NASA Cassini Significant Events 01/12/06 – 01/18/06
January 20, 2006
(Source: Cassini Project)
The most recent spacecraft telemetry was acquired Wednesday, January 18, from the Goldstone tracking stations. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” web page located at http://saturn.jpl.nasa.gov/operations/present-position.cfm .
Thursday, January 12 (DOY 012):
On Christmas Eve, 2005, the Z sigma ratio exceeded its limit for 10% of its persistence time due to the star tracker’s confusion when Rhea passed through its field of view (FOV). This ratio compares the measured star brightness to that expected, and Rhea’s interference was interpreted as an unexpected bright body. Since two of the four safing events we’ve had on the spacecraft were triggered by this Fault Protection (FP) monitor, the Spacecraft Operations Office decided to take some action to prevent any risk of losing the upcoming Titan-10 encounter, where Titan itself would appear in the tracker’s FOV and potentially cause a similar situation. We masked, and then unmasked, the Z sigma ratio FP monitor prior to T-10 on January 11. This masking prevents a call to safing but logs the event for future analysis. This mask/unmask strategy was successful, and we are investigating potential bright body interferences at future periapses.
Friday, January 13 (DOY 013):
All Cassini instrument teams have delivered 100% of the data that was scheduled to be submitted for the January, 2006, archive delivery. This includes science and house keeping data acquired from January 2005 through March 2005.
Saturday, January 14 (DOY 014):
One year ago today the Cassini/Huygens flight team was anxiously waiting to hear back from the Huygens Probe as it descended through the atmosphere of Titan. Here are some of the events from that day. All times referenced are Pacific Time.
12:10 AM – Loss of Signal from Cassini as it turns off Earth point to Probe relay attitude
2:12 AM – Probe begins transmission
3:25 AM – The Robert C. Byrd Green Bank Telescope (GBT) of the National Radio-astronomy Observatory in West Virginia, USA, detected the probe’s ‘carrier’ signal. Presence of this signal indicated that Huygens had survived its high-speed atmospheric entry, the back cover must have been ejected, the main parachute deployed, and the probe had begun to transmit. In other words, the probe is “alive”.
The parachute deployment sequence was initiated when the Probe reached Mach 1.5, and a pyrotechnic charge was fired deploying a 2.59m pilot chute. After a 30 second delay to ensure the shield was sufficiently far away to avoid instrument contamination, the science packages deployed and began to make measurements of Titan’s atmosphere.
After a further 15 minutes, the main parachute was jettisoned to avoid a protracted descent and a smaller 3.03 m diameter parachute was deployed.
The descent lasted about 147 minutes. Five batteries onboard the probe are sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes on Titan’s surface.
7:04 AM – Cassini is now on Earth Point 7:06 AM – End of the Probe Relay Sequence
7:07 AM – Begin 1st Playback Sequence
7:14 AM – Begin Solid State Recorder (SSR) Partition B4 Playback. Data from Huygens was relayed to the Cassini Orbiter passing overhead and stored on the SSRs. Closest approach distance was 60,000km.
10:00 AM – B4 Playback Complete
The probe signal was lost before the batteries expired, and before the orbiter went over the horizon – loss of signal was due to the probe AGC dropping below threshold due to the orbiter moving out of the beam-width of the probe antenna.
Radio Science/ Very Long Baseline Interferometry (VLBI) stations continued to receive data after loss of signal at the orbiter. After GBT set, Parkes, a 64-m radio telescope in Australia, received and recorded also via a Radio Science Receiver borrowed from the Canberra DSN complex. Parkes recorded the signal for over three hours after probe landing and set at 8:00 AM while the Probe was still transmitting and the signal was still present.
In addition to the GBT, sixteen other radio telescopes in Australia, China, Japan and the USA were involved in tracking the Huygens probe.
In the course of analyzing the data from the SSRs, it was determined that Huygens collected 2:27:13 of descent data, and 1:12:09 of surface data – far more surface data than was expected.
Not a single packet was dropped due to the Huygens receiver problem; this is a tribute to the mission redesign effort.
Sunday, January 15 (DOY 015):
Today Cassini executed the 10th targeted flyby of Titan at an altitude of 2043 kilometers. The Composite Infrared Spectrometer (CIRS) observed the northern limb at +55 degrees latitude both on the inbound and the outbound legs. This is expected to be on or near the transition to a possible winter polar vortex region over the northpole. CIRS also performed hemispheric temperature mapping in the stratosphere, increasing temporal coverage, and also adding the spatial coverage of the far-infrared composition mapping.
Especially exciting scientifically for the Visual and Infrared Mapping Spectrometer (VIMS) instrument was the opportunity for a 64X64 cube mosaic of Titan’s surface within 2 hours of closest approach. This opportunity allowed VIMS more high resolution data in an effort to better understand the surface geology and chemistry of Titan, and to continue the search for surface liquids and evidence of cryovolcanism. The targeted areas included the Huygens Landing Site, Xanadu, and the “Snail” feature previously imaged by VIMS.
At precisely 40 minutes before closest approach, the Ultraviolet Imaging Spectrograph (UVIS) instrument performed its first solar occultation to measure the compositional variations with altitude in Titan’s upper atmosphere. More specifically, with this occultation UVIS observed the extreme ultraviolet (EUV) spectrum below 110 nanometers to sample opacity from nitrogen and methane and possibly some other hydrocarbons.
The Imaging Science Subsystem (ISS) acquired a mosaic of Titan’s anti-Saturnian hemisphere, including Shangri-la, Dilmun, Mindango, Shikoku, and Antilia Faculae. ISS also performed a higher-resolution mosaic of the western portions of Dilmun and Shangri-la of which may provide stereo with later ISS observations of Antilia Faculae.
The entire suite of Magnetospheric and Plasma Science (MAPS) instruments, which includes the Cassini Plasma Spectrometer (CAPS), Cosmic Dust Analyzer (CDA), Ion and Neutral Mass Spectrometer (INMS), Magnetometer Subsystem (MAG), Magnetospheric Imaging Instrument (MIMI) and Radio and Plasma Wave Science (RPWS), also participated in this Titan encounter as they measured different aspects of Titan and its interaction with the magnetosphere. MAG was able to take full advantage of this encounter, as it was upstream of the Titan/magnetospheric interaction. The spacecraft flew through Titan’s middle ionosphere. Together with the T8 and T6 flybys, T10 will allow MAG to reconstruct the upstream equatorial ionospheric pile-up region.
MIMI observed details of the Titan/magnetospheric interaction within a one-hour period of closest approach. MIMI also observed Titan’s exosphere/magnetospheric interaction by imaging energetic neutral atoms (ENA) with the Ion and Neutral Camera (INCA). INMS obtained data regarding Titan’s atmospheric and ionospheric composition and thermal structure. This observation will also help INMS piece together the fundamentals of the magnetospheric/ionospheric interaction. RPWS studied the interaction of the magnetosphere with Titan at intermediate distances for evidence of ion pickup, radio emissions, density profiles, and the general wave environment.
Tuesday, January 17 (DOY 016):
Orbit Trim Maneuver (OTM) #50, the Titan-10 cleanup maneuver planned for January 18, 2006, was cancelled. This was the third cancelled OTM in a row. OTM-48, planned for January 2, was deleted in early November; OTM-49, the Titan 10 targeting maneuver, planned for January 12, was cancelled due to extremely small magnitude and duration, and OTM-50 was insignificant as well.
A command approval meeting was held today for the eight instrument expanded block files to be uplinked to the spacecraft in support of S18. The commands will go up beginning on January 22, and the sequence will begin execution on January 27.
Live update kick-off meetings were held today for both the third and final Inertial Vector Propagator (IVP) update in S17 and the first IVP update to execute in S18. Pointing analysis taking into account the cancellation of OTM-050 confirmed that both updates were unnecessary.
Periapsis for orbit 20 occurred today. At this time, RPWS was on a campaign to look for dust impacts, lightning whistlers – very low frequency radio waves generated by lightning – and measured the variation of plasma density inside of about 9 Saturn Radii using the upper hybrid resonance band.
Wrap up:
Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.
