Cassini/Huygens

Launch data: Designation  25008 / 97061A Launch date  15 Oct 1997 - 08:43 UT Launch site  CC, LC-40 Launch vehicle  Titan-401B/Centaur-T (4B-33/TC-21) Mission  Venus-Flyby, Earth-Flyby, Saturn-Orbiter Payload  Huygens Titan lander Heliocentric orbit Perihelion / Aphelion   Incl. to ecliptic   ° Period   min

Spacecraft data: Prime contractor  JPL Propulsion Module System built by Lockheed Martin/Denver Operator  NASA / ESA / ASI Platform   Mass at launch  2523 kg Dry Mass   kg Basic shape   Dimension  Total length: 6.7 m Max dia: 4.0 m Solar array   Stabilization   DC power  640 W Design lifetime  7 years - still in orbit around Saturn

Cassini assembly

Description:

• The Cassini spacecraft is a scientific platform designed to perform an in-depth study of the Saturnian system. After insertion into its orbit about Saturn in 2004, Cassini will perform detailed studies of Saturn's atmosphere, magnetosphere, rings and several of its moons. Chief among the goals is a thorough characterisation of the large moon, Titan. Titan's surface will be mapped using synthetic aperture radar and its atmosphere will be investigated by the ESA build Huygens probe that will descend via parachute. Scientists and engineers from the US and 16 European countries will participate in the mission.
• Spacecraft: 3-axis stabilised; power supplied by 3 RTG (628W at EOM); 4 meter HGA supporting S-, X-,Ku-, Ka-band signals, X-band telemetry at 249 kbps, 2 backup LGAs for emergency commanding; dual redundant flight computers; dual redundant 445N gimballed main engines (burning N2O4, MMH), 16 hydrazine ACS thrusters; redundant star sensors, sun sensors, HRG IRUs, reaction wheels; active thermal control using RHUs, heaters, louvers; redundant solid-state recorder; high level of spacecraft autonomy and fault protection 2.7 meter dia. Huygens probe deployed by 3 pyrotechnic release bolts, 3 parachutes used to control descent, heat shield uses AQ60 material developed by Aerospatiale, redundant S-band link (8 kbps max), lithium sulphur-dioxide (LiSO2) primary batteries, radar altimeter.
• Payload: The experiments carried aboard the Cassini orbiter include: Imaging Science Subsystem (ISS), Cassini Radar, Radio Science Subsystem (RSS), Ion and Neutral Mass Spectrometer (INMS), Visible and Infrared Mapping Spectrometer (VIMS), Composite Infrared Spectrometer (CIRS), Cosmic Dust Analyser (CDA), Radio and Plasma Wave Spectrometer (RPWS), Cassini Plasma Spectrometer (CAPS), Ultraviolet Imaging Spectrograph (UVIS), Magnetospheric Imaging Instrument (MIMI), Dual Technique Magnetometer (MAG). The Huygens probe experiments include: Descent Imager and Spectral Radiometer, Huygens Atmospheric Structure Instrument, Gas Chromatograph and Mass Spectrometer, Aerosol Collector Pyrolyzer, Surface Science Package, and the Doppler Wind Experiment.

Mission detail:

• The Cassini launch to Saturn, originally scheduled for Oct 6, 1997 will be delayed because overpressurized air hoses at the launch pad blew away some insulation on the Huygens Titan entry probe. They are still expecting to launch within the window, which extends to Nov 4.
• The NASA/ESA Cassini/Huygens Saturn probe was launched on Oct 15, 1997. The Titan took off at 0843 UTC, and separated from the Centaur at 0852 UTC. The first Centaur burn placed the Centaur/Cassini combination in a 168 x 446 km x 28.7 deg parking orbit at 0854 UTC. Centaur restarted at about 0913 UTC and shut down again at 0919 UTC, now on an escape trajectory from the Earth. It separated from Cassini at 0926 UTC and vented its remaining propellants to move its path away from the space probe.
• The Cassini probe made a flyby of Venus on Apr 26, 1998. This gravity assist maneuver is the first in a series Cassini will make in the inner solar system before heading out to Saturn. Cassini came to 284 km above the surface of Venus at about 1345:41 UTC.
• The Cassini probe to Saturn entered safe mode on Jan 11, 1999 due to an attitude determination problem, but returned safely to checking out its instruments on Jan 16.
• The Cassini probe flew past Venus on Jun 24, 1999 at a distance of 600 km.
• Cassini flew past Earth at a distance of 1171 km at 03:28 UTC on Aug 18, 1999. Before the swingby, Cassini was in an orbit passing near Venus, with a perihelion of 0.7 AU, and stretching out the the middle of the asteroid belt at 2.6 AU. Picking up speed from the Earth encounter, the probe's perihelion has slightly increased to 0.86 AU but its aphelion is now 7.2 AU, between Jupiter and Saturn.
• Closest approach with Jupiter was on Dec 30, 2000.
• The Cassini probe to Saturn made a course correction burn at 2000 UTC on Sep 10, 2003 changing its velocity by 0.12m/s. At the time Cassini was 1284 million km from the Sun, in an orbit of 1.4462 AU x 9.2769 AU with an inclination of 0.81 deg to the ecliptic plane (NB: 1 AU = 149.60 million km) and the correction altered the orbit by about ten parts per million. On Sep 14 Cassini was 137 million km from Saturn; Saturn's nominal gravitational sphere of influence is 55 million km in radius and Cassini will reach this point on Mar 10, 2004.
• The Cassini space probe entered Saturn's gravitational sphere of influence on Mar 9, 2004. This is the Laplacian sphere at 54.8 million km; the Hill tidal sphere at 94.4 million km was crossed on Dec 16, while the equigravisphere (static gravitational force ratio) at 23 million km was not reached until May 18; the latter ignores the effects of Saturn's orbital acceleration, so the Laplacian sphere is the relevant one for deciding whether to approximate Cassini's orbit as being around Saturn rather than around the Sun. On Mar 8, 2004 Cassini was in a 1.40 x 9.28 AU x 0.7 deg heliocentric orbit approaching the Saturnian system (orbital figures as periapsis - closest approach - x apoapsis - furthest distance - x inclination angle between orbit plane and reference plane, with the reference plane being the ecliptic in this case. The astronomical unit is 1 AU = 149.6 million km.)
• On Mar 10, 2004 the probe's osculating, hyperbolic Saturnian orbit was -24450 x infinity km, nominally an impact trajectory. The continuing effects of solar gravity raised the periapsis height above zero on May 4, and by Jun 11 its orbit was +18093 x infinity km inclined 17.3 deg to Saturn's equator, with a mildly hyperbolic eccentricity of 1.06 and a Saturn distance of 11.7 million km.
• Cassini flew 2068 km from the moon Phoebe (Saturn IX) at 1933 UTC on Jun 11, 2004. The scheduled Saturn orbit insertion burn is from 0112 to 0248 UTC on Jul 1, putting Cassini in a 19980 x 10000000 km x 16.8 deg orbit and setting it up for a distant 339000 km flyby of Titan (Saturn VI) at 0930 UTC on Jul 1.
• Approximate heliocentric orbits, showing how Cassini's flybys set it up for the Saturn encounter:

    
    Earth   0.97 x  1.01 AU x 0.00 deg (Mar 2004)
    Saturn  9.03 x 10.09 AU x 2.49 deg (Mar 2004)
  
    Cassini 0.67 x  1.01 AU x 1.24 deg (Jan 1998) Post launch
    Cassini 0.73 x  1.58 AU x 3.51 deg (Aug 1998) Post Venus 1
    Cassini 0.72 x  2.60 AU x 1.14 deg (Jul 1999) Post Venus 2
    Cassini 0.86 x  7.16 AU x 0.71 deg (Oct 1999) Post Earth flyby
    Cassini 1.40 x  9.28 AU x 0.70 deg (Mar 2004) Post Jupiter flyby
  

• After a long interplanetary voyage it entered into orbit around Saturn on July 1, 2004.
  The main engine fired from 0112 UTC to 0248 UTC on Jul 1; Cassini is now in a roughly 20300 x 9037181 km x 17.3 deg orbit around the ringed planet. The neutral mass spectrometer cover was ejected at 0315 UTC. A distant 339000 km Titan flyby on Jul 2 at around 0930 UTC gave tantalizing glimpses of the surface.
• The Cassini-Huygens space probe made a flyby of Titan on Oct 26, 2004. The Ta flyby closest approach was at 1530 UTC at an altitude of 1200 km above Titan's surface. (Light travel time to Earth was 1hr 14min so this corresponds to an Earth Received signal time of 1644 UTC, reported in some sources as the flyby time.) Cassini is falling inward towards Saturn, with closest approach at 1019 UTC on Oct 28; the Titan flyby changed the orbit to about 0.3 x 4.6 million km inclined 13.8 deg to the ring plane. This lowered the apoapsis by a factor 2 and sets the probe up for the Tb flyby of Titan on Dec 13.
• The Cassini spacecraft flew past Titan (Saturn VI) at 1138 UTC on Dec 13, 2004 lowering its Saturnian orbit further to 231000 km x 3533000 km x 8.2 deg from its previous 313000 x 4.6M km x 13.8 deg path. Only small orbit changes are now needed to set the Huygens probe up for its Titan entry on Jan 14. The Titan-B flyby was at an altitude of 1200 km above Titan's surface, similar to the earlier Titan-a flyby on Oct 26. At 0252 UTC on Dec 15, Cassini made a 72500 km flyby of Dione (Saturn IV), outside its gravitational sphere of influence but closer than Voyager 1's 161000 km approach.
• The Huygens Titan lander separated from Cassini orbiter on Dec 25, 2004 at approximately 02:00 UTC.
• The Cassini spacecraft made its Titan-4 flyby at 2005 UTC on Mar 31, 2005 passing 2402 km above 33.3 deg N 118.6 deg W. Closest approach to Saturn on this orbit was on Mar 29, completing a 20-day circuit which began with a 504 km Enceladus flyby and a 82000 km Tethys flyby on Mar 9. The flyby lowered the Saturnian apoapsis The north polar Titan-5 (06TI) flyby is due on 1912 UTC Apr 16 at a height of 1025 km above 74.0N 272W.
• Cassini made another pass through the inner Saturnian system on Jun 8, 2005 with a 156400 km periapsis at 1037 UTC. On this pass, there were distant encounters with the small moons Calypso (Saturn XIV) and Pallene (Saturn XXIII). Cassini has already made a lot of close approaches to Saturnian moons, not all of which involved science observations.
• Saturnian moon encounters within 120000 km from Jun 11, 2004 till Jun 08, 2005.
• Cassini made another flyby of Titan at 2058 UTC on Apr 30, 2006 at an altitude of 1855 km and an inertial velocity of 5.84 km/s.
• The Cassini spacecraft is in a 155000 x 2300000 km orbit around Saturn, after 5.5 years in the Saturnian system. On Dec 28, 2009 at 0017 UTC it made flyby 123TI/T64 of Titan at a height of 955 km; on Jan 12, 2010 at 2310 UTC it made Titan flyby 124TI/T65 at a height of 1073 km. Flyby 125TI/T66 is scheduled for Jan 28, 2010.
• Cassini flew 7490 km from Titan at 2228 UTC on Jan 28, 2010. The spacecraft's next flyby is of Rhea, on 2010 Mar 2.
• The Cassini probe made the closest ever flyby of Saturn's moon Mimas (Saturn I) at 1723 UTC on Feb 13, 2010 passing 9520 km from the icy world's surface. At 1742 UTC on Mar 2, Cassini flew only 101 km from Rhea (Saturn V), and the next day on Mar 3 at 1342 UTC passed 1817 km from the Dione Trojan moon, Helene (Saturn XII).
• The Cassini spacecraft made a 7461 km flyby of Titan at 1550 UTC on Apr 5, 2010 and is on course to pass Dione at an altitude of 500 km at 0516 UTC on Apr 7. The Titan flyby raised the height of Cassini's orbit from 114700 x 2383000 km x 0.37 deg to 152400 x 2646000 km x 0.37 deg.
• Cassini's plasma spectrometer instrument detected ions of molecular oxygen during a flyby of Dione in April 2010.
  Dione's atmosphere is extremely thin, about 5 trillion times less dense than the atmosphere at Earth's surface. Cassini's measurements indicate there is just one oxygen ion for every 0.67 cubic inches, or 2,250 ions per cubic foot.
• Cassini made a 2044 km flyby of Titan's north pole (T-69) on Jun 5, 2010 reducing orbit inclination around Saturn from 12 degrees to 2.0 deg.
• After apoapsis on Jun 11, 2010 it returned to Titan for the T-70 flyby on Jun 20 at 0127 UTC, making its closest ever pass at 880 km above the clouds to measure the dayside ionosphere. This pumped the inclination back up, and the orbit on Jun 21 was 119500 x 2207600 km x 19.1 deg. The next flyby is T-71 on Jul 7.
• The Cassini probe made a 99 km flyby of Dione on Dec 12, 2011 followed by a 3586 km flyby of Titan on Dec 13. Cassini has been in orbit around Saturn since 2005 Aug.
• The Cassini spacecraft flew past Enceladus at 74 km on both Apr 13 and May 2, 2012.