From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Galileo Update - 12/11/92
Followup-To: sci.space
News-Software: VAX/VMS VNEWS 1.3-4   
Keywords:  Galileo, JPL
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Sat, 12 Dec 1992 06:33:57 GMT

Forwarded from Neal Ausman, Galileo Mission Director

                                 GALILEO
                     MISSION DIRECTOR STATUS REPORT
                              POST-LAUNCH
                        December 4 - 10, 1992

SPACECRAFT

1.  On December 4, real-time commands were sent to change the telemetry rate
from 115.2 kbps to 28.8 kbps so that DSS-12 (Goldstone 34 meter antenna)
could process downlink telemetry.  This change was necessary when ground
station problems at DSS-14 (Goldstone 70 meter antenna) caused the Project
to request tracking support at DSS-12.  The spacecraft telemetry rate under
stored sequence control was switched back to 115.2 kbps after DSS-12 tracking
support ended.  Upon completion of commanding, the CDS (Command Data
Subsystem) command lock counter had increased by 4 which was 2 more than
expected.  No unplanned commands were received/processed by the spacecraft.
Analysis of this incident is in progress.

2.  On December 4, Part 1 of the EE-11 Earth encounter sequence memory load
was uplinked to the spacecraft without incident.  Part 2 of the EE-11 Earth
encounter sequence memory load was uplinked on December 7.  This sequence
covers spacecraft activities from December 7, 1992 to December 28, 1992 and
includes the Earth closest approach on December 8, 1992.

     The December 7 EE-11 uplink was delayed for approximately 45 minutes
while the ground station transmitter configuration was changed from 18kw with
4db command modulation suppression to 5.5kw with 0.5db command modulation
suppression to eliminate command feedthru degradation of downlink telemetry.

3.  During this reporting period, numerous science instrument
calibration/characterization activities were performed to take advantage of
the high telemetry data rates while close to the Earth.  Activities included
Magnetometer (MAG) scan platform interference test, Solid State Imaging (SSI)
boomscatter test, and a MAG calibration coil. All calibration/characterization
activities were performed nominally and data analysis is in progress.

4.  On December 5, real-time commands were sent to update the gyro drift
parameters using spacecraft gyro data collected on November 29.  This update
was performed to meet the scan platform pointing requirements in support
of Earth 2 science data collection when the star scanner shutter was closed.

5.  On December 5, real-time commands were sent to disable the AACS (Attitude
and Articulation Control Subsystem) sun-dependent algorithms and enable the
AACS bright body fault protection in preparation for the Earth 2 flyby.  The
commands executed nominally on the spacecraft prior to the start of the EE-11
Earth encounter sequence.

6.  On December 5 and 6, NO-OP commands were sent to reset the command loss
timer to 72 hours, its planned value during this mission phase.

7.  On December 8, Earth closest approach occurred at 7:09:25 AM PST at an
altitude of 303.1 km.  The Earth Gravity Assist (EGA) was performed flawlessly.
During the Earth closest approach time period, the Galileo spacecraft took
observations of the magnetosphere, Moon and Earth system.

8.  On December 8, approximately three hours after closest approach, real-time
commands were sent to enable the AACS attitude control sun dependent
algorithms to their nominal post fly-by state.  Also, the command loss timer
was reset to 11 days in accordance with the EE-11 sequence strategy.

9.  On December 8, real-time commands were sent to update the attitude control
bright body vector in the EE-11 Earth encounter sequence to permit star set
acquisition for the December 10 stored-sequence SITURN.

10. On December 8, after approximately 8 hours after closest approach,
real-time commands were sent at PI (Principal Investigator's) request to turn
off the Energetic Particle Detector (EPD) LEMMS-A detector bias.

11. On December 9, the Galileo Optical Communications Experiment from an
Earth-based Xmitter (GOPEX) experiment began.  This experiment consists of
pulsing a laser at the Galileo spacecraft from the Table Mountain Observatory
(TMO) and the Starfire Optical Range (SOR).  The Solid State Imaging (SSI)
camera is shuttered while slewing across the Earth resulting in a series of
illuminated pixels in the image.  The experiment is continuing at the writing
of this report.  Preliminary analysis of the data is in progress.

12. On December 10, the spacecraft executed an 11-degree SITURN.  The main
purpose of the SITURN was to maintain the spacecraft within plus or minus 10
degrees of the sun at the current solar distance.

13. The AC/DC bus imbalance measurements exhibited some change. The AC
measurement has ranged from 16DN to 17DN and now reads 17DN (3.9 volts).
The DC measurement has ranged from 115DN (13.4 volts) to 148DN (17.4 volts)
and now reads 132DN (15.5 volts).  These measurement variations are consistent
with the model developed by the AC/DC special anomaly team.

14. The Spacecraft status as of December 10, 1992, is as follows:

       a)  System Power Margin -  59 watts
       b)  Spin Configuration - Dual-Spin
       c)  Spin Rate/Sensor - 3.15rpm/Star Scanner
       d)  Spacecraft Attitude is approximately 4 degree
           off-sun (leading) and 95 degrees off-earth (leading)
       e)  Downlink telemetry rate/antenna-67.2kbps (coded)/LGA-1
       f)  General Thermal Control - all temperatures within
           acceptable range
       g)  RPM Tank Pressures - all within acceptable range
       h)  Orbiter Science- all instruments are powered on
           except the PPR
       i)  Probe/RRH - powered off, temperatures within
           acceptable range
       j)  CMD Loss Timer Setting - 264 hours
           Time To Initiation - 215 hours


TRAJECTORY

     As of noon Thursday, December 10, 1992, the Galileo Spacecraft trajectory
status was as follows:

	Distance from Earth         1,583,900 km (.01 AU)
	Distance from Sun           147,088,200 km (0.98 AU)
	Heliocentric Speed          140,500 km per hour
	Distance from Jupiter       857,457,800 km
	Round Trip Light Time       0 minutes, 12 seconds

SPECIAL TOPIC

1.  As of December 10, 1992, a total of 8786 real-time commands have been
transmitted to Galileo since Launch.  Of these, 3753  were initiated in the
sequence design process and 5033 initiated in the real-time command process.
In the past week, 74 real time commands were transmitted: 72 were initiated
in the sequence design process and 2 initiated in the real time command
process.  Major command activities this week included commands to change the
telemetry rate, uplink the EE-11 Earth encounter sequence memory load, update
gyro drift parameters, disable sun-dependent algorithms, enable bright body
fault protection, reset the command loss timer, enable the sun-dependent
algorithms, update the bright body vector, and turn the EPD detector bias off.

2.  Intermittent telemetry has been observed since Earth closest approach as
a result of a 6db variation in signal levels received at the tracking stations.
The causes for these variations is presently unknown, but is likely the result
of spacecraft boom/structural interference, high telecom cone angles
(>110 degrees) and possibly RF leakage from LGA-2 (Low Gain Antenna #2).
After the SITURN on December 10, the cone angle was approximately 95 degrees
and the ground received signal variations and data degradations were
considerably reduced.  Analysis of the trajectory and the stored-sequence
planned SITURN indicates that the cone angle will not again reach 100 degrees.
A stored-sequence SITURN on December 16, prior to the Earth/Moon conjunction
playback, will further reduce the cone angle to less than 85 degrees.  At cone
angels less than 85 degrees no boom/structural interferences is possible;
correspondingly telecommunication performance is expected to further improve.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children 
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
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