View source for CAESAR (spacecraft)

{{short description|Proposed sample-return mission to a comet}}
{{DISPLAYTITLE:CAESAR (spacecraft)}}
{{Infobox spaceflight |auto=all
| name                  = CAESAR
| names_list            = 
| image                 = Caesar-sample return concept 2018.png
| image_caption         = An artist's concept of CAESAR obtaining a sample from comet 67P.
| image_size            = 275px

| mission_type          = [[Sample-return mission|Sample return]]
| operator              = [[NASA]]
| website               = {{URL|http://caesar.cornell.edu}}
| mission_duration      = {{time interval|August 2024|November 2038|show=ym|sep=,}} (proposed)
 
| manufacturer          = [[Northrop Grumman Innovation Systems|Northrop Grumman]] (proposed)<ref name='EGU 2018'/>
| dimensions            = Solar panels length: 43.5 m <ref name='Squyres Nov2018'>{{cite web |title= PSW 2399 Comets and the Origin of Life |last=Squyres |first=Steven |date=7 November 2018 |publisher=PSW Science |url=https://www.youtube.com/watch?v=aypCA2RTy54 |access-date=2019-03-10}}</ref>
| power                 = 
| launch_date           = August 2024 (proposed)<ref name="SBAG18Squyres">{{cite conference|url=https://www.lpi.usra.edu/sbag/meetings/jan2018/presentations/3-15pm-Squyres.pdf|title=CAESAR: Project Overview |conference=18th Meeting of the NASA Small Bodies Assessment Group. 17–18 January 2018. Ames Research Center, California.|publisher=[[Lunar and Planetary Institute]]|first=Steve|last=Squyres|date=2018}}</ref>

| landing_date          = November 2038 (proposed)<ref name="SBAG18Squyres"/><ref name='Messenger 2018'/>
| landing_site          = [[Utah Test and Training Range]]<ref name="SBAG18Squyres"/>

|interplanetary         = 
 {{Infobox spaceflight/IP
   |type                = orbiter
   |object              = Comet [[67P/Churyumov–Gerasimenko]]
   |arrival_date        = January 2029 (proposed)<ref name="SBAG18Squyres" />
   |departure_date      = February 2032 (proposed)<ref name="SBAG18Squyres" />
   |sample_mass         = {{convert|80|to|800|g|abbr=on}}
 }}

| programme             = [[New Frontiers program]]
| previous_mission      = [[OSIRIS-REx]]
| next_mission          = [[Dragonfly (Titan space probe)|''Dragonfly'']]
}}

'''CAESAR''' ('''Comet Astrobiology Exploration Sample Return''') is a [[sample-return mission]] concept to comet [[67P/Churyumov–Gerasimenko]]. The mission was proposed in 2017 to NASA's [[New 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, the [[Dragonfly (Titan space probe)|''Dragonfly'']] mission, was chosen instead.<ref name="nyt20190627">{{cite news|url=https://www.nytimes.com/2019/06/27/science/nasa-titan-dragonfly-caesar.html|title=NASA Announces New Dragonfly Drone Mission to Explore Titan|work=[[The New York Times]]|first=David|last=Brown|date=27 June 2019|access-date=27 June 2019}}</ref>

Had it been selected in June 2019, it would have launched between 2024 and 2025, with a capsule delivering a sample back to Earth in 2038. The Principal Investigator is Alexander Hayes of [[Cornell University]] in Ithaca, New York. ''CAESAR'' would be managed by NASA's [[Goddard Space Flight Center]] in Greenbelt, Maryland. [[Extraterrestrial sample curation|Curation]] of the returned sample would take place at NASA's [[Astromaterials Research and Exploration Science Directorate]], based at [[Johnson Space Center]] in Houston, Texas.

The ''CAESAR'' team chose comet 67P over other cometary targets in part because the data collected by the [[Rosetta (spacecraft)|''Rosetta'' 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.<ref name="nyt20171219">{{cite news|url=https://www.nytimes.com/2017/12/19/science/nasa-new-frontiers-finalists.html|title=Finalists in NASA's Spacecraft Sweepstakes: A Drone on Titan, and a Comet-Chaser|work=[[The New York Times]]|first=Kenneth|last=Chang|date=19 December 2017|access-date=8 January 2018}}</ref> The ''Rosetta'' mission also provides a vast geologic context for this mission's sample-return analysis.

==Overview==
[[File:Comet 67P on 31 January 2015 - NAVCAM.jpg|thumb|The Comet [[67P/Churyumov–Gerasimenko]] as seen by ''Rosetta'' in 2015; ''CAESAR''{{'s}} proposed target.]]
The two [[New Frontiers program]] Mission 4 finalists, announced on 20 December 2017, were [[Dragonfly (Titan space probe)|''Dragonfly'']] to Titan, and ''CAESAR''.<ref name="ibtimes">{{cite news |url=http://www.ibtimes.com/nasas-new-frontier-mission-will-search-alien-life-or-reveal-solar-systems-history-2631073|title=NASA's New Frontier Mission Will Search For Alien Life Or Reveal The Solar System's History|work=International Business Times|first=Elana|last=Glowatz|date=20 December 2017}}</ref> Comet 67P was previously explored by the European Space Agency's [[Rosetta (spacecraft)|''Rosetta'']] probe and its lander [[Philae (spacecraft)|''Philae'']] 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.<ref name="nyt20171219"/>

The ''CAESAR'' and ''Dragonfly'' missions received {{US$|4 million}} funding each through the end of 2018 to further develop and mature their concepts.<ref name="nyt20171219"/> NASA selected the [[Dragonfly (Titan space probe)|''Dragonfly'']] mission on 27 June 2019 to build and launch in 2026.<ref name="nyt20190627"/><ref name="ibtimes"/><ref name="nyt20171219"/>

===Background===
A comet [[sample-return mission]] was one of the goals in a list of options for a New Frontiers mission in both the 2003 and the 2011 [[Planetary Science Decadal Survey]], which were guiding surveys among those in the scientific community of what and where NASA should prioritize.<ref name="nasa-newfront">{{cite web|url=https://discoverynewfrontiers.nasa.gov/program/index.cfml|title=New Frontiers Program: Overview|publisher=NASA|url-status=dead|archive-url=https://web.archive.org/web/20170126051523/https://discoverynewfrontiers.nasa.gov/program/index.cfml|archive-date=26 January 2017}}</ref> Another comet mission proposal, ''[[Comet Hopper]]'', was one of three [[Discovery Program]] finalists that received {{US$|3 million}} in May 2011 to develop a detailed concept study; however, it was not selected.<ref name='Taylor'>{{cite news|url=http://www.tgdaily.com/space-features/55816-nasa-picks-project-shortlist-for-next-discovery-mission|title=NASA picks project shortlist for next Discovery mission|work=Tech Guru Daily|first=Kate|last=Taylor|date=9 May 2011|access-date=28 October 2015|archive-date=6 October 2018|archive-url=https://web.archive.org/web/20181006212756/https://www.tgdaily.com/space-features/55816-nasa-picks-project-shortlist-for-next-discovery-mission|url-status=dead}}</ref> NASA has launched several missions to comets in the late 1990s and 2000s; these missions include ''[[Deep Space 1]]'' (launched 1998), [[Stardust (spacecraft)|''Stardust'']] (launched 1999), ''[[CONTOUR]]'' (launched 2002 but failed after launch), and [[Deep Impact (spacecraft)|''Deep Impact'']] (launched 2005), as well as some participation on the [[Rosetta (spacecraft)|''Rosetta'']] mission.

===Astrobiology===
''CAESAR''{{'s}} objectives were to understand the [[formation and evolution of the Solar System|formation of the Solar System]] and how these components came together to form planets and give [[Abiogenesis|rise to life]].<ref name='Messenger 2018'>{{cite conference|title=The CAESAR New Frontiers Comet Sample Return Mission|conference=Japan Geosciences Union Meeting. 20–24 May 2018. Chiba, Japan. |first=Scott R.|last=Messenger|date=2018|hdl=2060/20180002990|id=JSC-E-DAA-TN54564}}</ref> Some researchers have hypothesized that Earth may have been seeded with [[organic compound]]s early in its development by [[tholin]]-rich comets, providing the raw material necessary for [[abiogenesis|life to emerge]].<ref name='Squyres Nov2018'/><ref name= "sagan1979">{{cite journal|title=Tholins: organic chemistry of interstellar grains and gas|journal=Nature|first1=Carl|last1=Sagan|author1-link=Carl Sagan|first2=Bishun|last2=Khare|author2-link=Bishun Khare|name-list-style=amp|volume=277|issue=5692 |pages=102–107|date=11 January 1979|doi=10.1038/277102a0|bibcode=1979Natur.277..102S|s2cid=4261076}}</ref><ref name="cometary tholins">{{cite journal|title=Production and Chemical Analysis of Cometary Ice Tholins |journal=Icarus |first1=Gene D.|last1=McDonald|first2=Linda J.|last2=Whited|first3=Cynthia|last3=DeRuiter|first4=Bishun N.|last4=Khare|first5=Archita|last5=Patnaik|first6=Carl|last6=Sagan|display-authors=1 |volume=122|issue=1|pages=107–117|date=July 1996|doi=10.1006/icar.1996.0112|bibcode=1996Icar..122..107M|doi-access=free}}</ref> Tholins were detected by the [[Rosetta (spacecraft)|''Rosetta'']] mission to comet [[67P/Churyumov–Gerasimenko]].<ref>{{cite journal|title=OSIRIS observations of meter-sized exposures of H2O ice at the surface of 67P/Churyumov-Gerasimenko and interpretation using laboratory experiments|journal=Astronomy & Astrophysics|first1=A.|last1=Pommerol|first2=N.|last2=Thomas|first3=M. R.|last3=El-Maarry|first4=M.|last4=Pajola|first5=O.|last5=Groussin|display-authors=1|volume=583|at=A25 |date=November 2015 |doi=10.1051/0004-6361/201525977|bibcode=2015A&A...583A..25P|url=https://www.research.unipd.it/bitstream/11577/3182682/1/aa25977-15.pdf|doi-access=free}}</ref><ref>{{cite journal |url=https://www.science.org/doi/10.1126/science.aab0673|title=CHO-bearing organic compounds at the surface of 67P/Churyumov-Gerasimenko revealed by Ptolemy|journal=Science|first1=I. P.|last1=Wright |first2=S.|last2=Sheridan |first3=S. J.|last3=Barber|first4=G. H.|last4=Morgan|first5=D. J.|last5=Andrews|first6=A. D.|last6=Morse|display-authors=1|volume=349|issue=6247|pages=aab0673|date=31 July 2015 |doi=10.1126/science.aab0673|pmid=26228155|bibcode=2015Sci...349b0673W|s2cid=206637053}}</ref>

==Spacecraft==
The spacecraft would be built by [[Northrop Grumman Innovation Systems]] and it would inherit technology used by the successful [[Dawn (spacecraft)|''Dawn'']] mission.<ref name="EGU 2018">{{cite conference |title=An Overview of the Comet Astrobiology Exploration Sample Return (CAESAR) New Frontiers Mission |conference=20th EGU General Assembly. 4–13 April 2018. Vienna, Austria. |first1=Daniel |last1=Glavin |first2=Steven |last2=Squyres |date=2018 |bibcode=2018EGUGA..20.4823G}}</ref> Navigation, sample site selection, and sample documentation are enabled by the camera suite, provided by [[Malin Space Science Systems]].<ref name='Messenger 2018'/> 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).<ref name="Soderblom2018">{{Cite conference |last=Soderblom |first=Jason |last2=Hayes |first2=Alex |last3=Houghton |first3=Martin |last4=King |first4=Todd |last5=Ravine |first5=Mike |last6=Tansock |first6=Joe |last7=Squyers |first7=Steve |display-authors=1 |date=2018 |title=The CAESAR New Frontiers Mission: Overview and Imaging Objectives |url=https://digitalcommons.usu.edu/calcon/CALCON2018/all2018content/32/ |conference=2018 CALCON Technical Meeting. 18–21 June 2018. Logan, Utah.}}</ref>

The robotic arm (TAG) and the Sample Acquisition System would be provided by [[Honeybee Robotics]].<ref name='Messenger 2018'/> The sample return capsule and heatshield are provided by the Japanese space agency [[JAXA]].<ref name='Squyres Nov2018'/>

===Propulsion===
[[File:NASA NEXT Ion thruster.712983main NEXT LDT Thrusterhi-res full.jpg|thumb|The NASA's Evolutionary Xenon Thruster (NEXT) operation in a vacuum chamber.]]
The propulsion system on ''CAESAR'' would be [[NEXT (ion thruster)|NASA's Evolutionary Xenon Thruster]] (NEXT),<ref name="SBAG18Squyres"/><ref name='Messenger 2018'/> a type of [[solar electric propulsion]].  It would employ three NEXT thrusters, with one used as a spare.<ref>{{cite conference |title=Electric Propulsion Research and Development at NASA |conference=Spacecraft Propulsion 2018. 14–18 May 2018. Seville, Spain. |first1=George |last1=Schmidt |first2=David |last2=Jacobson |first3=Michael |last3=Patterson |first4=Gani |last4=Ganapathi |first5=John |last5=Brophy |first6=Richard |last6=Hofer |display-authors=1 |date=2018 |hdl=2060/20180004691 |id=SP-2018-00389}}</ref> The propellant is [[xenon]].

==Sample return==
The spacecraft would not land on the comet, but would momentarily contact the surface with its TAG (Touch-And-Go) robotic arm, as done by ''[[OSIRIS-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.<ref name="SBAG18Squyres"/> The sampler mechanism on the arm would produce a burst of [[nitrogen]] gas to blow [[regolith]] particles into the sampler head located at the end of the arm. ''CAESAR'' would collect between {{convert|80|and|800|g|abbr=on}} of regolith from the comet. The maximum pebble size would be {{convert|4.5|cm|in|abbr=on}}.<ref name="SBAG18Squyres"/> The system has enough compressed nitrogen gas for three samplings.<ref name='Squyres Nov2018'/>

The system would separate the [[Volatile (astrogeology)|volatiles]] from the solid substances into separate containers and preserve the samples cold for the return trip.<ref name='Squyres Nov2018'/><ref name="curation">{{cite conference |url=https://www.hou.usra.edu/meetings/lpsc2018/pdf/1339.pdf |title=The CAESAR New Frontiers Mission: 5. Contamination, Recovery, and Curation|conference=49th Lunar and Planetary Science Conference. 19–23 March 2018. The Woodlands, Texas. |first1=K. |last1=Nakamura-Messenger |display-authors=etal |date=2018}}</ref> 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.<ref name="nyt20171219"/> The sample-return capsule (SRC) would be provided by [[JAXA]] and its design is based upon the SRC flown on the ''[[Hayabusa]]'' and ''[[Hayabusa2]]'' spacecraft.<ref name='Messenger 2018'/> The capsule would parachute down at the [[Utah Test and Training Range]] (UTTR), and it would be transported to NASA's [[Johnson Space Center]] for curation and analyses at the laboratory called [[Astromaterials Research and Exploration Science Directorate]] (ARES).<ref name='EGU 2018'/> A small portion of the sample will also be curated at Japan's [[Extraterrestrial Sample Curation Center]].<ref name='Squyres Nov2018'/> Most of the sample (≥75% of the total) would be preserved for analysis by future generations of scientists.<ref name="curation"/><ref name='Squyres Nov2018'/>

==See also==
* {{annotated link|List of missions to comets}}
* {{annotated link|TAGSAM}}

==References==
{{reflist}}

{{Astrobiology}}
{{Comet spacecraft}}
{{Planetary Missions Program Office|New Frontiers=y}}
{{Japanese space program}}

{{Use dmy dates|date=July 2018}}

[[Category:Missions to comets]]
[[Category:New Frontiers program proposals]]
[[Category:Origin of life]]
[[Category:Proposed NASA space probes]]
[[Category:Proposed astrobiology space missions]]
[[Category:Sample return missions]]