Berkeley - An aging, 7,000-pound satellite
built and operated by the University of California, Berkeley,
is expected to fall from orbit today (Wednesday, Jan. 30),
making a fiery landing somewhere in the Pacific Ocean and
ending astronomers' first attempt to map the region around
our star in a window of the electromagnetic spectrum never
before explored- the extreme ultraviolet.
The Extreme Ultraviolet Explorer, or EUVE, was launched June 7, 1992, and is expected to re-enter the atmosphere as early as 7 p.m. PST today, sprinkling debris over a 500- to 625-mile swath of ocean.
"The probability of the few EUVE surviving pieces falling into a populated area and hurting someone is very small. It is more likely that the small pieces will fall into the ocean or fall harmlessly to the ground," said Ronald E. Mahmot, project manager for Space Science Mission Operations at Goddard Space Flight Center in Greenbelt, Md. The satellite could re-enter the atmosphere as late as 4 a.m. PST on Jan. 31.
UC Berkeley scientists who have spent the past 10 years analyzing data from the satellite and proving to the skeptical that astronomers can learn valuable information from looking though this neglected window will gather Thursday night for a crash party at Becket's bar in Berkeley.
"We all feel real good about this," said Roger Malina, a UC Berkeley research astronomer who has directed the project since 1996. "EUVE opened up the extreme ultraviolet part of the spectrum and found more than 1,000 sources in the sky. It led to more than a thousand papers, and some 300 undergraduate students were trained on the project. It was a job well done."
During its early years, EUVE was operated from Goddard, with scientific operations centered on the UC Berkeley campus. In 1997, control of EUVE flight operations was transitioned from Goddard to UC Berkeley and remained there until the program's termination on Jan. 31, 2001. Slated for only three years, EUVE was operational for eight. NASA twice extended its scientific mission.
In 1996, when Goddard's then-director Joe Rothenberg announced the transition, he said, "This marks the first time existing mission operations have been transferred from Goddard to a university."
UC Berkeley's successful operation of EUVE proved that universities can operate satellites cheaply and effectively, and paved the way for numerous other mission's handed over by NASA, Malina said. One of these is the High Energy Solar Spectroscopic Imager, or HESSI, scheduled for launch Feb. 5. Designed, built and operated by an international consortium led by UC Berkeley, HESSI embarks on a two- to three-year mission to study violent explosions on the sun, called solar flares.
Extreme ultraviolet (EUV) radiation is visible only to instruments above Earth's atmosphere. Radiation at these energies is emitted by multi-million degree coronae on stars, by giant eruptions on novae, by the hot surfaces of white dwarfs, and by other exotic sources in the cosmos.
When EUVE was first proposed by astronomer Stuart Bowyer, now Professor of the Graduate School at UC Berkeley, some objected that dust and gas around the sun would prevent the satellite from seeing more than a couple dozen sources of extreme ultraviolet radiation. Bowyer's persistence proved the critics wrong. EUVE was able to see thousands of hot stars and more than three dozen sources outside our galaxy.
"Years ago, a lot of our colleagues thought we were crazy to observe in the EUV," Bowyer, said in 1992. "Everyone 'knew' that trying to look through the interstellar medium at these wavelengths would be like trying to use a telescope in a San Francisco fog."
Instead, EUVE demonstrated that the nature and density of the interstellar medium are different from what most expected. Patches of the ISM are ionized - electrons have been removed from atoms, mostly hydrogen - rendering it transparent to extreme ultraviolet light. The transparent areas riddle the interstellar medium like holes in Swiss cheese, and in some directions even remote EUV objects outside the galaxy can be seen.
In 2000, Bowyer was awarded the Massey Medal by the Committee on Space Research (COSPAR) for his "outstanding contributions to the development of space research, interpreted in the widest sense, in which a leadership role is of particular importance."
Its scientific life over, EUVE gradually descended from orbit because of drag from the Earth's atmosphere. It will start to break up when it falls to within 50 miles of the Earth, at which point EUVE will have only four or five 90-minute orbits left before re-entering the Earth's atmosphere, NASA Goddard engineers said yesterday. Engineers will not know the re-entry point until approximately 12 hours prior to impact.
Unlike the Compton Gamma Ray Observatory, which was safely de-orbited June 4, 2000, EUVE does not have an on-board propulsion system to allow engineers to control its re-entry. Much of EUVE will burn up in the atmosphere before ever reaching the ground. However, estimates show that up to nine objects, ranging from approximately four to 100 pounds, may survive re-entry. Much of this debris is made of titanium and stainless steel.
EUVE is in a 28.5-degree orbit and could re-enter in any location within this orbit range. This range includes areas as far north as Orlando, Fla., and as far south as Brisbane, Australia.
Observations similar to those of EUVE continue from the Chandra X-ray observatory and in an upcoming satellite, the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) mission, being built now by scientists at UC Berkeley's Space Sciences Laboratory.