National space agency officials are seriously considering a plan that would send a robot spacecraft through the tail of Halley's Comet in 1986 and return a sample of the tail to Earth five or six years later.
The plan is far enough along that scientists at the Jet Propulsion Laboratory at Pasadena, Calif., were told yesterday to draw up at least two options for the National Aeronautics and Space Administration to consider. One would involve development of a spacecraft that could photograph the comet before flying through its tail to pick up a sample; the other would be a simpler spacecraft that would do little more than pick up a sample and return it to Earth.
The craft with the photo capability would cost about $250 million, the other about $150 million.
Three times in the last six years, the Jet Propulsion Laboratory has proposed instrumented missions to Halley's Comet, which will circle the sun in February, 1986, (not since 1910 has it come that close to Earth). The first two ideas were turned down because each involved an expensive rendezvous with the comet and required a new kind of electric engine to match the spacecraft's speed with the comet's.
The JPL's third proposal, costing $250 million, would involve only a photographic flyby of the comet and would not bring back a sample of the tail material. James M. Beggs, the new NASA administrator who was with the space agency in the Nixon administration, left little doubt in an interview that he prefers the latest proposal of a mission that would return a sample of the comet's tail to Earth.
"The feeling I've got for a mission to Halley is that it doesn't rank way up there on the priority list," Beggs told The Washington Post, "unless you fly the more serious mission and bring some stuff out of the tail material back to Earth for us to study."
In part, Beggs is against a flyby photographic mission to the comet because it resembles somewhat the missions already planned by the Soviet Union, Japan and the European Space Agency.
Beggs said if there is any extra money in the upcoming space budget for pure exploration he would rather spend it on a second spacecraft to swing around the north or south pole of the sun than spend it on a photographic flyby of Halley. President Reagan cut out the second "Solar Polar" spacecraft from his space budget this year, leaving a single European spacecraft to fly around one of the poles of the sun in 1989.
How much money will be spent next year on exploration depends on how much the space shuttle needs to complete its first four test flights, which are due to end next summer. The chance that the shuttle will sail through these four flights without trouble is slim, meaning that the likelihood of extra money for exploration is also slim.
If the space agency chooses to fly through the tail of Halley's Comet and return with samples to Earth, it must decide this year. The JPL will need all the time it can get to design and build a spacecraft that could be carried into Earth orbit by the shuttle astronauts in July 1985 and sent on a curving path that would intercept the comet during its closest approach to the sun.
The spacecraft would be equipped with a shield plated with some kind of adhesive material that would gather up the dust in the comet's tail as it flew through. On passing through the tail, which is millions of miles across, the craft would continue to follow a curving path through space that would bring it back in Earth orbit five or six years later, to be retrieved by the space shuttle.
The return of the dust from Halley's Comet would be perhaps more important than the first rocks brought back from the moon. Scientists believe that the stuff comets are made of is the oldest material in the solar system, primordial matter whose origins go farther back in time than any of the planets or moons in the solar system.