THE Hubble Space Telescope continues to show it is a superior instrument in spite of its flawed main mirror. For several months, pictures of unprecedented sharpness have been arriving on science reporters' desks as the telescope team releases the best of its early harvest. Gleaned largely from test runs, they promise a richer scientific harvest soon to come.
But their main significance is in the story they tell of the Hubble project as a whole.
To begin with, they show that the telescope, even in its present state, can return dividends on the $1.5 billion investment of public funds that it represents. Release of the pictures is partly a public relations effort to make that point.
What is more important, the pictures remind us that the Hubble program is more than orbiting hardware. It is a team of scientists, engineers, and administrators that has overcome serious technical adversity to rescue the program from what could have been spectacular failure.
No one minimizes Hubble's troubles. The telescope's promised ability to see even very faint distant objects with unprecedented clarity involves more than being above the atmosphere. It also depends on focusing at least 70 percent of a star's light into a spot only 0.1 arc-seconds across.
Instead, the spherical aberration mistakenly ground into the telescope's main mirror smears something like 88 percent of the light into a halo surrounding that tiny spot. Because of this, Hubble can't image objects dimmer than the 25th magnitude. Astronomers had hoped to see objects as faint as magnitudes 28 to 30.
Thus Hubble has a sensitivity typical of ground-based telescopes. Yet, with the help of elaborate computer processing, the Hubble team has learned how to glean information even from the smeary halo around star images.
The result is that, what Hubble can image, it sees with 10 times the sharpness with which astronomers have seen such objects from the ground. This is why pictures taken as part of test runs intrigue astronomers with their promise of sharp-eyed observing yet to come.
The nebula in the constellation Orion - a gas cloud some 1,500 light years away - shows knots, threads, and other details, such as new-formed stars, not seen before. The core of a distant galaxy is seen clearly where ground-based pictures reveal only an unresolved smear. A great jet that astronomers have seen shooting from another galaxy shows braiding and other details that challenge theorists to explain the forces at work.
Yet another Hubble photo resolves the core of a globule star cluster into individual stars. This will help astronomers understand how such star groupings evolve.
Hubble suffers more than mirror trouble. Its solar panels warp when it moves from night into day, causing it to wobble. Part of the telescope pointing system failed Dec. 3, but controllers still can orient it.
But this is another item to fix when astronauts visit Hubble late in 1993 to restore it to full effectiveness. They will replace the solar panels and one instrument and add corrective mirrors for other observing instruments.
Meanwhile, let's cheer on the Hubble operational team, whose skill has partly compensated for the manufacturing and managerial incompetence that produced the flawed mirror.