Cassini retirement
The planned end of mission for Cassini is disposal by a controlled fall into Saturn's atmosphere on September 15, 2017.[1][2] This method was chosen because it is imperative to ensure protection and prevent biological contamination to any of the moons of Saturn now thought to offer potential habitability environments.[3]
However, this plan was chosen prior to future planetary flagship missions being put on hold indefinitely in 2013.[4][clarification needed] Factors that can have an impact on the mission end method are the amount of rocket fuel it has left, the health of the spacecraft, and funding for operations on Earth.[5]
Some possibilities for Cassini's later stages were aerobraking into orbit around Titan,[5] leaving the Saturn system,[5] or making close approaches and/or changing its orbit.[5] For example, it could collect solar wind data in a heliocentric orbit.[1]
End of mission planning
| Colour | Meaning[1] |
|---|---|
| Red | Poor |
| Yellow | Fair |
| Light Green | Good |
| Green | Excellent |
During planning for its extended missions, various future plans for Cassini were evaluated on the basis of science return, cost, and time.[1][6] Some of the options examined include collision with Saturn atmosphere, an icy satellite, or rings; another was departure from Saturn orbit to Jupiter, Uranus, Neptune, or a centaur.[1] Other options included leaving it in certain stable orbits around Saturn, or departure to a heliocentric orbit.[1] Each plan requires certain amounts of time and changes in velocity.[1] Another possibility was aerobraking into orbit around Titan.[5]
This table is based on page 19 of Cassini Extended Missions (NASA), from 2008.[1]
| Option | Set-up requirements | Execution time | Operability +
assurance of EOL |
Velocity change (delta-v)
required |
Science evaluation circa 2008 |
|---|---|---|---|---|---|
| Saturn impact – short-period orbits | High inclination achievable via any XXM design | 2–10 months total | Short time between last encounter and impact | 5–30 m/s | D-ring option satisfies unachieved AO goals; cheap and easily achievable |
| Saturn impact – 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 | 5–35 m/s | Operations costs required for 3 years with no science could be applied elsewhere |
| Impact icy satellite | Can be implemented from any geometry | 0.5–3 months total | Short time between last encounter and impact | 5–15 m/s | Cheap and achievable anywhere/time |
| Impact 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 | 5–15 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 years, Uranus 20 years, Neptune 40 years) | Planetary impact can only be guaranteed shortly after escape for Jupiter | 5–35 m/s | Giant-planet science unlikely |
| Escape to heliocentric orbit | Can be implemented from any geometry | 9–18 months to escape, open-ended Solar orbit | Last encounter goes to escape | 5–30 m/s | Solar wind data only |
| Escape to 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 | 5–30 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 | 50 m/s | Limited Saturn / magnetospheric science, but for long period of time |
| Stable orbit outside 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 |
On 4 July 2014, the Cassini science team announced that the proximal orbits of the probe would be named the "Cassini Grand Finale". This would be immediately preceded by a gradual shift in inclination to better view Saturn's polar hexagon, and a very close flyby of Enceladus to closer study its cryovolcanism.[7]
See also
References
- ^ a b c d e f g h i j Spilker, Linda (1 April 2008). "Cassini Extended Missions" (PDF). Lunar and Planetary Institute. Archived from the original (PDF) on 2008-04-23.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Mason, Betsy (3 February 2010). "Cassini Gets Life Extension to Explore Saturn Until 2017". Wired. Archived from the original on 2010-02-09.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Blabber, Phillipa; Verrecchia, Angélique (3 April 2014). "Cassini-Huygens: Preventing Biological Contamination". Space Safety Magazine. Retrieved 2015-08-01.
- ^ Whittington, Mark (15 February 2012). "NASA Flagship Planetary Missions on Hold Indefinitely". Yahoo. Archived from the original on 2013-09-02.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ a b c d e Bailey, Frederick; Rabstejnek, Paul. "Cassini Mission and Results". Oglethorpe University. Archived from the original on 2008-02-19.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Pappalardo, Bob; Spiker, Linda (15 March 2009). "Cassini Proposed Extended-Extended Mission (XXM)" (PDF). Lunar and Planetary Institute. Archived from the original (PDF) on 2012-07-18.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ "Cassini Names Final Mission Phase Its 'Grand Finale'". Astrobiology Magazine. 4 July 2014. Retrieved 2015-08-01.