Selected Articles from the
April 1999 Odyssey
Editor: Norm Cook
- Exotic Technologies Finish Road Test on Cosmic Highway
- Astronomers Discover "Middleweight" Black Holes
Exotic Technologies Finish Road Test
on Cosmic Highway
NOTE: OASIS Secretary Bob Gounley is an engineer working on the Deep Space 1 project.
NASA's Deep Space 1 mission has successfully demonstrated most of its exotic technologies in space--including an ion engine that is expected to be ten times more efficient than conventional liquid or solid rocket engines--proving they are ready for use in science missions of the 21st century.
Of the 12 advanced technologies onboard the spacecraft, seven have completed testing, including the ion propulsion system, solar array, and new technologies in communications, microelectronics, and spacecraft structures.
"We've taken these technologies around the test track, and now they're ready for the production line," said Dr. Marc Rayman, deputy mission manager and chief mission engineer for Deep Space 1 at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
Launched October 24, Deep Space 1 is the first mission under NASA's New Millennium Program, which features flight testing of new technology, rather than science, as its main focus. These new technologies will make spacecraft of the future smaller, cheaper, more reliable, and more independent of human control.
By summer, engineers expect to have finished testing all 12 advanced technologies aboard the spacecraft.
Testing of two technologies that make the Deep Space 1 less reliant on humans is 75 percent complete, while testing of a third is scheduled to begin in May. These technologies include a robotic navigator, called AutoNav, that will guide the spacecraft to a rendezvous with asteroid 1992 KD on July 29 without active human control from the Earth.
In addition, Deep Space 1's two advanced science instruments--a combination camera/spectrometer and an instrument that studies electrically charged particles emitted by the Sun and other sources-- are on schedule, having finished 75 percent of their tests.
"What has pleased us more than anything is how well the technologies have been working in general," Rayman said, noting that their performance is remarkably close to engineers' estimates developed before launch.
"Of course, everything hasn't worked perfectly on the first try," Rayman added. "If it had, it would mean that we had not been sufficiently aggressive in selecting the technologies. Diagnosing the behavior of the various technologies is a fundamental part of Deep Space 1's objective of enabling future space science missions."
When the ion propulsion system was first activated November 10, the engine shut itself off after 4-1/2 minutes, and engineers were unable to restart it later that day. During the next attempt two weeks later, however, the engine started up easily and has performed flawlessly since then, logging more than 1,300 hours of operation.
Engineers believe the problem was caused by a piece of grit stuck to high-voltage grids within the ion engine. The grit was later dislodged, they believe, when parts expanded and contracted as the ion engine was exposed alternately to sunlight and shade.
Engineers also discovered after launch that stray light enters the camera/spectrometer, resulting in streaks of light when pictures are taken with a long exposure. The streaks are a result of how the instrument was mounted on the spacecraft, Rayman said.
The camera should be able to take acceptable pictures when Deep Space 1 flies by asteroid 1992 KD this summer, because it will use short exposures.
Despite such glitches, the great majority of the advanced technologies have worked extremely well, according to Rayman. "Mission designers and scientists can now confidently use them on future missions," he said.
Deep Space 1 will continue testing technologies until its prime mission concludes on September 18. NASA is considering a possible extended mission that would take the spacecraft on flybys of two comets in 2001.
The Deep Space 1 mission is managed for NASA's Office of Space Science, Washington, DC, by JPL, a division of the California Institute of Technology, Pasadena, CA. Spectrum Astro Inc., Gilbert, AZ, was JPL's primary industrial partner in spacecraft development.
Astronomers Discover "Middleweight"
Black Holes
The field of black holes, formerly dominated by heavyweights packing the gravitational punch of a billion Suns and lightweights just a few times heavier than our Sun, now has a new contender--a just-discovered mysterious class of "middleweight" black holes.
Astronomers at NASA and Carnegie Mellon University have independently found evidence for the new type of black holes in spiral-shaped galaxies throughout the Universe. The newfound black holes, formed by an unknown process, are 100 to 10,000 times as massive as the Sun, yet each occupies less space than the Moon.
Until now, scientists knew about two types of black holes: stellar and supermassive. Stellar black holes are the remains of dead stars several times heavier than the Sun, compressed to a diameter of a few miles or less. Supermassive black holes have mind-boggling masses of one million to one billion Suns and may have formed in the early universe from giant gas clouds or from the collapse of clusters of immense numbers of stars.
The astronomers identified the new class of black holes through X-ray light, the final cries of energy emitted from gas and particles spiraling into a black hole.
Dr. Edward Colbert and Dr. Richard Mushotzky, astronomers at NASA's Goddard Space Flight Center, Greenbelt, MD, first saw hints of the new class of black holes while studying X-rays from 39 relatively nearby galaxies. Dr. Andrew Ptak and Dr. Richard Griffiths at Carnegie Mellon University studied X-ray light from a galaxy not included in Colbert and Mushotzky's set, galaxy M82. Both teams found unique X- ray light indicative of a new black hole class.
"Our intent was to understand what was producing an unusual class of X-ray luminosities near the centers of many galaxies," said Colbert. "With data from the 1970s, we couldn't determine whether they had features associated with supermassive black holes or stellar black holes. So we took a fresh look with newer data."
Colbert and Mushotzky found telltale clues for a new type of black hole in the spectrum of the X-ray light. Such colors are judged by comparing the intensity of X-rays with shorter wavelengths to those with longer wavelengths.
Supermassive black holes are thought to power a phenomenon called Active Galactic Nuclei, which are extremely compact and energetic objects seen in the core of one percent of all galaxies and are typically very bright X-ray sources. The luminosities that Colbert and Mushotzky analyzed have colors different from those found in Active Galactic Nuclei, suggesting the source is something other than a typical supermassive black hole.
Ptak and Griffiths acted on the belief among astronomers that black holes of various sizes must exist and likely reside in "irregular" galaxies (galaxies not spiral or elliptical in shape). M82 is one such galaxy, called a starburst galaxy because of the high rate of star formation found inside. Such a scenario leads to a higher rate of supernovae, or star explosions, the precursor of stellar black holes.
"Millions of black holes and neutron stars have formed in M82 over the last 10 million years," Ptak said. "Now, we are noticing that some of these may be coalescing into a larger-mass black hole." Ptak said this is the most viable current theory for intermediate black hole formation. Colbert also said the intermediate class suggested by his and Mushotzky's observations might be formed by "the continual merging of stellar black holes." In other words, stellar black holes that approach each other too closely under certain circumstances can merge to form a more massive single black hole.
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