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Science News, Jan 14, 1995 by Ron Cowen

From a visit to Jupiter to studies of distant quasars, 18 launches highlight the new year in space science. Although NASA craft dominate the lineup, the European Space Agency (ESA) has several key launches, including one of its most costly space probes to date, the Infrared Space Observatory. Japanese, Argentine, and Russian craft also figure in the array of launches.

In part because of holdovers originally slated for launch last year, many of the 1995 missions are devoted to studies of the sun and its interaction with Earth.

"1995 is the big year for space physics," says Louis J. Demas, chief of the flight programs branch of NASA's space division in Washington, D.C. "All the elements of the International Solar-Terrestrial Physics program should be up and operating." The program is a cooperative effort to study the sun's effect on Earth.

Mechanical and operational delays may alter flight schedules, but the following calendar provides the space agencies' best estimates for the year ahead.

February

* Kicking off the 1995 schedule, the space shuttle deploys the Far Ultraviolet Imaging Spectrograph in early February. For 40 hours, this free-flying instrument will study diffuse sources of ultraviolet (UV) radiation, including the sky background, emissions from nearby galaxies, and clouds of dust and gas. The shuttle will retrieve and return the spectrograph to Earth.

* The month also includes the launch of a suite of devices designed to study infrared emissions from our galaxy. The Infrared Telescope in Space (IRTS), a Japanese-U.S. mission, carries four instruments.

Two spectrometers will record the intensity of particular wavelengths of infrared light radiated by sources in the Milky Way, while a photometer will record the overall infrared brightness of objects in our galaxy. Together, these devices and one other detector will study cool stars and map the location of gas clouds.

Mounted on an orbiting platform known as the Space Flyer, the IRTS will soar aloft on an expendable Japanese rocket and gather data for about a month. The shuttle will retrieve the satellite in the summer.

* In late February, a trio of UV detectors first flown in December 1990 will orbit Earth for 2 weeks. Collectively known as Astro 2, these instruments will take the spectra of astronomical objects and study the polarization of their light -- all at far-ultraviolet wavelengths. Because such radiation can't penetrate Earth's atmosphere, ground-based telescopes can't detect it.

Flown in the shuttle's payload bay, Astro 2 will generally study fainter targets during the night portion of its orbit, when Earth lies between the shuttle and the sun, and brighter targets during the day. Astronomers on board the shuttle will point the telescopes and oversee observations, the last NASA mission to feature such hands-on studies in this century.

March

* NASA launches the third in its series of probes to measure global concentrations of ozone, the fragile blanket of gas that shields life on Earth from the most harmful type of solar UV radiation. Known as the Total Ozone Mapping Spectrometer (TOMS), this instrument gauges ozone concentrations indirectly, by comparing the amount of solar UV energy striking our planet to the amount scattered back into space by Earth's atmosphere. The greater the amount of scattered UV light, the lower the concentration of ozone. TOMS will operate for at least 2 years.

April

* Two Earth-orbiting missions hitch a ride on a U.S. Pegasus rocket. The Satelite de Aplicaciones Cientificas-B (SAC-B), the first flight of an Argentine craft, carries five scientific instruments. This 3-year mission includes three spectrometers, two of them studying high- and low-energy X rays from solar flares. SAC-B also includes a telescope to record the diffuse X-ray background over a major portion of the sky and an instrument to search for the mysterious flashes of energetic radiation known as gamma-ray bursts.

These cosmic flashbulbs rank "as the most important mystery in astrophysics today," says Daniel W. Weedman, director of NASA's astrophysics division. The bursts radiate as much energy as 1 billion suns in a few seconds and then disappear without a trace. Of unknown origin, these bursts rarely, if ever, repeat and have no proven counterpart at lower energies (SN: 12/17/94, p.404).

* To study these fleeting flashes more closely, a satellite known as the High Energy Transient Experiment (HETE) shares the Pegasus launch with SAC-B. HETE carries Japanese, French, and U.S. instruments on its 3-year mission. They include a spectrometer to measure gamma-ray bursts in the energy range between 6,000 and 1 million electronvolts. Another detector will study the lower-energy, X-ray component of the flashes.

One of the most puzzling aspects of the bursts is that no one has ever seen a confirmed UV or visible-light counterpart. In the hope of observing one, HETE includes four UV cameras set to scan the sky whenever a gamma-ray burst appears.

These instruments will help pinpoint the location of gamma-ray bursts with a precision that far exceeds the capabilities of NASA's Compton Gamma Ray Observatory, which has studied the energetic flashes since 1990. "HETE is one of the big hopes for actually localizing and identifying the gamma-ray bursts," Weedman says.