Astro’s 4 Telescopes May Fill In Gaps About Space

Imagine seeing the full complexity of a movie like “Lawrence of Arabia” when all you had previously seen was a 60-second trailer, or the vibrant detail to be gained from studying a Matisse painting when all you had previously seen was a black-and-white print.

Roughly speaking, that is the kind of improvement astronomers hope to gain this Wednesday at 12:40 a.m. when the space shuttle Columbia carries the $150-million Astro observatory into orbit. The three ultraviolet telescopes and one X-ray telescope aboard the shuttle will afford astronomers an unprecedented view of the universe in a broad range of wavelengths that hitherto have been largely inaccessible, blocked from ground-based telescopes by the absorbing power of the atmosphere.

In a mission of unusual ambition and complexity, and the first ever to be devoted to a single scientific discipline, the seven-man crew of Columbia--which includes five astrophysicists--and their counterparts on Earth will work around the clock for 10 days, taking as many as 300 pictures with each instrument before packing them up and bringing them home.

The mission is a sharp contrast to the recent flight of the shuttle Discovery, which five weeks ago launched the Hubble Space Telescope. Hubble will view the stars in great detail for the next 15 years, and the differences between it and Astro have sparked a strong rivalry between the crews of the two shuttles.

“We get to be astronomers,” said Astro mission specialist Jeffrey A. Hoffman. “All they (the Discovery crew) do is throw out a telescope. Anybody can do that.” Added mission specialist Robert A. R. Parker: “We’ll be sending down science data while (the) space telescope is still doing engineering checkout.”

The Hubble and Astro telescopes differ from each other in much the same manner as a spyglass does from binoculars. Hubble is designed to look at very narrow regions of space at very high resolution. Astro is meant to study much broader regions, but with less resolution. The Astro telescopes also observe at a variety of wavelengths to which Hubble is blind.

During the 10-day mission, astronomers will study a variety of celestial objects ranging from planets and moons in the outer solar system to Supernova 1987a--an exploding star, located about 160,000 light-years from Earth, that was first detected in January 1987; from nearby “starburst” galaxies that have an unusually high rate of star formation, to distant quasars that are the oldest and brightest objects known.

They will also get their first look at large portions of the sky that have never been viewed in either ultraviolet or X-ray wavelengths because of the atmosphere, and they may even see the first direct evidence for the existence of black holes--those mysterious and elusive collapsed stars that are so heavy and dense that not even light can escape their intense gravitational pull.

“Each of the instruments is designed to do something that no other existing telescope or spacecraft can do,” said astronomer Stephen P. Maran of NASA’s Goddard Space Flight Center in Greenbelt, Md. “It’s going to provide an important source of knowledge about what goes on in space.”

In their leftover time, the Columbia crew will teach a science lesson from space that will be beamed by satellite to high schools around the country. And payload specialist Ronald A. Parise will attempt to make ham radio contact with Soviet cosmonauts aboard the space station Mir--perhaps to commiserate with the cosmonauts on their need to repair some insulation before returning to Earth.

Each of the four telescopes, to be mounted on pallets in the payload bay of Columbia, has its own mission to perform, although their roles are complementary. In fact, the three ultraviolet telescopes will be operated in unison to provide different pictures of the same celestial objects. The X-ray telescope will be operated independently of the other three; sometimes it will photograph the same stars as the ultraviolet telescopes, other times it will photograph other objects.

The largest of the telescopes is the Hopkins Ultraviolet Telescope or HUT, designed by astronomer Arthur F. Davidsen and his colleagues at Johns Hopkins University in Baltimore. It has a 36-inch mirror coated with the rare metal iridium to allow it to reflect an unusually broad spectrum of ultraviolet frequencies.

HUT also has an exceptionally sensitive electronic detector coated with cesium iodide, which allows it to “see” incoming ultraviolet photons. This detector must never come in contact with normal air--especially water vapor--because that would destroy its ultraviolet sensitivity. High-efficiency vacuum pumps must be used to keep it in a near-vacuum continuously, except for brief transition periods in a dry nitrogen atmosphere.

“One of the most challenging and significant projects” for HUT will be the search for helium in the intergalactic medium, Davidsen said. When the universe was formed in the Big Bang, astrophysicists believe, its principal components were hydrogen and helium. “It’s that primordial hydrogen and helium, out of which everything else came, that we would like to detect directly,” he said.

Helium absorbs light at ultraviolet wavelengths detectable only by HUT. “Either we will detect it, or we will set a very stringent limit” on the amount of matter that can be present in intergalactic space, Davidsen said. The question of how much invisible matter is present in the “vacuum” of space is a crucial one because it determines whether the universe will eventually collapse in on itself or expand forever.

The next largest telescope, with a 15-inch mirror, is the Ultraviolet Imaging Telescope or UIT, designed and built by astronomer Theodore P. Stecher and his colleagues at Goddard. It is the only one of the four instruments that will not produce data during the Columbia flight. Instead, it carries enough film to make 2,000 exposures during the flight. The photos will be developed after Astro is returned to Earth.

UIT has the largest field of view of any ultraviolet telescope ever built. It “covers a vastly larger piece of the sky” than Hubble, Maran said, and thus can be used to discover new objects that will be studied in detail by Hubble.

Unlike Hubble, which responds to both visible and ultraviolet light, UIT responds only to ultraviolet light. “When you look at a globular star cluster in visible light, it is dominated by the red giant stars,” Maran said. “But they all drop away in the ultraviolet, so you can look and discover large numbers of white dwarfs, which are shrunken down and quite hot.”

UIT will also be used to search for an “ultraviolet light echo” of the explosion that created Supernova 1987a. According to conventional theory, the ultraviolet light output of the supernova should have peaked just hours after the original explosion, while the output of visible light peaked 85 days later.

Both light peaks should cause “echoes” when the bright light is reflected by interstellar dust and bounced back to Earth, appearing in telescopes as faint and ever-enlarging circles surrounding the supernova. One astronomer, Arlen Crotts, has already discovered the visible light echoes, and researchers hope to observe the ultraviolet light echoes with UIT. By comparing the intensities of the light in the two wavelengths, researchers should be able to determine the microscopic composition of the dust grains and their arrangement in the clouds.

The properties of interstellar dust are also the focus of the third ultraviolet telescope, the Wisconsin Ultraviolet Photo-Polarimeter Experiment, also known as WUPPE, which has a 20-inch mirror. It was designed and built by astronomer Arthur D. Code and his colleagues at the University of Wisconsin in Madison. It will observe polarized ultraviolet light, which has been virtually unstudied.

Normally, the electromagnetic radiation that is light vibrates uniformly in all directions, like the pistons on an old-fashioned radial airplane engine. Polarized light, in contrast, vibrates preferentially in one direction like the pistons in a four-cylinder automobile.

Although ultraviolet light is not normally polarized, it can be polarized by passing through strong electric fields or by interaction with interstellar dust. Studying its polarity will thus reveal a great deal about the magnetic fields of other stars and about the composition of interstellar gases.

The fourth and final telescope is the Broad Band X-Ray Telescope or BBXRT, designed and built by Peter J. Serlemitsos and his colleagues at Goddard. It has an unusual new design.

X-rays are not reflected by mirrors in the same way as normal light. Instead, they are reflected only when they strike the mirror at a very shallow angle. Hence, conventional X-ray telescopes use very large, highly polished metal mirrors that, in fact, have only a very small effective X-ray collecting area.

Serlemitsos developed a design in which literally hundreds of very thin sheets of gold-coated aluminum foil can be nestled close together to reflect an unusually large proportion of the X-rays entering the telescope, making possible unusual X-ray gathering power.

One prime target of BBXRT will be Supernova 1987a. Researchers hope it will provide the first firm evidence of the existence of the neutron star that most astronomers are sure must be at its center. Visible and ultraviolet light from the neutron star are scattered by the large amount of debris around it, but X-rays should easily pass through.

“All the heavy elements in the universe have been formed in such explosions,” Serlemitsos said. “If we can trace the amounts and distribution of the heavy elements (in the supernova), we can start putting together good models of how heavy elements are built.”

To maximize their viewing time in orbit, the astronauts will be divided into two teams, Red and Blue, which will work 12-hour shifts each. When the Red team is on duty, Columbia pilot Guy S. Gardner, 42, will fly the shuttle to point the payload bay in the direction from which observations will be made, mission specialist Parker, 53, will operate the aiming system for the ultraviolet telescopes and payload specialist Parise, 38, will operate the telescopes themselves.

When the Blue team is on duty, mission specialist John M. Lounge, 43, will fly Columbia, mission specialist Hoffman, 45, will operate the aiming system and payload specialist Samuel T. Durrance, 46, will operate the telescopes. Shuttle commander Vance D. Brand, 58 and on his fourth flight, will work a staggered shift that overlaps with both teams.

The BBXRT will be operated remotely from Goddard.