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1993-05-03
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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
GALILEO VENUS FLYBY
GENERAL RELEASE
NASA's Galileo spacecraft will obtain its first
gravity assist on the long road to Jupiter on the night of
February 9-10 when it flies by the planet Venus at a distance
of some 10,000 miles (16,000 kilometers) above the cloudtops.
Although the sole objective of this flyby is to
pump up Galileo's orbit so that it can eventually reach
Jupiter (two Earth flybys will also be required), scientists
will use the opportunity to turn the spacecraft's planetary
sensors on the cloud-shrouded planet, in order to study its
atmosphere and environment.
The scientific data will have to be stored on the
spacecraft tape recorder until late October, when Galileo is
close enough to Earth to play them back over its low-gain
antenna.
The Venus observations were selected by Galileo
scientists and mission controllers at the Caltech Jet
Propulsion Laboratory on the basis of (1) not risking Jupiter
observations in the 1995-1997 Jovian orbital phase, (2) not
exceeding the capacity of the tape, and (3) getting the best
new scientific information about Venus.
The nearest planet to Earth in space, Venus is also
closest to our planet in size, with a diameter 5 percent
smaller, and a mass almost 20 percent less than Earth. A
massive atmosphere topped by thick clouds blankets the
surface, imposing a pressure about 100 times that at sea
level here, as well as trapping the Sun's heat and raising
the temperature above the melting point of lead.
Venus has been observed from Earth with ever
improving technology and by nearly 20 spacecraft operated by
NASA and the Soviet space program, which have flown by,
orbited and sent probes into the atmosphere and to the
surface. Radar systems (the only way to see through the
atmosphere) have mapped much of the surface at gradually
improving resolution. Later this year, NASA's Magellan
mission will orbit Venus for high-resolution global radar
mapping. Previous missions have raised new questions about
the atmosphere's structure and behavior; Galileo's
instruments could provide some answers.
Galileo was launched October 18, 1989, aboard space
shuttle Atlantis; an Inertial Upper Stage rocket boosted it
out of Earth orbit toward Venus. This system could not give
the spacecraft enough velocity to reach Jupiter directly, as
originally designed; thus the Venus-Earth-Earth swingby
scheme was devised.
The Venus flyby geometry was designed to swing the
spacecraft back to Earth on December 8, 1990, for a 600-mile
flyby angled to put Galileo in a two-year elliptical orbit
around the Sun, bringing it back again on December 8, 1992. This third planetary swingby will boost the spacecraft into
an ellipse long enough to reach Jupiter in December 1995 to
begin its two-year scientific study of the giant planet,
including putting an atmospheric probe into the Jovian
clouds.
The Galileo project was developed and is operated
by the Jet Propulsion Laboratory for NASA's Office of Space
Science and Applications. JPL also designed and built the
main part of the spacecraft, which will orbit Jupiter for
about 22 months. The atmospheric probe was managed by NASA
Ames Research Center. Communications with the spacecraft are
maintained by the JPL-managed Deep Space Network, with
tracking stations in California, Australia, and Spain.
#####
1/24/90.jhw
GALILEO VENUS FLYBY DETAILS
Trajectory
Previous trajectory correction maneuver: Dec. 22, 1989
Venus closest approach: about 10,000 miles (16,000 km) above
cloudtops, at 9:59 p.m. PST Feb. 9, 1990
(just before 1 a.m. EST Feb. 10)
Speed change: 4,990 mph (2.2 km/sec), from 83,750 to 88,740
mph in solar orbit
Perihelion: 2 a.m. PST Feb. 25, 65 million miles (0.699 a.u.)
from Sun
Next maneuver: Spring 1990
Science
Imaging: day-side (except lightning search), mostly violet
filter, a little clear, some near-infrared. No color images.
First images acquired, about 9 p.m. Feb 9; last images 7 days
later.
Infrared: night-side lower cloud mapping and atmospheric
studies; two partial-disk mosaics, plus scans for water and
other gas distribution.
First mosaic: 6 p.m. Feb. 9; last mosaic, 10:30 p.m.;
additional spectra taken with imaging for 7 days.
Ultraviolet: scans for upper atmosphere composition and
distribution.
First scan: 9 p.m. Feb. 9; last scan: midnight or later.
Photopolarimeter/radiometer: scans and maps of cloud-top
temperature and other physical properties, perhaps lightning.
First map: 5 a.m. Feb. 9; last scan: midnight or later.
Fields and particles (dust detector, magnetometers, charged-
particle detectors, plasma-wave): dust and mag, as near
continuous as possible through the period around the flyby.
Magnetometer has special co-observations with Pioneer Venus
Orbiter. Charged-particle observations particularly intense,
7 p.m.-midnight Feb. 9.
No real-time science return; all data recorded on 3 tracks of
4-track tape recorder for playback near Earth in late October.