CAESAR (Comet Astrobiology Exploration Sample Return) is asample-return mission concept to comet67P/Churyumov–Gerasimenko. The mission was proposed in 2017 to NASA'sNew Frontiers program mission 4, and on 20 December 2017 it was one of two finalists selected for further concept development. On 27 June 2019, the other finalist, theDragonfly mission, was chosen instead.[5]
TheCAESAR team chose comet 67P over other cometary targets in part because the data collected by theRosetta mission, which studied the comet from 2014 to 2016, allows the spacecraft to be designed to the conditions there, increasing the mission's chance of success.[6] TheRosetta mission also provides a vast geologic context for this mission's sample-return analysis.
The twoNew Frontiers program Mission 4 finalists, announced on 20 December 2017, wereDragonfly to Titan, andCAESAR.[7] Comet 67P was previously explored by the European Space Agency'sRosetta probe and its landerPhilae during 2014-2016 to determine its origin and history. Squyres explained that knowing the existing conditions at the comet allows them to design systems that would dramatically improve the chances for success.[6]
TheCAESAR andDragonfly missions receivedUS$4 million funding each through the end of 2018 to further develop and mature their concepts.[6] NASA selected theDragonfly mission on 27 June 2019 to build and launch in 2026.[5][7][6]
A cometsample-return mission was one of the goals in a list of options for a New Frontiers mission in both the 2003 and the 2011Planetary Science Decadal Survey, which were guiding surveys among those in the scientific community of what and where NASA should prioritize.[8] Another comet mission proposal,Comet Hopper, was one of threeDiscovery Program finalists that receivedUS$3 million in May 2011 to develop a detailed concept study; however, it was not selected.[9] NASA has launched several missions to comets in the late 1990s and 2000s; these missions includeDeep Space 1 (launched 1998),Stardust (launched 1999),CONTOUR (launched 2002 but failed after launch), andDeep Impact (launched 2005), as well as some participation on theRosetta mission.
The spacecraft would be built byNorthrop Grumman Innovation Systems and it would inherit technology used by the successfulDawn mission.[1] Navigation, sample site selection, and sample documentation are enabled by the camera suite, provided byMalin Space Science Systems.[4] This camera suite consists of six cameras of varying fields of view and focal ranges: narrow angle camera (NAC), medium angle camera (MAC), touch-and-go camera (TAGCAM), two navigation cameras (NAVCAMs), and a sample container camera (CANCAM).[14]
The robotic arm (TAG) and the Sample Acquisition System would be provided byHoneybee Robotics.[4] The sample return capsule and heatshield are provided by the Japanese space agencyJAXA.[2]
The spacecraft would not land on the comet, but would momentarily contact the surface with its TAG (Touch-And-Go) robotic arm, as done byOSIRIS-REx on an asteroid, including raising the solar arrays into a Y-shaped configuration to minimize the chance of dust accumulation during contact and provide more ground clearance.[3] The sampler mechanism on the arm would produce a burst ofnitrogen gas to blowregolith particles into the sampler head located at the end of the arm.CAESAR would collect between 80 and 800 g (2.8 and 28.2 oz) of regolith from the comet. The maximum pebble size would be 4.5 cm (1.8 in).[3] The system has enough compressed nitrogen gas for three samplings.[2]
The system would separate thevolatiles from the solid substances into separate containers and preserve the samples cold for the return trip.[2][16] The spacecraft would head back to Earth and drop off the sample in a capsule, which would re-enter Earth's atmosphere and parachute down to the surface in 2038.[6] The sample-return capsule (SRC) would be provided byJAXA and its design is based upon the SRC flown on theHayabusa andHayabusa2 spacecraft.[4] The capsule would parachute down at theUtah Test and Training Range (UTTR), and it would be transported to NASA'sJohnson Space Center for curation and analyses at the laboratory calledAstromaterials Research and Exploration Science Directorate (ARES).[1] A small portion of the sample will also be curated at Japan'sExtraterrestrial Sample Curation Center.[2] Most of the sample (≥75% of the total) would be preserved for analysis by future generations of scientists.[16][2]
^abcGlavin, Daniel; Squyres, Steven (2018).An Overview of the Comet Astrobiology Exploration Sample Return (CAESAR) New Frontiers Mission. 20th EGU General Assembly. 4–13 April 2018. Vienna, Austria.Bibcode:2018EGUGA..20.4823G.
^abcdefMessenger, Scott R. (2018).The CAESAR New Frontiers Comet Sample Return Mission. Japan Geosciences Union Meeting. 20–24 May 2018. Chiba, Japan.hdl:2060/20180002990. JSC-E-DAA-TN54564.
^Schmidt, George; et al. (2018).Electric Propulsion Research and Development at NASA. Spacecraft Propulsion 2018. 14–18 May 2018. Seville, Spain.hdl:2060/20180004691. SP-2018-00389.
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