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Space sciences '91: NASA looks for a brighter new year.

Space Sciences '91

NASA hopes for better luck in 1991 than last year as it plots a series of diverse scientific feats, ranging from the first close look at an asteroid to mapping extraterrestrial sources of the most energetic radiation in the electromagnetic spectrum.

Besides the Hubble Space Telescope's flawed mirror, NASA found itself contending in 1990 with communications problems on the Venus-orbiting Magellan radar mapper, multiple woes with the shuttle-borne, multi-telescope package called Astro, and hydrogen leaks that grounded the shuttle fleet for five months.

Looking ahead, the agency's latest flight schedule for 1991 takes a more cautious approach to specific mission launch dates than did past manifests. Previously, NASA listed an exact date for each upcoming liftoff. The new schedules, released Dec. 5, specify launchings only by the month -- "a reasonable expectation as to when the launch will occur," according to one of the manifest's notes.

"This manifest, we think, more accurately reflects the realities of flying space shuttles," says Brian D. Welch of NASA's Johnson Space Center in Houston. Acknowledging the range of potentially unforeseeable complications, he says, "You just can't always make a launch by a specific date."

With that as a given, the calendar calls for a rich assortment of projects in the new year:

* NASA expects its first 1991 science mission to begin in April, when the shuttle Atlantis lifts a satellite called the Gamma Ray Observatory (GRO) into a 450-kilometer-high Earth orbit. Although gamma rays constitute the highest-energy radiation in the electromagnetic spectrum. Earth's atmosphere blocks them from reaching observers on the planet's surface.

As astronomers seek evidence of black holes and neutron stars, GRO's tour instruments will measure gamma-ray emissions from the Milky Way and beyond over a range of 50,000 to 30 billion electron-volts.

Though the craft is designed to last at least two years, NASA says it might extend GRO's lease on life another eight years by using an on-board propulsion system to occasionally raise its altitude.

* The calendar's next space milestone has a particular date -- May 16 -- but this does not mark a launching. On that day, Magellan should begin radar-mapping the surface of Venus for a second time. A primary objective of this second mapping is to determine the heights of surface features. By imaging the features at a different angle this time, scientists will be able to construct three-dimensional pictures for topographical mapping.

This recharting exercise should also fill in two data gaps, says spacecraft systems engineer John P. Slonski at NASA's Jet Propulsion Laboratory in Pasadena, Calif. The first gap occurred when signal losses from Magellan forced engineers to delay the initiation of the first mapping from late last August to Sept. 15. The sun's blocking of the craft's data transmissions to Earth last October caused the second gap.

* Also in May, the shuttle Columbia will orbit Earth for eight days with Spacelab -- a European-built, multipurpose science workshop -- in its cargo bay. This mission, Spacelab's fourth outing, will focus on life sciences research. For example, as part of NASA's continuing effort to assess potential ill effects of long-term stays in space, the four physicians included in Spacelab's seven-person crew will test one another's physiological responses to the near-weightlessness experienced in space -- including effects on balance, the lungs and the cardiovascular system.

* In July NASA's schedule calls for astronauts aboard Discovery to deploy another of the Tracking and Data Relay Satellites. NASA uses these satellites to link communications between ground stations and most of its Earth-orbiting satellites.

* The Extreme Ultraviolet Explorer satellite (EUVE) will get an August launch from an unmanned Delta rocket. This 2-1/2-year mission aims to make the first sky survey of spectral emissions between ultraviolet light and X-rays. These wavelengths are particularly useful for studying stars that have matured into compact, ultrahot "white dwarfs."

EUVE will carry four telescopes to chart about 95 percent of the sky to an accuracy of 0.1 degree. It will also conduct follow-up observations of particularly interesting extreme-ultraviolet sources andand measure the opacity of the interstellar medium.

Engineers designed this satellite so that when its original mission ends, shuttle astronauts can replace its scientific instruments with another batch. This in-orbit substitution will transform EUVE into the X-ray Timing Explorer, a probe to measure fluctuations in the brightness and spectrum of bright X-ray sources for studies of neutron stars and black holes.

* On Oct. 29, the Galileo spacecraft will become the first satellite to closely examine an asteroid. Since its launch on Oct. 18, 1988, Galileo has sped through an intricate route of speed-increasing gravity maneuvers that have already whipped the craft around Venus and Earth. The probe's ultimate goal is to orbit Jupiter in 1995.

On its way, Galileo will pass "minor planet" Gaspra. This rocky asteroid seems unlikely to prove a star of the mission, since the limited spectral measurements available from Earth suggest it is just a chunk of stone some 15 km across. Galileo should whip by Gaspra at a relative top speed of more than 28,800 km per hour, taking pictures and spectral measurements as it passes within 1,600 km of the asteroid's surface.

The spacecraft will continue along a circular route carrying it past Earth again on Dec. 8, 1992. After this second, accelerating rendezvous with its home planet, Galileo will finally head for Jupiter, possibly passing a second asteroid named Ida along the way.

* The protective ozone layer in Earth's upper atmosphere -- imperiled by some chemicals including the chlorofluorocarbons -- will be the focus of the Upper Atmosphere Research Satellite (UARS), set for release from the shuttle Discovery in November. Expected to operate for three years, UARS will carry nine instruments to compile a planet-wide data base about the chemistry and motions of the upper atmosphere, the effects of the sun's radiation on the upper atmosphere, and changes in the amount and distribution of ozone and other atmospheric gases.

* In December, the shuttle Atlantis will carry the International Microgravity Laboratory aloft to study how the reduced gravity of space affects the properties of different materials and the workings of mechanical devices. NASA hopes the microgravity study will, like Columbia's biomedical mission in May, help write the textbooks for astronauts working on space station Freedom. The European Space Agency, France's National Center of Space Studies, the National Research Council of Canada, Japan's National Space Development Agency and the German Aerospace Research Establishment helped NASA develop the mission.

Scientists continue to await the detection -- which may or may not occur this year -- of the shock wave formed where the solar wind collides at supersonic speed with a similar flow of charged particles coming in from other stars. The only craft that might do the job are Voyagers 1 and 2 and Pioneers 10 and 11. Launched between 1972 and 1977, all four are now headed away from the sun toward an invisible zone called the hellopause -- a region that some scientists define as the true edge of the solar system.
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Title Annotation:includes month-by-month list of upcoming space missions
Author:Eberhart, Jonathan
Publication:Science News
Date:Jan 12, 1991
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