Satellite launched to trace the evolution of galaxies

Posted: April 28, 2003

A diminutive satellite with a monumental goal of mapping the history of star formation in a million galaxies streaked into space today atop an air-launched rocket booster.

NASA's Galaxy Evolution Explorer began its journey skyward at 7:03 a.m. EDT when the Orbital Sciences carrier jet, dubbed Stargazer, took off from Cape Canaveral Air Force Station, Florida, bound for a launch zone 100 miles off the coast.

File image of Pegasus rocket launch. Photo: NASA
At 8:00 a.m., the pilot aboard the modified L-1011 aircraft pushed a button to cast free the 51,000-pound winged Pegasus XL rocket about 39,000 feet over the Atlantic Ocean. After plunging for five seconds, the solid-fueled first stage ignited, propelling the slender white rocket into the clear morning sky on a tail of super-hot golden flame.

Eleven minutes later, the three-stage rocket completed its duty by releasing the GALEX spacecraft into an orbit approximately 430 miles above Earth with an inclination of 29 degrees to the equator.

"The flight appears to be right on the mark," NASA launch manager Chuck Dovale said.

The craft's science instrument will be activated and the protective cover on the telescope opened during the next few days. Following a series of tests and calibrations that will last through late-May, the $71.6 million craft will begin 28 months of science observations to survey 10 billion years of the Universe's history.

"This mission will provide the first comprehensive map of a Universe of galaxies under construction and bring us closer to understanding how they, and our own Milky Way, were built," said Christopher Martin, GALEX's principal investigator from the California Institute of Technology.

An artist's concept of GALEX deployed in orbit. Credit: NASA
"(GALEX) is designed specifically to measure the distances and star formation rate in a million galaxies. It is going to help us put together a picture of the Universe we see today -- how stars formed in galaxies, how galaxies evolved through time, what caused star formation and led to the development of heavy elements of the periodic table," said James Fanson, the GALEX project manager from NASA's Jet Propulsion Laboratory.

A member of NASA's Small Explorer program, GALEX is the first ultraviolet survey of the Universe. The craft carries a 19.7-inch telescope with near- and far-ultraviolet detectors.

"Ultraviolet is really the last portion of the electromagnetic spectrum where we don't have a survey of the Universe. So it fills in that last gap," Fanson said. "Being a survey mission, we are going to collect an enormous volume of data that will constitute a huge legacy for the entire scientific community."

"The Galaxy Evolution Explorer is crucial to understanding how galaxies, the basic structures of our universe, form and function," added Anne Kinney, director of astronomy and physics in the Office of Space Science at NASA Headquarters. "Its ultraviolet observations will round out the knowledge we gain from observations in infrared and other wavelengths."

Weighing just 609 pounds and standing 6 feet high, the satellite is small when compared to other orbiting observatories like Hubble and Chandra. But project officials point out that GALEX's size is ample to do the job while also keeping the mission costs relatively low.

The GALEX spacecraft during pre-launch testing at Kennedy Space Center. Credit: NASA
"It might seem surprising that you could make such a powerful investigation into such a small vehicle," Fanson said. "The way we measure the star formation rate in the galaxy is by measuring the ultraviolet luminosity -- how bright it is in the ultraviolet. That turns out to be a very sensitive measurement of the rate that galaxy is forming.

"The very massive stars are extremely luminous because they are very hot. Because they are so hot they give off their light in the ultraviolet part of the spectrum. Because they are so hot they don't live for very long. If you can find these UV bright stars, you know they only recently formed. And that is how you can tell the formation rate is for that moment in the galaxy.

"These stars are so luminous in the ultraviolet that you don't need a large telescope to see them. But you have to be above the Earth's atmosphere."

Getting GALEX into space was accomplished for roughly $23 million using the 33rd flight of Orbital's Pegasus rocket, which debuted in 1990. It marked the 19th straight success for Pegasus since 1997.

This was the second of four Pegasus launches on the 2003 manifest. NASA's SORCE satellite was successfully deployed in January. The commercial OrbView 3 Earth-imaging spacecraft is slated for launch June 1 from Vandenberg Air Force Base, California. Another mission for NASA will follow from California, this one carrying the Canadian SciSat-1 ozone research satellite in July.

If all goes well, GALEX officials hope NASA might provide additional funding to keep the cosmic observations continuing beyond the 28-month mission currently slated. The satellite design doesn't include any life-limiting consumables onboard, like propellant. Money is the key to extending the project.

"What we would do with additional time is continue with surveys to get better sensitivity," Fanson said of an extended mission. "The more time we spend observing on the sky, the better signal-to-noise ratio and the more sensitive the survey becomes."

He added, "As a project manager, there are few opportunities in a career to be associated with a mission that will give you a fundamentally new view of the Universe.

"Typically when you see the Universe for the first time in a new way there are unexpected surprises that come from the data. So that is one of the things we are looking for -- the surprises."

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