Scientists working to get the hard-luck Astro observatory into space aboard the shuttle Columbia will have to wait at least another 10 weeks before NASA tries again to put their telescopes into orbit.
The National Aeronautics and Space Administration said yesterday that Columbia, grounded again Monday night by its third hydrogen fuel leak, will have to be rolled back from the launch pad to make way for the launch of a secret shuttle mission that the Defense Department has scheduled for November aboard the shuttle Atlantis.
That makes the Astro observatory now third in line for launch, and NASA said it now will fly no sooner than Dec. 1. Complications in the repair of Columbia's fuel leak could delay the launch even longer.
Until yesterday, NASA was telling the Astro astronomers to plan for a launch as early as Oct. 26, second behind the Ulysses solar probe, which, because of the position of the planets, must fly between Oct. 5 and Oct. 23 aboard the shuttle Discovery.
"Of course we're frustrated by every delay, particularly when we get all the way up to the day of the launch before they discover these leaks," said Arthur F. Davidsen, a Johns Hopkins University astronomer and principal investigator for the Hopkins Ultraviolet Telescope.
"The main thing is that you really get your hopes up, and each time they are dashed. We're beginning to feel like Charlie Brown, who gets up to kick the football year after year, only to have it pulled away."
The Hopkins Ultraviolet Telescope is one of four telescopes in the Astro observatory, three of them built in Maryland. The telescopes are designed to study the universe in the ultraviolet and X-ray ranges of the spectrum, providing unprecedented images and spectrographic data from some of the hottest objects in the universe.
The telescopes are to remain in the shuttle cargo bay during the 10-day mission, and return to Earth with Columbia.
The shuttle's crew of seven includes two Maryland astronauts, one of them Hopkins astronomer Samuel T. Durrance, of Lutherville.
Durrance has taken the latest delays well, Davidsen said, "but there is a limit to what anybody can take without feeling some level of frustration. Sure, Sam is getting frustrated. He just handles it better."
First readied for launch in the spring of 1986, Astro was grounded by the Challenger explosion in January of that year. It was returned to the launch pad in April of this year, but has been delayed four times since then by fuel leaks and an electronic failure.
It is now the most-delayed shuttle mission in NASA history.
Looking on the bright side, Davidsen said the October launch deadline had put Astro scientists on "a very tight deadline" for rewriting the mission's detailed observation schedule to fit the new launch schedule.
"In fact, it would have been impossible to do it properly, to get everything pre-planned," he said.
With a December launch, Davidsen said, "we have a little more time, so everybody can put together a more sensitive plan, and get all the data checked and processed so the crew goes on board with all the time lines in place. So that's good."
And, if there's a "silver lining" in the delay, Davidsen said, it may be the reappearance in November of a quasar called 3C273, the brightest quasar in the sky and the highest-priority target for the Hopkins telescope.
"We're interested in finding out whether we can prove whether quasars have supermassive black holes at their centers," Davidsen said.
3C273 "disappeared from view for us in August, after having been perfectly placed for us in May. It comes back into view in November."
In all, there have been 15 or 20 launch dates for Astro, only one related to the astronomy instruments themselves. But scientists are now beginning to worry about deterioration of the telescopes.
"These instruments have been ready to go, sitting in Florida since 1985," Davidsen said. "The age of all these components is something that gets a lot of concern."
"HUT really is so advanced that it's not in any sense obsolete, or remotely in danger of becoming obsolete," he said. "We are working in an area that's not been tackled by any experiments at all. That, at least, is reassuring.
"But all the hardware was put together in the early to mid-'80s. . . . And it's just sitting."
Of special concern aboard the telescope are pumps used to keep the delicate ultraviolet sensors in a high vacuum, protected from the air until they can be opened and exposed to the light in the vacuum of space.
"These pumps have finite lifetimes," Davidsen said. But the main pump has been running off and on for years -- relieved by external pumps only during certain phases of assembly. It has run non-stop at least since April.
There is a backup pump on board, he said, but "we prefer not to have to get to the backup until we're in flight."
The pumps are designed to run longer than this, "but we're getting up to a region where it is not negligible anymore," he said.
Astro scientists are now asking NASA to allow them to run tests of all Astro's scientific instruments.
"Now we've got the time," Davidsen said. Such tests "haven't been done since last spring," and "we're beginning to worry whether we're going to launch something that's still functional."