Prolonging a failing science satellite
By JAMES OBERG, UPI Science News
HOUSTON, Jan. 27 (UPI) -- It often takes a close brush with death to make human beings appreciate life.
The same process, it seems, also works with space satellites and with the mysterious phenomena they are used to study.
After nine years in space, NASA's Compton Gamma Ray Observatory has exceeded its design lifetime and vastly exceeded the hopes of space scientists. It has contributed immensely to the knowledge of one of the most baffling -- and potentially most dangerous -- phenomena, gamma ray bursts.
Gamma ray bursts are avalanches of high-energy radiation which suddenly appear and then die out all over the sky. First detected by accident by military satellites scanning for nuclear weapons, the origin of gamma ray bursts remained a mystery until CGRO results showed the bursts came from distant galaxies.
This meant they are the most energetic explosions discovered. Astrophysicists still speculate on what causes them, although the two leading theories involve colliding neutron stars, or collapsing super-heavy stars which create "hypernovas," or "collapsars."
A recent breakdown in one of the CGRO's steering gyroscopes has raised concerns that the satellite might uncontrollably fall to earth. Since the 17-ton vehicle contains structural elements with a good chance of reaching the surface intact, the odds of human injury are perhaps one in a thousand, the highest for any satellite ever launched.
NASA had planned to steer the satellite into a controlled safe splashdown in the Pacific Ocean, But since additional equipment failures might make the satellite unable to steer accurately, NASA engineers are working to develop alternative steering techniques. Otherwise, safety considerations require that the CGRO be terminated in mid-March.
Scientists involved with the project have responded by celebrating the satellite's accomplishments and by describing the value of prolonged operations. If NASA can find a way to do this safely, CGRO may have many months, even years, of productive work ahead of it.
Neil Gehrels, project scientist for CGRO, described for UPI the kinds of additional work the spacecraft still could do. Although CGRO has mapped the entire sky in several radiation bands, there is additional work to be done. "We are working to fill in the less exposed areas over the next three years or so," Gehrels told UPI.
CGRO is also mapping the distribution of antimatter and of newly formed elements spewed out of supernovas.
The spacecraft also waits for unpredictable events that promise insights when measured by its instruments. One of the most spectacular is called "a Type I supernova." Statistically, one bright enough for CGRO observation occurs about every 10 years. "We have our fingers crossed each year for a new one," Gehrels said.
In addition, CGRO measures gamma rays from solar flares, another surprising discovery. The Sun will reach a sunspot and flare maximum in 2001. In the next year or two, Gehrels said, "we hope to study large flares and a whole group of smaller flares."
NASA scientist Gerald Fishman is in charge of CGRO's main gamma ray burst detector, one of four instruments on the satellite. In an interview with UPI, he stressed how the spacecraft still provides unique capabilities.
For example, unlike follow-on satellites with narrowly focused views, the CGRO continuously scans the sky. Fishman said, "The all-sky monitoring capability is not replaceable by anything even on the drawing boards."
Unfortunately for its reputation among the public, CGRO doesn't send back pretty pictures like the Hubble Space Telescope. Fishman is often asked for pictures. "I wish we could," he said. "They make a big impact."
Other scientists associated with the project told UPI privately that this lack of public-relations "gee whiz" images dampens the enthusiasm of NASA managers in Washington. Yet according to Fishman, a recent survey of science news stories showed that the spacecraft's value was not entirely unsung. "CGRO came out on top," he said, "above Hubble and the planetary missions."
To encourage scientific progress in understanding gamma ray bursts, NASA annually sponsors a week-long symposium on the latest results and theories. Some 200 astronomers attended the latest symposium last October at the Marshall Space Center in Huntsville, Ala.
The conferees were mostly agreed that the bursts represented the destruction of massive objects. "We're interested in dead and dying things," Dale Frail of the National Radio Astronomy Observatory in Socorro, N.M., told a reporter. "Our highest ambition is to know who that dying thing is."
Frail is a radio astronomer, watching the end of the spectrum where signals are heard when the "corpse is cold and still," as one member of the audience worded it. Frail joked that at the other end of the spectrum, where CGRO makes its observations, astronomers are "interested in hearing the death rattle."
More than just inanimate astronomical bodies may be dying in each burst, however. In a recent issue of the "Journal of the British Interplanetary Society", Paul Annis of the Fermi National Accelerator Laboratory in Illinois speculated that such bursts explain why it appears that intelligent life has not already spread throughout our galaxy.
"If one assumes that they are in fact lethal to land based life throughout the galaxy," he argues, "one has a mechanism that prevents the rise of intelligence until the mean time between bursts is comparable to the timescale for the evolution of intelligence."
Annis calculated that in our own galaxy such bursts, which billions of years ago occurred every few million years, now occur at least 200 million years apart. And that figure is about the same as the duration required for the rise of land-based intelligence on Earth.
"It is likely that intelligent life has recently sprouted many places in the Galaxy," he concludes, "and that at least a few are busily engaged in spreading." They would also have reached a technology level that would allow most of them to survive any new gamma ray bursts.
This haunting interpretation suggests that the hundreds of GRBs being observed every year by CGRO do not just mark the deaths of neutron stars and collapsars. Each may represent ecological catastrophes on a galactic scale, as hundreds or even thousands of life-bearing planets in a particular galaxy are sterilized.