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The launch of NASA's Extreme Ultraviolet Explorer (EUVE) satellite heralds a major step forward in understanding the physics of astronomical objects seen in a newly opened window of the electromagnetic spectrum called the extreme ultraviolet.
The study of the universe in the extreme ultraviolet is still in its infancy. EUVE will be the first satellite to make both spectroscopic and wide-band observations over the entire extreme ultraviolet region.
This unique satellite consists of three scanner telescopes and a dual-purpose survey/spectrometer telescope. EUVE will map the entire sky to determine the existence, direction, brightness and temperature of numerous objects that are sources of extreme ultraviolet radiation. Some of the objects EUVE is likely to detect are white dwarf stars, neutron stars, binary star systems and the hot outer atmospheres (coronae) of red dwarf stars and stars similar to our Sun.
Goddard Space Flight Center, Greenbelt, Md., is responsible for the management of EUVE. The satellite will be launched in early 1992 for NASA by the U.S. Air Force from Cape Canaveral Air Station, Fla., aboard a Delta II expendable launch vehicle.
Following launch and an in-orbit checkout lasting about 30 days, the EUVE telescopes will scan the sky for new sources of extreme ultraviolet radiation. The first six months will be devoted to an all-sky survey, at which time the entire sky will be mapped and the locations and brightness of thousands of objects will be measured. Simultaneously with the all-sky survey, the deep survey telescope will take longer duration measurements on a restricted region in the sky with a sensitivity 10 to 50 times greater than the scanning telescopes.
From the many objects of astronomical interest discovered during the EUVE all-sky survey and other objects already thought to be observable in the extreme ultraviolet, guest observers will propose to study targets using the spacecraft's extreme ultraviolet spectrometer. The spectroscopic studies will begin after the all-sky survey and are planned to last one or more years.
Extreme ultraviolet light is located in the spectrum between ultraviolet light and x-rays. From Earth, only visible light and radio waves are easily detectable; the atmosphere absorbs other wavelengths.
Astronomical observations in the far ultraviolet and soft X-ray regions over the past 20 years have shown that interstellar space is far more transparent to the passage of extreme ultraviolet radiation than previously believed. In addition, major technological advances in the development of detectors, mirrors, gratings and filters have made it possible to build instruments with sufficient sensitivity to make extreme ultraviolet astronomy a reality.
Through EUVE observations, astronomers will learn about the physical properties and chemical compositions of selected objects and the compositions of stars, planets and other sources of extreme ultraviolet radiation. Since so little is known about the extreme ultraviolet, "It's almost a given that you will find what you don't expect to see," said Goddard's Dr. Yoji Kondo, EUVE project scientist. "It's like a traveler being turned loose into a new world."
EUVE contains four telescopes, each 40 centimeters across. The three scanner telescopes and the deep survey/spectrometer telescope represent the state-of-the-art in extreme ultraviolet astronomy. These instruments, developed by scientists and engineers at the University of California-Berkeley, are mounted in the payload module, which is installed as a unit on the Explorer Platform spacecraft. Each telescope uses metal mirrors that reflect extreme ultraviolet light at grazing angles. The telescopes are equipped with filters made from thin films of metals and other substances, layered to isolate the desired regions of the EUV spectrum for observation.
Each of the EUVE scanner telescopes is about as large as a 55-gallon oil drum and weighs about 260 pounds (about 188 kilograms). The deep survey telescope/spectrometer weighs about 710 pounds (323 kilograms).
Goddard is responsible for the design, construction, integration, checkout and operation of the EUVE spacecraft. James Barrowman is the project manager for Explorer and Attached Payloads, Frank Volpe is deputy project manager for EUVE.
EUVE will be operated from a Payload Operations Control Center (POCC) at Goddard Space Flight Center. Commands will be sent to the spacecraft from the POCC, and data obtained by the spacecraft will be routed through to the control center and then to the Science Operations Center at the Center for Extreme Ultraviolet Astrophysics at the University of California, Berkeley. Berkeley's Dr. Stuart Bowyer and Dr. Roger Malina are principal investigators of EUVE.