November 1982:JPL space report

GALILEO ON TARGET

The writer Mark Twain once cabled a correction from
Europe to the Associated Press, “The report of my death was
an exaggeration.” In a similar vein, the press has reported the
end of the Galileo mission to Jupiter several times in the last
year. Now, however, continued funding seems assured, and
Galileo, along with the Voyager 2 encounters with Uranus
(1986) and Neptune (1989), should form the backbone of JPL’s
interplanetary programme for this decade.

The basic plan of the mission is to insert a 1600 kg spacecraft
into orbit about Jupiter after first deploying a 335 kg probe
into the Jovian atmosphere. The orbiter will conduct measurements in the Jovian system concerning the planet, rings,
and Galilean satellites, with at least 11 satellite encounters
within 24 months after insertion into orbit about the planet.
Some of these encounters, using satellite gravity-assist, will be
as close as a few hundred km and will provide unmatched
opportunities for determining the chemical composition and
fine-scale structure of these bodies. Supplementing the optical
imaging system will be an ultraviolet spectrometer, an infrared
spectrometer and a radiometer for measuring temperature
profiles, as well as several field-and-particle instruments. The
Galileo Probe will carry instruments designed to measure the
temperature, pressure and chemical composition of the Jovian
atmosphere. The orbiter will provide a relay link communicating the probe measurements back to Earth.

The May 1985 launch will involve an Air Force Inertial
Upper Stage (IUS) rather than the wide-body Centaur that was
originally planned (the Shuttle is to be used for the initial
launch phase). In order to compensate for the loss in capability
resulting from this change, two actions are being taken: (1) a
kick stage will be added on top of the IUS, and (2) the trajectory
will incorporate a gravity assist from Earth. This type of
trajectory, termed a AVEGA (AV-Earth-Gravity-Assist), features a loop in the inner Solar System of approximately two
years’ duration (shaped by a velocity change or AV) which is
followed by a very close, 200 km flyby of the Earth in order to
be boosted into the Earth-Jupiter leg of the trajectory. Arrival
at Jupiter is scheduled for late 1989 or early 1990, depending
upon the exact trajectory which is selected. JPL’s Mariner 10
mission to Venus and Mercury was the first mission to employ
gravity-assist techniques.

PLANETARY IMAGE FACILITY

The Regional Planetary Image Facility located at JPL is a
joint effort between the Laboratory and NASA in order to
provide a reference library of planetary and satellite images.
The emphasis is, of course, upon images returned by space
probes, but Earth-based photography and relevant topographic
and geologic materials are also available.

An extensive list of missions comprises the source for the
collection including Rangers 7-9; Surveyors 1, 3, 5-7; Lunar
Orbiters 1-5; Apollos 8, 10-17; Mariners 4,6, 7, 9, 10; Vikings
1, 2 and Voyagers 1, 2.

The Facility, which opened in 1979, contains approximately
225,000 images accessible in photographic files and also on a
versatile, computerised filing system using a video disc.
Approximately 20 parameters, including planetary latitude and
longitude, spacecraft range-to-planet, and lighting angle can be
specified by the user of the video disc system. The programme
responds to this input with a listing of all images which satisfy
these criteria. The images themselves can then be displayed
on a TV screen in black and white, with plans to extend the
capability to a colour display of those images which were
originally produced in colour.

The video disc itself is a silvery plate that resembles an
ordinary gramophone record in shape. It was produced by first photographing the original prints one-by-one onto 35 mm film,
transferring these to 1 in. video tape and then, finally, loading
the contents of the tape onto the video disc.

Head Librarian Leslie Pieri demonstrated the remarkable
properties of the disc by stepping through a sequence of Viking
Orbiter images at the rate of five frames per second. As I
watched the TV screen I partially enjoyed the perspective of
the Orbiter since the images are stored sequentially, by consecutive orbit.

VIKING MISSION CONTINUES

In the summer of 1976 the planet Mars was visited by a
small fleet of four spacecraft: two orbiters and two landers.
Today the orbiters are silent but the Viking 1 lander continues
to return data from its location in Chryse Planitia, the Plains
of Gold. It is scheduled to return imaging, meteorology, radio
science and engineering data up to the late 1980s.

More than 4,500 pictures have been returned from the
landers and over 50,000 were received from the two orbiters.
The latter pair mapped about 97% of the Martian surface at
a resolution of 300 m, while 2% of the surface was resolved at
the 25 m level. Although much valuable material was obtained
by the imaging sequences taken from the landers, most of it
was of a static nature; very few changes occur on the Martian
surface. Only two small surface slides were noted in four years
of the extended mission (the follow-on to the initial mission
segment), in addition to seasonal coloration changes due to the
transport of material, and the phenomenon of winter frost.