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the Belly of an Airplane: Galaxies
Dr. Tony Phillips
On April 28th a NASA spacecraft named GALEX left Earth. Its
mission: to learn how galaxies are born, how they grow, and how they
"GALEX-short for Galaxy Evolution Explorer-is like a time
machine," says Caltech astronomer Peter Friedman. It can see
galaxies as far away as 10 billion light years, which is like looking
10 billion years into the past. The key to the mission is
GALEX's ultraviolet (UV) telescope. UV rays are a telltale sign
of hot young stars, newly formed, and also of galaxies crashing
together. By studying the ultraviolet light emitted by galaxies,
Friedman and colleagues hope to trace their evolution spanning billons
This kind of work can't be done from the ground because Earth's
atmosphere absorbs the most energetic UV rays. GALEX would have
to go to space. To get it there, mission planners turned to
Orbital Science Corporation's Pegasus rocket.
"Pegasus rockets are unusual because of the way they're
launched-from the belly of an airplane," says GALEX Project Engineer
Frank Surber of JPL.
It works like this: a modified L-1011 airliner nicknamed
Stargazer carries the rocket to an altitude of 39,000 feet. The
pilot pushes a button and the Pegasus drops free. For 5 seconds
it plunges toward Earth, unpowered, which gives the Stargazer
time to get away. Then the rocket ignites its engines and surges
skyward. The travel time to space: only 11 minutes.
"The aircraft eliminates the need for a large first stage on the
rocket," explains Surber. "Because Stargazer can be used
for many missions, it becomes a re-useable first stage and makes the
launch system cheaper in the long run." (To take advantage of
this inexpensive launch system, GALEX designers had to make their
spacecraft weigh less than 1000 lbs-the most a Pegasus can
A Pegasus has three stages--not counting the aircraft. "Its three
solid rocket engines are similar to the black powder rockets used by
amateurs. The main difference is that the fuel is cast into a solid
chunk called a 'grain'-about the consistency of tire rubber.
Like black powder rockets, once the grain is lit it burns to
completion. There's no turning back."
In this case, turning back was not required. The rocket carried
GALEX to Earth orbit and deployed the spacecraft flawlessly. On
May 22nd, the UV telescope opened its cover and began observing
galaxies-"first light" for GALEX and another success story for
For adults, find out more about the GALEX mission at
http://www.galex.caltech.edu/ . Kids can read and see a video about
Pegasus at http://spaceplace.nasa.gov/galex/pegasus.html.
L-1011 "Stargazer" takes off to carry Pegasus rocket on the first
39,000 feet of its climb to deliver a spacecraft to
article was provided by the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National
Aeronautics and Space Administration.
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