Astronauts Bearing Gifts

ASA astronauts paid a visit to the Hubble Space Telescope in February 1997. They didn’t arrive empty-handed. Like well-mannered guests, the astronauts brought gifts. These weren’t just ordinary gifts. They were fancy new scientific instruments: a spectrograph and an infrared camera. The new gifts greatly improve Hubble’s ability to see the universe.

The new instruments were installed during Hubble’s second tuneup - the second servicing mission since the telescope was deployed in 1990. For five days, the 12-ton telescope played the gracious host to four astronauts from the space shuttle Discovery. The astronauts’ first order of business was to replace two aging scientific instruments with two new ones: the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Space Telescope Imaging Spectrograph (STIS).

With NICMOS’s infrared eyes, Hubble sees things it never saw before. The new camera allows the telescope to see objects in near-infrared wavelengths, which are slightly longer than visible light. Infrared light penetrates dust and gas; visible light does not. We see the red glow of a sunset because dust in our atmosphere allows red light to travel through it. Infrared observations are especially important to study the dust and gas clouds where stars are born and ancient light from very distant objects that began traveling through space billions of years ago.

STIS gives the telescope a more talented spectrograph than the one it replaced. That’s because STIS gathers more information for every target observation. Spectrographs collect crucial information about celestial objects, such as their temperature, velocity, and chemical composition. STIS collects light from hundreds of points across a target. The old spectrograph gathered light from just one point. STIS’s mission is to hunt for black holes - compact, dense, invisible objects that gobble up anything that get near them.

To store all of this new information, the astronauts added a solid state tape recorder, which stores 10 times more scientific data than Hubble’s two reel-to-reel recorders. Another job on their repair list was replacing a Fine Guidance Sensor, which finds the stars necessary to take images of targets. The astronauts also had time to perform a little cosmetic surgery on Hubble’s skin, repairing tears in the telescope’s thermal blanket. None of this work fazed Hubble; the telescope was used to all the fuss. Astronauts from the space shuttle Endeavour had caught up with the orbiting telescope in 1993. After hauling Hubble onto the shuttle’s cargo bay, the astronauts spent five days tuning it up.

The mission’s most important objective was to install two devices to fix Hubble’s vision problem. Because Hubble’s primary mirror was incorrectly shaped, the telescope could not focus light to a single sharp point. Instead, it saw a fuzzy halo around objects it observed. Once Hubble received its corrective glasses, it began seeing clearly again.

Installing new instruments like Hubble’s corrective glasses hasn’t been a problem for astronauts. That’s because NASA scientists designed Hubble for servicing in space. The telescope’s instruments were created as modular units, comparable to dresser drawers that can be easily removed and replaced. Designers also equipped the telescope with handholds and other special features to make servicing tasks less difficult for astronauts wearing bulky spacesuits.

Hubble was designed for servicing in space because it needs frequent tuneups to keep it in top shape. Astronauts will visit the telescope again in 1999, 2002, and 2005 to install new components and instruments that represent the cutting edge of technology.

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