Pasadena, Calif. — Ask Richard P. Laeser about the Voyager 2 spacecraft and you get a broad smile. ``We're doing great!,'' he exclaims. Managers of other planetary projects at the NASA Jet Propulsion Laboratory (JPL) worry about the future. The Challenger accident upset their launch schedules. Budget cuts crimp their plans.
But there's no gloom in the office of Voyager's boss. JPL is America's leading center for planetary exploration and Voyager is its centerpiece. It's a well-funded, successful program with a bright future.
Although overshadowed at the time by the Challenger tragedy, Voyager's survey of little-known Uranus last January was a stunning achievement. Now Mr. Laeser and his colleagues look forward to unveiling Neptune. Voyager 2 should reach that distant planet in a little less than two years.
``I will guarantee that, if the spacecraft should live all the way out to August '89, this is going to be a spectacular mission,'' Laeser says. He adds, ``It's going to be the closest flyby of anything the Voyager spacecraft has made.''
By then, the craft will have spent 12 years in space. Its equipment has seen hard service and is now obsolete, but Laeser has confidence in his team's ability to get the most out of it. Thinking back to earlier technical troubles and their subsequent resolution, he says, ``Right now, we have a healthier spacecraft leaving Uranus than we did five years ago leaving Saturn.''
The project's funding situation is healthy too. Laeser points out that his office has slightly underrun its budget every year while its estimates of future needs ``have been very accurate.''
``We get what we ask for because we're believed,'' he says.
The project originally was intended only to study Jupiter and Saturn. That's all the first of its two spacecraft did. Voyager 1 now is heading out of the solar system toward interstellar space with no more planets in its path. Voyager 2, however, was allowed to go on to visit two additional planets.
For Voyager's navigators, Neptune will be their most challenging target yet. The planet will be roughly 30 times farther from the sun than is Earth. The navigators won't know its position in August 1989 with the fine accuracy they would like to have to guide their craft. Furthermore, at that distance, it takes about 10 hours for radio signals to make a round trip between Earth and Voyager. That makes it more difficult for navigators to use last minute data from the spacecraft itself to adjust its trajectory as it closes in on Neptune.
To make things even more challenging, observers have recently discovered that Neptune has ring arcs -- that is, incomplete rings. Laeser notes that one of these will lie across Voyager's path on its current trajectory. ``So,'' he says, ``over the next few months, we're wrestling and wringing our hands quite a bit about this somewhat difficult decision of what trajectory to actually fly.''
He further explains that detailed analysis of Voyager's present course suggests that it would come so close to Neptune that it might be dragged into the planet's atmosphere. ``This whole business of extending this mission gets a little more into the sporty domain than is classically NASA,'' Laeser says. But, he adds, ``it makes a lot of fun for us.''
For Laeser and his colleagues, Voyager's success is more than a technical triumph. They also beat the US bureaucratic system.
In the early 1970s, the planets were about to come into a rare alignment. A spacecraft could be sent to Jupiter in such a way that the jovian gravity would boost it on to Saturn. Saturn would then send it to Uranus and Uranus would pass it to Neptune. American space scientists outlined an ambitious program to take advantage of the opportunity. They called it ``The Grand Tour.''
However, the Nixon/Ford administrations would only fund surveys of Jupiter and Saturn. That was the Voyager project's officially authorized objective. In particular, project officials were directed to make a thorough study of Saturn's rings and of its atmosphere-bearing satellite Titan.
Voyager 1 met all these goals. ``In fact,'' Laeser explains, ``[it] satisfied all our contractual requirements with NASA.'' That gave his team leeway to send in the backup spacecraft -- Voyager 2 -- on a trajectory that was less than optimal for surveying Saturn but that put the craft on course for Uranus and Neptune.
Last of three articles.