From: Jet Propulsion Laboratory
Posted: Friday, May 11, 2012
The most recent spacecraft tracking and telemetry data were collected on May 9 using the Deep Space Network's 70 meter Station 43 at Canberra, Australia. Aside from the issues in work with the Cosmic Dust Analyzer (CDA) and the Ultrastable Oscillator (see the January 5, 2012 Significant Events), the Cassini spacecraft is in an excellent state of health and its subsystems are operating normally. Information on the present position of the Cassini spacecraft may be found on the "Present Position" page at: http://saturn.jpl.nasa.gov/mission/presentposition/.
This week's highlight was the targeted E-19 close encounter with Saturn's 500 kilometer diameter snow-white moon Enceladus on Wednesday. The flyby delivered the final in a set of three Enceladus encounters designed to give real-time Radio Science measurements of Enceladus's gravity field. It also included another pass through the plume from the geysers. More information on E-19 may be found here: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20120502/
Wednesday, May 2 (DOY 123)
During the Enceladus E-19 flyby, the spacecraft turned frequently under control of the Attitude and Articulation Control (AACS) Reaction Wheel Assemblies (RWA) to properly point the Optical Remote Sensing (ORS) instruments and the Magnetospheric and Plasma Science (MAPS) instruments. All the telemetry data from their many observations went to the Solid-State Recorder (SSR) for later playback to Earth. Radio Science experiments operate differently. For long periods around and during closest approach to Enceladus (74 kilometers), Cassini was oriented to keep its high-gain antenna dish pointed to Earth while receiving a frequency-stable signal from the Deep Space Network (DSN). Cassini's downlink, locked to this reference signal, was received on Earth an hour and 13 minutes later. Its Doppler shift was accurately measured, providing the Radio Science data that contains information about mass distribution within Enceladus. Not to waste any Earth-pointed time, though, telemetry data were also played back from the SSR during the Radio Science experiment.
Cassini passed periapsis, this orbit's closest point to Saturn at 136,000 kilometers above the clouds, going 68,213 kilometers per hour relative to the planet.
The busy day concluded with Cassini turning its ORS instruments to Dione 8,000 kilometers away (for which pointing vectors were updated last week via realtime command). With Dione squarely in view, the Composite Infrared Spectrometer (CIRS) and Imaging Science Subsystem (ISS) scanned its equatorial latitudes on the leading hemisphere, with a chance to observe the fractured region and do further searches for evidence of out-gassing or recent activity.
The illustrated feature "Cassini, Saturn Moon Photographer" was published on the Cassini website: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20120502/
Thursday, May 3 (DOY 124)
The Cosmic Dust Analyzer (CDA) exhibited telemetry packet production problems again, and was powered off by realtime command following an anomaly meeting today.
The Ultraviolet Imaging Spectrograph (UVIS) performed an instrument calibration, and ISS made a 9-hour observation of one of Saturn's outer irregular satellites, Ymir, a tiny, dark body in a retrograde orbit 23 million kilometers away.
The AACS team performed an RWA Y-bias maneuver, stabilizing the spacecraft via thrusters and setting the RWAs to the required speeds. Thrusters usually impart a small delta-V. Since the spacecraft was out of communication with Earth, the Navigation team relied on telemetry played back later to estimate the effect on Cassini's orbit.
The main engines' protective cover was stowed to its open position.
Friday, May 4 (DOY 125)
The Cassini Plasma Spectrometer (CAPS), a direct-sensing instrument, measured the ambient co-rotating plasma at low latitude in Saturn's magnetosphere for half the day. The spacecraft was 1.5 million kilometers from Saturn as it continued coasting outbound from periapsis.
Saturday, May 5 (DOY 126)
Playback of telemetry from the icy satellite observations, including Enceladus and Dione, was completed this morning after three daily sessions with the DSN's 70 meter aperture station at Goldstone.
The MAPS instruments, directly sensing ambient conditions, continued to acquire measurements in Saturn's outer magnetosphere and magnetosheath. By doing this once every four to six months, these instruments are able to observe Saturn's magnetosphere over a solar cycle, from one solar minimum to the next, and investigate periodicities and how the Saturn kilometric radiation period is imposed on the magnetosphere.
Sunday, May 6 (DOY 127)
OTM-320, the E-19 clean-up maneuver scheduled for today, was found to be unnecessary because of the small E-19 target miss, and was canceled.
Monday, May 7 (DOY 128)
The MAPS instruments continued their observations in Saturn's outer magnetosphere.
An image of Saturn's 200 kilometer wide, cratered moon Janus, which orbits outside the F ring, is featured at: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4519
Tuesday, May 08 (DOY 129)
On three days this week including today, ISS monitored distant Titan, with CIRS and the Visible and Infrared Mapping Spectrometer (VIMS) also taking measurements.
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