Hubble Problem Simple, Can Be Corrected
DANBURY, Conn. (AP) _ A thin washer may have caused the focusing flaw in the $1.5 billion Hubble Space Telescope, and a space shuttle mission can easily fix much of the problem, NASA officials say.
″The Hubble could actually be better than it could be now,″ Charles Pellerin, NASA director of astrophysics, said Thursday.
Pellerin and members of a NASA investigative team held a news conference after two days of hearings at Hughes Danbury Optical Systems Inc., maker of the flawed primary mirror that is producing blurry pictures from the orbiting observatory.
The investigating board has decided that the misgrinding of the mirror was caused by a spacing error of 1.3 millimeters in a measuring device used to guide the manufacturing process, said Lew Allen, director of NASA’s Jet Propulsion Laboratory who heads the team.
The lens assembly in the device, called a reflective null corrector, ″appears to have space washers in its mounting to the baseplate,″ Allen said. ″If the washers were inapprpriately installed, this could have caused the spacing error,″ he said.
But, he added, other possibilities are being investigated. The board also is continuing to investigate how such″a single, but costly error″ could have occurred, he said.
″The error that we discovered is one that leads to an essentially pure spherical aberration, and that’s relatively easy to correct,″ Allen said.
Pellerin said that all that needs to be done is remove the Hubble’s wide- field planetary camera during a previously scheduled shuttle mission in 1993 and replace it with a camera designed to correct the error.
The camera was going to be replaced during the 1993 mission anyway because machinery undergoes extraordinary wear and tear in space, Pellerin said.
″The only thing that’s different is we didn’t anticipate doing this because of optical problems,″ he said.
The main camera is the Hubble’s most powerful instrument, designed to peer almost to the edge of the universe and produce the telescope’s most exciting discoveries.
NASA officials said earlier that replacing the camera won’t solve the problem for the Hubble’s faint-object camera and other instruments, which still will receive poorly focused light from the flawed mirror. Compared with the main camera, however, those instruments are much less severely impaired by the bad mirror.
The discovery of the flaw shortly after the Hubble was launched April 25 proved a major embarrassment for NASA. The telescope is designed to take clearer pictures of the far reaches of space than are possible from ground- based telescopes.
The 1.3-millimeter error is huge in optics terms, Allen said. Pellerin likened it to a room that was accidentally built 3 feet too long.
Allen said a test had indicated the error when the mirror was manufactured in the early 1980s at a division of Perkin-Elmer Corp. that was bought last year by Hughes. But he said Perkin-Elmer engineers had placed complete faith in the null corrector and disregarded the test results.
While declining to say whether Hughes Danbury was to blame for the error, Allen did say NASA was not aware of the results that showed there was an error.
″As we go back through the documents, we don’t find any case where they called this to the attention of NASA,″ he said.
Thomas Arconti, spokesman for Hughes Danbury, said only that the company would continue to work with NASA to find the answers to the remaining questions.
Pellerin said the news would not shake NASA’s confidence in Hughes Danbury, which is working on other NASA optics projects and made other highly technical parts of the telescope. ″Everything that’s difficult is working fine,″ he said.
Allen said during the team’s two days at Hughes Danbury, it interviewed former and current employees who worked on the telescope. He said they were all cooperative, even though it was hard for them to accept that they had made an error.
″People find it very hard to say ‘oops,’ ″ he said. ″They instead say that we had good reasons for doing what we did, we had no reason to think it was wrong and so on. ... Everyone we talked to is finding it very hard to not be proud of what he did when he thought it was very good work.″
The team will return to Hughes Danbury on Sept. 12 and 13, Allen said.