On Way to Neptune : Aging Voyager Spacecraft Still Taking Orders

The intrepid Voyager 2 spacecraft, hurtling through the solar system on its way to a fourth planetary encounter, responded to orders relayed by flight engineers at the Jet Propulsion Laboratory on Friday and fired up its small rockets to make a course change.

The maneuver is one of several that Voyager will have to perform as it journeys toward an encounter with Neptune in 1989. But since the old spacecraft is already well past its original life expectancy, any response to commands from Earth is welcome, according to project officials.

“The preliminary indications were that it went fine,” said Lanny Miller, head of the flight engineering team at the Jet Propulsion Laboratory, the space agency’s lead center for unmanned missions. He said engineers will not be absolutely sure it worked until they have analyzed data over the next few days.

Time of Arrival Changed

Miller said Voyager’s hydrazine thrusters were fired for about 70 minutes early Friday morning “to change the time of arrival (at Neptune) to be in sync with the motions of the satellites.” Since Neptune’s moons are as important to scientists as the planet itself, engineers want the probe to arrive at Neptune when the moons are in the best position relative to the craft’s course.

Voyager is to pass within 3,100 miles of Neptune and 25,000 miles of the planet’s large moon, Triton. Scientists have speculated that Triton could have lakes of liquid nitrogen.

Friday’s maneuver was intended to boost Voyager’s speed by about 20 m.p.h. The craft is zipping across the solar system at 43,380 m.p.h., but that speed will increase when it gets closer to the planet and is subjected to its gravitational pull.

Voyager is expected to reach Neptune at 9 p.m. Aug. 24, 1989.

3 Planets Visited

When it was launched Aug. 20, 1977, Voyager was programmed to visit two planets, Jupiter and Saturn. It performed so well during those encounters in 1979 and 1981 and was in such good condition that JPL engineers reprogrammed it to visit Uranus. It arrived there Jan. 24, 1986, and sent back spectacular photographs of the planet and its moons.

Engineers used the gravitational field of Uranus to whip the craft on out toward Neptune, the eighth planet from the sun. After its rendezvous with Neptune, Voyager will continue on out of the solar system, leaving only distant Pluto unvisited by man-made probes.