Shuttle Concludes Longest Flight

After more than 250 orbits of the Earth, the space shuttle Endeavour landed at Edwards Air Force Base, completing a 16 day mission, the longest shuttle mission ever. The seven crew member mission was devoted almost entirely to astronomical studies with the Astro-2 payload. Astro-2 contained three Ultra-Violet (UV) telescopes which performed tasks not possible from the ground.

STS-67 With ASTRO-2 Payload

"This has been an outstanding mission," said Astro-2 Mission Scientist Dr. Charles Meegan as the mission drew to a close. "We had planned to explore 23 different science programs and we 'nailed' them all."

"From my point of view, this mission has been nothing short of absolutely spectacular," said Hopkins Ultraviolet Telescope (HUT) Principal Investigator Dr. Arthur Davidsen. "It's been 17 years since we began thinking about doing far ultraviolet spectroscopy with HUT as a complement to what we can do with the Hubble Space Telescope and this is a dream come true. "

More than 200 separate successful observations were made of over 100 celestial objects selected by HUT investigators. All of these observations made up 21 separate investigations, 14 carried out by permanent members of the HUT team and 7 by guest investigators who joined the HUT team for Astro-2.

One of Davidsen's primary objectives for HUT during Astro-2 was to use two high redshift quasars as background lighting to search for helium in the space between galaxies. Detecting helium in intergalactic space and determining how much of it is there could provide answers to the questions about the Big Bang that is believed to have marked the beginning of our universe.

In other Astro-2 observations, HUT made simultaneous ultraviolet measurements with the Hubble Space Telescope of Jupiter's aurora, or northern lights, and its effect on the planet. HUT scientists also studied the atmosphere of Jupiter's moon Io and the torus (donut-shaped cloud) of ionized gas it produces around Jupiter.

Ultraviolet emissions from the atmospheres of Venus and Mars were also targets of observations for HUT during this mission.

Another of Astro-2's instruments, the Ultraviolet Imaging Telescope (UIT), took wide-field images of objects in ultraviolet light on film. UIT made for the first time ultraviolet images of the entire moon. These images will be studied to investigate the changes in UV reflectivity with known changes in lunar surface features. This information can then be used to compare with the reflectivity of other planetary satellites in our solar system to understand more about their surfaces and the physical processes that have been responsible for their evolution.

Observations of some of the faintest galaxies in the universe were photographed by UIT during Astro-2. Astronomers took advantage of the very dark sky background, using UIT to photograph very low surface brightness galaxies. "This could be the UIT observation with most potential for surprises," said UIT team member Dr. Steve Maran. "Ground-based observations show an unexpected blue glow. Our ultraviolet images may tell us where it's coming from."

Scientists for UIT will spend the next several years analyzing their data from Astro-2. Some of these data include a census of rare, hot stars (with temperatures over 15,000 degrees Kelvin) in about a dozen star clusters. These hot stars, very much more evolved than the sun, have shed their outer layers so that scientists can see almost down to their nuclear-burning cores.