Despite claims by NASA officials that much of the Hubble Space Telescope's scientific mission can still be accomplished before repairs are made to the satellite in 1993, astronomers familiar with the project say almost the entire science program will be degraded in some way by the telescope's blurry vision.
Officials of the National Aeronautics and Space Administration had said repeatedly last week that, despite severe problems with the telescope's mirrors, the scientific goals of the project will be met. Hubble program scientist Edward Weiler, for example, said he believed "100 percent of our highest priority science" would eventually be performed over the telescope's 15-year lifespan.
All agree that the most imperiled instrument is the Wide Field Planetary Camera (WFPC). Viewed by many astronomers as the most crucial device aboard, WFPC was designed to take detailed pictures using visible light. Because the focus of the telescope is flawed, WFPC is "severely compromised," said James Westphal, the principal investigator in charge of the camera and a professor of astronomy at the California Institute of Technology.
A replacement wide-field camera is to be installed in 1993, which should correct the telescope's poor vision with the equivalent of a new monocle. In the meantime, NASA officials said, they planned to shift their emphasis to four other instruments on board.
But astronomers say the Hubble's flaws will also degrade the quality of observations made with those instruments, which "see" invisible ultraviolet light.
Astronomers involved with the ultraviolet cameras and spectrographs say they will still be able to accomplish new and exciting science. But depending on the instrument, they will also have to sacrifice many difficult observations that Hubble was designed to make.
"There was certainly a variety of things we hoped to do that will be difficult because of the degraded image, but we'll still be able to do a lot," said Bruce Margon, professor of astronomy at the University of Washington in Seattle and a member of the team of scientists that supplied Hubble's Faint Object Spectrograph (FOS).
FOS is designed to work with both visible and ultraviolet light emanating from distant, faint stars and galaxies. Many of the observations using visible light may be abandoned in favor of dissecting the spectrum of ultraviolet light, which can yield much about the age, temperature and components of celestial objects.
But because of Hubble's flaw, FOS will have more difficulty sorting out the spectra of stars and objects that are close together.
Another device, called the Faint Object Camera, will also be plagued by Hubble's flaw. While the camera will be able to use visible light to focus on objects a thousand times fainter than is possible from ground-based telescopes, the FOC will fail to find the extremely faint objects it was supposed to see, said Ivan R. King, an astronomer at the University of California at Berkeley.
A third instrument, the Goddard High Resolution Spectrograph (GHRS), will share the same problems, said Stephen Maran, senior staff scientist at Goddard Space Flight Center and a member of the team that will use GHRS. The resolution, in some cases, will be about half as much as hoped for. Observing time will have to increase, in some cases by as much as four times, and researchers will have to settle for more fuzzy spectra. Maran estimated that the GHRS team will lose about 25 percent of the science they had planned to do.
By some accounts, half the science scheduled for the High Speed Photometer (HSP) could be lost. One of the goals of HSP was to study the atmospheres of planets in our solar system by using stars as sources of background light and by taking very fast pictures of the planets. Because of Hubble's flawed vision, the method would be difficult.
NASA officials maintain that Hubble will eventually prove a scientific success. A group of scientists in charge of the various devices aboard Hubble met last week to assess the damage.
Their mood "changed dramatically from the first day to the second day," said Weiler, "as they started thinking of the things they can do as opposed to what they can't do."