JPL Studies Deep-Space Nuclear Craft

An ambitious program that would send a nuclear-powered spacecraft into deep space at more than 225,000 m.p.h. is under study by the Jet Propulsion Laboratory.

Although the proposal is in only the earliest planning stages, it could carry the beleaguered laboratory into the 21st Century with a program that could send back scientific data for more than 50 years, according to officials with JPL, a National Aeronautics and Space Administration facility managed by Caltech.

JPL officials view the proposal as the beginning of the age of deep-space exploration.

The proposal, conceived by JPL Director Lew Allen, offers a glimmer of hope to the laboratory’s scientists, who have seen many of their programs thrust into limbo by the grounding of the nation’s fleet of space shuttles.

$220,000 for Planning

The planning is being funded by $220,000 in “discretionary” funds that Allen is authorized to allocate for the development of new ideas.

The project is called TAU, for Thousand Astronomical Units, the distance the probe would be designed to travel. An astronomical unit is the distance between the sun and the Earth, about 93 million miles.

Early planning calls for the spacecraft to be equipped with a 1.5-meter telescope so that it could look back at this solar system as it speeds through the galaxy. The telescope would also be used to make exacting measurements of the distance to other stars.

Allen assigned the task of defining the goals of the proposed mission to a husband-and-wife team of astronomers, Aden and Marjorie Meinel. Both are 65 and neither expects to be on the job if and when the spacecraft finally begins to send back data.

“Both of us will have retired long before then,” Meinel said. “That’s why we’re looking for young astronomers to work on the project. We’ll wave goodby to it, but they will reap the benefits.”

He said that is part of “the grand old tradition of astronomy.”

“Many astronomers start a project that will not yield a benefit until the next generation,” he said. “You do your part, and the next generation builds on the base.”

He said if the mission could be defined and the spacecraft designed and funded by 1999, it could be launched by the year 2005. The ambitious goal of traveling a thousand times the distance to the sun, and sending back data for half a century, is not considered unrealistic, he added, because of advancements in electronics and propulsion systems.

Other missions have been designed for exploration of the solar system, and although some spacecraft are expected to eventually reach deep space, they are traveling so slowly that it will take millions of years for them to get there. Voyagers 1 and 2, for example, which have already explored other planets, are expected to go beyond the solar system, but they are traveling at only about 36,000 m.p.h.

Ride Beam of Light

The TAU spacecraft, by contrast, would continue building up speed through its nuclear propulsion system for 10 years, reaching a speed of about 225,000 m.p.h. by the time it passed the planet Pluto. The spacecraft would, in effect, ride a beam of light, accelerated by electrically charged atoms expelled by the reactor to produce thrust.

When it reached great distances from the Earth, it would enable scientists to make exact measurements of the distance of far-off objects. Such measurements are limited trigonometrically by the distance between two points from which angular measurements can be made. If those points can be moved far apart, the triangulation yields a more exacting measurement, so if one of those points can be on a spacecraft billions of miles away, the results should be exact.

Meinel said that at this point, his and his wife’s assignment is to create a “straw-man mission” to “combine all the science objectives within the constraints of an actual spacecraft design.”

‘Define a System’

“Everybody gets involved,” he added. Different scientists would like to see different results, so the Meinel’s will try to “define a system” as they sort through various proposals and try to come up with a design that would have a good chance of succeeding.

One possible objective, for example, would be to have the spacecraft journey to the Oort Cloud, an area at the edge of the sun’s gravitational influence. The cloud, named after Dutch astronomer Jan Oort, who first postulated its existence, is thought to be the repository of primitive objects left over from the formation of the solar system.

In theory, every now and then a passing star or some other gravitational influence plucks a chunk of debris from the cloud and sends it toward the sun, and another comet is born. The spacecraft could turn its telescope on the cloud as it draws closer, possibly determining whether it is, in fact, the home of trillions of potential comets.