Scheduling science aboard the shuttle.

Scheduling science aboard the shuttle

The May 5 explosion at one of two plants manufacturing the ammonium perchlorate oxidizer for the space shuttle's solid-propellant booster rockets has added yet another uncertainty to the struggle to get the shuttle program flying again. A new plant is to be built by the oxidizer manufacturer whose facility was destroyed, while an addition is planned by the other firm. But it is yet unclear how soon production will be back to normal, or how existing supplies (some of which go to the Defense Department) will be allocated until that rate is reached. As of this week, according to a NASA official, there was only enough ammonium perchlorate left for four shuttle missions, and production for a fifth flight is just getting underway.

The first shuttle launch since Challenger has now been delayed from late August until at least Sept. 3, several NASA officials said this week. They estimate the oxidizer shortage could make itself felt for two years. At present there are 18 shuttle missions scheduled to take place over that span, and the agency is now working to minimize the effects of the oxidizer shortage.

Among the 18 flights are seven science-oriented missions. Some can be delayed if necessary, but others depend on being launched within narrow ranges of dates. First on the science list is Magellan, to map the surface of Venus by radar. Now targeted for launch next April 27, it is to be the first U.S. spacecraft sent to another planet since 1978. It depends on Venus being in the proper position, however, and if the launch is delayed past May 27, it will have to wait until May of 1991. Magellan has been on the fifth mission in line, but in order to keep it on schedule, NASA this week had all but committed itself to moving the mission up to number four.

Also tightly limited in its launch window is the Galileo orbiter and probe of Jupiter, now set for launch on Oct. 8, 1989. Galileo, too, has a few weeks' cushion, but if delayed too much it will face a 22-month delay. Galileo and Magellan have priority on the calendar, but the oxidizer shortage could force choices to be made among the other candidates.

The Hubble Space Telescope will be operating from an orbit around the earth, so its launching is not locked to the positions of other planets. However, it is expensive to keep on the ground. It is now set for a flight next June 1, though project officials say privately that Aug. 30 may be a more realistic date.

A mission called Astro 1, which will operate from within the shuttle's payload bay, originally consisted primarily of three ultraviolet telescopes, but it now includes an X-ray telescope to look at the supernova 1987A. Like the Hubble telescope, it does not have to be launched in a certain short time span, except that astronomers want it to be in orbit before it misses key events in the young supernova's evolution.

Other science missions in the first two years of the shuttle's new life include the Gamma Ray Observatory (one of a series of "great observatories" that are a major part of NASA's new science plans), a life-sciences mission using the European Spacelab research module, and a mission called Atlas 1, which is to be the first in a series of spacecraft designed to study the sun throughout an entire 11-year cycle of solar activity.