baalke@mars.jpl.nasa.gov (Ron Baalke) (12/15/90)
GALILEO STATUS REPORT
December 14, 1990
As of noon (PST) Thursday, December 13, 1990, the Galileo spacecraft is
2,328,560 miles from the Earth and traveling at a heliocentric speed of
80,060 miles per hour; distance to the Sun is 89, 661,240 miles (0.97 AU).
The spacecraft is in all-spin configuration and spinning at 2.89 rpm. Round
trip light time is 0 minute, 22 seconds.
The Galileo spacecraft superbly completed its Earth flyby gravity assist
on December 8. Galileo's closest approach to Earth occurred at 12:34:34 PST
at an altitude of 597 miles; only 0.4 seconds late and 5 miles high with
respect to the target.
In preparation for the Earth 1 encounter, several commands were sent
primarily to configure the spacecraft's attitude control and power state
consistent with Earth flyby needs. On December 7, a NO-OP command was sent
to reset the command loss timer to 3 days. Other commands sent that day
included disabling the system sunpoint fault protection and attitude control
sun algorithms, Delayed Action Commands (DACs) to power cycle the RTG Boom
heaters off/on and several DACs to position the scan platform for NIMS (Near
Infrared Mapping Spectrometer) thermal control and to update Earth spin movie
scan platform pointing. Most of the DACs were executed on December 8 before
the Earth flyby; the Earth spin movie updates were executed on December 11
and 12. About 20 minutes prior to closest approach, the PLS (Plasma)
instrument was also powered off, via DACs, to assure PLS thermal safety.
After the Earth flyby, commands were sent to configure the attitude
control subsystem and the system fault protection back to its pre-encounter
cruise state.
The LGA-1 (Low Gain Antenna 1) to LGA-2 antenna switch was successfully
performed from the stored sequence on December 8. The switch occurred about
20 minutes prior to Earth closest approach. The on-board switch command was
backed up by a real-time ground command about 1 minute after the on-board
switch.
The 21st RPM (Retro Propulsion Module) thruster flushing activity was
successfully completed December 9. Thruster temperature profiles were similar
to those observed on previous flushing activities.
A SITURN to lead the sun was successfully completed on December 10. The
turn, about 4 degrees, resulted in the spacecraft leading the sun about 2
degrees; another SITURN, about 6 degrees, was successfully performed on
December 13 and resulted in the spacecraft leading the sun by about 2.3
degrees. For both activities the spacecraft performance was normal and without
incident.
Subsequent to the SITURN on December 10, the sun gate fault protection
was re-enabled to provide protection from faults which could result in the
spacecraft being in a thermally unsafe off-sun attitude. After the Earth
flyby, the resulting trajectory will bring the spacecraft to 0.9 AU of the sun
on January 11, 1991.
An attitude control Target Motion Compensation (TMC) test was
successfully performed on December 10. Attitude control data was collected at
various clock and cone angles to assess the effectiveness of TMC. Analysis
of the data is in process and results will be used for the GASPRA encounter
in October 91.
Another set of Delayed Action Commands (DACs) were sent on December 12 to
cycle the radio frequency subsystem ranging channel off/on to improve
telecommunications link performance at 115.2 kbps and 7.68 kbps. The
commands will be executed by the spacecraft on December 14, 15, 16, and 17.
A non-interactive command was successfully sent to the EPD (Energetic
Particle Detector) on December 7 to put the instrument in its scan mode in
preparation for Earth encounter data collection.
Two non-interactive DACs were sent and executed on December 12 to lower
the HIC (Heavy Ion Counter) LET detector energy threshold and then return it
to its normal setting about 2 hours later. This command action was taken in
response to the Principal Investigators request after observing higher than
expected counts in the LET detector; later these higher counts were discovered
to be a normal characteristic of the detector.
Three non-interactive DACs were sent and executed on December 13 to the
DDS (Dust Detector) to increase its sensitivity. Action to lower the
instruments threshold was taken in response to noise signatures observed post
Earth flyby; these commands will properly configure the DDS for interplanetary
cruise.
A total of about 3400 photographs were successfully taken between
December 7 and December 13. About 1850 were taken within 36 hours of closest
approach and 1500 were taken for the spin movie on December 11 and 12. All
images were successfully returned except for 22 images of the spin movie,
namely, 10 contiguous frames in one segment (2 color filters) and 12
contiguous frames in another segment (2 color filters). The image data loss
experienced was expected due to known DSS (Deep Space Station) view period
constraints.
The AC and DC bus imbalance measurements remained relatively stable. The
AC measurement remained about 2 DN and now reads 45.6 volts. The DC
measurement varied about 30 DN from near 1 volt to 4.5 volts. All other
power-related measurements and spacecraft telemetry are normal.
The Project reviewed and approved the VE-14 cruise plan on December 13.
This sequence controls spacecraft activities from February 18 to April 29,
1991.
The no major problems were reported with GDS (Ground Data Systems)
operations in support of Earth Closest Approach (ECA) support. A better than
expected signal strength at switch from Low Gain Antenna 1 (LGA-1) to LGA-2
permitted 34 meter antenna and 26 meter antenna in Spain to continue to
acquire data for an additional 15 minutes through the end of track prior to
ECA. Prompt and measured response by DSN (Deep Space Network), NOCC (Network
Operations Control Center) and Station personnel to an alarm at the Australia
34 meter station early in the post ECA pass permitted continued data
acquisition with no loss of data.
___ _____ ___
/_ /| /____/ \ /_ /|
| | | | __ \ /| | | | Ron Baalke | baalke@mars.jpl.nasa.gov
___| | | | |__) |/ | | |___ Jet Propulsion Lab | baalke@jems.jpl.nasa.gov
/___| | | | ___/ | |/__ /| M/S 301-355 |
|_____|/ |_|/ |_____|/ Pasadena, CA 91109 |