figure shows artist view of the deployable entry system (a 6m ADEPT) carrying a large lander as payload before entry into Venus separating from the flyby spacecraft. The ADEPT concept has been assessed through design and mission focused studies at large and small scales for Venus. It has the potential to provide significant payload mass capability compared to conventional rigid entry system for small, medium, and large payload classes. Since ADEPT configuration is folded during launch into much smaller cross section (See Figure 5-3.5), ADEPT is better suited for delivery of small spacecraft to orbit or a payload to the interior or surface using secondary payload adapters such as ESPA rings, where packaging is a constraint. With the successful sounding rocket flight test in September of 2018, ADEPT targeted development for Venus is at TRL 5. Completion of ADEPT technology with a focus on secondary payload will enable small spacecraft aerocapture and entry missions. There are also inflatable versions of the ADEPT approach – the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) [21], which have been tested in Earth re-entry tests. A concept for a Venus Atmospheric Maneuverable Platform (VAMP) envisages using an inflatable structure for entry and flotation.

Figure 5-3.5. ADEPT in stowed state (left) and in deployed state (right). The figure on the right is a 2m ground test article built and tested.

5.4 Descent and Deployment (From upper atmosphere to destination) Descent/deployment capabilities are relevant to the same mission modes as for entry. For probes,

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aerial platforms, and landers, it is necessary to control the rate of descent and stabilize vehicle attitude during its passage to the surface through a progressively denser atmosphere. For a probe and landed missions, velocity and attitude must be controlled during descent to provide adequate time to sample the different regions of the atmosphere, while limiting the dwell time at altitudes where the environment is harsh (e.g., hot and corrosive). This may require different sizes of parachutes or other aerodynamic structures. Special materials must be used to accommodate the high temperature and acidity of the atmosphere, but these materials are available. For a landed mission, the objective is usually to bring the vehicle to the surface as quickly as possible to minimize the thermal input to the landing module. Maintaining attitude stability and minimizing jitter during descent is important to acquire images during descent with minimal motion blur. These are engineering challenges with no new technology required. For aerial platforms, it is necessary to establish the conditions required for successful deployment of these vehicles. A successful balloon deployment and inflation test was conducted in the Earth’s atmosphere during parachute descent at a velocity of 6.5 m/s [22]. This descent velocity is readily achievable for deployment in the mid-cloud level of the Venus atmosphere (57–65 km). The needed descent velocity for airplane deployment is dependent of the specific design of the aircraft, but again the dense atmosphere is favorable. Drop-sondes deployed from an aerial platform could be used to sample the atmosphere in multiple locations. Deep drop-sondes, which are able to descend close to the surface, could also be used in conjunction with the platforms that deploy them to relay large amounts of high-resolution imaging data on potential landing sites, but would require technology development in order to generate images near the surface. To date, all Venus descent systems studied or flown have been unguided. Incorporating guidance, with improved navigation, could enable more accurate targeting; this is discussed further in subsequent sections.

5.5 Landing Compared to Mars, the dense, hot atmosphere on Venus makes the descent phase far longer, with terminal velocity far slower, and makes thermal survivability during descent an important issue. Venera landers went to smooth plains terrains. Since 2010, Venus lander studies and proposals have considered missions to land in the much rougher, higher elevation tesserae terrain. There are two general approaches to the challenge of landing on the rough terrain. One is to make the lander system robust to all possible eventualities. This is not just about surviving but also being positioned on the surface to carry out the science mission; a vehicle that tips over and prevents its sampling arm from reaching the surface may result in mission failure. The other approach is to find a safe area within the general area of challenging terrain and target that safe area. This second approach increases the potential return of surface science data by opening the possibilities for more instruments that might not be otherwise considered if not for precision targeting. Hazard Tolerance: recent focus of mission planning. By analyzing the geomorphology data from previous missions (i.e., Magellan RADAR, Venera/Vega lander imagery) models of the worst case scenarios of slope have been developed to gain a better understanding what types of terrain might be encountered. This method is meant for a semi-targeted landing of a broad region and will be the tool of choice for near-term landed missions. Hazard tolerance was the mode selected for the ViTaL study [23] as well as for the recently proposed New Frontiers 2018 VICI Venus proposed lander mission [24]. In the future, it should be feasible to draw on the pin-point landing and hazard avoidance technologies that have been developed by the Mars program and also by the STMD under the Autonomous Landing and Hazard Avoidance Technology (ALHAT) program [ 25 ]. Considerations related to pin-point landing and hazard avoidance include:

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1. Pin-Point Landing involves guiding the vehicle to a designated point on the surface by correlating images obtained from the lander as it descends with a map of the surface that was created from prior orbital reconnaissance. This capability has reached TRL 8 for Mars and will be employed in the 2020 Mars rover mission, using visible spectrum descent images and orbital reconnaissance. For Venus, the descent images would probably be acquired in the near infrared. The reference map would be based on radar—either from Magellan or a new mission. Using heterogeneous data sets like this has been studied and appears feasible. The control function would be quite different from landing on Mars and would use a steerable parachute or aerodynamic control surfaces, not propulsion. Steerable parachutes have been used on Earth in precision drops from aircraft for several decades and have been studied for Mars. For Venus, it would be necessary to study how large an initial landing error could be compensated for and how precise the ultimate landing could be. 2. Hazard Avoidance could be used independently or in combination with pin-point landing. It would acquire surface information (imaging, LIDAR, and radar) during the final stages of descent to identify areas of hazard and use onboard GNC capabilities to avoid them. Such capabilities have reached TRL 7 for Lunar applications [23]. Hazard avoidance will be part of the 2020 Mars landing, but using hazard maps generated onboard rather than during terminal descent. Hazard avoidance is now being extended for application to Europa, including onboard hazard detection. Analogous guidance and navigation capabilities have also reached a high level of maturity for navigating to the surface of primitive bodies. Rapid progress in miniaturization of high performance processors, cameras, and inertial measurement units for Earth applications may be applicable for Venus descent and allow significant reduction in the size and power consumption of avionics for guided descent. 5.6 Entry, Descent, and Landing (EDL) Modeling & Simulation EDL Modeling & Simulation (M&S) capabilities are needed for implementation of all mission modes designated in Table 4-1 except for remote sensing missions. M&S capabilities are on the critical for Venusian EDL given the harshness of the entry environment and the inability to "test as you fly" in these conditions. Venus entry missions can leverage ongoing investments in aerosciences and material response modeling capabilities, but there are several unique aspects of the Venus environment that require dedicated development:

1. Aerothermal Models: Predicting the convective aerothermal environment during Venusian entry will rely on Agency tools such as DPLR [26] and LAURA [27]. Those largely include models for Venus at the current time, although some updates may be required for certain entry conditions, particularly those that encounter turbulent flow. Required updates are largely in- plan in the currently funded Entry Systems Modeling Project [28].

2. Shock Layer Radiation Models: Although the Venusian atmosphere is chemically similar to Mars, entry velocities are much higher, which greatly increases the importance of shock layer radiation to overall heating levels. Current databases in the Agency workhorse codes NEQAIR [29] and HARA [30] include relevant models for Venusian shock layer heating, but those models are based on limited validation data, particularly for afterbody radiation, which may contribute over half of the total heat load during entry. Required updates are not currently in-plan in the Entry Systems Modeling Project.

3. Thermal Protection Material Response Models: As noted in Section 5.3, there are several TPS materials under consideration at the current time. High-fidelity response models will be

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required for any new material proposed for Venusian entry. The high entry velocity results in a high-heating, high shear environment on the TPS that can only be partially tested on ground, therefore the ultimate design and risk analysis of any Venus entry mission will be reliant on accurate physics-based models of TPS performance. Some of the required updates are in-plan in the Entry Systems Modeling Project, but some aspects of TPS performance in a high-shear environment may require dedicated investment.

4. Descent Aerodynamics Models: At lower speeds models are required to ensure stable behavior of the entry vehicle, both before and after deployment of the parachute (or other aerodynamic structure). Required updates are largely in-plan in the Entry Systems Modeling Project.

5. Flight Dynamics Models: Flight dynamics codes, such as POST2 [31], provide end-to-end simulation of the entire EDL sequence, including the impact of errors or dispersions. While this capability is certainly critical path for any Venusian EDL mission, current capability is likely largely sufficient for future mission needs. 6. Descent GNC Models: For pin-point landing and hazard avoidance technology development, models and simulations are needed of the performance of navigation sensors, hazard detection sensors, and the entire guidance, navigation, and control subsystem. Versions of such modeling and simulation capabilities have already been developed for guided descent for other planetary bodies, particularly Mars and the Moon; however, such models must be updated to include relevant characteristics of the Venus environment (e.g. atmosphere) and related data sets (e.g. prior radar maps for descent navigation).

5.7 Aerial Platforms-Flight A recent Venus Aerial Platform (VAP) Study [10] commissioned by NASA has examined the importance of mobility in the future exploration of Venus. Concepts examined range from fixed altitude balloons that are swept around Venus in the super-rotating flow, variable altitude platforms that can change altitude but have no other dimension of control, and platforms with some degree of three dimensional control. The study found that variable altitude platforms occupy the sweet spot in the option space as they offer a significant increment in science over the fixed altitude platforms without the major increment in size and complexity and low technology maturity of the platforms with lateral control. In addition, mobility system improvements in instruments, power, communications, and support capabilities for specific mission architectures are needed. Some of those needed improvements are identified here and elaborated upon in parts of Section 6 .0 Subsystems and Section 7.0 Instruments. The most mature aerial platform designed for operation near 55 km is the super-pressure balloon. Two 3.4-m diameter helium super-pressure balloons were successfully deployed and flown in June 1985 by the Soviet Union. Each balloon returned in situ measurements for about 48 hours. It was tracked by an international consortium, led by the Soviet Union and France, and in which NASA participated. Over the last decade, work at NASA and to a lesser extent at ESA, has focused on balloons with a larger payload capability and a potential life time of several months [32]. The technology for a Venus balloon with a payload capacity of 45 kg has been demonstrated and is ready [19] to fly. Development of a larger 7-m balloon with a 100-kg capability was never completed and this is reflected in the maturity designation in Figure 5.7.1. A number of approaches to Variable Altitude balloons were identifies in the VAP study which are strong candidates for a mission implementation. A competitive program to determine which of these concepts is most suited to operation in the Venus environment and can yield the best scientific

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performance is needed. Further development of the fixed altitude balloon is also desirable. Superpressure balloons are a component of variable altitude balloons and also represent a lower cost, lower risk alternative for a Venus mission. Subsystem developments that could enhance the performance of a balloon include wind assisted balloon navigation and autonomous on-board landmark-based or relay satellite based navigation. They require advances in on-board guidance and control.

Fig 5-7.1. Comparison of Venus Aerial Platform concepts in terms of Science Value, Size and Complexity and Technology Maturity. Variable altitude balloons represent the sweet spot in the trade study.

5.8 Landers 5.8.1 Landers – Short Duration During the 1970s and 1980s, the Soviet Union successfully landed seven probes (Venera 8, 9, 10, 13, 14, and VEGA 1 and 2) that operated on the surface of Venus for periods of 1 to 2 hours and returned images as well as other scientific data. This was accomplished with thermally insulated vehicles that maintained imaging sensors, communications systems, computers, and energy storage systems at temperatures below 100°C. The vehicles consisted of insulated pressure vessels, which also contained solid-liquid phase-change material (PCM) to extend surface lifetime. Deployment of similar short- duration missions using passive thermal control, which can survive on the surface of Venus for a period of hours, is viewed as an engineering development rather than a technology development. Work in the last 5 years, has opened up the possibility of extending the lifetime of these landers by an order of magnitude to 20 to 25 hours—making it possible to carry out missions in which scientists have time to respond to the data and make decisions on limited follow-up observations rather than a totally autonomous mission of 2 to 3 hours duration. These technologies include the use PCMs employing the liquid-vapor transition in water and ammonia [33]. These technologies should certainly be considered, and developed if deemed feasible, for lander mission to the Venus tesserae.

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5.8.2 Landers – Long Duration Recently developed high temperature electronics, sensors, and other technologies have matured to a state where a simple long-life scientific probe would be feasible for Venus operations. Development has begun on a small probe system to enable such a long-lived surface mission: Long- Lived In-Situ Solar System Explorer (LLISSE) [12]. Such a probe would provide measurements to make progress in our understanding of key questions for Venus exploration. For example, landed missions that can monitor conditions at the Venus surface for one half to one full Venus day can observe the excursion from day to night cycles of illumination, surface winds, and temperatures, and with the appropriate sensors can monitor for short term changes in atmospheric gases due to stochastic events such as volcanic eruptions. Even the very small day-night temperature shift at the surface may be enough to change certain chemical stability regions if the surface-atmosphere composition is very near the equilibrium chemistry of some constituents [11]. Further, the potential of a long-lived seismometer system on the surface of Venus (has also been studied [13] Development is on-going high-temperature electronic circuits for sensors, data handling, communications, and power management to TRL 6 by 2019-2021 [12] to allow operation of such a long-lived lander. However, there is presently no low-power data storage, which implies periodic transmission of data. This is sufficient for the long-term monitoring goals, but suggests a coordinated orbiter to support lander telecom. High temperature technology development related to improved power sources (such as higher density batteries), developments of low power memory, improved communications throughput, and an in-situ camera system would enhance long-lived missions.

Figure 5.8.1 Artist concept of the Long-Lived In-Situ Solar System Explorer (LLISSE)

A mission mode that could conduct long-term precision geophysical and other measurements in the high temperature Venus environment might also be considered with active cooling. This approach would involve active cooling of the lander with Stirling power generation and refrigeration. The technical challenges are formidable and, in addition, would require a large amount of radioisotope material. It is a more realistic target for the far-term. Power for this mission mode could be provided by radioisotope power using a thermoelectric transducer exploiting the Peltier effect. Although currently available Multi-Mission Radioisotope Thermoelectric Generators (MMRTGs) are not designed to operate in this environment, there are thermocouples that are capable of operating very efficiently under conditions where the cold junction of the devices is at Venus surface ambient temperature. 5.9 Mobility – Surface or near surface Mobile platforms (Fig. 5-4) that would operate on the surface or in the lower atmosphere with a

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mobility range of tens to hundreds of kilometers could analyze surface compositional variations on a regional scale. Instruments on this platform would conduct geochemical and mineralogical measurements at multiple sites, undertake remote sensing from low altitudes (<1 km), and provide panoramic and high-resolution images correlated with composition.

Fig 5-4: These concepts for regional surface exploration would float above the surface in the dense atmosphere (top) or employ wheeled vehicles [34-35] (bottom). Unlike the landers discussed above, these systems must include payload compartments maintaining temperatures at or below Earth ambient for imaging instruments, unless high temperature optical instrumentation makes significant new advances. Achieving high fidelity, visible imaging, and remote sensing infrared measurements often requires cooling sensors to well below Earth ambient temperature. Operation at Venus surface temperatures would require high temperature sensor maturation. Other instruments may be operable in the range 150° to 200°C. Both power and cooling systems that can operate at Venus temperatures would need to be developed. The mobility range for such vehicles is core to their science return. Concepts for floating platforms capable of traversing the altitude range of the Venus surface and hence accessing all terrain types have been devised; however, the near surface conditions on Venus are not well known. Wheeled or legged vehicles require many more mechanisms that would be vulnerable to the conditions near the surface and issues of long-term exposure to the corrosive conditions of the near surface would need to be explored. Attaining the designated 10- to 100-km range would be challenging.

5.10 Ascent Vehicle Venus Surface Sample Return (VSSR) is a long-range objective. Past studies of VSSR [36] have used architectures modeled on Mars Surface Sample Return in which a sample canister would be brought from the surface to Venus orbit where it is captured by an orbiting vehicle. The concept is at a very low level of maturity and is not likely to advance before there is progress in the development of ascent vehicles for Mars Surface Sample Return, which is a much easier task.

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5.11 Small Platforms The rapid advances in spacecraft miniaturization that have led to the development of CubeSats are creating new opportunities for Venus exploration. The Venus Bridge Study led by VEXAG explored the potential of small platforms for the exploration of Venus [11]. As described in an earlier section it was concluded that SmallSat and CubeSat technology can make important contributions to Venus exploration. Orbiters and various kinds of in situ vehicles using the technology (including skimmers, probes, balloons and landers) can make important scientific contributions. However, the technology of these platforms is immature. MarCO (Mars CubeSat One), the first CubeSat in deep space, has not yet reached Mars, will flyby the planet, and does not have the capability to orbit Mars. For these platforms to reach their full potential, propulsion systems enabling both injection on a Venus crossing orbit and insertion into useful orbits or Venus will be needed. Both ion propulsion and chemical propulsion systems will play key roles. In addition, deployable antennas that can provide improved telecommunications links are highly desirable. Finally, methods of achieving low cost for these missions without incurring a reliability penalty are key. Small companies spearheading small SmallSat and CubeSat development may be the key to it fulfilling its potential. Small platforms that enable new landed mission concepts and approaches is also highlighted in the Venus Bridge and other studies [11-13]. In particular, recent advances in high-temperature electronics and sensor technology suggest the potential use of small simple lander platforms operational for extended periods on the Venus surface providing significant science at significantly reduced costs. These lightweight systems can be delivered, for example, as a secondary launch from lunar missions, and may be deployed to the surface from an aeroshell, balloons, or a lander. Investigations considered with these platforms range from meteorology, atmospheric chemistry, and seismology. The development of these small platforms suggest a new potential option for Venus surface exploration that can both complement other missions and be a pathfinder for future mission with extended surface operations. 5.12 Automation and Autonomy Significant aspects of Venus exploration are challenged by limited time or capability for human- in-the-loop interactions during the mission. Machine-based intelligence can optimize Science Return by providing operation independent of human intervention. The use of machine-based intelligence can vary from the use of automated systems carrying out a set sequence of actions to increasingly autonomous systems with the capability for situational awareness, decision-making, and response. Automated and autonomous systems have been used in planetary exploration for years. However, these advanced systems are notably increasing in capability and applicability with the potential to significantly impact future Venus exploration. Examples for Venus orbital, atmospheric, and lander missions respectively include: 1) Automated location of a desired surface target for image navigation and reduction of data volume. 2) Altitude and mission control of a Venus balloon including optimization of atmospheric sampling, power handling and conservation, and altitude adjustment for characterization of atmospheric flow streams. 3) Autonomous lander operation on the surface over an ~ 2+ hour span to carry out the maximum number of experiments with on-site data quality evaluation, validation, and repeat of experiments as needed. For more complex missions with multiple components, autonomous systems can collect and correlate data from the same phenomena observed from difference vantage points to potentially identify events and patterns. Overall, leveraging advances in automation and autonomy in other fields can potentially significantly broaden future Venus mission options. Advanced automation, autonomy, and GN&C capabilities typically require advanced onboard computing capabilities, which must have minimal size, weight, and power (SWaP) consumption to fit within onboard resource constraints. Venus orbiters, aerial platforms, and descent systems face less extreme environments than long-lived surface platforms and lower atmosphere mobility systems,

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which expands the range of potential solutions for advanced processors and other avionics. NASA’s High Performance Space Computing (HPSC) [37] is developing advanced computing systems that will be robust to high radiation environments. Aerial platforms and descent systems for Venus are shielded from such radiation; commercial grade electronics may offer significant improvements in performance and SWaP in those applications, such as processors developed for high reliability, high computational throughput, and low power consumption for smart automobiles.

6.0 Subsystem Technologies This section focuses on those subsystem elements that are critical to the implementation of the systems solutions discussed above.

6.1 Power Subsystems 6.1.1 Energy Storage – Batteries Of the mission modes described in Table 4-1, many could be implemented successfully with existing technology from orbiter, balloon, as well as probe and lander missions. Batteries for long duration missions are in development [38] as well as work addressing requirements for missions such as LLISSE [12, 39]. Batteries are a strong driver for other long-lived lander mission designs e.g., a missions performing seismic studies would be significantly enhanced be continuous, long-term operation [13]. Thus, batteries with higher power density, reduced self-discharge, and rechargability would enable expanded mission capabilities. Secondary batteries may also be required to handle peak loads in conjunction with a robust radioisotope power system. 6.1.2 Energy Generation – Solar Remote sensing from space with orbital or flyby missions could be implemented with existing capabilities. Solar power is not needed for short duration probes or landers but may be a viable for long- lived aerial platforms designed to float within the clouds. For landers deployed on the surface, the amount of solar energy reaching the surface is limited, and the challenges of developing efficient energy converters to operate at these temperatures are also notable. Standard solar cells that operate at higher temperatures generally do so sensing blue and ultraviolet radiation, and very little radiation of these wavelengths penetrates to the surface of Venus. However, other approaches can be considered and have been explored [40]. Concepts have been developed under the HOTTech program for low altitude balloon systems that travel between the surface and about 20 km above the surface where there is sufficient solar energy to generate power and the temperature is cool enough for efficient conversions. Electrical contacts have been developed under the HOTTech program that can survive exposure at the surface [41]. Advances in solar power technology could be enabling for aerial platforms for operation within or above the clouds. Airplanes require efficient, lightweight, and acid-resistant panels clad on both sides of the deployable wings of an airplane. Long-duration balloons are less demanding since no power is needed to maintain lift, but very lightweight, acid-resistant systems are needed to minimize the payload mass. Standard solar power generation within the Venus clouds is very sensitive to solar zenith angle, which is determined on Venus by both latitude and time of day, and depth within the clouds. Technology developed within the HOTTech program will enable aerial platforms to descend below the level in the clouds for optimal power generation and still survive [41]. 6.1.3 Energy Generation – Radioisotope Power Radioisotope power could play an important part in the in situ exploration of Venus Floating platforms could benefit from radioisotope power on the night side of Venus (although trades with battery options are needed), and as these platforms approach the polar vortex, radioisotope power could extend operations. 1) Advanced Stirling Radioisotope Generator (ASRG): A highly efficient Stirling engines

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coupled with linear alternators to convert radioisotope heat to electrical energy. This technology could be implemented on an aerial platform at Venus provided it uses a low ballistic coefficient entry system, such as ADEPT, to mitigate the g loads on entry. The development of ASRG flight units was cancelled in November 2013. Its future prospects are uncertain although the Stirling engines remain in development. 2) ASRG for High G Conditions: For such entry systems, the ASRG would need to be ruggedized so that it could tolerate and operate through the entry phase. The feasibility of this has not been assessed. There is no current development work on such a device. 3) ASRG for High Temperature: For operation near the Venus surface, a version of the ASRG capable of operating with its cold end near Venus surface temperatures of approaching 500oC is needed. Research was performed on this very challenging development but is no longer being conducted. However, design stage of a Stirling power/cooler for Venus was achieved with the fabrication of an evaluation unit being considered when this activity was suspended [42-43]. A challenge would be the materials involved [44] and availability of radioisotope power units. 4) High Temperature Thermoelectric Converter: This is an alternative to the ASRG for operation near the Venus surface. It would be designed to operate with its cold end at Venus ambient. An advantage is that it does not require high temperature electronics While all four of these options are technically feasible, the qualification challenges associated with the use of radioactive sources are formidable particularly if modifications to the packaging of the General Purpose Heat Source (GPHS) modules are needed. This has motivated interest in various forms of alternative energy source for Venus. 6.1.4 Alternative Energy Sources For long duration operation, deep within the Venus atmosphere, it is possible to exploit wind shear and temperature gradients to harvest energy. A wind turbine concept is being developed [12]. Given the high density of the atmosphere at the Venus surface, even winds at velocities of ~ 1m/s provides the capability of providing adequate force to produce ~0.4W [ 45 ]. Development of both a rechargeable battery and power circuitry is on-going to enable such capabilities. Additional alternative energy sources under active or recent investigation include ‘lithium candles’ using ambient

atmosphere (CO2) as oxidizer for a thermal engine, and clockwork power using gravity or buoyant forces to drive mechanical generators [38, 46]. Another technological approach was described in the Venus Geoscience Aerobot study [19]. In this concept, a reversible fluid balloon, cycling up and down used the Venus atmospheric temperature gradient as a heat engine and also harvested power with a rotor beneath the balloon. There are certainly other approaches that should be considered.

6.2 Thermal Control 6.2.1 Passive Thermal Control Thermal control systems serve two functions in deep-atmosphere and surface probes. The first is to minimize the heat transfer from the environment to the probe. The second is to accommodate the heat generated by the internal components (e.g., power system, transmitter, and instruments). Passive thermal control was used on each of the Venera landers that operated for up to 2 hours on the surface of Venus. The elements are a) insulating materials to prevent heat leaking into the lander b) the thermal capacity of the lander, and c) phase-change materials (PCMs) to absorb the heat entering the lander to mitigate the temperature rise. Minimizing the heat leaks due to windows and cabling is an important part of the design process. 1) Large Landers: The readiness of this technology is very high for lifetimes of 2 to 3 hours. As

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noted in Section 5.3, liquid vapor PCMs may extend this by a factor of 10, but the technology is immature. Techniques use either water or ammonia as the phase change material, and the PCM may be coupled with a lithium getter to avoid the need to vent to the atmosphere. 2) Microprobes/Dropsondes: A major impact of technology advances could be in extending the performance of these devices. Analyses conducted for the Venus Aerial Platform study indicated that a streamlined vehicle as small as 5 kg could reach the surface and return surface images. Advances in insulation and phase change materials could extend the lifetime of such a vehicle. 3) Aerial Platforms: The science community has established a need for aerial platforms that could repeatedly descend to the base of the Venus clouds near 40 km where temperatures approach 127 ºC. In contrast with the passive control systems for large landers and microprobes, the passive cooling system for this application would be used repeatedly as the platform cycled between the upper clouds where temperatures are near -23ºC and the cloud base. At the upper range, a diode heat pipe would be use to efficiently extract heat from a phase change material in the instrument module and chill it to near the ambient temperature. When the vehicles descends, the conduction path would be shut off so that the lifetime at the lower extreme of the range could enable prolonged observations limited by heat leaks and power dissipation by the electronic systems. 6.2.2 Active Thermal Control Following an extensive assessment of the technology, the 2007 Extreme Environments Report identified an approach to a scalable, efficient, powered refrigeration/cooling system for maintaining temperatures at operational levels for the payload and the subsystems for extended periods of time (as long as months) [5]. The current state of development of active thermal-control technologies (Fig. 6- 1) capable of operating in the Venus near-surface environment is low. At present, active coolers also require very high power that needs the efficiency of a Stirling-type radioisotope generator to be feasible.

Fig. 6-1. Concept for active thermal control of a long-lived Venus lander uses Stirling-cycle technology for both generating electrical energy and cooling the electronics bay to enable operation at Venus surface ambient temperature.

6.3 Extreme Environments Technologies

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6.3.1 High-Temperature Electronics There are several technical approaches to exploring the surface or near-surface of Venus: 1) Medium-Temperature Semiconductor-Based Electronics: Medium-temperature (200–300°C) electronics are not only technically less difficult than electronics that operate at Venus surface temperatures but also have terrestrial commercial applications. A broad set of component options, including microprocessor and memory devices exist. For Venus surface missions, medium- temperature electronics could be used along with a Stirling-based power system/cooler. The use of medium-temperature electronics with cooling systems would significantly reduce the delta-T required, and hence reduce the amount of power required to achieve long-duration surface missions as compared to systems cooled to Earth-ambient temperatures. These electronics could be used for aerial platforms operating near or below the cloud base, where temperatures reach values higher than can be tolerated by conventional silicon electronics. In this case, no cooling systems would be needed.

2) High Temperature – Silicon Carbide Semiconductor-based electronics: Recent advances have been made to enable the first microcircuits of moderate complexity that have shown extended operation in Venus simulated surface conditions [47] (Figure 6.3.2) in the Glenn Extreme Environments Rig (GEER) and for thousands of hours at 500 °C in Earth air ovens [48]. These circuits continue to be up scaled in complexity and circuits with near 200 transistors per chip have been shown operational for 60 in simulated Venus surface conditions without cooling or environmental protection [12, 49 ]. Development is on-going to design, fabricate, and demonstrate circuits to provide operations for a long-live surface lander. This includes all aspects of the electronics necessary to conduct a simple mission: circuits for power management, signal conditioning electronics for multiple sensors (e.g., pressure, chemical species, temperature, and wind), conversion into digital signals, and communication of the data at up to 100 MHz in frequency. The proof-of-concept demonstration of these technologies is scheduled to take place between 2019-2021, and provide a complete, although simple, operational system. Further, notable progress has been made in understanding which materials are viable in Venus surface conditions including chemistry [ 50 ]. These developments in high temperature electronics since the last Venus Technology Plan are considered a paradigm shift in what is possible for Venus surface operations extending functionality from on the order of 2 hours to months. However, are approximately at the level of 1980’s electronics and, e.g., these systems do not have internal memory and so data is broadcast periodically to an orbiter. While high temperature memory is planned to be available in both ROM and RAM [38], decreases in power consumption and increased storage will be needed for some mission scenarios. Glass-based Ni alloy wires pressure seal in fiberglass sleeves

3mm x 3mm Ceramic Before Venus test SiC Chip substrate

After Venus test

Figure 6-2 SiC High Temperature Electronics Before and After 21.7 days of testing in simulated Venus surface conditions [47]. Continued circuit operation was demonstrated throughout this test period.

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3) Other High Temperature Electronics– In Digital Vacuum Electronics: Efforts in this area have exploited the properties of carbon nanotube electron sources which operate as field emitters without the need for a heated cathode. This field is immature but shows a great deal of potential for low-powered, high-temperature memory and logic devices because, unlike semiconductors, there are no temperature-dependent leakage currents to deal with [51]. In Gallium Nitride Electronics, high- electron-mobility transistor devices with pinch- off values of less than 2 V have been demonstrated at 500°C. More advanced circuits that are under development have increased complexity [38]. Substrates, passive components, and integration techniques (as well as packaging) require development. This technology is still at a lower level of maturity. 6.3.2 High-Temperature Mechanisms Robotic mechanism technology has matured over the past 15 years to enable short duration (<1 day) surface missions with refined capabilities, primarily sample acquisition and delivery. A general purpose electromagnetic actuator (motor, feedback sensor and gearbox) has been tested in environmental chambers that operate at full Venus temperature and pressure.

Long duration (60+ days) surface and low atmosphere missions have been proposed for which even high performance aerospace grade materials, coatings and lubricants need to be re-evaluated for

compatibility with corrosive chemical species (including H2S and SO2) found in the surface atmosphere. Other effects of extended exposure to high ambient temperature include overaging of high strength metals. Ceramics offer a partial solution but rigorous design and analysis methods need to be developed and material formulations, processing steps and test methods need to be standardized. High-fidelity environment testing is expensive, time-consuming and available only in a select few facilities.

There are a broad range of higher-level mechanism requirements for Venus surface missions and lower atmosphere missions, of which only some can be touched on here:

1) High-temperature mechanisms for surface missions: A substantial amount of development is needed in this area. Motors and encoders exist today that have operated for long periods at Venus surface temperatures. Many of the required mechanism components, materials, lubricants, etc. have been developed for operation at Venus temperatures. Significant materials development, along with and testing and qualification for the full Venus environment is still required, especially at the system level. 2) High-temperature mechanisms for sample acquisition and storage: Sample handling and caching techniques need to be tested with the mechanisms and instruments for the full Venus surface environment. This includes the algorithms for control and various faults conditions. 3) High-temperature mechanisms for descent guidance and control. Enabling any degree of guidance during descent will require developing mechanisms that can steer the descent system during at least some portion of the descent. Depending on the altitude range where guidance is employed, this would face temperature and corrosion challenges present at altitudes ranging from the middle atmosphere (e.g. ~ 55 km) to the surface. This would be a relatively short-duration application, since Venus descent takes roughly under one hour.

6.4 Communications As with Mars, we need to consider communications for the “Trunk Line” between Venus and Earth and the proximity communications between assets that are deployed to accomplish specific

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science activities and those assets (typically orbiters) that have the powerful trunk line communications capabilities. These trunk line communications would be: 1. Communications for orbiters: Communications systems exist today for Venus orbiters with the ability to communicate at rates up to 10 Mb/s. However, optical communications for Venus-to- Earth communications would enhance the data rate for the missions by at least a factor of 10. Development of three key enabling components of a Deep Space Optical Communications (DSOC) were developed by the STMD Game Changing Development program: a low frequency vibration isolation platform; a ground-based photon counting array; and a flight photon counting receiver for the uplink signal. These technologies are now being integrated into the DSOC Flight Laser Transceiver (FLT) and ground-based receiver to enable photon-efficient communications with the capability to discern faint laser signals from background "noise" from solar energy scattered by the Earth's atmosphere. DSOC's FLT will be advanced to NASA Technology Readiness Level 7. The DSOC payload, which will undergo ground validation testing in 2018-19, is scheduled to launch in 2022 aboard NASA's robotic Psyche mission to a metal asteroid. Psyche will reach its destination in 2026, at which point the DSOC payload is expected to help transmit the clearest, quickest information ever obtained from an expedition into the solar system. Optical communications could greatly enhance the capabilities of any future Venus mission involving radar imaging and interferometry provided an optical communications ground infrastructure is also developed. 2. Proximity Communications - probes, sondes and aerial platforms: Communications systems also exist for atmospheric or short duration surface missions supported by relay orbiters. Application of the Mars relay link communication protocols would enable asset leveraging. For in situ atmospheric missions with direct-to-Earth communications, the development of phased-array antennas and other more efficient antenna designs would greatly enhance data return. The IRIS V2.1 Deep Space Transponder developed at JPL is a Deep Space transponder targeted for Class-D space flight projects, utilizing COTS-grade components. Iris V2.1’s features include ~0.5 U volume, 1.2 kg mass, 35 W DC power consumption when fully transponding at 3.8 W radio frequency output. It is interoperable with NASA’s Deep Space Network (DSN) at X-Band frequencies (7.2 GHz uplink, 8.4 GHz downlink) for command, telemetry, and navigation. It will be used on MarCO to relay data from the INSIGHT lander back to Earth. In future, this technology will be important for SmallSat and CubeSat orbiters, small low cost probes and aerial platforms. 3. Communications on the Surface: Surface-to-orbit communications systems for long- duration surface missions is under development for long-lived landers. Communication frequencies up to ~100 MHz at data rates of 36 bps are planned by 2021. The development of this communications system is closely coupled with the electronics development to enable higher frequencies transmissions at adequate power levels [12-13]. Reduction of the power needed for data transmission and increasing both frequency and data rates are areas of future development.

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6.5 Guidance, Navigation, and Control Guidance, navigation, and control (GN&C) for the orbital spacecraft envisaged here present no unusual requirements. For the in situ elements, GN&C is needed for a range of motion planning, sensing, and vehicle control tasks to achieve desired maneuvers in order to accomplish specific goals. A recent assessment of GN&C technologies covers in situ missions at Mars, Venus, and Titan [52]. Here, we focus specifically on the state of technology for Venus missions. 1) Landed Missions—As described in the landing section (5.5) above, the application of pin- point landing and hazard avoidance technologies would be important for safe landing of a far-term landed mission to the Venus tesserae. While much of this technology has been developed for other applications, the Venus-unique needs include: 1) Infrared sensors for imaging the surface during much of the descent phase; 2) Techniques for matching heterogeneous data sets, in this case infrared and radar imaging data to support pin-point landing; and 3) Methods for achieving control authority in thick, hot atmospheres, including various forms of gliding decelerators (e.g. steerable parachutes, other aerodynamic control surfaces). For hazard avoidance, previous and ongoing work on capabilities for the Moon, Mars, primitive bodies, Europa, and Titan landers is germane, but work is required on hazard detection sensors that survive and operate in the Venus low-altitude thermal environment and on methods to achieve control authority in the dense Venus atmosphere that are efficient from mass, cost, and capability perspectives. 2) Aerial Platforms—Knowledge of the position, velocity, and attitude (especially azimuth) of the platform is important for certain scientific objectives as well as for enabling high-gain communications. Adequate position knowledge is possible by radiometric tracking from Earth when aerial platforms are in line-of-site from Earth. Beyond line-of-sight, position estimation possibilities include (1) using radiometric measurements from orbiters, including using SmallSats and CubeSats, and (2) for aerial platforms that descend below the cloud deck, onboard registration of night-side images of the surface to global radar maps of the surface created from orbiters [53]. For attitude, tilt is readily measurable with inertial sensors, but azimuth is difficult to obtain within or below the cloud deck, since Venus has no magnetic field useable for this purpose and since celestial sensing is greatly limited by the clouds. Potential solutions include onboard radio direction-finding on signals from Earth or orbiters, and onboard registration of surface imagery to global radar maps when the platform is below the clouds on the night side. Both of these methods would only be possible part of the time. Progress in miniaturization of onboard navigation grade inertial measurement units (IMUs) could sustain position, velocity, and attitude knowledge for brief periods of time after each measurement from external sources, but at most for a few hours. 3) Mobile Platforms on The Venus Surface or in the Lower Atmosphere: These classes of mobility platforms require position and heading knowledge to control their motion. Depending the level of autonomy they embody, they may also may require onboard perception systems for hazard detection and for recognizing science targets.

7.0 Instruments This section is structured in six segments: remote sensing instruments (active and passive) that can be deployed on an orbiter; instruments that can be implemented on a probe or balloon and would primarily sense the atmosphere; and three categories of landed instruments.

7.1 Remote Sensing—Active Because of the dense atmosphere of Venus, techniques that are useful to study the surface of airless bodies and Mars, such as visual imaging, gamma ray detection, and most applications of

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infrared sensing are not useful. However, radar, which has been used on both NASA (Magellan) and Soviet-era Venera spacecraft, is an effective tool for characterizing the surface. Improvements since that time enable much higher resolution images to be obtained. A variety of techniques have been used for characterizing the atmosphere as exemplified by ESA Venus Express. In addition, to the application of radiotechniques for characterizing the surface, radio waves can also be used to probe the atmosphere. In the classical radiooccultation technique used since the inception of planetary exploration, the radio signal from the spacecraft is observed from Earth as it passes behind the planet. The advent of SmallSats and CubeSats makes it possible to contemplate cross links between pairs of spacecraft. The number of transects will increase as the square of the number of spacecraft making it possible to greatly increase atmospheric coverage.

7.2 Remote Sensing – Passive Since the completion of the 2014 Technology Plan, new techniques of passive remote sensing have been developed that are applicable to Venus and there has also been progress in miniaturizing instrumentation. Seismic events couple to the atmosphere as infrasound and when those waves dissipate in the upper atmosphere they can modulate electron densities and optical emission in a manner that is observable from space. Space detection of tsunamis has been demonstrated on Earth. On Venus, seismic waves are coupled 60X more efficiently because of the dense atmosphere and much smaller quakes should be detectable. Infrared spectral imaging techniques have been investigated that could detect events on both the nightside and dayside of Venus. Probing the tenuous reaches of the upper atmosphere on Venus, which has previously required Discovery class missions are larger may now be possible using miniaturized submillimeter sensors (Reference Gordon Chin GSFC)

7.3 In Situ Aerial Platform and Probe Many instruments needed for a variety of atmospheric probes and higher-altitude aerial platforms that maintain internal temperatures well below Venus surface ambient are relatively mature. Many of the advancements needed are better described as achievable engineering challenges specific to missions or measurements rather than significant technology advancements. However, miniaturization of instruments would be of great benefit because payloads are also constrained in mass, power, and volume for these applications. The Venus Aerial Platform study [10] has identified several categories of observation where technology advances would enhance scientific capabilities: 1) Atmospheric Composition: Mass spectroscopy is the standard method for precision measurements coupled with targeted measurements using a Tunable Laser Spectrometer (TSL) where very high precision is needed. Progress in the development of Quadrupole Ion Trap Mass spectrometers (QITMS) could enable aerial platforms with small science payload capability to do high caliber science. 2) Cloud Particle Size and Composition: The complex cloud structure of Venus has been characterized in past missions but comprehensive understanding of the cloud-forming aerosols and their precursors remains elusive. Optical techniques for characterizing particle sizes can be coupled with mass spectrometry techniques for measuring particle composition. However, there are no such hybrid instruments capable of doing this today and the feasibility of miniaturizing heritage nephelometers to the point that they could be included as a payload on a long-duration platform is undemonstrated. 3) Atmospheric Structure; Techniques for measuring atmospheric structure have been honed on past probe missions but not all are applicable to a floating or flying platform. Most critical are methods for measuring position and velocity of the platform so that the velocity of the winds can be inferred. 4) Aerial Platform Geophysics: The proximity of the platform to the surface and contact with the atmosphere enable several important geophysical techniques including infrasound seismology,

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remnant magnetism, electromagnetic (EM) sounding and gravimetry. Miniaturized instruments are needed and where feasible they should be demonstrated in Earth analog experiments.

7.4 In Situ –Landed Missions: Ambient Temperature Operation A primary focus of these missions is to perform elemental, mineralogical, and petrologic analysis on the surface of Venus. With such limited lifetimes on the surface, time is of the essence so the speed with which these measurements can be conducted is vital. A Venus Science Priorities for Laboratory Measurements and Instrument Definition Workshop [54] was conducted in April, 2015 to: 1) present, discuss, and document the status of existing and developing instrument technologies that will enable future Venus missions; and (2) present, discuss, and document the status and needs of laboratory experiments and data that support and enhance fundamental Venus science as well as future mission preparation. The report suggests that miniaturization and increased sensitivity of heritage instruments, such as mass spectrometers, will unlock new opportunities for Venus exploration. In addition, a new generation of mature optical instruments are able to conduct an increasing portion of chemical analysis with the benefit of fewer moving parts and lower power requirements than traditional approaches. In all cases (even of those with flight heritage) instruments must be tested against the expected harsh conditions of the Venus atmosphere, especially those that are likely to be encountered near the surface. Calibration of all of these instruments with a Venus reference atmosphere chemistry and physical environment provides further value and resiliency to future missions. Technical developments in the following instruments can have a major impact. 1) X ray Diffraction and Fluorescence: These techniques measure the composition of elements and minerals in a powdered sample placed in the instrument by irradiating it with an X-ray beam. The Chemistry and Mineralogy (CheMin) instrument on the Curiosity rover employs this technique and worked successfully on Mars, but it took 27 hours of integration time to analyze the mineralogy of a sample [55]. Planetary Instrument for X-ray Lithochemistry [PIXL] is an arm mounted XRF instrument selected for the Mars 2020 roverthat is capable of fine-scale elemental analysis [56]. Both CheMin and PIXL types of instrument currently require sample collection and transport into the lander for analysis. The Science and Technology Definition Team (STDT) for the Venus Flagship Mission [7] recognized that speed of operation would be critical for a short lifetime Venus mission and identified the use of a high-flux X-ray source based on a carbon nanotube X-ray emitter as a technology solution in development that would alleviate the problem. 2) Raman and Laser Induced Breakdown Spectroscopy (LIBS): For the Venus Surface and Atmosphere Geochemical Explorer (SAGE) and Venus In Situ Compositional Investigation (VICI) New Frontiers missions, a team at Los Alamos National Laboratory studied another type of instrument, which is placed inside the lander and measures both elemental composition and mineralogy [57-58]. These instruments are based on the ChemCam and SuperCam instrument architecture currently operating on the Curiosity rover on Mars [59- 60], and under construction for the Mars 2020 rover. The key difference between these techniques and XRF/XRD is the ability to rapidly probe the samples remotely by directing a laser beam through the window of the pressure vessel to the Venus surface, and they do not require bringing a sample inside the pressure vessel. The LIBS signal is reduced in the Venus atmosphere and requires instrument enhancements enhancements developed for SuperCam relative to the original ChemCam design. The LIBS analysis ablates material, which may help in investigating the depth of surface weathering by probing below the rock surface. Some have hypothesized that the near-surface atmosphere (thermal and pressure gradients) could have an effect on the focus of the LIBS ablation laser. The magnitude of this potential turbulence and the impact on the LIBS laser needs to be conclusively resolved and this is one of the priorities of the New Frontiers Technology Development funding to the VICI team. In

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contrast, it has been conclusively demonstrated that Raman analysis [58, 61-62] under Venus surface conditions is not affected by the supercritical atmosphere. and a SuperCam architecture is sufficient to meet the science requirements. Another instrument with planetary heritage is Scanning Habitable Environments with Raman Luminescence for Organics and Chemicals (SHERLOC) [63]. SHERLOC is an arm-mounted UV Raman and fluorescence instrument selected for the Mars 2020 rover designed to specifically detect organics and biological signatures on Mars. An architecture similar to SHERLOC could have some mineralogical analysis advantages on Venus independent of the astrobiological focus of the SHERLOC instrument for Mars. 3) Fine-Scale Contextual Elemental and Mineralogical Analysis: The Raman-LIBS analysis described above has the ability to identify the nature of individual mineral grains in a rock or a soil sample, at microscopic resolution. The Mars 2020 Science Definition Team [64] recognized the geological importance of fine-scale imaging, fine-scale elemental analysis, and fine-scale mineralogy in their geologic context. That is, simultaneous acquisition of all three measurements is critical for understanding the relationship between different sample sites, whether on a microscopic or macroscopic scale. This requires, in addition to the techniques above, a microscopic imager analogous to the Mars Hand Lens Imager (MAHLI) instrument onboard the Mars Science Laboratory. We can anticipate that similar requirements are ultimately going to be important on Venus. The ability to do such measurements in situ, where they will be most interesting, will be technologically challenging.

7.5 In Situ – Landed Missions: High Temperature Operational (Sensors) Because of the severe environment, obtaining long-duration measurements on the surface of Venus is challenging. However, focused investigations are now considered to be viable by the mid 2020’s through the use of small long-lived platforms that leverage the capability of electronics and sensors designed to operate without thermal, chemical, or pressure protection. One small sat mission concept [13] proposes to deliver two landers to the surface of Venus for 120 days of operation. The science is focused on seismometry and temporal meteorology, and includes a seismometer, meteorology suite, a heat flux instrument, and finally an imaging package consisting of two cube sat cameras which will operate a short time at the beginning of the mission. Active development of Venus surface-appropriate technology (e.g. a meterology suite, ruggedized MEMS seismometer and heat flux sensor, and high bandwidth communications) enhance the near-term viability of such a mission. 7.6 In Situ – Long Duration – Mobile Laboratory Most concepts for a long-duration surface laboratory have assumed that much of the instrument would be contained in a protected volume whose temperature is controlled to near-Earth ambient and where instruments developed to operate in terrestrial laboratories (or which have heritage in Martian environments) could function. However, this may be impractical due to requiring active cooling, with a corresponding increase in mass and power budget. These challenges for long-duration missions all still apply but are even more difficult due to the power needed to operate instruments in constant listening modes or at the least, to obtain many repeated samples. Therefore, it is important to understand what can be done with sensors, electronics, and actuators that are operate at Venus surface ambient temperature. Significant thermal control achievements, enabling mature sensors to be used or high-temperature electronics systems, sensors, memory, etc. specific to those instruments are likely to be needed. Furthermore, the ability to reliably mobilize a platform on the Venus surface for a long period of time will require advances in conventional motors (permanent magnets with high Curie temperatures, and windings resistant to the corrosive atmosphere) and/or less conventional approaches that may include, e.g., wind-driven sails [45], balloon “bouncers” [65], or mechanical walkers [34-

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35].

8.0 Infrastructure Overview 1. Ames Research Center (ARC) Arc Jet Interaction Heating Facility (IHF) Facility Enhancement: The new 3” nozzle funded by SMD enahanced the NASA ARC IHF capability considerably and the capability allowed HEEET to be demonstrated for entry conditions ~ 5000 W/cm2 and > 5 atm. Missions ( NF-4) that planned to use HEEET have opted to fly low entry flight path angle taking advantage of the mass efficiency of HEEET to achieve low entry g’load. In order to verify/qualify HEEET design for future missions, it is necessary to have a slightly bigger ( ~ 4.5” dia) nozzle. This will be the lowest cost to address future mission risks. 2. Glenn Extreme Environment Rig (GEER): The GEER vessel, operated by Glenn Research Center, has been operational since Spring of 2015. This 0.8 m3 pressure vessel is capable of maintaining the physical and chemical conditions of the surface of Venus for an indefinite period of time, with continuous tests thus far of up to 80 days. Multiple user ports and a large hatch allow for accommodation of test articles ranging from 1 mm diameter geologic samples to complete instruments. Power and data feedthroughs have been custom developed to operate in the unique thermochemical environment, and a suite of candidate spacecraft component materials have been characterized for resistance to the Venus environment, Additionally, science investigations have used the vessel to re-create the surface conditions of Venus in order to study the unique behavior of surface-atmosphere interaction. GEER continues to gain new functional and analytic capability and is guided by annual reviews by an independent science advisory panel. GEER provides unmatched capability to mix and maintain an eight- component gas mixture in a large pressure vessel with precise thermal and chemical control.. 3. Goddard Flight Center: A small Venus pressure test chamber, also known as vici (Venus in-situ chamber investigations) s available for testing of small components/instruments and running short-term experiments. The operating range of the chamber is room pressure to ~1380 psi (~96bar), 25°C to 490°C, and the ‘working’ gas is typically CO2. Gas mixtures

that incorporate the three most abundant gases on Venus, CO2, N2, and SO2, are also used depending on the experiment. The chamber interior or functional work volume is a five-inch diameter 316 stainless steel cylinder with approximately 11 inches of vertical space. Electrical/tubing feedthroughs and small sight windows are options that can be incorporated as needed into any particular test. There are pending plans to upgrade the chamber to a more resistant alloy. 4. Venus Optical Analysis Chamber: Los Alamos National Laboratory has two – 2 m long, 110 mm diameter chambers that are capable of optically probing

o samples under 92 atm of supercritical CO2 at 465 C. These two chambers can be operated independently (2 m long path length) or together (4 m long path length). The chamber can be capped with sapphire, quartz or a steel plug on one or both ends of the chamber. It enables both active remote sensing with a laser as well as passive spectroscopy.

9.0 Technology Highlights Since 2014 Venus Technology Roadmap presented in this document has notable differences from the previous version in 2014. Recent technology advancements have changed the landscape of Venus exploration and thus the Findings of this present Venus Technology Plan. In particular, Table 8.1

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shows 2014 Finding and a 2018 State-of-The-Art Summary. This Table highlights that, although due to the unique challenges of Venus exploration further development is needed, advancements in Venus relevant technology in the last four years have been significant.

Table 8.1 2014 Technology Plan Findings and 2018 Summary of the Present State-of-the-Art 2014 Finding 2018 State-of-the-Art Summary 1. Entry Technology for Venus: The thermal protection system HEEET is nearly fully mature (TPS) technology developed for missions involving entry into technology and will be delivered in the Venus atmosphere has not been used for many decades, FY’19 for mission infusion. This and the ability to easily replicate it has been lost. Two closes a very large gap for Venus attractive options for replacing the prior technology, 3D aerocapture, entry, descent and landed Woven TPS and ADEPT technology, are currently under missions. ADEPT with a sounding development under the sponsorship of the Space Technology rocket sub-orbital flight test requires Missions Directorate (STMD). …This development needs minimal additional development for the continued endorsement of the Planetary Science enabling small and cube-sat missions Division (PSD). to Venus. See Section 5.3 2. High-Temperature Subsystems and Components for Notable advancements have been Long-Duration (months) Surface Operations: made in moderately complex high Advances in high-temperature electronics and thermo temperature electronics with electric power generators would enable long-duration demonstration Venus simulated missions on the surface of Venus operating for periods conditions for up to 60 days. These of as long as a year, where the sensors and all other electronics are the foundation for components operate at Venus surface ambient development of a long-lived lander temperature. …. Development of the high temperature with an array of high temperature electronics, sensors and the thermo-electric power sensors intended for Venus surface sources designed for operating in the Venus ambient operation for up to 120 days or more. would be enabling for future missions. See section 6.3.1. Technology investments are needed Aerial Platforms for Missions to Measure 3. including new science instrumentation Atmospheric Chemical and Physical Properties: and modeling tools to characterize the Aerial platforms have a broad impact on exploration of behavior of vehicles in the Venus Venus. After more than a decade of development, the environment. However, there are no technology for deploying balloon payloads approaching technological show stoppers to 100 kg with floating lifetimes in excess of 30 days near impede the development of these 55 km altitude is approaching maturity. Vehicles for capabilities. Flight tests using the operation at higher and lower elevations in the middle Earth environments as an analog for atmosphere and with the ability to change and maintain Venus will be needed to optimize specific altitudes are much less mature and need both the vehicles and science development. A buoyant vehicle, operating close to the experiments. See section 7.3 Venus surface requires major development. Aerial platforms would be an essential part of any atmospheric or surface sample mission. Development of these aerial platform technologies is enabling for mid-term and far-term missions. A workshop focused on instruments In Situ Instruments for Landed Missions: Since the 4. for Venus surface was conducted. Planetary Science Decadal Survey in 2011, there has Laser induced breakdown been significant progress in instruments for surface spectroscopy (LIBS) and Raman geology and geochemistry (e.g., laser induced spectroscopy has been demonstrated. breakdown spectroscopy [LIBS] in conjunction with NASA awarded technology remote Raman spectroscopy has been demonstrated). development funding to the VICI Advances in other instruments for “rapid petrology” also New Frontiers 4 mission to mature the appear possible spurred in part by developments VEMCam (Raman and LIBS) underway for investigating the surface of Mars. A instruments. See Section 7.4 workshop focused on instruments for Venus surface

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operations would be helpful for defining future directions and such a workshop is planned for January 2015. Development of three key enabling 5. Deep Space Optical Communications: Development components of a Deep Space Optical of deep space optical communications technology Communications (DSOC) were would enhance the performance of missions involving developed by the Space Technology high resolutions radar imaging of the surface of Venus Missions Directorate (STMD) Game enabling mapping to be completed much more rapidly Changing Development program: a than with RF communications systems. NASA STMD low frequency vibration isolation is currently developing the key component technologies platform; a ground-based photon for deep space communications and NASA’s Space counting array; and a flight photon Communications and Navigations Directorate (SCaN) counting receiver for the uplink is planning on a 10-m optical ground station by 2015. signal. These technologies are now Implementation of a flight experiment of optical being integrated into a system communications would represent a major step scheduled to launch in 2022. See forward in the adoption of the technology, and if Section 6.4. implemented on a Venus orbiter mission, it could

significantly enhance the science return. Investments are presently on-going in Advanced Power and Cooling Technology for Long- 6. battery and power technology with the Duration Surface Operations: Most scientific objective of enabling small platform objectives at the Venus surface require sensors that long-lived surface landers. Some operate at temperatures well below 100oC. Current advancements have been made in passively cooled systems are limited to a lifetime of 3 passive cooling approaches, but to 5 hours. Advanced liquid-vapor phase change overall limited work has been done in cooling could extend lifetimes to 24 hours and could advancing technologies such as benefit the Tessera lander conceived as a mid-term Stirling cycle-engine to enable power mission. Highly efficient mechanical thermal and cooling since the 2014 conversion and cooling devices (typified by the Stirling Technology Plan. See Section 6.1 cycle-engines and capable of operating in a 460oC environment) are required for this purpose. With lifetimes of months, these are enabling for the Venus mobile surface and near-surface laboratory mission concepts. Investments in advanced power and cooling technology are needed to enable both mid-term and far-term missions. 7. Advanced Descent and Landing: Lander missions for the Precision landing and hazard mid-term would target the Tessarae regions of Venus which avoidance technologies have reached radar imaging indicates to be extremely rough and irregular TRL 7 to 8 for missions to the Moon topography. Following the Mars model, achieving safe and Mars and are under development landings in regions of complex topography will require the for Europa. These methods require development of improved targeting accuracy and precision significant further work for adaptation landing techniques potentially accompanied by hazard to the dense, hot atmosphere and long avoidance during the terminal-descent phase. New concepts descent time at Venus. See Section are needed for adapting methods of terrain relative 5.4-5.6, and 6.5. navigation and guidance to operation in the dense Venus atmosphere.

10.0 Findings The following findings are based on the work discussed within this document, feedback from the Venus Technology Forum of November 19, 2013, and additional responses from members of the VEXAG community. The findings are grouped into two sets of findings,

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Technology Development and Infrastructure Development. Each of these is in priority order. 1. Entry Technology for Venus: Successful delivery of HEEET at TRL 6, has eliminated one of the critical technology gap identified in 2014 for in-situ Venus missions. HEEET and PICA are two NASA developed technologies that provide broad cover for a large class of Venus in-situ missions. Given in- situ mission cadence to Venus is bound to remain low and unpredictable, these capabilities must be maintianied. It is critical the SMD-PSD ensure the entry technology capability does not atrophy, and that periodic assessment and small investments be made to ensure both HEEET and PICA continue to be available.

2. High-Temperature Subsystems and Components for Long-Duration (months) Surface Operations: Advances in high-temperature electronics have been significant with paradigm changing advancements achieved in the last 4 years. Nonetheless, these are simpler electronics system with significant development still needed to achieve the capabilities of conventional electronics. Development of other high temperature technologies have also seen investment and advancements. Power generation of different, higher density forms would enable long-duration missions on the surface of Venus, but have seen limited recent development overall. Development of the high temperature electronics, sensors and the high density power sources designed for operating in the Venus ambient with increasing levels of capability would be enabling for future missions 3. Aerial Platforms for Missions to Measure Atmospheric Chemical and Physical Properties: The Aerial Platform study has suggested a way forward for Venus atmospheric investigations. This includes a competitive program to determine which Variable Altitude balloons approach is most suited to operation for Venus exploration. Advances in Guidance, Navigation and Control for Venus flight will have particular impact on aerial platforms. Technology development includes instruments for atmospheric composition, cloud particle size /composition, atmospheric structure, and geophysics. Development of these aerial platform technologies is an enabling capability. 4. In Situ Instruments for Landed Missions: In Situ Instruments for Landed Missions: Advances in capabilities in instrumentation for other planetary applications will continue to have strong impact on the corresponding capabilities for Venus landers. However, in some cases, implementation of these instrument systems for Venus specific applications can be challenging given, e.g., increased complexity in sample handling related to short lived Lander Missions. Further, while leveraging instrument development from other planetary applications has its role, development of specific instruments meeting unique Venus science needs is necessary. The adaptation of flight demonstrated technology to Venus applications and the development of new instrument systems uniquely targeted to the Venus environment should continue to be supported. 5. Venus Communications and Navigation Infrastructure: The establishment of a low cost orbiting communication platform infrastructure at Venus for the support of in situ exploration would be an enabling foundation for future Venus exploration. Such an infrastructure would be based on the advancement of smallsat and cubesat

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technology and as such can be implemented at much lower cost than the Mars orbital infrastructure. Such orbiters could also aid position estimation for aerial platforms when the aerial platforms are out of sight of Earth-based tracking stations. As with Mars, the orbiters would also conduct independent science measurements. Study of the feasibility of and methods for establishing such a communications and navigation infrastructure is recommended. 6. Advanced Cooling Technology for Long-Duration Surface Operations: Current passively cooled systems are limited to a lifetime of 3 to 5 hours with possible extension to 24 hours. Highly efficient mechanical thermal conversion and cooling devices (typified by the Stirling cycle-engines and capable of operating in a 460oC environment) are required for this purpose. With lifetimes of months, these are enabling for the Venus mobile surface and near-surface laboratory mission concepts. Investments in advanced cooling technology have been limited and are needed to enable future missions. 7. Advanced Descent and Landing: Lander mission proposals have begun to Tessearae regions of Venus, which radar imaging indicates to be extremely rough and irregular topography. In the near term, this uses unguided descent with large landing ellipses and hazard tolerant landing systems to cope with rocks and steep slopes. To enable targeting smaller ellipses or rougher terrain beyond the near term requires developing techniques for improved targeting accuracy, potentially accompanied by hazard avoidance during the terminal descent phase. Probes and sondes with surface imaging capability may also benefit from descent guidance. New concepts are needed for adapting precision descent and landing hazard avoidance technologies to operation in the dense, hot Venus atmosphere. 8. Autonomy and Automation: Increasing capabilities for automation and autonomous decision-making combined with increasing computing power can change the way missions are conducted. Leveraging development in these fields can enhance the science delivered across a range of possible mission scenarios from orbital, aerial, to landed and to exploit synergies between data acquired from the different platforms. Efforts to transition automation and autonomous technologies to Venus specific applications would enhance science delivered and mission success. 9. Small Platforms: SmallSat, CubeSat and other small platform technology can make important contributions to Venus exploration. Orbiters and in situ aerial vehicles using this technology can make important scientific contributions, while small platforms lander systems can open new possibilities in Venus explorations. These small platforms can complement the more traditional concepts of Venus mission design with an unique niche in Venus exploration. The development of small platform concepts as an addition to larger missions, as well as a new mission type or mission augmentation, is an integral part of a complete multistage Venus exploration program.

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evolve as new technologies, such as autonomy, begin to have a role in mission planning. Infrastructure is a major resource that should continue to be supported and expanded in a manner that meets the evolving needs of the broad Venus community. 2. Environmental Modelling and Simulation: There is there is a strong need for a system science approach to Venus modeling including coupling of different models, e.g. interior models coupled to surface models. Further, laboratory data is needed to provide improved input to these models. Establishing and maintaining such a broad but interdependent infrastructure is strongly recommended.

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11.0 Acronyms and Abbreviations ADEPT Adaptable Deployable Entry and Placement Technology ALHAT Autonomous Landing and Hazard Avoidance Technology ASRG Advanced Stirling Radioisotope Generator ARC: Ames Research Center ESA European Space Agency GCD Game-Changing Development GN&C guidance, navigation, and control GOI Goals, Objectives and Investigations for Venus Exploration GRC Glenn Research Center GSFC Goddard Space Flight Center HEEET High Energy Entry Environment Technology HIAD Hypersonic Inflatable Aerodynamic Decelerator IHF (Ames Research Center) Interaction Heating Facility JAXA Japanese Space Agency JPL Jet Propulsion Laboratory LIBS laser induced breakdown spectroscopy LIDAR light detection and ranging LLISSE Long-Lived In-Situ Solar System Explorer MAV micro-aerial vehicle MMRTG Multi-Mission Radioisotope Thermoelectric Generator PCM phase-change material PSD Planetary Science Division RF radio frequency RVE Roadmap for Venus Exploration SCaN Space Communications and Navigations (Directorate) SMD (NASA) Science Mission Directorate STDT Science and Technology Definition Team STIM Science and Technology Interchange Meeting STMD (NASA) Space Technology Mission Directorate TPS thermal protective system TRL technology readiness level VAMP Venus Atmosphericaneuverable Platform VEXAG Venus Exploration Analysis Group VSSR Venus Surface Sample Return

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12.0 References

1. Venus Goals Objectives and Investigations Document, posted on VEXAG website,http://www.lpi.usra.edu/vexag/reports/Goals-Objectives-Investigations- Table.pdf 2. Roadmap for Venus Exploration (RVE) Document, VEXAG website, http://www.lpi.usra.edu/vexag/reports/Roadmap-Draft-21Feb14.pdf 3. Vision and Voyages for Planetary Science in the Decade 2013-2022, National Research Council, 2011. 4. Solar System Exploration Roadmap, NASA Planetary Science Division, 2006. 5. E. Kolowa et al., Extreme Environments Technologies for Future Space Missions, JPL D-32832 (internal document), Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 2007. (http://solarsystem.nasa.gov/multimedia/download-detail.cfm?DL_ID=322, accessed Feb. 28, 2014). 6. J. A. Cutts, T. S. Balint, E. Chassefiere, and E. A. Kolawa, Technology Perspectives in the Future Exploration of Venus, in Exploring Venus as a Terrestrial Planet, American Geophysical Union, Washington, D.C., Geophysical Monograph Series, Vol. 176, pp. 207–225, 2007. 7. Venus Flagship Mission Study, Report of the Venus Science and Definition Team, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, April 2009. 8. T. S. Balint, J. A. Cutts, M. Bullock, J. Garvin, S. Gorevan, J. Hall, P. Hughes, G. Hunter, S. Khanna, E. Kolawa, V. Kerzhanovich, and E. Venkatapathy, Technologies for Future Venus Exploration, White Paper to the Planetary Science Decadal Survey, Sept. 2009. 9. Planetary Science Deep Space SmallSat Studies (PSDS3) program, https://www.nasa.gov/feature/nasa- selects-cubesat-smallsat-mission-concept-studies 10. Aerial Platforms For the Scientific Exploration of Venus, Summary Report The Venus Aerial Platforms Study Team, August, 2018. 11. R. Grimm and Martha Gilmore, VEXAG Venus Bridge Study https://www.lpi.usra.edu/vexag/reports/Venus_Bridge_Summary_Slides.pdf 12. T. Kremic, G. Hunter, J. Rock, “Long-Lived In-Situ Solar System Explorer”, (2017) VEXAG presentation located at: https://www.lpi.usra.edu/vexag/meetings/archive/vexag_15/presentations/8-Kremic-LLISSE.pdf 13. T. Kremic, R. Ghail, M. Gilmore, W. Kiefer, S. Limaye, G. Hunter, C. Tolbert, M. Pauken, and C. Wilson, Seismic and Atmospheric Exploration of Venus Final Report, https://www.lpi.usra.edu/vexag/reports/SAEVe-6-25-2018.pdf 14. 2018 Workshop on Autonomy for Future NASA Science Missions, October 10-11, 2018,Pittsburgh, PA, https://science.nasa.gov/technology/2018-autonomy-workshop 15. D. G. Murri, R. W. Powell, and J. L. Prince, “Development of Autonomous Aerobraking: Phase 1” NASA/TM-2012-217328/NESC-RP-09-00605 16. D. G. Murri, Development of Autonomous Aerobraking: Phase 2” NASA/TM-2013- 218032/ NESC-RP- 09-00605 17. Z. R. Putnam, and R,. D. Braun “Drag Modulation Flight Control System Options for Planetary Aerocapture,” 51st AIAA Aerospace Sciences Meeting, AIAA Paper 2013-0030, Jan. 2013. 18. E. Venkatapathy, P. Wercinski, K. Hamm, B. Yount, D. Prabhu, B. Smith, J. Arnold, A. Makino, P. Gage and K. Peterson, “Adaptive Deployable Entry and Placement Technology (ADEPT): Technology Development Project funded by Game Changing Development Program of the Office of the Chief Technologist,” International Planetary Probe Workshop, Toulouse, Fr., June 22–26, 2012. 19. Ginger Gardiner, “Heatshield for Extreme Entry Environment Technology (HEEET): A broader mission”, Composites World Magazine, August 2018. https://www.compositesworld.com/articles/heatshield- for-extreme-entry-environment-technology-heeet-a-broader-mission. 20. Bally Ribbon Mills, Bally, PA, https://info.ballyribbon.com 21. https://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/index.html

Venus Technology Plan DRAFT

22. J. L. Hall, A. H. Yavrouian, V. V. Kerzhanovich, T. Fredrickson, C. Sandy, Michael T. Pauken, Eric Kulczycki, Gerald J. Walsh, M. Said, and S. Day, “Technology Development for a Long duration, Mid- Cloud Level Venus Balloon,” Advances in Space Research, vol. 48, no. 7, pp. 1238–1247, October 2011. 23. Venus Intrepid Tessera Lander: Mission Concept Study Report to the NRC Decadal Survey Inner Planets Panel, 2010. 24. L. Glaze, “VICI: Venus In situ Composition Investigations”, European Planetary Science Congress 2017, EPSC Abstracts, vol. 11, 2017. 25. “Autonomous Landing and Hazard Avoidance Technology (ALHAT) – Technology Demonstration Mission,” NASA website, http://www.nasa.gov/mission_pages/tdm/alhat/index.html 26. M. Wright, T. White, and N. Mangini, “Data-Parallel Line Relaxation (DPLR) Code User Manual Acadia- Version 4.01.1,” NASA TM-2009-215388, October 2009. 27. A. Mazaheri, P. Gnoffo, C. Johnston, and B. Kleb, “LAURA Users Manual,” Tech. Rep. NASA TM 2010- 216836, 2010 28. https://gameon.nasa.gov/projects-2/entry-systems-modeling/ 29. B. Cruden, and A. Brandis, “Updates to the NEQAIR Radiation Solver,” Radiation and High Temperature Gas Workshop, November 2014. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150022164.pdf 30. C. Johnston, B. Hollis, B., and K. Sutton, “Spectrum Modeling for Air Shock-Layer Radiation at Lunar- Return Conditions,” Journal of Spacecraft and Rockets, Vol. 45, No. 5, 2008, pp. 865-878. 31. R. W. Powell, S. A. Striepe, P. N. Desai, E. M. Queen, P.V. Tartabini, G. I. Brauer, D. E. Cornick, D. W. Olson, F. M. Petersen, R. Stevenson, M. C. Engel, S. M. Marsh, “Program to Optimize Simulated Trajectories (POST II), Vol. II Utilization Manual.” Version 1.1.1.G, May 2000. 32. J. L. Hall and A. H. Yavrouian, “Pinhole Effects on Venus Superpressure Balloon Lifetime,” AIAA Paper 2013-1292, presented at the 2013 Balloon Systems Conference, Daytona Beach, FL, March 26–28, 2013. 33. D. Bugby, S. Seghi, E. Kroliczek, and M. Pauken, “Novel Architecture for a Long Life, Lightweight Venus Lander,” AIP Conference Proceedings, vol. 1103, pp. 39–50, 2009. 34. G. A. Landis and K. C. Mellott, “Venus surface power and cooling systems”, Acta Astronautica, v. 61, 11– 12, Pages 995-1001, 2007. 35. J. Sauder, E. Hilgemann, J. Kawata, K. Stack, A. Parness, and M. Johnson (2015) Automaton Rover for Extreme Environment (AREE): Rethinking an Approach to Rover Mobility. 15th Meeting of the Venus Exploration Analysis Group, Laurel, MD 36. T. Sweetser, J. Cameron, G.-S. Chen, J. Cutts, R. Gershman, M. S. Gilmore, J. L. Hall, V. Kerzhanovich, A. McRonald, E. Nilsen, W. Petrick, D. Rodgers, C. Sauer, B. Wilcox, A. Yavrouian, W. Zimmerman, Venus Surface Sample Return: A Weighty High Pressure Challenge,” American Astronautical Society, 2001 (also Scientific & Technical Information, NASA Center for Aerospace Information). 37. https://gameon.nasa.gov/projects/high-performance-spaceflight-computing-hpsc/ 38. Q..V. Nguyen, HOTTech Program Overview, 5th Annual Meeting of the Venus Exploration Analysis Group (VEXAG) November 14–16, 2017. Laurel, Maryland, https://www.lpi.usra.edu/vexag/meetings/archive/vexag_15/presentations/2-Nguyen-HOTTech- Overview.pdf 39. Based on requested for proposals: https://govtribe.com/project/nasa-next-generation-space-relay- architecture-concept-study 40. G. A. Landis and E. Haag. "Analysis of Solar Cell Efficiency for Venus Atmos-phere and Surface Missions", 11th International Energy Conversion Engineering Confer-ence, Joint Propulsion Conferences, (AIAA 2013-4028), 2013. https://doi.org/10.2514/6.2013-4028 41. J. Grandidier, A. P. Kirk, M. L. Osowski, P. K. Gogna, S. Fan, M. L. Lee, et al., "Low-Intensity High- Temperature (LIHT) Solar Cells for Venus Atmosphere," Submitted to IEEE Journal of Photovoltaics, 2018. 42. Long Lived Venus Lander Cooling System Study And Conceptual Design, Solicitation Number: NC10326157Q 45

Venus Technology Plan DRAFT

https://www.fbo.gov/index?s=opportunity&mode=form&id=f8755bd2f27c33f3dde284e3e7b76e8a&tab= core&_cview=0 43. Sierra Lobo, Inc, Thermoacoustic Duplex Technology for Cooling and Powering a Venus Lander, https://www.sbir.gov/sbirsearch/detail/411683 44. F. Ritzert, M. V. Nathal, J. Salem, N. Jacobson, J. Nesbitt, “Advanced Stirling Duplex Materials Assessment for Potential Venus Mission Heater Head Application”, 9th Annual International Energy Conversion Engineering Conference (IECEC); 31 Jul. - 3 Aug. 2011; San Diego, CA; , 2011. 45. G. A. Landis, S. R. Oleson, T. Kremic, R. D. Patel, E. T. Reehorst, and G. R. Hopkins. "Small Wind- powered Missions to the Surface of Venus", AIAA SPACE and Astronautics Forum and Exposition, AIAA SPACE Forum, (AIAA 2017-5336) https://doi.org/10.2514/6.2017-5336 46. S. R. Oleson and M. Paul. "COMPASS Final Report: Advanced Lithium Ion Venus Explorer (ALIVE)." (2016). Found at: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2016 0011272.pdf 47. P. Neudeck, R. D. Meredith, L. Y. Chen, D. J. Spry, L. M. Nakley, and G. W. Hunter, “Prolonged silicon carbide integrated circuit operation in Venus surface atmospheric conditions”. (2016) AIPAdvances. http://aip.scitation.org/doi/10.1063/1.4973429. 48. D. J. Spry, P. G. Neudeck, D. Lukco, L. Y. Chen, M. J. Krasowski, N. F. Prokop, C. W. Chang, and G. M. Beheim, “Prolonged 500 °C Operation of 100+ Transistor Silicon Carbide Integrated Circuits, “presented at 2017 International Conference on Silicon Carbide and Related Materials, Sept. 17-22, Washington, DC.. 49. P. Voosen, “Armed with tough computer chips, scientists are ready to return to the hell of Venus,” http://www.sciencemag.org/news/2017/11/armed-tough-computer-chips-scientists-are-ready-return-hell- venus 50. D. Lukco, D. J. Spry, R. P. Harvey, G. C. C. Costa, R. S. Okojie, A. Avishai, L. M. Nakley, P. G. Neudeck, G. W. Hunter, Chemical Analysis of Materials Exposed to Venus Temperature and Surface Atmosphere, Earth and Space Science, Volume 5, Issue 7, June2018, https://doi.org/10.1029/2017EA000355 51. H. Manohara, R. Toda, R. H. Lin, A. Liao, and M. Mojarradi, “Carbon Nanotube-Based Digital Vacuum Electronics and Miniature Instrumentation for Space Exploration,” Proceedings of SPIE, vol. 7594, 2010 52. M. Quadrelli and M. McHenry, Guidance Navigations and Control Assessment for Future Planetary Science Missions: Part III Surface Guidance Navigation and Control, JPL D-78106 (internal document), Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, April 2013. 53. A. Ansar and L. Matthies, “Multi-Modal Image Registration for Localization in Titan’s Atmosphere,” IEEE/RSJ International Conference on Intelligent Robots and Systems, October 2009. 54. Venus Science Priorities for Laboratory Measurements and Instrument Definition Workshop Report, April 7-8, 2015, National Institute of Aerospace Langley, VA https://www.lpi.usra.edu/vexag/reports/Venus-Sci- Priority-Lab-Meas-Inst-Definition-Workshop.pdf 55. D. L. Bish et al., “X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater,” Science, vol. 341, no. 6153, Sept. 27, 2013. 56. A. Allwood, J. Hurowitz, L. W. A. Wade, R. P. Hodyss, D. Flannery, “Seeking ancient microbial biosignatures with PIXL on Mars 2020”, American Geophysical Union 2014 Fall Meeting, 2014, Vol.2014 57. S. M. Clegg, S. K. Sharma, A. K. Misra, et al., “Raman and Laser-Induced Breakdown Spectroscopy (LIBS) Remote Chemical Analysis under Venus Atmospheric Pressure,” 43rd Lunar and Planetary Science Conference, 2012. (http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2105.pdf) 58. S. M. Clegg, R. Wiens, A. K. Misra, K. Anupam, S. K. Sharma, J. Lambert, S. Bender, R. Newell, K. Nowak-Lovato, S. Smrekar, M. D. Dyar, S. Maurice, “Planetary Geochemical Investigations Using Raman and Laser-Induced Breakdown Spectroscopy”, Applied Spectroscopy, September 2014, Vol.68(9), pp.925- 936. 59. S. Maurice et. al. “The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Science Objectives and Mast Unit Description”, Space Science Reviews, 2012, Vol.170(1), pp.95-166. 60. R. Wiens et. al. “The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Body Unit and Combined System Tests”, Space Science Reviews, 2012, Vol.170(1), pp.167-227 61. S. K. Sharma, A. K. Misra, S. M. Clegg, J. E. Barefield, R. C. Wiens, and T. Acosta, “Time-resolved remote Raman study of minerals under supercritical CO2 and high temperatures relevant to Venus exploration”, Phil. Trans. R. Soc. A 2010 368, 3167-3191 46

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62. S. K. Sharma, A. K. Misra, S. M. Clegg, J. E. Barefield, R. C. Wiens, T. E. Acosta, and D. E. Bates, “Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration”, Spectrochimica Acta Part A 80 (2011) 75– 81. 63. L. W. Beegle, R. Bhartia, L. DeFlores, M. Darrach, R. D. Kidd, W. Abbey, S. Asher, A. Burton, S. M. Clegg, P. G. Conrad, K. Edgett, B. L. Ehlmann, F. Langenforst, M. Fries, W. Hug, K. Nealson, J. Popp, P. Sorbon, A. Steele, R. Wiens, K. Williford, “SHERLOC; Scanning Habitable Environments with Raman Luminescence for Organics and Chemicals, an investigation for 2020”, 45th lunar and planetary science conference, 2014, Vol.45. 64. J. F. Mustard et al., Report of the Mars 2020 Science Definition Team, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, July 1, 2013. (http://marsmobile.jpl.nasa.gov/mars2020/files/m2020/SDT-Report%20Finalv6.pdf 65. A. Bachelder et al. (1999), Venus Geoscience Aerobot Study (VEGAS), Proceedings of the AIAA International Balloon Technology Conference, AIAA-99-3856.