Planet program is shaky. Although frustrated by launch delays and budget cuts, NASA's Jet Propulsion Laboratory is moving ahead with missions to the planets and interstellar space.

They're proud of America's planet exploration at the Jet Propulsion Laboratory (JPL). You see it as soon as you're past the gate. Dominating the trees and fountains on the sun-baked plaza, a giant chart tracks the Voyager spacecraft. One is headed toward a rendezvous with Neptune, the other on course for the stars. Their inspection of Jupiter, Saturn, Uranus, and perhaps Neptune epitomize a golden age.

But here at the leading center for that exploration, those whose achievements span the solar system wonder if they'll ever see such an epoch again. For today, America's planetary program lies in shambles.

The Challenger accident knocked schedules awry -- postponing some missions, curtailing others. Budget limits cloud the outlook for new projects. And the bold plans of the Solar System Exploration Committee (SSEC) of the NASA Advisory Council, laid out in the committee's report ``Planetary Exploration through the Year 2000,'' have acquired the flavor of science fiction. As SSEC chairman David Morrison of the University of Hawaii observed after release of Part 2 of the report in August, ``We're not sure we have even got a strategy left.''

The planetary staff at JPL, part of the National Aeronautics and Space Administration, is making the best of the situation. Some of them are preparing the Galileo for a 1989 launch, although it may well be postponed again. This mission to orbit Jupiter and probe its atmosphere was to have left Earth by shuttle last May. Other staff people are pushing ahead with the Mars Observer, which is to make a detailed survey of the Martian climate. Their expected 1990 launch has just been rescheduled for 1992.

For many, the symbolism of the Voyager chart is as poignant as it is proud.

``There's always hope,'' says JPL's deputy director, Robert S. Parks. He adds, ``[NASA Administrator James] Fletcher tells us he believes it's an important program. . . . But when it really gets down to the budget crunch, they haven't really demonstrated that very well yet.''

NASA's new manifest for shuttle missions has not lessened that concern. It does provide for launching Magellan -- a Venus radar-mapping mission -- in May 1989. But it slips the launch of the Mars Observer by roughly two years. American Mars scientists want this mission to maintain research momentum. They now have a substantial lead in Martian science, but fear they could lose itt to the Soviets, who plan a Mars mission in 1988.

``I think, in '90, we have a mission that's every bit as attractive as [the Soviet] '88 mission,'' says Mars Observer project manager William J. Purdy Jr. By 1992, however, the Soviets are proposing to have a mission at the red planet that would include balloons in its atmosphere, landers on its surface, and polar orbiting satellites. By waiting until 1992 to launch Mars Observer, the US may well sacrifice its research lead.

Finally, the new manifest leaves two major solar system missions in limbo. Galileo and the US/European sun-observing Ulysses both need to launch in the fall of 1989 or slip 13 months. The manifest merely allows for one unspecified ``planetary mission opportunity.'' So Ulysses and Galileo project managers still don't know what to plan for.

Planet explorers worry that the country may lose the sharp edge of its planetary research competence. ``It takes a long time to develop [that competence], and it's got to be used more or less continually in order to keep it sharp and effective,'' Mr. Parks says.

NASA's planned missions to Venus, Mars, and Jupiter should return important data throughout the 1990s. But, as Parks points out, the ``real development engineering work'' on them is over.

(For more on the Pioneer and Voyager planet probes, see Page 35.)

The SSEC is urging several new projects that would keep engineering skills sharp. They include a new generation of spacecraft -- the Mariner Mark II. It would be a general-purpose vehicle that could be outfitted for different missions and produced to a more or less standard design. So far, there's no indication that any such new ``starts'' are included in NASA's budget planning.

``We have not been able to convince the system, apparently, that to [follow the SSEC advice] is a budget issue,'' Parks observes. He warns, ``We can very well see that, if that [situation] continues for any extended period of time, we all lose our capability to do development work on planetary missions.''

More than engineering skill is at stake. Space scientists fear that, with no fresh mission to look forward to, students will become discouraged. Stanford University physicist J. Gethyn Timothy says that ``as to the training of the next generation of space scientists, we have a horrendous situation on our hands.''

As for the future of JPL itself, Parks says, ``We don't see any long-term threat to an effective and an important JPL.''

There's plenty of work to do in satellite-based studies of Earth, in radio astronomy, and in other science/engineering areas where the laboratory has special strength. The issue, he says, is whether there is equivalent long-term hope for an effective planetary program.

First of three articles. Next: Who has priority?