Johns Hopkins Gazette: November 7, 1994

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
     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
     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
     "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

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
     "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

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

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