49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083) 1332.pdf

THE CAESAR NEW FRONTIERS MISSION: 1. OVERVIEW. S. W. Squyres1, K. Nakamura-Messenger2, D. F. Mitchell3, V. E. Moran3, M. B. Houghton3, D. P. Glavin3, A. G. Hayes1, D. S. Lauretta4, and the CAESAR Project Team. 1Cornell University, Ithaca NY 14853, 2NASA Johnson Space Center, Houston TX 77058, 3NASA Goddard Space Flight Center, Greenbelt MD 20771, 4University of Arizona, Tucson AZ 85721.

Introduction: The Comet Astrobiology Explora- ple collection is verified by direct imaging of the sam- tion Sample Return (CAESAR) mission will acquire ple container interior, and a load cell in the TAG Arm and return to Earth for laboratory analysis a minimum measures sample mass. An engineering model of the of 80 g of surface material from the nucleus of comet SAS has been tested in zero gravity and vacuum at the 67P/Churyumov-Gerasimenko (67P). CAESAR will NASA Glenn Zero Gravity Research Facility, over a characterize the surface region sampled, preserve the range of adverse surface strength properties, slopes, collected sample in a pristine state, and return evolved and particle size distributions. Honeybee Robotics pro- volatiles by capturing them in a separate gas reservoir. vides the SAS. Comet sample analyses can provide unparalleled Once successful sample collection has been veri- knowledge about presolar history through the initial fied, and while the sample is still cold (< -80 °C), the stages of planet formation to the origin of life. TAG Arm inserts the sample container into the Sample CAESAR’s sample analysis objectives address ques- Containment System (SCS), mounted inside the Sam- tions regarding the nature of Solar System starting ma- ple Return Capsule (SRC). The SCS immediately seals terials and how these fundamental components came the sample, preventing material from escaping into together to form planets and give rise to life. space. The SCS seal uses a stainless steel knife edge To this end, CAESAR will determine the nature driven into a copper gasket, and has been shown via and abundances of interstellar dust grains and molecu- test to substantially exceed leak rate requirements after lar cloud materials, and characterize the origins and having been sealed under a range of cold and dirty ages of refractory solar nebula condensates. It will conditions. Honeybee Robotics also provides the SCS. trace the history of volatile reservoirs, delineate the The SCS then slowly warms the sample from the chemical pathways that led from simple interstellar cold temperatures at which it was collected to typical species to complex and prebiotic molecules, and con- comet surface temperatures near perihelion. As gases strain the geological and dynamic evolution of the evolve from the solid sample, they pass from the SCS comet. And it will evaluate the potential role of comets into a 5-liter passively cooled gas reservoir in the Gas in delivering water and organics to the early Earth. Containment System (GCS), also mounted in the SRC, CAESAR will achieve these goals by carrying out co- separating them from the solid sample and thereby ordinated sample analyses that will link macroscopic protecting the solid sample from alteration. Once H2O properties of the comet with microscale mineralogy, has sublimated from the solid sample, the GCS is chemistry, and isotopic studies of volatiles and solids. sealed to capture the volatiles it contains, and the SCS Science Implementation: Collection of a sample is vented to space to maintain the solid sample under from the surface of comet 67P is enabled by the vacuum. The SCS vent is closed before Earth entry to CAESAR Camera Suite: A set of cameras that together prevent atmospheric contamination. Continuous rec- provide images to support sample site selection, per- ords of sample temperature, pressure, and H2O vapor form optical navigation, and document the sample be- partial pressure are collected from sealing at the comet fore, during, and after collection. The Camera Suite until opening on Earth. The interiors of the SCS, GCS, also provides geologic context for the sample, and and associated plumbing are coated with high-purity builds on Rosetta results by documenting changes to gold to minimize surface reactivity and catalysis. God- 67P through the two perihelion passages that will have dard Space Flight Center (GSFC) provides the GCS. occurred since it was visited by that mission. Malin The pristine nature of the sample is preserved using Space Science Systems provides the Camera Suite. stringent cleaning protocols during fabrication, and The sample is collected by the Sample Acquisition careful mission design during spacecraft operations. System (SAS), which has been specifically designed Ground and flight witness materials thoroughly docu- for the surface properties of comet 67P observed by the ment any contamination. The team follows rigorous Rosetta/Philae mission. It contacts the comet surface cleanliness and documentation protocols through all during a touch-and-go (TAG) maneuver at least 5 se- mission phases. conds long, mounted on a three-degree-of-freedom The CAESAR SRC is provided by the Japanese TAG Arm. During surface contact, pneumatic jets di- Aerosapace Exploration Agency (JAXA). Its design is rect the sample into a 1.5-liter sample container. Sam- based on the SRC flown on the Hayabusa and Haya- 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083) 1332.pdf

busa2 missions. Like its predecessors, the CAESAR cm/pixel. From these images, the team selects a prima- SRC drops its heat shield during parachute descent, ry TAG site. greatly simplifying thermal control of the comet sam- CAESAR is capable of executing at least three ple. The aerodynamic stability in the transonic regime TAG campaigns (each consisting of 2 rehearsals and 1 of the Hayabusa SRC design allows use of a subsonic TAG), at any solar distance between 3.5 AU and aphe- drogue parachute, providing ease of flight testing. lion. The TAG sequence draws significantly from The SRC lands at the Utah Test and Training OSIRIS-REx, with modifications to accommodate the Range (UTTR) and is immediately placed in cold stor- physical properties of 67P. age. Phase change material sealed in aluminum hous- Data for TAG guidance is provided by both optical ings mounted on the GCS assures that no melting of navigation and laser ranging. After a deorbit burn, H2O will occur even if SRC recovery is delayed for three deterministic propulsive maneuvers refined by a hours. All recovered hardware is transported to the closed-loop linear correction from an onboard naviga- Johnson Space Center, where the samples are removed tion system deliver the spacecraft to within 25 m (3-σ) and delivered to the dedicated CAESAR curation facil- of the selected TAG site. Surface contact lasts for at ity. After preliminary examination, samples are made least 5 seconds, with contact force controlled by a con- available to the worldwide scientific community. stant-force spring in the TAG Arm. After sample col- Mission Implementation: GSFC provides lection, the spacecraft automatically executes a back- CAESAR project management, systems engineering, away burn. The TAGCAM camera, mounted on the safety and mission assurance, contamination control, spacecraft, images the SAS and surface at five frames/s mission operations, and many other important func- during TAG, documenting TAG at 1 mm/pixel. The tions. Orbital ATK develops the spacecraft, based on CANCAM camera, mounted within the SAS, images Dawn mission heritage, which like CAESAR uses so- inside the sample container at ten frames/s, document- lar electric propulsion. KinetX Aerospace and GSFC ing sample collection. perform mission navigation, the same team of that is After verifying and stowing the sample, CAESAR navigating OSIRIS-REx. executes gas transfer to the GCS, and begins a slow The CAESAR spacecraft is derived from Orbital drift away from the comet. Proximity operations could ATK’s GEOStar-3 electric propulsion spacecraft, with be completed in as little as 17 months, but physics dic- a configuration that emulates the arrangement used for tates that the drift continues until the IPS can be reac- the Dawn mission. It uses three redundant NEXT-C tivated at 3.5 AU, about 4.6 years after arrival at the thrusters and power processing strings, supporting op- comet. Because proximity operations can be performed eration of two thrusters across the full throttle range. at any solar distance between 3.5 and aphelion, time- Power is provided by Roll-Out Solar Arrays (30 kW at line margin is an ample 3.2 years. 1 AU)built by Deployable Space Systems. The IPS is re-activated in November of 2033. The CAESAR launches on a high-performance launch inbound cruise includes an Earth flyby, but no asteroid vehicle in the summer of 2024 from Cape Canaveral. flyby will be conducted. Landing at UTTR takes place The ion propulsion system (IPS) is activated after a 60- at 9:14 AM local time on November 20, 2038. day commissioning phase, operating with a conserva- Summary: CAESAR will return the first sample tive duty cycle of no more than 90%. The outbound from a comet nucleus. The payload has been designed cruise includes an Earth flyby, and can be tailored to to maximize the scientific value of the sample, includ- include a flyby of the 12-km B-type asteroid 2809 ing both its non-volatile and volatile components. The Vernadskij. CAESAR arrives at 67P in December of choice of comet provides substantial risk reduction, 2028. achieving the mission within a constrained New Fron- CAESAR enters orbit around 67P, lowering its or- tiers budget. Most of the sample (≥75%) will be set bital altitude slowly and sequentially over a period of aside for analysis by generations of scientists using months. During an initial survey, the color Narrow continually advancing tools and methods, yielding an Angle Camera is used to search for natural satellites, enduring scientific treasure that only sample return can determine changes that have occurred since Rosetta, provide. and produce a global topographic map. Images of in- creasing resolution are used to downselect to 16 and then 8 candidate TAG sites. A subsequent detailed survey phase provides images that are used to down- select to the final 4 candidate TAG sites. These sites are documented with 7-color stereo images at 2.3 cm/pixel, and monochromatic stereo images at 0.6