June 04, 2012
Credit: Credit: Eutelsat
Michael Mecham/San Francisco
Astronomers have floated X-ray detectors on balloons, launched them on sounding rockets and put them on satellites since the late 1950s to sweep the sky. The goal is to unravel the story of a violent universe, where black holes swallow light, neutron stars are born and stars the size of the Sun puff up as red giants only to collapse in death as white dwarfs.
Since Earth's atmosphere absorbs X-rays, astronomers wanting to use them need to rise above it. Their work so far has concentrated on detecting low-energy X-rays; the high-energy field has been investigated only in wide-angle views. Astronomers at the California Institute of Technology (Caltech) want to capitalize on the ability of high-energy X-rays to penetrate the cosmic dust that obscures the hearts of galaxies, where unseen black holes may be hiding out. Give us sharp, clearly focused images and we'll give you exciting science, they promise.
NASA hopes the Nuclear Spectroscopic Telescope Array (NuStar) satellite will do just that. Championed for nearly a decade at Caltech by principal investigator Fiona Harrison, NuStar is set for launch on June 13 on an Orbital Sciences Corp. Pegasus XL rocket. Harrison expects the 780-lb. satellite to provide images that are 10 times crisper and 100 times more sensitive than those of previous X-ray observatories.
The 11th mission in NASA's Small Explorer program, NuStar is funded at $165-170 million and will be capable of penetrating “supermassive” black holes that are dim at all wavelengths of light. One prime target is Sagittarius A at the heart of the Milky Way, which has a mass 4 million times greater than the Sun's, says Project Scientist Daniel Stern of the Jet Propulsion Laboratory (JPL). Astronomers are looking for “sleepers”—undetected black holes—and their more active cousins, which shine brightly as they swallow cosmic gas and dust.
The NuStar task list includes locating the remnants of collapsed stars, mapping historic supernova remnants and observing high-energy gamma-ray sources. NuStar's X-ray telescope should help astronomers understand how particles in some galaxies are accelerated to within a fraction of a percent of the speed of light.
The nominal mission length is two years but it could be extended to five. The spacecraft is distinguished by an instrument package that combines state-of-the-art high-energy detectors from Caltech, advanced mirrors and coatings, and the judicious employment of light-weight extendable mast technology from ATK Aerospace of Goleta, Calif. NuStar's bus is based on Orbital Sciences' LEOStar-2 design. Spacecraft and launcher integration were completed at Vandenberg AFB, Calif. The combined payload is to be flown by Orbital's L-1011 launch aircraft to Kwajalein in the central Pacific Ocean on June 5.
The 56-ft.-long Pegasus XL gives small payloads a launch flexibility they cannot achieve if they ride as piggyback payloads on a larger mission. The three stage, solid-fueled rocket will be dropped from the L-1011's belly at 41,000 ft. about 100 mi. from the Kwajalein atoll in the Marshall Islands. First-stage ignition will take place 5 sec. after the release.