Maker, NASA blamed for Hubble's defect.

Maker, NASA blamed for Hubble's defect

ANASA-appointed panel concluded last week that the space agency and the contractor it hired to build the Hubble Space Telescope's primary mirror deserve equal blame for not detecting -- prior to Hubble's launch -- the serious optical aberration that today flaws the telescope's vision. In its final report, the panel observed that at least one of the mirror's prelaunch tests precisely identified the mirror problem.

There were other portents of the mirror's flaw as well. But the mirror maker and NASA's one on-site inspector never heeded these warnings, the panel says.

Two years before building the mirror, the Danbury, Conn.-based contractor, then called Perkin-Elmer Corp., fabricated a scaled-down mock-up. Because the company so carefully crafted this 1.5-meter test mirror, "the feeling was, 'Okay, the guys [making the full-size mirror] know how to do it now, so let's let them,'" explains panel member Roger Angel, an astronomer and mirror designer at the University of Arizona in Tucson. However, the panel says, the contractor, now called Hughes Danburry Optical Systems, Inc., failed to employ that same precision in making the 2.4-meter mirror actually used on Hubble.

Several clues during the production of Hubble's mirror should have strongly hinted that factors other than size differentiated it from the test mirror. For example, the panel found that the mirror designers needed to increase the spacing between two elements of a testing device called a null corrector. That the designers had to alter this spacing "ought to have been a clue" that the mirror wasn't focusing as intended, says Lew Allen, head of the investigating board and director of NASA's Jet Propulsion Laboratory in Pasadena, Calif. His panel also found evidence of poor quality control in the production (SN: 10/6/90, p.220) and testing of Hubble's mirror by both the contractor and NASA's inspector.

The contractor did hold frequent project reviews, Angel notes. However, Angel says, "conflicts in the measurements they were getting were never discussed."

Why not? "That mentality at the time was, 'Get out of my way; let me get on with the job.'"

The panel found, for example, that the actual Hubble mirror passed on null-corrector test but failed a less sensitive one that followed. And although that second test precisely identified the spherical aberration, its finding was ignored. "That's what makes your jaw drop," says Angel.