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1993-04-23
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OFFICE OF PUBLIC INFQRMATION
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. PHONE (213) 354-5011
FOR IMMEDIATE RELEASE
After more than four years exploring Mars, NASA's
Viking Orbiter 1 has almost reached the end of its mission.
The orbiter has used almost all its
attitude-control
gas, that keeps its solar panels pointed to the Sun and the
an-
tenna aimed at Earth. When the gas is exhausted -- probably
about
July 23 -- controllers at Jet Propulsion Laboratory will send
commands to turn off Viking Orbiter 1 to end its long and
productive
mission.
Meanwhile, Viking Lander 1 is programmed to operate
un-
attended on Mars into 1990, perhaps to be extended into 1994.
During the most recent phase of Viking's mission
the
orbiter has taken about 30 pictures a day of a region
southwest of
Olympus Mons and the three volcanoes on the Tharsis Ridge, an
area
of particular interest for its large, river-like channels.
That
sequence will continue through July 12.
Project officials plan a full program for Orbiter
1's
îfinal days. How much of the program can be completed will
depend
on the amount of attitude-control gas remaining. Here is a
timeline
of events that are proposed to be carried out if the orbiter
con-
tinues to be cooperative:
July 13, 14: The spacecraft will take a series of
high-
resolution photos of the summit caldera of Olympus Mons.
These
should be the highest-resolution ever obtained of the caldera
of
the solar system's largest known volcano.
(more)
-2-
July 15 through 18: The spacecraft will perform
three
controlled burns of its rocket engines. Those burns are part
of
a series of engineering tests to provide data that will
benefit
future space missions. One effect of the burns will be to
change
the spacecraft's orbit from its present 370 kilometers (230
miles)
periapsis and 34,000 kilometers (21,127 miles) apoapsis to
350
kilometers (220 miles) periapsis and 56,000 kilometers
(34,800
miles) apoapsis. The new orbit will satisfy the condition, in
ac-
cordance with planetary-quarantine provisions, of notimpacting,
and thereby not contaminating, the planet before the year
2019.
July 20 to 23: Additional engineering tests will be
con-
ducted, principally on the radio system, and the final orbit
will
be determined.
Current extrapolation of the supply and usage rate
of
attitude-control gas indicates July 23 is the approximate
date of
depletion, but flight controllers say there is probably a
one-week
uncertainty in that date, so the orbiter could run out of gas
as
early as July 16 or as late as July 30.
If it should turn out that there is still gas
remaining,
then about July 27 Orbiter 1 will make a final high-altitude
global
survey of the visible portion of the Mars disk -- 25 pictures
through each of three filters, for a total of 75 frames.
When the gas is exhausted, the orbiter's radio
transmit-
ter will be commanded off for the last time, and the
spacecraft
will continue silently orbiting Mars for many decades.
Viking 1 was launched to Mars Aug. 20, 1975, and
arrived
June 19, 1976. Viking Lander 1 touched down on the Martian
surface
-more- î
-3-
July 20, l976, with a 90-day mission expectation. That
mission com-
pleted, it has now observed the planet for more than two full
Mars
years -- four Earth years on July 20.
As long as it survives, Viking Lander 1 will
continue to
collect photos and weather data from the Martian surface and,
on
command from Earth, transmit them on approximately a weekly
basis.
Viking Orbiter 2 ran out of attitude-control gas
and
was commanded off July 24, 1978. Viking Lander 2 was turned
off
after its last relay transmission April 11, 1980.
The Viking Project -- today with fewer than 30
people
engaged in flight operations and science data processing --
is man-
aged for NASA's Office of Space Science by Jet Propulsion
Laboratory.
#####
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