Adventure, Science Push Astrophysicist Skyward By Emil Venere The clock is counting down, and Sam Durrance is sitting in a chair facing skyward in the mid-deck of the space shuttle. The only thing in his immediate view is a row of lockers. At ignition he feels a lurching sensation, followed by vibration. Endeavour's three main engines and two solid-fuel rocket boosters are pushing the shuttle upward with a force that exerts three times Earth's gravity on its crew. Two minutes later the boosters run out of fuel and are jettisoned, causing a marked decrease in thrust. The ride becomes much smoother. In another minute the craft has left the planet's atmosphere, and five minutes after that the shuttle is orbiting Earth. It all happens that fast, an exhilarating eight or nine minutes from blastoff to orbit. "It's a pretty exciting ride," said Dr. Durrance, a Hopkins astrophysicist and a payload specialist on the upcoming Astro-2 mission. "There are lots of different changes in the acceleration as you go uphill--we call it uphill." Repeat performance Dr. Durrance enjoys adventure. He also loves the science of astrophysics. And soon he'll get a chance to pursue both, as Hopkins returns to space with the second flight of the Astro Observatory. A principal research scientist in the Department of Physics and Astronomy, Dr. Durrance, 51, was a payload specialist aboard the shuttle Columbia during the nine-day Astro-1 mission, in December 1990. He will repeat that role on Astro-2, scheduled for a Feb. 23 launch. The mission will last nearly twice as many days as Astro-1, keeping astronomers busy around the clock with an ambitious schedule to study more than 300 objects. Astro-2, housed in the space shuttle's cargo bay, will be a package of three instruments that detect ultraviolet light. One of those instruments is the Hopkins Ultraviolet Telescope, designed and built at Hopkins. HUT opens a window on the universe that is invisible to other telescopes. Visions from beyond People cannot see ultraviolet light because its wavelengths are too short. Most UV light is filtered out by the ozone layer in the Earth's stratosphere. However, many stars and other astronomical objects reveal a complex story about their history and composition through the ultraviolet radiation they emit. By placing telescopes above Earth's atmosphere, astronomers study ultraviolet light from the distant cosmos and the Earth's own galactic neighborhood. Astro-2's other instruments include the Ultraviolet Imaging Telescope, developed by NASA's Goddard Space Flight Center, and the Wisconsin Ultraviolet Photo-Polarimeter Experiment, a University of Wisconsin project. Both those instruments also flew on Astro-1. But only HUT has been improved significantly since then. The primary mirror has been coated with silicon carbide, replacing the iridium coating on the original mirror. The new coating is much more reflective to the shortest ultraviolet wavelengths detected by HUT. Silicon carbide also has been placed on the spectrograph grating, a device that diffracts ultraviolet light into a spectrum so that it can be analyzed. These and other improvements have made HUT three times as sensitive as its Astro-1 version. Heightened sensitivity, together with improvements to other hardware and the length of the mission, will enable astronomers to gather a wealth of information, perhaps 10 times as much data as HUT scientists gathered during Astro-1. The result should be a mountain of information that will keep Hopkins scientists busy years after the Astro-2 mission. They are still writing articles based on data from Astro-1, four years ago. HUT scientists on the Astro-2 mission will pursue more than a dozen projects ranging from the study of how stars evolve, to analyzing the atmospheres of Jupiter and Venus and probing the nature of active galaxies, which radiate enormous amounts of energy from their unusually bright centers. The HUT astronomers will be joined by seven teams of "guest investigators," scientists from around the country who were selected by NASA to take advantage of the mission. Finding the smoking gun But HUT's major goal will be to search for one of the most coveted jewels of cosmology: the primordial helium gas still believed to be lingering from the birth of the cosmos. In essence, astronomers are trying to find the smoking gun, the ash remnants of the explosive genesis of the universe. Confirming its existence would lend strong support to the Big Bang theory of how the universe was born. Astronomers using the Hubble Space Telescope have discovered evidence that the helium does exist, but those findings are not conclusive. "We think it would be very surprising if we didn't find it with HUT," said Arthur Davidsen, the Hopkins astrophysicist leading the project. Dr. Davidsen, who specializes in ultraviolet astronomy, conceived the idea for HUT in 1978 and has spent much of his career on the project. Only HUT is designed specifically to detect the short wavelengths of ultraviolet radiation that are necessary to search most effectively for intergalactic helium. Astronomers plan to use HUT to analyze light emitted by extremely distant objects called quasars as their radiation passes through the vast intervening regions of space, much as one would see the beam of a distant flashlight shining through a hazy mist. The light will be studied with a spectrograph on HUT. The resulting spectrum will be scrutinized for any evidence of the distinctive "absorption features" associated with helium. The last chance Historical perspective adds a tone of urgency to the mission. Although HUT itself worked flawlessly on Astro-1, computer problems and glitches in the system that points the three telescopes prevented HUT scientists from pursuing their main goal. Astronomers had expected some necessary fine tuning, a reality in all new big-science projects. In fact, before the shuttle Challenger exploded in 1986, the Astro observatory was planned to have at least three and perhaps as many as six missions, which would have given scientists plenty of time to iron out any glitches. But after the accident, scientists were hard-pressed to persuade NASA to allow even two Astro missions. "It required considerable convincing, shall we say," Dr. Davidsen said. One reason NASA agreed to fly the observatory again was HUT's outstanding record on Astro-1, he said. The HUT team enjoyed considerable success, gathering information on 77 objects and publishing more than 50 research papers. Now the glitches have been ironed out. But instead of five future missions, the team has just one more chance to use HUT. Because Astro-2 probably represents the telescope's final flight, it's now or never to use HUT for its highest calling. "This time we're really going to do it, no matter what, because it's our last chance," Dr. Davidsen said. "It's the most significant scientific goal we have." The HUT team includes about two dozen Hopkins faculty, staff and graduate students from the Bloomberg Center for Physics and Astronomy and the Applied Physics Laboratory. For scientists who have labored a decade or more on HUT, their hard work is coming to a sharp focus: the launch at Kennedy Space Center, in Florida, and the hectic days of managing the mission from NASA's Marshall Space Flight Center, in Huntsville, Ala. "When you put that much of your life into a project and it all goes by in two weeks, it would be a big hit to your career if it was just wiped out," said astronomer William P. Blair, who joined the project in 1984. "But if it works well, it's a big boost." Time for adjustments Dr. Blair, an associate research professor, knows all too well how demanding those two weeks are going to be. His job, as it was on Astro-1, will be to constantly adjust the schedule of astronomical observations as the mission progresses. Every time a launch is delayed, that means different objects will be in the observatory's field of view. HUT's viewing schedule is designed with a precise timeline based on the space shuttle's relative position as it orbits the Earth. The timeline assigns a certain amount of viewing for specific objects, or "targets." But even a short launch delay means the timeline must be adjusted. Three teams of scientists will view targets around the clock. Some of the 300 objects will be viewed more than once during the mission, for a total of about 400 targets that the shuttle and observatory must be pointed toward. Those pointings have to be precisely scheduled into the timeline, often on short notice. Making matters even more difficult, HUT cannot be aimed closer than a 45 degree angle to the sun because bright sunlight would destroy the telescope's sensitive ultraviolet detector. "It's a very complicated business," said Dr. Blair, a mission deputy project scientist. "If we launch two hours late there are a number of targets whose visibility changes dramatically relative to the shuttle's orbit. "Even if we have a timeline in place for Feb. 23, and we fly exactly on that timeline, there will be changes to that timeline because people change their priorities after they start seeing data." A long haul The Feb. 23 launch date is almost certain to be delayed into early March. Space missions are, by their nature, subject to routine delays. But no one's complaining. Many HUT scientists have been on the project so long a few more slips in the launch schedule do not amount to much. Since they first started working on HUT, astronomers have seen the world change around them, their families sprout children and their professional lives flourish. And they have weathered a tragedy in the nation's space program that threatened the future of HUT. The payoff is near. "The exciting part is yet to come, after the data comes in," said project scientist Gerard Kriss, an astrophysicist who joined the team nine years ago. He plans to use the trove of HUT data to study relatively nearby active galaxies, those about 50 million light-years away. Dr. Kriss, an associate research professor, hopes to learn more about the structure of such galaxies, which appear to be driven by engines producing enormous energy. But long before scientists have a chance to see a hint of data, all eyes will be on Endeavour as it hurtles through the atmosphere on its breathtaking trek to orbit. "That is the primary reason I've devoted 10 years of my career to this... the experience itself," Dr. Durrance said. "It has an emotional impact." ----------------------------------------------------------------- Hut Information Now Has World Wide Web site HUT is now on-line. The project has a new World Wide Web page that can be accessed using Mosaic. With access through a Windows environment, users can learn all about HUT, Astro-1, Astro-2 and the scientists. They also can pull up pictures of the telescope and other visual offerings. "We will continue to add to this information as time and energy permit, but it is accessible and useful now," Hopkins astrophysicist William P. Blair said. The address is http://praxis.pha.jhu.edu/hut.html. -----------------------------------------------------------------