Titan Fly-by - 20 April 2009
20 April 2009
On Monday, 20 April, Cassini returns to Saturn's largest moon for the mission's fifty-fourth targeted encounter with Titan: T53. The closest approach to Titan occurs at 00:20:45 UT at an altitude of 3600 kilometres above the surface and at a speed of 5.8 kilometres per second. The latitude at closest approach is 7.7°S and the encounter occurs on orbit number 109.This encounter is set up with two manoeuvres: an apoapsis manoeuvre on 12 April and a Titan approach manoeuvre, scheduled for 17 April. T53 is the second fly-by in a series of eleven inbound encounters and the ninth Titan encounter in Cassini's Equinox Mission. It occurs just under four days before Saturn closest approach.
Science Highlights
- Ultraviolet Imaging Spectrograph (UVIS)
Solar and stellar occultations by Titan are the most valuable Titan observations for UVIS because they provide detailed vertical profiles of nitrogen (in the EUV channel during solar occultation) and hydrocarbons, HCN, and aerosols (in the FUV channel during stellar occultations). On T53 UVIS observes a long stellar occultation and a solar occultation. The two occultation observations probe different parts of the atmosphere.
The solar occultation, using the extreme ultraviolet (EUV) channel, samples the neutral nitrogen from above about 900 kilometres altitude up to about 2300 kilometres. This range overlaps the atmospheric region sampled by INMS and by Cassini's attitude control system, or AACS. Solar occultation measurements give a measure of the density profile of the main constituent of the atmosphere, and the rate of change of the N2 density with altitude gives information on the temperature.
The stellar occultations use the UVIS far ultraviolet (FUV) channel. The longer wavelengths do not give a good measure of N2, but do sample a number of hydrocarbons and haze from about 300 kilometre altitude to 1600 kilometre altitude. The upper end of this altitude range overlaps with INMS and the lower end overlaps with CIRS. INMS, CAPS and UVIS have already shown that complex organic chemistry is going on at the 1000-kilometre level in Titan's atmosphere. The stellar occultation in T53 is a very slow one, the slowest in Cassini’s extended mission, but not the slowest in the mission so far. These slow occultations allow more signal to be acquired in a given altitude range, and are therefore very valuable. - Cassini Radar (RADAR)
RADAR captures radiometry outbound. - Visual and Infrared Mapping Spectrometer (VIMS)
VIMS will ridealong with CIRS for daytime observations 2 hours after closest approach. Along with monitoring of tropical clouds, VIMS may get images at 20 km/pixel resolution of an area located in the southern hemisphere close to the South pole (30-90°S, 240-300°W). - Composite Infrared Spectrometer (CIRS)
CIRS conducts far-infrared vertical temperature and aerosol mapping at low latitudes. - Imaging Science Subsystem (ISS)
ISS will ride along with VIMS to image Titan's trailing hemisphere at high southern latitudes and with CIRS to monitor clouds. (0.5-hour illuminated prime observation primarily for photometry.) - Magnetospheric Imaging Instrument (MIMI)
MIMI measures energetic ion and electron energy input to Titan's atmosphere. Sun obscures ENA. - Dual Technique Magnetometer (MAG)
T53 is another flank-out, post-dusk, high altitude fly-by that will be a good complement to T52 in order to characterize the background field for a similar local time with respect to Saturn and different SKR longitudes. - Radio and Plasma Wave Science (RPWS)
RPWS will measure thermal plasmas in Titan's ionosphere and surrounding environment; search for lightning in Titan's atmosphere; and investigate the interaction of Titan with Saturn's magnetosphere.
Table of Events
26 March 2009
| Time UTC | Time wrt T-53 |
Activity |
| 10:05:00 | -24d14h | Start of Sequence S49 that contains Titan-52 |
17 April 2009
| Time UTC | Time wrt T-53 |
Activity |
| 23:33:00 | -03d 01h | OTM #190 prime. Titan-53 targeting manoeuvre |
18 April 2009
| Time UTC | Time wrt T-53 |
Activity |
| 23:33:00 | -02d 01h | OTM #190 backup |
19 April 2009
| Time UTC | Time wrt T-53 |
Activity |
| 08:18:00 | -16h 02m | Start of the TOST segment |
| 08:18:00 | -16h 02m | Turn cameras to Titan |
| 08:58:00 | -15h 22m | New waypoint |
| 08:58:00 | -15h 22m | Deadtime, 15 minutes and 42 seconds long. Used to accommodate changes in fly-by time |
| 09:13:42 | -15h 07m | Titan atmospheric observations - CIRS. Obtain information on CO, HCN, CH4. Integrate on disk at airmass 1.5-2.0 |
| 14:20:45 | -10h 00m | Titan surface observations - ISS. Global map |
| 15:20:45 | -09h 00m | Titan surface observations - VIMS. Observation of the night side of Titan at phase angle of 110°. Look for clouds and emission features |
| 19:20:45 | -05h 00m | Titan surface observations - VIMS. Regional map |
| 21:20:45 | -03h 00m | Titan atmospheric observations - UVIS. UVIS FUV observation of Titan occulting Alpha Eri |
| 22:45:45 | -01h 35m | Titan atmospheric observations - CIRS. Limb scanning for aerosols |
| 23:22:55 | -00h 58m | Titan atmospheric observations - CIRS. Vertical temperature sounding of Titan's tropopause & stratosphere. Slow radial scans |
20 April 2009
| Time UTC | Time wrt T-53 |
Activity |
| 00:10:45 | -00h 10m | Titan atmospheric observations - UVIS. Solar occultation by Titan. EUV solar occultation port centred on Sun. Slit aligned tangent to limb |
| 00:07:22 | -00h 13m | Earth occultation; 13 minute duration |
| 00:09:26 | -00h 11m | Solar occultation; 9 minute duration |
| 00:20:45 | +00h 00m | Titan-53 Fly-by Closest Approach Time Altitude = 3600 km, speed = 5.8 kms-1, 149° phase at closest approach |
| 00:41:13 | +00h 21m | Descending ring plane crossing |
| 00:46:45 | +00h 26m | Titan atmospheric observations - CIRS. |
| 01:35:45 | +01h 15m | Titan surface observations - VIMS. Titan mosaicking/regional mapping. Phase ~75°. A data cube every 5 minutes. Phase = 76°, lat =60°S, lon = 255° - New territory at 20 km/pixel |
| 02:20:45 | +02h 00m | Titan surface observations - RADAR. Outbound radiometry |
| 06:20:45 | +06h 00m | Titan surface observations - VIMS. Regional mapping and mosaics |
| 08:50:45 | +08h 30m | Titan surface observations - ISS. NAC global map |
| 09:20:45 | +09h 00m | Titan surface observations - VIMS. Global map |
| 14:20:45 | +14h 00m | Titan atmospheric observations - CIRS. Obtain information on the thermal structure of Titan's stratosphere |
| 22:20:45 | +22h 00m | Deadtime, 17 minutes and 14 seconds long. Used to accommodate changes in fly-by time |
| 22:38:00 | +22h 18m | Turn to Earth-line |
| 23:18:00 | +22h 58m | Playback of T53 data. A 34-meter ground station |
21 April 2009
| Time UTC | Time wrt T-53 |
Activity |
| 08:18:00 | +01d 08h | Playback of T53 data. Canberra 70m ground station |
Last Update: 1 September 2019