baalke@mars.jpl.nasa.gov (Ron Baalke) (12/22/89)
GALILEO MISSION STATUS
December 20, 1989
The Galileo spacecraft is 11.3 million miles or just over 1
light-minute from Earth today. It is just over halfway (or about
93 million miles) along its path to Venus encounter, and is going
67,104 mph in its orbit. The spin configuration is in cruise mode,
with the upper part of the spacecraft spinning at 3.15 rpm around the
axis pointed within a couple of degrees of the Sun, and the lower part
despun, fixed in orientation.
The EV-4 (Earth-Venus #4) sequence is currently in effect,
defining spacecraft operating states and functions. The celestial reference
loss and science alarm monitors are disabled as planned. The
telemetry rate is 1200 bits per second, and telemetry indicates
that all temperatures and pressures are at acceptable levels.
The spacecraft's attitude sun point angle is currently at 1.87 degrees,
plus or minus 0.3 degrees.
The spacecraft DC voltage imbalance measurement, which
indicates the potential difference between the power busbars and
the spacecraft chassis, has been fluctuating. The DC bus voltage imbalance
has been slowly increasing and has reach nearly 17.3 volts. This does not
reflect a fluctuation in spacecraft electrical power, which
continues to show the normal margin. Nor does it pose any hazard
to the spacecraft, which was designed to function at any level of
imbalance up to short-to-chassis; Voyager 1 has been operating
acceptably since early 1988 in this condition.
On Friday the Galileo spacecraft will perform its
second trajectory change, moving the Venus closest approach
point to the desired 10,000 miles from planet center (about
6,200 miles above the cloud tops). Closest approach will
occur about 10 p.m. PDT February 9. At injection, the aim
point was biased out to several hundred miles from Venus.
This maneuver, will thrust mostly at right angles to the sun
line, with a magnitude of about 3/4 of 1 meter per second
(about 1/20 the first maneuver). It will be done in four
segments or pulse chains, taking about 2-1/4 hours in all.
All of the orbiter science instruments are off except for the
magnetometer and HIC. Next week all the orbiter science instruments will
be checked out in a four-day programmed sequence, preparing
for Venus encounter.
Ron Baalke | baalke@mars.jpl.nasa.gov
Jet Propulsion Lab M/S 301-355 | baalke@jems.jpl.nasa.gov
4800 Oak Grove Dr. |
Pasadena, CA 91109 |