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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
FOR IMMEDIATE RELEASE April 20, 1989
NASA's Voyager 2 spacecraft, only four months away
from its flyby of the planet Neptune, today completed one of
the last major change-of-course maneuvers it will make before
reaching the planet in August.
Voyager 2, launched in 1977, is operated by the Jet
Propulsion Laboratory, Pasadena, Calif. Today's maneuver
aimed the spacecraft toward the point at which it will most
closely fly by Neptune, passing just 4,850 kilometers (3,013
miles) from the planet's cloud tops at 9 p.m. Pacific
Daylight Time on Aug. 24, 1989. Five hours later, the
spacecraft will fly about 39,000 kilometers (24,000 miles)
from Neptune's moon Triton.
The maneuver was started at 11:01 a.m. and ended at
1:20 p.m. (PDT), according to Voyager mission controllers at
JPL.
In addition to adjusting the course of the
spacecraft, today's trajectory change served as the first and
only rehearsal for a similar maneuver that the spacecraft
will execute when Voyager is just four days from its closest
approach to Neptune. The technique is called a roll-turn
maneuver. Instead of using the spacecraft's trajectory
correction thrusters to propel the spacecraft, mission
controllers use the on-board gyroscopes to cause Voyager to
roll in a given direction. The manuever keeps Voyager's
radio dish facing antennas on Earth throughout the maneuver
and allows mission controllers to remain in contact with the
spacecraft.
This technique will be especially critical when
mission controllers fine-tune Voyager's course in August. It
will prevent the signal command blackout that would occur if
the usual propulsive maneuvers were performed. Using the
roll-turn technique then will ensure the ability to send
Voyager the set of computer commands that the spacecraft
needs to carry out the most critical activities of the
Neptune flyby.
Voyager 2 is now 4.293 billion kilometers (2.668
billion miles) from Earth. It is controlled by radio
commands sent from giant NASA dish antennas in California,
Spain and Australia. The spacecraft is so far away that
information radioed at light speed (186,000 miles per second)
takes nearly four hours to reach the Earth.
The Neptune flyby will be Voyager 2's fourth and
final planetary encounter before the spacecraft heads out of
the solar system to explore interstellar space.
Voyager 2 was launched in 1977, as was a twin
spacecraft, Voyager 1. Voyager 1 completed flybys of Jupiter
and Saturn and their moons, and is headed out of the solar
system. After its Jupiter and Saturn encounters, Voyager 2was sent on to explore Uranus, which it flew past in January
1986, and Neptune. The spacecraft is now about 183 million
kilometers (114 million miles) from Neptune.
The Voyager project is managed by JPL for NASA's
Office of Space Science and Applications.
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