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Titan Flyby - 19 July 2007

Titan Flyby - 19 July 2007

16 July 2007

This week, Cassini returns to Titan for its thirty-fifth targeted encounter with Saturn's largest moon: Titan-34. The closest approach to Titan occurs on Thursday, 19 July, at 01:11:20 UT at an altitude of 1332 kilometres above the surface and at a speed of 6.2 kilometres per second. The latitude at closest approach is 1.3° N and the encounter occurs on orbit number 48.

This encounter is set up with two manoeuvres: an apoapsis manoeuvre on 8 July, and a Titan approach manoeuvre on 15 July. This is the first inbound Titan encounter since T24, and occurs just under two days before Saturn closest approach.

Science Activities

  • Visual and Infrared Mapping Spectrometer (VIMS)
    VIMS will carry out high resolution mapping for geology and composition at Titan closest approach. On approach, the instrument will examine mid-latitude cloud formation and evolution. Previous observations monitored mid-latitude clouds in the southern hemisphere, which were originally discovered via ground-based observations. Some scientists theorize that these clouds are the natural consequence of the circulation and condensation of atmospheric material, while others believe they are plumes from active geologic events. If the former model is true, mid-latitude clouds should form in the north as Titan transitions from a southern summer to a northern summer. VIMS will also seek possible hotspots from volcanoes or other features. The data from these sequences is valuable for cloud evolution, photometry, movies, and the search for hotspots, lightning, and aurorae (none of which have been found yet). These flybys cover mostly large solar phase angles, but these observations are valuable for deriving the phase function of the surface and the haze, and for viewing clouds.
  • Radio Science Subsystem (RSS)
    T34 is the last RSS Titan bistatic observation in the Cassini nominal mission. In bistatic observations, radio signals from Cassini are directed at Titan and after reflecting on the surface can be detected by ground stations on Earth. The T34 observation is conducted on the inbound approach to Titan, roughly from -77 to -12 minutes relative to closest approach time. During that period, the Cassini high gain antenna boresight is continuously manoeuvred to point to the region on Titan's surface from where mirror-like (specular) reflection, if detectable, can be observed by the NASA DSN ground receiving stations at Goldstone and Canberra. The T34 experiment enjoys the unique advantage of an observation geometry near the Brewster angle of likely surface compositions throughout the 65 minutes observation period. This special geometry allows unambiguous determination of the surface dielectric constant, and hence its physical state and properties, from simultaneous measurement of the RCP and LCP (right and left circularly polarized) echo components, if detectable. The surface region probed extends from about -12° to -7° South latitude and about 217° to 225° West longitude (roughly 25° west of the Huygens landing site). Potential detectability of a weak echo strongly depends on the potential presence of relatively flat (liquid or solid) Titan terrain within the high gain antenna footprint over the surface region probed (the ground track). The T34 observation geometry also enjoys the advantage of extending in time till near closest approach where a smaller distance to the surface enhances the measurement signal-to-noise ratio, hence enhances potential detectability of any weak surface echo.
  • Dual Technique Magnetometer (MAG)
    T34 is one of the most important flybys for MAG. This is the only Titan encounter in the nominal mission that occurs when the direction of incoming UV photons from the Sun and the plasma flow resulting from the rotation of Saturn's magnetosphere are parallel. As a result, Titan's interaction during T34 is expected to be similar to the solar wind interaction with Venus, Mars or comets, which are characterized by the formation of a 'magnetic barrier' (made from piled-up magnetic field lines from Saturn) above a well developed dayside ionosphere. During the flyby, Cassini will explore this magnetic barrier as well as Titan's ionosphere, which is most strongly developed because of the maximum ionization sources. Is there any chance of encountering Titan in the solar wind in T34, or other Titan flybys? Although unlikely for T34, Cassini found Titan at the edge of Saturn's magnetosphere during T32, implying that the satellite - when it is located near the subsolar region - can be immersed in the shocked solar wind during periods of high solar wind pressure.
  • Composite Infrared Spectrometer (CIRS)
    CIRS measurements will seek to determine Titan's atmospheric deuterium to hydrogen ratio. Voyager IRIS measured only one isotope - the D/H in methane - but at a much lower value than the giant planet value. The Huygens probe also measured D/H, which was roughly ten times greater than the giant planet value. CIRS (and INMS) observations will help explain this puzzle.
  • Imaging Science Subsystem (ISS)
    T34 is the only Titan flyby covering a subset of the terrain for the sub-Saturnian hemisphere. T34 also gives us the closest view of region between Belet and Senkyo. This isn't the best view, since this part of the surface is at a fairly high emission angle off to the right of the disk - the best viewing geometry occurs during a non-targeted encounter in Rev 51 - but this observation and the non-targeted encounter are the only views of this territory in the nominal mission. More observations will be needed to fill in coverage of this part of Titan in the extended mission.
  • Ultraviolet Imaging Spectrograph (UVIS)
    The team will obtain spectral images of Titan in the EUV and FUV to map the aurora and dayglow, to map hydrocarbon absorption, and to measure scattering and absorption by aerosols in the stratosphere.

Table of Events

14 July 2007

Time UTC Time wrt
01:06:00 -05d 00h Start of Sequence S32 which contains Titan-34

15 July 2007

Time UTC Time wrt
16:06:00 -03d 09h OTM #121 Prime. Titan-34 targeting manoeuvre

16 July 2007

Time UTC Time wrt
15:51:00 -02d 09h OTM #121 Backup

18 July 2007

Time UTC Time wrt
00:51:00 -01d 00h Start of the TOST segment
00:51:00 -01d 00h Turn cameras to Titan
01:21:00 -23h 50m Deadtime, 27 minutes and 20 seconds long. Used to accommodate changes in flyby time
01:48:20 -23h 23m Titan atmospheric observations. Obtain information on the thermal structure of Titan's stratosphere
09:11:20 -16h 00m ISS nightside imaging. Search for and monitor lightning/aurora
10:11:20 -15h 00m Titan atmospheric observations. Obtain information on CO, HCN, CH4. Integrate on disk at airmass 1.5-2.0
12:11:20 -13h 00m Titan atmospheric observations. Cloud map
16:11:20 -09h 00m Titan surface observations. Slow scans across Titan's visible hemisphere to form spectral images
21:20:20 -03h 51m Operating mode transition
21:41:20 -03h 30m Titan surface observations. Slow scans across Titan's visible hemisphere to form spectral images
22:11:20 -03h 00m ISS nightside imaging. Search for and monitor lightning/aurora
23:33:20 -01h 38m Radio Science surface observations. Bistatic scattering measurements at three radio wavelengths to determine the physical properties of Titan's surface, including reflectivity, dielectric constant, and roughness

19 July 2007

Time UTC Time wrt
01:06:20 -00h 05m Titan surface observations.
01:11:20 +00h 00m Titan-34 Flyby Closest Approach Time. Altitude = 1332 km, speed = 6.2 km/s, 34° phase at closest approach
01:40:20 +00h 29m Operating mode transition
02:01:27 +00h 50m Titan surface observations. high-resolution cubes of Titan's surface
03:11:20 +02h 00m ISS imaging. NAC regional map
05:11:20 +04h 00m Titan atmospheric observations. Obtain information on surface & tropopause temperatures, and on tropospheric CH4. Scan or contiguous steps across disk
06:11:20 +05h 00m ISS imaging. NAC global map
09:47:20 +08h 36m ISS imaging. WAC photometry
10:11:20 +09h 00m Titan atmospheric observations. Obtain information on CO, HCN, CH4. Integrate on disk at airmass 1.5-2.0
15:01:00 +13h 50m Deadtime, 5 minutes long. Used to accommodate changes in flyby time
15:06:00 +13h 55m Turn to Earth-line
15:36:00 +14h 25m Playback of T34 Data. Goldstone 70M and 34M

20 July 2007

Time UTC Time wrt
15:01:49 +01d 14h Descending ring plane crossing
20:31:00 +01d 19h Saturn periapse, R = 5.4 RS, lat = 0°, phase = 130°

Last Update: 1 September 2019
14-Jun-2024 08:07 UT

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