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Smallsat Aerocapture to Enable a New Paradigm of Planetary Missions

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Smallsat Aerocapture to Enable a New Paradigm of Planetary Missions SmallSat Aerocapture to Enable a New Paradigm of Planetary Missions Alex Austin, Adam Nelessen, Bill Ethiraj Venkatapathy, Robin Beck, Robert Braun, Michael Werner, Evan Strauss, Joshua Ravich, Mark Jesick Paul Wercinski, Michael Aftosmis, Roelke Jet Propulsion Laboratory, California Michael Wilder, Gary Allen CU Boulder Institute of Technology NASA Ames Research Center Boulder, CO 80309 Pasadena, CA 91109 Moffett Field, CA 94035 [email protected] 818-393-7521 [email protected] [email protected] Abstract— This paper presents a technology development system requirements, which concluded that mature TPS initiative focused on delivering SmallSats to orbit a variety of materials are adequate for this mission. CFD simulations were bodies using aerocapture. Aerocapture uses the drag of a single used to assess the risk of recontact by the drag skirt during the pass through the atmosphere to capture into orbit instead of jettison event. relying on large quantities of rocket fuel. Using drag modulation flight control, an aerocapture vehicle adjusts its drag area This study has concluded that aerocapture for SmallSats could during atmospheric flight through a single-stage jettison of a be a viable way to increase the delivered mass to Venus and can drag skirt, allowing it to target a particular science orbit in the also be used at other destinations. With increasing interest in presence of atmospheric uncertainties. A team from JPL, NASA SmallSats and the challenges associated with performing orbit Ames, and CU Boulder has worked to address the key insertion burns on small platforms, this technology could enable challenges and determine the feasibility of an aerocapture a new paradigm of planetary science missions. system for SmallSats less than 180kg. Key challenges include the ability to accurately target an orbit, stability through atmospheric flight and the jettison event, and aerothermal stresses due to high heat rates. TABLE OF CONTENTS Aerocapture is a compelling technology for orbital missions to 1. INTRODUCTION ....................................................... 1 Venus, Mars, Earth, Titan, Uranus, and Neptune, where 2. DRAG MODULATION AEROCAPTURE TRADE eliminating the propellant for an orbit insertion burn can result in significantly more delivered payload mass. For this study, SPACE .......................................................................... 2 Venus was selected due to recent NASA interest in Venus 3. REFERENCE MISSION CONCEPT ............................ 3 SmallSat science missions, as well as the prevalence of delivery 4. EXO-ATMOSPHERIC TRAJECTORIES AND options due to co-manifesting with potentially many larger TARGETING ................................................................. 4 missions using Venus for gravity assist flybys. In addition, performing aerocapture at Venus would demonstrate the 5. ATMOSPHERIC MODELING AND MONTE CARLO technology’s robustness to aerothermal extremes. A survey of SIMULATIONS ………………………………………..6 potential deployment conditions was performed that confirmed 6. HEATING ENVIRONMENT AND THERMAL that the aerocapture SmallSat could be hosted by either PROTECTION SYSTEMS ............................................. 11 dedicated Venus-bound missions or missions performing a flyby. 7. NOTIONAL FLIGHT SYSTEM DESIGN ................... 12 8. MECHANICAL SYSTEM DESIGN ........................... 13 There are multiple options for the drag skirt, including a rigid 9. AERODYNAMICS ANALYSIS FOR MULTI-BODY heat shield or a deployable system to decrease volume. For this study, a rigid system was selected to minimize complexity. A SEPARATION .............................................................. 14 representative SmallSat was designed to allocate the mass and 10. CONCLUSIONS ..................................................... 17 volume for the hardware needed for a planetary science mission. 11. FUTURE WORK PLANNED................................... 17 In addition, a separation system was designed to ensure a clean separation of the drag skirt from the flight system without ACKNOWLEDGEMENTS ............................................ 18 imparting tipoff forces. The total spacecraft mass is estimated to REFERENCES ............................................................. 18 be 68 kg, with 26 kg of useful mass delivered to orbit for BIOGRAPHY ............................................................... 19 instruments and supporting subsystems. This is up to 85% more useful mass when compared to a propulsive orbit insertion, depending on the orbit altitude. 1. INTRODUCTION Key to analyzing the feasibility of aerocapture is the analysis of Aerocapture has long been considered a compelling the atmospheric trajectory, which was performed with 3 degree- technology that could significantly enhance science return or of-freedom simulations and Monte Carlo analyses to characterize the orbit targeting accuracy. In addition, reduce costs for orbital missions to Mars, Venus, Titan, aerothermal sizing was performed to assess thermal protection Uranus, and Neptune [1][2][3][4]. Aerocapture uses the drag from a single hyperbolic atmospheric pass to provide the 978-1-5386-6854-2/19/$31.00 ©2019 IEEE 1 delta-V needed for orbit insertion (OI), rather than a large 1. Vehicle stability throughout atmospheric flight, burn of a rocket engine. Studies suggest that, compared to and the effects of tipoff and/or potential propulsive OI, aerocapture using “traditional” planetary recontact between the two bodies after spacecraft can increase delivered payload mass by 15% at separation Mars, 70% at Venus, more than 200% at Titan and Uranus, 2. Guidance and control architecture for targeting a and an estimated 800% or more at Neptune [2]. Aerocapture precise science orbit despite navigational and is particularly well-suited for SmallSat OI, due to the atmospheric uncertainties difficulty of designing and integrating a propulsion system to 3. Aerothermal stresses on the vehicle due to high perform hundreds to thousands of meters per second delta-V heat rates on a small platform. Other proposed orbit insertion methods for SmallSats, such as solar electric propulsion, are In order to address these key challenges and determine the potentially difficult to implement and can result in long cruise feasibility of this aerocapture system for use in SmallSat times to the destination, which can stress SmallSat hardware planetary missions, a multi-organizational team was formed capabilities. Aerocapture presents a potentially fast and efficient way for small platforms to enter orbit around from collaborators at the Jet Propulsion Laboratory (JPL), planetary bodies and accomplish meaningful science Ames Research Center (ARC), and the University of objectives. Colorado at Boulder (CU Boulder). Spanning various areas of expertise, this team brings a wealth of experience to In order to target a specific science orbit and account for day- address the key challenges of drag modulation aerocapture. of-flight uncertainties in the atmosphere, a control system is needed. Many aerocapture studies to date have focused on bank-angle lift modulation, which requires complex control 2. DRAG MODULATION AEROCAPTURE algorithms and an integral propulsive reaction control TRADE SPACE system. The aerocapture technology described in this paper is drag modulation aerocapture, which shows promise of being The aerocapture maneuver concept of operations is made up simpler and more cost-effective than bank-angle lift methods of three main phases: exo-atmospheric coast, atmospheric [5]. Drag modulation aerocapture uses in-flight deceleration, and orbit operations. There are a number of transformations of an entry vehicle’s drag area to control the different design choices for each phase, which result in many amount of deceleration produced during an atmospheric pass. types of mission architectures. The simplest form of drag modulation aerocapture is the Exo-atmospheric Coast single-stage discrete-event architecture, which is depicted in Before the aerocapture maneuver begins, the spacecraft must Figure 1. One possible way to execute the single-stage navigate to or be brought to the vicinity of the planetary body discrete-event maneuver is to enter the atmosphere in a low ballistic coefficient configuration, with a large drag skirt and then target a specific entry flight path angle (EFPA) and deployed, and then to transition to high ballistic coefficient entry velocity at the atmospheric interface. The three main by jettisoning or folding the drag skirt. Such a single-stage delivery options identified were: discrete-event architecture was previously studied within the 1. Direct injection of SmallSat from Earth context of an Earth SmallSat Flight Test of Aerocapture [6]. 2. Delivery of SmallSat by host targeting the body Additional information on the fundamentals of drag 3. Delivery of SmallSat by host flying by the body modulation aerocapture can be found in Reference 5. Option 1 provides the most flexibility for the mission, especially if the vehicle can perform the Earth escape burn from a location such as geostationary transfer orbit (GTO), as there are many launches to GTO that can carry a SmallSat as a secondary payload. The vehicle could also potentially be launched as a secondary payload with a primary mission that is going to the target body, but then released after the injection burn, similar to the MarCO spacecrafts that traveled with the InSight Mars lander. While options 2 and 3 may have more
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