PJS@GROUCH.JPL.NASA.GOV (Peter Scott) (03/30/89)
The following is excerpted without permission from NASA Activities, February
1989, Volume 20, #2:
Magellan: Exploring Venus as Never Before
-----------------------------------------
Scheduled for launch April 28, 1989, aboard Space Shuttle Atlantis,
the spacecraft Magellan will conduct the most comprehensive observation
of the surface and gravitational features of Venus ever undertaken.
During its 243-day (one Venus rotation) primary mission, the spacecraft
will map up to 90% of the planet with high-resolution imaging radar.
[...]
Magellan's high-resolution radar will reveal surface features as small as
273 to 377 yards [by curious coincidence, these figures just happen to
be close to 250 to 345 meters...]. This performance exceeds that of all
previous U.S. and Soviet missions to the sister planet.
[...]
After launch from the shuttle, Magellan will be propelled onto its Venus
trajectory by an Inertial Upper Stage, two-stage booster rocket. Once away
from the gravitational pull of Earth, the spacecraft will cruise for 15
months (1.5 orbits of the Sun) before reaching its destination. [...]
Magellan is a 7,826-pound, three-axis-stabilized craft. Solar panels and
three gyroscopic momentum wheels will provide energy and control the motion
of the spacecraft.
Onboard electrical power will be supplied by the two solar panels, totalling
15.1 square yards. The array will always be pointed towards the Sun, despite
the changing Earth-Sun-spacecraft geometry during the mission, and will
be capable of producing 1,029 watts during the mapping phase. Two
nickel-cadmium batteries will provide power during times of solar occultation
and allow normal spacecraft operations independent of solar illumination.
[...]
With conventional radar, the resolution of an image depends on antenna size:
the bigger the antenna, the better the resolution. A large antenna on a
spacecraft, however, would be expensive and difficult to manipulate. To
solve this problem, Magellan's synthetic aperture radar (SAR) will create
high-resolution radar images by using computer processing on Earth to simulate
a large antenna on the spacecraft. The onboard radar system will operate
as though it has a huge antenna, hundreds of yards long, when the antenna
is actually 12 feet in diameter.
During the 37.2-minute data acquisition phase of each orbit, the SAR will
transmit several thousand pulses of radio energy each second. [...] the
pulses will illuminate a 15.5-mile-wide swath of the planet's surface [...].
[...]
Magellan's orientation will be carefully controlled by three momentum wheels,
assisted, when necessary, by 12 small gas-thruster motors.
Magellan is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif
[yay!].
Peter Scott (pjs@grouch.jpl.nasa.gov)