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Titan Fly-by - 4 April 2009

Titan Fly-by - 4 April 2009

3 April 2009

On Saturday, 4 April, the Cassini spacecraft returns to Saturn's largest moon for the mission's fifty-third targeted encounter with Titan: T52. The closest approach to Titan occurs at 01:47:47 UT at an altitude of 4150 kilometres above the surface and at a speed of 5.8 kilometres per second. The latitude at closest approach is 2.8°S and the encounter occurs on orbit number 108.

The T52 fly-by occurs just eight days after the previous fly-by T51. Unlike other fly-bys, this encounter is set up with only one manoeuvre: a combined post-fly-by cleanup/Titan approach manoeuvre, on 29 March. The fly-by is unique because this revolution is a circular orbit. T52 is the first fly-by in a series of eleven inbound encounters and the eighth Titan encounter in Cassini's Equinox Mission. It occurs just under five days before Saturn closest approach.

Science Highlights

  • Radio Science Subsystem (RSS)
    The RSS observations on T52 include ionospheric and atmospheric occultations and bistatic surface scattering on both the inbound and outbound legs of the fly-by. The T52 egress atmospheric occultation is one of the highest priority RSS occultations of Cassini's extended mission. It will be the first Cassini occultation (in fact the first since Voyager in 1980) to probe near-equatorial latitude (~0°). The ingress occultation will probe mid-northern latitude (~57°). These occultations will shed more light on latitudinal variability of the electron density profile of Titan's ionosphere, temperature/pressure profile, extinction profile, and small scale-structure of the neutral atmosphere. The RSS occultations are the only Cassini observations able to map the thermal structure of the atmosphere down to the surface with high spatial resolution (tens of metres). They require implementation of a critical manoeuvre to steer the spacecraft during the observations to keep track of the radio signal as it bends through the atmosphere. To maximize chances of success, the manoeuvre design is usually updated and radiated to Cassini the week before execution of the experiment. The T52 inbound bistatic scattering observation will probe for the first time high-northern latitude regions of Titan's surface (55-70°N; ~0-10° west longitude), and the outbound bistatic will probe mid-southern latitude region (~40°S; ~260-300° west longitude). The incidence angle for both the inbound and the outbound scattering observations is close to the Brewster angle range of likely surface compositions. Same- and cross-polarized components of the quasi-specular surface echo, if detectable, provide information about the dielectric constant and physical state of the surface region probed.
  • Ultraviolet Imaging Spectrograph (UVIS)
    Solar and stellar occultations by Titan are the most valuable Titan atmospheric 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). In T52, UVIS takes advantage of an exceptionally slow occultation, among the slowest in Cassini's Equinox Mission, to probe Titan's polar vortex region. The experiment is self-calibrating (the information comes from a ratio of signal during occultation to signal of the unocculted Sun or star just before or after occultation). These profiles probe altitudes between 300 km and 2400 km which fill the gap between CIRS and INMS measurements. Much of the chemistry and aerosol formation occurs in this altitude range. Observations taken over the course of the mission will collectively provide coverage at many latitudes and local times and these will be used to study meridional and local time gradients in the upper atmosphere. Knowledge of these gradients is important for understanding the meridional circulation and other dynamical and chemical processes.
  • Cassini Radar (RADAR)
    RADAR captures radiometry on the inbound leg of the fly-by. Though distant, the observations provide good North polar coverage, filling a gap in brightness temperature maps.
  • Visual and Infrared Mapping Spectrometer (VIMS)
    VIMS will ride along 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 will conduct surface temperature mapping on outbound, and far-infrared stratosphere composition study.
  • Imaging Science Subsystem (ISS)
    ISS will acquire full-disk and global- to regional-mapping mosaics of Titan's trailing hemisphere at high southern latitudes and will ride along with CIRS to monitor clouds. Observations will target very high southern latitudes at a variety of resolutions.
  • Magnetospheric Imaging Instrument (MIMI)
    MIMI will measure energetic ion and electron energy input to Titan's atmosphere.
  • Dual Technique Magnetometer (MAG)
    T52 is a flank-out, post-dusk, high altitude (>4000 km) fly-by that will be useful to characterize the background field in which Titan sits.
  • 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
10:05:00 -08d 16h Start of sequence S49 that contains Titan-52

29 March 2009

Time UTC Time wrt
07:05:00 -05d 19h OTM #186 prime. Titan-52 targeting manoeuvre

30 march 2009

Time UTC Time wrt
00:50:00 -05d 01h OTM #186 Backup

1 April 2009

Time UTC Time wrt
00:35:00 -03d 01h OTM #186 alternate prime. Alternative Titan-52 targeting manoeuvre
17:05:00 -02d 09h OTM #186 alternate backup

3 April 2009

Time UTC Time wrt
09:34:00 -16h 13m Start of the TOST segment
09:34:00 -16h 13m Turn cameras to Titan
10:14:00 -15h 33m New waypoint
10:14:00 -15h 33m Deadtime, 15 minutes and 34 seconds long. Used to accommodate changes in fly-by time
10:29:34 -15h 18m Titan atmospheric observations - CIRS. Obtain information on the thermal structure of Titan's stratosphere
12:17:47 -13h 30m Titan surface observations - ISS.
Monitoring for surface/atmosphere changes; attempt to see surface colour variations; monitor limb hazes
12:47:47 -13h 00m Titan surface observations - VIMS.
Stare at Titan for cloud mapping. Unilluminated approach
16:47:47 -09h 00m Titan global map - VIMS.
Unilluminated approach
19:27:47 -06h 20m RADAR Titan observations.
Inbound Radiometry-part 1
21:27:47 -04h 20m Transition to thruster control
21:28:47 -04h 19m RADAR Titan observations.
Inbound Radiometry-part2
22:27:47 -03h 20m Titan atmospheric observations - UVIS.
Titan occults star alpha Eri. UVIS FUV occultation slit boresite on star for the entire time

4 April 2009

Time UTC Time wrt
00:27:47 -01h 20m RSS ingress bistatic observation.
Bistatic scattering measurements at three radio wavelengths to determine the physical properties of Titan's surface, including reflectivity, dielectric constant, and roughness
01:25:47 -00h 22m RSS occultation.
RSS ingress/egress occultation of Titan's atmosphere and ionosphere
01:29:37 -00h 18m Apoapse
01:36:54 -00h 11m Earth occultation, 10 minute duration
01:38:54 -00h 09m Solar occultation, 6 minute duration
01:47:47 +00h 00m Titan-52 Fly-by Closest Approach Time
Altitude = 4150 km, speed = 5.8 kms-1, 151° phase at closest approach
01:59:47 +00h 12m RSS egress bistatic observation.
Bistatic scattering measurements at three radio wavelengths to determine the physical properties of Titan's surface, including reflectivity, dielectric constant, and roughness
02:09:47 +00h 22m Descending ring plane crossing
03:15:47 +01h 28m Transition off of thruster control
03:37:47 +01h 50m Titan atmospheric observations - CIRS.
Obtain information on surface & tropopause temperatures, and on tropospheric CH4
05:17:47 +03h 30m Titan surface observations - ISS.
Regional map
06:47:47 +05h 00m Titan surface observations - ISS.
Global map
10:47:47 +09h 00m Titan atmospheric observations - CIRS.
Obtain information on CO, HCN, CH4. Integrate on disk at airmass 1.5-2.0
13:47:47 +12h 00m Titan surface observations - ISS.
Global map
15:47:47 +14h 00m Titan atmospheric observations - CIRS. Obtain information on the thermal structure of Titan's stratosphere.
Last Update: 1 September 2019
21-Jan-2021 02:47 UT

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