Cassini retirement

Short description: Retirement of NASA's Cassini spacecraft on 15 September 2017

Artist's concept of Cassini's controlled atmospheric entry into Saturn

The Cassini space probe was deliberately disposed of via a controlled fall into Saturn's atmosphere on September 15, 2017, ending its nearly two-decade-long mission.[1][2][3][4] This method was chosen to prevent biological contamination of any of the moons of Saturn now thought to offer potentially habitable environments.[5] Factors that influenced the mission end method included the amount of rocket fuel left,33 kg (73 lb) of plutonium-238, the health of the spacecraft, and funding for operations on Earth.[6]

Some possibilities for Cassini's later stages were aerobraking into orbit around Titan,[6] leaving the Saturn system,[6] or making close approaches and/or changing its orbit.[6] For example, it could have collected solar wind data in a heliocentric orbit.[3]

## Contents

* 1 End of mission options
* 2 Atmospheric entry and destruction
* 3 See also
* 4 References
* 5 Further reading
* 6 External links

## End of mission options

Color  | Meaning[3]

|

Red  | Poor
Orange  | Fair
Yellow  | Good
Green  | Excellent

During planning for its extended missions, various future plans for Cassini were evaluated on the basis of scientific value, cost, and time.[3][7] Some of the options examined included collision with Saturn atmosphere, an icy satellite, or rings; another was departure from Saturn orbit to Jupiter, Uranus, Neptune, or a centaur.[3][8] Other options included leaving it in certain stable orbits around Saturn, or departure to a heliocentric orbit.[3] Each plan required certain amounts of time and changes in velocity.[3] Another possibility was aerobraking into orbit around Titan.[6]

This table is based on page 19 of Cassini Extended Missions (NASA), from 2008.[3]

Cassini end of mission options with science evaluation circa 2008[3] Type  | Option  | Set-up requirements  | Execution time  | Operability +
assurance of EOL | Velocity change
(Δv) required  | Science evaluation ca. 2008

|
|
|
|
|
|

Impact
with ...  | Saturn's surface:
short-period orbits  | High inclination achievable via
any XXM design  | 2–10 months total  | Short time between last encounter and impact  | 005–30 m/s  | D-ring option satisfies unachieved original mission goals;
cheap and easily achievable
Saturn's surface:
long-period orbits  | Specific orientation and inclination required  | 4–22 months to set up long period orbit +
3 years for final orbit  | 3 years between last encounter and impact  | 005–35 m/s  | Operations costs required for 3 years
with no science could be applied elsewhere
icy satellite | Can be implemented from any geometry  | 0.5–3 months total  | Short time between last encounter and impact  | 005–15 m/s  | Cheap and achievable anywhere/time
main rings | Can be implemented from any geometry  | 0.5–3 months total  | Short time between last encounter and impact
but difficult to prove spacecraft destruction  | 005–15 m/s  | Cheap and achievable anywhere/time;
close-in science before impact
Escape
to ...  | giant planet | Specific orbit period, orientation and
inclination required + specific departure dates  | 1.4–2.4 years to escape + long transfer time:
Jupiter 12, Uranus 20, Neptune 40 years  | Planetary impact can only be guaranteed
shortly after escape for Jupiter  | 005–35 m/s  | Giant-planet science unlikely
heliocentric orbit | Can be implemented from any geometry  | 9–18 months to escape, open-ended Solar orbit  | Last encounter goes to escape  | 005–30 m/s  | Solar wind data only
Centaur | Large target set offers wide range
of departures  | 1–2 years to escape + 3+ year transfer  | Last encounter goes to escape; must maintain
teams for 3+ years for centaur science  | 005–30 m/s  | Multi-year lifetime and funding seems better spent in target-rich Saturnian environment
Stable
orbit
outside ...  | Titan  | Specific orientation and orbit period required  | 13–24 months + open-ended time in stable orbit  | 200 days between last encounter and final orbit  | 050 m/s  | Limited Saturn / magnetospheric science, but for long period of time
Phoebe | Specific orientation and orbit period required  | 8+ years + open-ended time in stable orbit  | Many months between last encounter and final orbit  | 120 m/s  | Solar wind data; very rare passages through magnetotail

## Atmospheric entry and destruction

Animation of Cassini's Grand Finale
Cassini * Saturn Last image taken by Cassini, at 19:59 UTC (14 September 2017).

On July 4, 2014, the Cassini science team announced that the proximal orbits of the probe would be named the "Grand Finale".[9] This would be immediately preceded by a gradual shift in inclination to better view Saturn's polar hexagon, and a flyby of Enceladus to more closely study its cryovolcanism.[10] This was followed by a dive into Saturn's atmosphere.[9]

There was budgetary drama in 2013–14 about NASA receiving U.S. government funding for the Grand Finale. The two phases of the Grand Finale ended up being the equivalent of having two separate Discovery Program-class missions in that the Grand Finale was completely different from the main Cassini regular mission. The U.S. government in late 2014 approved the Grand Finale at the cost of $200 million. This was far cheaper than building two new probes in separate Discovery-class missions.[11]

Scientific data was collected using eight of its twelve science instruments. All of the probe's magnetosphere and plasma science instruments, plus the spacecraft's radio science system, and its infrared and ultraviolet spectrometers collected data during the final plunge. The data rates flowing back from Saturn could not support imaging during the final plunge, so all pictures were downlinked (transmitted back to Earth) and cameras were switched off, before the final plunge began.[12] The predicted altitude for loss of signal was approximately 1,500 km (930 mi) above Saturn's cloud tops, when the spacecraft began to tumble and burn up like a meteor.[13]

Cassini's final transmissions were received by the Canberra Deep Space Communication Complex, located in Australia at 18:55:46 AEST. In a bittersweet ending for the scientists involved, some of whom had been involved in the mission for decades,[14][15] data was received for 30 seconds longer than anticipated, and the spacecraft's ultimate demise was predicted to have occurred within 45 seconds after that.[16] Homages were paid on social media.[17] NASA's video won an Emmy for "Outstanding Original Interactive Program".[18]

Cassini impact site on Saturn (visual/IR mapping spectrometer; September 15, 2017)

## See also

* Deliberate crash landings on extraterrestrial bodies
* Timeline of Cassini–Huygens

## References

1. ↑ Brown, Dwayne; Cantillo, Laurie; Dyches, Preston (September 15, 2017). "NASA's Cassini Spacecraft Ends Its Historic Exploration of Saturn". NASA. https://www.jpl.nasa.gov/news/news.php?feature=6948.
2. ↑ Chang, Kenneth (September 14, 2017). "Cassini Vanishes Into Saturn, Its Mission Celebrated and Mourned". The New York Times. https://www.nytimes.com/2017/09/14/science/cassini-grand-finale-saturn.html.
3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Spilker, Linda (April 1, 2008). "Cassini Extended Missions". Lunar and Planetary Institute. http://www.lpi.usra.edu/opag/march_08_meeting/presentations/spilker.pdf.
4. ↑ Mason, Betsy (February 3, 2010). "Cassini Gets Life Extension to Explore Saturn Until 2017". Wired. https://www.wired.com/wiredscience/2010/02/cassini-life-extension-2017/.
5. ↑ Blabber, Phillipa; Verrecchia, Angélique (April 3, 2014). "Cassini-Huygens: Preventing Biological Contamination". Space Safety Magazine. http://www.spacesafetymagazine.com/space-exploration/extraterrestrial-life/cassini-huygens-preventing-biological-contamination/.
6. ↑ 6.0 6.1 6.2 6.3 6.4 Bailey, Frederick; Rabstejnek, Paul. "Cassini Mission and Results". Oglethorpe University. http://www.oglethorpe.edu/faculty/~m_rulison/Astronomy/Group/Summer 00/Cassini/ASTRONOMY PROJECT.htm.
7. ↑ Pappalardo, Bob; Spilker, Linda (March 15, 2009). "Cassini Proposed Extended-Extended Mission (XXM)". Lunar and Planetary Institute. http://www.lpi.usra.edu/opag/march09/presentations/pappalardo.pdf.
8. ↑ Okutsu, Masataka, et al. "Cassini End-of-Life Escape Trajectories to the Outer Planets (AAS 07-258)." ADVANCES IN THE ASTRONAUTICAL SCIENCES 129.1 (2008): 117.
9. ↑ 9.0 9.1 "The Grand Finale Toolkit". https://saturn.jpl.nasa.gov/mission/grand-finale/overview/.
10. ↑ "Cassini Names Final Mission Phase Its 'Grand Finale'". Astrobiology Magazine. July 4, 2014. http://www.astrobio.net/topic/solar-system/saturn/cassini-names-final-mission-phase-grand-finale/.
11. ↑ "Cassini's awesomeness fully funded through mission's dramatic end in…". https://www.planetary.org/articles/cassinis-awesomeness-fully.
12. ↑ Cassini conducts last picture show. Jonathan Amos. BBC News. 14 September 2017.
13. ↑ Cassini Spacecraft Makes Its Final Approach to Saturn. JPL, NASA News. September 13, 2017.
14. ↑ Branson-Potts, Hailey (2017-09-15). "Cassini scientists celebrate the mission's end with a few hundred of their closest friends". http://www.latimes.com/science/sciencenow/la-sci-sn-cassini-scene-caltech-20170915-htmlstory.html.
15. ↑ Chang, Kenneth (2017-09-15). "Cassini Vanishes Into Saturn, Its Mission Celebrated and Mourned". https://www.nytimes.com/2017/09/14/science/cassini-grand-finale-saturn.html.
16. ↑ Netburn, Deborah (2017-09-15). "As NASA's Cassini mission flames out over Saturn, scientists mark bittersweet end of mission". http://www.latimes.com/science/sciencenow/la-sci-sn-cassini-ends-scene-20170915-story.html.
17. ↑ Kaplan, Karen (2017-09-15). "Cassini plunges to its death at Saturn, and humanity says goodbye". http://www.latimes.com/science/sciencenow/la-sci-sn-cassini-saturn-farewell-20170915-htmlstory.html.
18. ↑ "Nominees/Winners | Television Academy". Academy of Television Arts & Sciences. http://www.emmys.com/awards/nominees-winners/2018/outstanding-original-interactive-program.

## Further reading

* Ralph Lorenz (2018). NASA/ESA/ASI Cassini-Huygens: 1997 onwards (Cassini orbiter, Huygens probe and future exploration concepts) (Owners' Workshop Manual). Haynes Manuals, UK. ISBN 978-1-78521-111-9.

## External links

* Cassini-Huygens at ESA
* Cassini-Huygens main page at NASA
* Cassini Mission Homepage by the Jet Propulsion Laboratory
* Cassini-Huygens Mission Profile by NASA's Solar System Exploration
* Grand Finale Overview at NASA

* v
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Cassini–Huygens

Spacecraft|

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Saturn

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Astronomy|

* Delta Octantis
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Exploration|

* Cassini–Huygens (Huygens)
* timeline
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* Pioneer 11
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* Voyager 1
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Related|

* Fiction
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* In Saturn's Rings (2018 documentary)

* v
* t
* e

Spacecraft missions to Saturn

Past|

| Flybys|

* Pioneer 11
* Voyager 1
* Voyager 2

|

Orbiters|

* Cassini–Huygens
* timeline
* retirement

Landers|

* Huygens (on Titan)

Planned|

* Dragonfly (to Titan, 2026)

Proposed|

| to Saturn and rings|

* Kronos
* Saturn Atmospheric Entry Probe
* SPRITE
* Titan Saturn System Mission

|

to Enceladus|

* Enceladus Life Finder
* Enceladus Explorer
* Life Investigation For Enceladus

to Titan|

* AVIATR
* Oceanus
* TALISE
* Titan Mare Explorer

to several moons|

* Explorer of Enceladus and Titan
* Journey to Enceladus and Titan

* There are no ongoing missions to Saturn

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2017 in space

* « 2016

2018 »

Impact events|

* Bolides in 2017
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Selected NEOs|

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Exoplanets |

* HATS-36b
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Discoveries|

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Space exploration|

* Cassini retirement

* Category:2016 in space — Category:2017 in space — Category:2018 in space

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