SSC16-XII-05 Cubesat Application for Planetary Entry (CAPE) Missions: Micro-Return Capsule (MIRCA) Jaime Esper NASA Goddard Space Flight Center 8800 Greenbelt Rd.; +1(301)286-1124 [email protected] ABSTRACT The Cubesat Application for Planetary Entry Missions (CAPE) concept describes a high-performing Cubesat system which includes a propulsion module and miniaturized technologies capable of surviving atmospheric entry heating, while reliably transmitting scientific and engineering data. The Micro Return Capsule (MIRCA) is CAPE’s first planetary entry probe flight prototype. Within this context, this paper briefly describes CAPE’s configuration and typical operational scenario, and summarizes ongoing work on the design and basic aerodynamic characteristics of the prototype MIRCA vehicle. CAPE not only opens the door to new planetary mission capabilities, it also offers relatively low-cost opportunities especially suitable to university participation. In broad terms, CAPE consists of two main functional components: the “service module” (SM), and “CAPE’s entry probe” (CEP). The SM contains the subsystems necessary to support vehicle targeting (propulsion, ACS, computer, power) and the communications capability to relay data from the CEP probe to an orbiting “mother-ship”. The CEP itself carries the scientific instrumentation capable of measuring atmospheric properties (such as density, temperature, composition), and embedded engineering sensors for Entry, Descent, and Landing (EDL). The first flight of MIRCA was successfully completed on 10 October 2015 as a “piggy-back” payload onboard a NASA stratospheric balloon launched from Ft. Sumner, NM. INTRODUCTION CAPE So far, no microprobe (less than 10 kg) has entered CAPE consists of two main functional components: the another planetary atmosphere and successfully relayed “service module” (SM), and “CAPE’s entry probe” data back to Earth. Although the Deep Space 2 Mars (CEP). The SM contains the subsystems necessary to microprobes did reach their destination (total mass about support vehicle targeting (propulsion, ACS, computer, 6.5 kg each), unfortunately they were lost due to a power) and the communications capability to relay data combination of delivery system failures and other from the CEP probe to an orbiting mother-ship. The unknown factors. This paper describes a planetary entry CEP itself carries the scientific instrumentation capable probe based on the widely popular Cubesat-class of measuring atmospheric properties (such as density, spacecraft specification (Cubesat Application for temperature, composition), and embedded engineering Planetary Entry Missions, or CAPE probes) [1], [2]. Within sensors for Entry, Descent, and Landing (EDL) a science operational context, CAPE probes may be sent technology monitoring and assessment. Figure 1 from Earth to study a celestial body’s atmosphere, or to illustrates the complete CAPE system in its flight and land on some high-value target on its surface. Either one stowed configurations. The total system mass is less than or multiple probes may be targeted to distributed 5 kg. The solar array generates about 17W at 1 AU, and locations throughout the geographic landscape and could the SM nominally consumes less than 11W of power. be released systematically and methodically from an The CEP itself consumes less than 5W. orbiting spacecraft. CAPE vehicles would each have their own propulsion, and hence would be capable of targeting regions identified by the mother ship (MS) as high-interest. This enables a completely new capability for science not possible with traditional “drop-and- flyby” schemes. To supplement its flexibility, each probe would incorporate a communications architecture that provides a high-level of assurance its precious data is acquired and transmitted back to Earth for analysis. Esper 1 30th Annual AIAA/USU Conference on Small Satellites Micro-thruster CAPE entry probes can provide essential insight into the bulk properties of planetary atmospheres. Sent in numbers, they render the potential to observe multiple in-situ locations in a planet or satellite’s atmosphere. Deployed Array CAPE opens up an entirely new capability and manner CubeSat of exploration for NASA, with high potential for 2U Service Module Service university and student participation. UHF or MIRCA S-Band In order to reduce CAPE’s implementation risks, a CEP Entry Probe Entry Planetary Comm. ~1U Microprobe re-entry demonstrator is currently being designed and prototyped at the NASA Goddard Space Flight Center Figure 1: CAPE in its deployed configuration, and (GSFC). The Micro Return Capsule (MIRCA) is stowed inside deployment system CAPE’s first planetary entry probe flight prototype. The primary objectives are to verify MIRCA’s avionics Figure 2 shows a generic CAPE operations concept, architecture, communications and operations concept, from system deployment to probe release and entry into and aerodynamic stability. a given planetary atmosphere. Other scenarios include direct entry on arrival. Three mission phases are Entry probes have provided essential insight into the identified: 1. Deployment, 2. Targeting, and 3. Planetary bulk properties of planetary atmospheres by measuring Entry. In the initial phase the vehicle rides inside a their density, temperature, and composition. Much deployment system, and is released by the mother-ship information can be inferred from accelerometers, rate in a prescribed drop-off orbit. This drop-off orbit is gyros, thermal and pressure sensors alone. This is adjusted in a way that ensures atmospheric entry within exemplified by accelerometer data acquired through the the capabilities of CAPE’s thruster system, but at a safe experimental SMART (Small Rocket/Spacecraft altitude for the mother-ship. During the targeting and Technology) spacecraft prototype, which re-entered orbit adjustment phase, CAPE uses its own thrusters to Earth’s atmosphere after launching from a sounding slowly target a particular entry corridor. Since entry rocket in 2011 (Fig. 3) [3]. dispersion is expected to be large, a “ground track” path (or great circle on the planet’s surface), rather than a 6 X Accel Y Accel Z Accel specific spot is targeted. The final mission phase is Vehicle Coordinates 5 planetary entry. At this time, the SM is maneuvered to X 4 allow for a slightly delayed entry from the CEP. CEP to Z SM cross-link communications will ensure data is 3 Y relayed to the orbiting MS, although direct communication to the MS is also possible (depending on 2 Onset of Significant Aerodynamic Forcing orbital mechanics and view factors). Since the SM will (G) ACCELERATION (~ 50 km Altitude) be trailing behind the CEP, it will go through 1 communications blackout after the probe has completed 0 its entry phase, and hence will be capable of relaying a -1 full set of probe scientific and engineering data. The SM 270 275 280 285 290 295 300 305 310 315 320 MISSION ELAPSED TIME (S) will continue to relay communications until it burns up in the atmosphere. SMART Flight Data 3. Planetary Entry 1. Deployment A. Entry probe 2. Targeting and deployment orbit adjustment B. CEP survival C. Communications from CEP to SM D. SM demise after Density3.2km = Pressure / (Rgas*Temp) probe data re- = 0.912 kg/m3 transmission. Figure 3: SMART re-entry data at 50km (top) and Figure 2: CAPE typical mission phases. 3km altitude (bottom). Esper 2 30th Annual AIAA/USU Conference on Small Satellites As can be seen, significant atmospheric forcing begins at test, a sapphire filter is used with a spectral band pass an altitude of about 50 km (stratopause), although between 0.1 and 7 m. Center wavelengths of sample environmental conditions can moderately shift this gases detectable within this band pass range are shown interface’s location. Although this result is far from in Table 1 for the Earth’s atmosphere [5]. Gas mixing surprising for Earth’s atmosphere, simple and direct ratios and the corresponding atmospheric absorption measurements like these can be a critical piece of spectra will vary depending on altitude. Hence, detection information in the determination of the structure of extra- of atmospheric gas species as the vehicle descends terrestrial atmospheres. Coupled with pressure and provides invaluable information not only on atmospheric temperature sensors, a simple entry probe would provide composition, but also its structure. Measurements will be direct confirmation of remote sensing measurements tempered by heat shield ablation materials during the (e.g., estimation of the atmospheric gas constant and critical heat-loading phase of the vehicle flight. mean molecular weight). Figure 4 shows data obtained Notwithstanding, this information is also of great by the Huygens Atmospheric Structure Instrument engineering interest, and provides a measure of TPS (HASI), with sensing instrumentation similar to the one performance. described in this paper [4]. Since a probe altimeter is not feasible at this time, a CEP’s altitude will be modeled Table 1: Earth atmospheric gases absorption center from its trajectory and timing signals relayed to the frequencies for visible and near-IR bands. release (mother) ship. Alternatively, a MS may already Gas Center Wavelength (µm) be carrying a science Radar which could also be used to CH4 1.66, 2.2, 3.3 range to the entry vehicle during its flight. CO2 1.4, 1.6, 2.0, 2.7, 4.3 CO 2.34, 4.67 H2O 0.72, 0.82, 0.94, 1.1, 1.38, 1.87, 2.7 N2O 2.87, 4.06, 4.5 O3 3.3, 4.74 O2 0.63, 0.69, 0.76, 1.06, 1.27, 1.58 Important considerations have been the demonstration of an inexpensive planetary entry probe, and assessment of its science performance, constraints and capabilities. To that effect, MIRCA has been built and is currently undergoing testing. A picture of MIRCA during bench test is shown in Fig. 5. Within the context of CAPE probes, it is quite feasible Figure 4: Titan’s atmospheric structure inferred (actually expected) that these entry vehicles will be sent from temperature and pressure sensors (Ref.