Hubble due for a house call Telescope: Astronauts to replace equipment that has faltered or become seriously outdated.

Seven American astronauts are set to rocket back to the Hubble Space Telescope early tomorrow for NASA's second in-flight house call on the 7-year-old orbiting observatory.

In the first of four spacewalks totaling nearly 25 hours, two pairs of astro-handymen are to install new, more advanced cameras and spectrographs. Astronomers say the gear will extend man's view closer to the origins of the universe, and deeper into dust-shrouded galaxies and stellar nurseries.


When that's done, NASA has a lengthy list of chores for the astronauts. The repair teams will take turns replacing equipment that has faltered or grown seriously outdated since the space telescope was designed in the 1970s.

"We're increasing the productivity of Hubble, to keep [it] in the forefront of science," said Dr. John Campbell, associate director of the flight project directorate at the Goddard Space Flight Center in Greenbelt.


The excitement at NASA turned chief Hubble scientist Dr. Edward Weiler positively metaphoric: He compared astronomy before Hubble to a two-lane highway. The 1993 repairs, he said, put it on an interstate.

But the 1997 upgrade, he said, "gives us four-wheel drive. It will enable us to get off the interstates and into the forests and hills where there aren't any roads."

If the shuttle has enough fuel, the crew will also try to boost Hubble into a longer-lasting orbit five miles higher.

The 10-day, $795 million mission is scheduled to begin early tomorrow with a spectacular 3: 56 a.m. launch from the Kennedy Space Center in Florida. The veteran crew members are Navy Cmdr. Kenneth Bowersox (commander); Air Force Lt. Col. Scott "Doc" Horowitz (pilot); and mission specialists Gregory Harbaugh, Steven Smith, Joseph Tanner, Dr. Steven Hawley and Air Force Col. Mark Lee.

If all goes well, the crew will chase down and capture the space telescope just before 2 a.m. Thursday.

Each of the six-hour spacewalks is scheduled to begin at 11: 21 p.m. on Thursday, Friday, Saturday and Sunday. They will be televised live on NASA Select TV, which is available on some cable and satellite TV systems.

Discovery should return to the Kennedy Space Center in a tricky 2: 43 a.m. landing Feb. 21. This is the second of four planned trips to Hubble; the next follow in 1999 and 2002.

1993 repairs


In some respects, NASA has less on the line this time than in December 1993, when astronauts had to prove they could fix a 12-ton, bus-size satellite hurtling through space at 17,500 mph.

Taxpayers and astronomers were also watching in 1993 to see whether the repairs would correct the blurred vision that had made the $2 billion telescope a public embarrassment, and a scientific disappointment, after its launch in 1990.

They could, and they did.

Hubble's discoveries since the 1993 repairs have made headlines and dominated astronomical conferences worldwide. Its best pictures have captured the public imagination, turning up in books, on posters and T-shirts.

"Not only is Hubble delivering answers to long-standing questions, it is now beginning to shake some of our long-held beliefs," Weiler said.

It has challenged whole textbook chapters on the life cycles of stars. Hubble astronomers have found that the universe appears to be younger than the presumed ages of some of its oldest stars. That paradox has forced theoreticians to re-examine what they'd been taught about the pace of stellar aging and death.


But that's OK, Weiler said. "It's the things you don't expect that are the most fun."

Among the Hubble discoveries:

A spectacular view of star nurseries amid the towering pillars of dust and gas in the Eagle Nebula.

A "deep field" view of what seemed like a nearly empty speck of sky. Hubble found it filled with 1,500 young galaxies, some appearing as they did soon after the beginning of the universe. Their forms are helping scientists understand galactic birth and evolution.

Conclusive evidence that black holes -- objects so dense not even light can escape their gravity -- are common and may lie at the core of most galaxies.

Detection of dust disks in the Orion Nebula that suggest that planetary systems may be forming around many stars in our Milky Way.


Detailed views of a comet's collision with Jupiter; photographic records of weather on Mars; the first surface map of Pluto; and evidence for oxygen in the atmospheres of the Jovian moons Europa and Ganymede.

One-chance rendezvous

The astronauts will have just one chance to rendezvous with Hubble. Orbiting 368 miles up, Hubble is near the limits of the shuttle's range. Discovery will not have fuel to make a second attempt.

The first job for astronauts Lee and Smith will be to remove the telescope's Faint Object Spectrograph and the Goddard High Resolution Spectrograph, which have been on board since Hubble's launch in 1990.

The task is like sliding two 750-pound refrigerators out of a closet with quarter-inch clearances.

They'll be replaced by two new, state-of-the-art instruments. The first is the $125 million Space Telescope Imaging Spectrograph (STIS). Developed at the Goddard Space Flight Center, STIS combines all the most critical capabilities of the retired spectrographs but adds new advances as well.


Spectrographs don't take photographs. They break starlight into its component wavelengths. The resulting patterns, or spectra, can be read like stellar blueprints, revealing such things as the source's distance, chemistry, direction, speed, temperature and density.

STIS is capable of focusing on as many as 512 objects or points in space at the same time, sampling conditions across the width of targeted stars and galaxies. It is also sensitive to finer detail, and to visible and ultraviolet wavelengths 15 to 35 times broader than the old Goddard instrument.

"With STIS, we can survey many more galaxies and observe longer. That makes STIS a more powerful black hole hunter," said Dr. Bruce Woodgate, the instrument's principal investigator.

It will accelerate the search for more distant galaxies, reaching back closer to the Big Bang that most scientists believe was the origin of the universe.

The second new instrument is the $105 million Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Built by University of Arizona scientists, it contains three cameras that will open Hubble's eyes to the infrared spectrum for the first time.


Infrared wavelengths are longer than visible light -- just beyond the red end of the spectrum -- but shorter than radio waves. We can't see infrared radiation, but we can perceive some as heat, like that from hot fireplace coals.

Astronomers want Hubble to see in infrared for three reasons. First, much infrared radiation is lost in Earth's atmosphere, making ground observation difficult.

Second, they want to see to the most distant reaches of the universe. Light from those distances has been stretched as it traveled the billions of light years to Earth. That's because the entire universe is expanding, lengthening those light waves and shifting them from the visible to the infrared.

And third, the births of most stars and planets occur deep inside vast clouds of dust and gas that block visible light. Wavelengths in the "near" infrared, however, are able to penetrate.

NICMOS' near-infrared detectors will allow astronomers to peer "into the wombs of dust that shroud the origins of things like planets and galaxies," said Dr. Rodger Thompson, NICMOS' principal investigator.

The detectors are cooled to minus 355 degrees Fahrenheit with 230 pounds of frozen nitrogen. The cold will keep them at peak sensitivity for five years, when the nitrogen runs out.


The NICMOS cameras are capable of both imaging and spectrometry at different magnifications, with dozens of prisms, gratings, filters and polarizers for more detailed analyses.

Additional chores

Tasks on the remaining three spacewalks include:

Replacement of a malfunctioning Fine Guidance Sensor, one of three. The suitcase-size sensors help aim the telescope by finding and tracking key "guide stars." They also do precise measurements of stellar motions, which can reveal the presence of hidden planets. But the sensors did not benefit from the 1993 optical repairs. The new one carries its own corrective optics and should improve Hubble's performance.

Replacement of two 1970s-era reel-to-reel recorders. One will be exchanged for a modern, solid-state recorder that stores 12 billion bits of data on silicon chips -- 10 times the capacity of the tape device. Hubble's new instruments demand the higher capacity.

Replacement of a balky Reaction Wheel Assembly, one of three. The device acts like a flywheel to help turn the telescope, which has no thrusters.


Replacement of a variety of electronics devices, including: one of four Data Interface Units, which manage command instructions; and one of two Solar Array Drive Electronics units, which control movements of the solar panels.

Check out Hubble on the Internet

The Internet holds a vast amount of information on the Hubble Space Telescope, the space shuttles and space exploration. Some key sites:

Space Telescope Science Institute: latest discoveries, photos, teacher information and student activities. http: //

Space shuttle: mission information, launch data, crew biographies, photos, videos, technical manuals, sighting information. http: //

Office of Space Flight: general information on space exploration. http: //


NASA TV: daily schedule. http: //

Space education: information for teachers. http: //

Live Web casts: Twice-daily interviews during the mission from the Space Telescope Science Institute through the Web page of the Exploratorium science museum in San Francisco. http: //

Pub Date: 2/10/97