ATLAS 3 Public Affairs Status Report #19 6:00 p.m. CST, Nov. 12, 1994 MET 9/7:00 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. Two unique atmospheric instruments concluded almost eight days of very successful operations, as STS-66 Payload Commander Ellen Ochoa retrieved the German Space Agency's reusable CRISTA-SPAS satellite this morning. Its two instruments -- the German Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA), from the University of Wuppertal, and the Middle Atmospheric High Resolution Spectrograph Investigation (MAHRSI), from the U.S. Naval Research Laboratory in Washington, D.C. -- were designed to measure concentrations and distribution of trace gases in Earth's atmosphere on a global scale. Dr. Dirk Offermann, principal investigator for the CRISTA experiment, reported that his instrument performed almost flawlessly as it gathered unprecedented three-dimensional profiles of the atmosphere. About 100 gigabits of data from 180 hours of CRISTA observing time are stored on magnetic tapes onboard the satellite. "The measurement speed of CRISTA is so high, that conventional satellites would deliver this data set in about half a year," said German Space Agency representative Dr. Wolfgang Frings. CRISTA will be the first instrument to provide such detailed information on the "weather" in the upper atmosphere -- the dynamics of winds, temperature changes and movements which distribute the gases that influence ozone chemistry. According to Offermann, the CRISTA investigation is not finished yet. A campaign of balloon and rocket experiments will continue for about two weeks, providing additional comparisons on the dynamic atmosphere. Post-flight calibrations at Kennedy Space Center will check on the accuracy and precision of CRISTA measurements. "This is an important capability only offered by the Space Shuttle, because it brings instruments back to Earth," Offermann said. "Like CRISTA, we have had a most amazing week," said MAHRSI Principal Investigator Dr. Robert Conway. The instrument accomplished what he termed the "difficult and rather delicate" task of collecting high-resolution, global maps of hydroxyl in the middle atmosphere. It also did almost 30 hours of nitric oxide mapping, much of it in cooperation with the Shuttle Solar Ultraviolet Backscatter (SSBUV) experiment. Both gases are active catalysts in ozone destruction. Conway compared some early MAHRSI hydroxyl measurements with water vapor data from the Millimeter Wave Atmospheric Sounder (MAS), collected during the mission's first atmospheric research period. "Water vapor is a parent molecule of hydroxyl, because the production of hydroxyl depends on the abundance of water vapor," explained Conway. "By combining the MAS water vapor maps with MAHRSI's maps of hydroxyl abundances, we have two parts of the puzzle for understanding the photochemistry of ozone." The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment has completed atmospheric observations for ATLAS 3, after having accumulated the equivalent of 110,000 floppy disks of data -- more than from all three of its previous flights combined. Today ATMOS viewed the sun directly, rather than using it to illuminate Earth's atmosphere. The current angle of the Shuttle's orbit in relation to the sun would spread atmospheric observations over such a wide area that they would not be useful. "It would be like taking the temperature of Los Angeles and Mexico City at the same time," said ATMOS Assistant Project Manager Gregory Goodson. The unusual illumination conditions of the STS-66 orbit, which changed gradually over the course of the flight, were planned to accommodate the requirements of both ATMOS and CRISTA. Sensitive infrared measurements of the full sun provide an essential reference for ATMOS scientists because they must remove solar spectra from their atmospheric observations to properly interpret results. Solar scientists will get valuable information about the sun's chemistry and physics from the high-resolution infrared spectra as well. Spectacular Earth scenes broadcast from Shuttle cameras today supported the Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment's "reflectivity measurements." The video and SSBUV spectra will be compared to determine how various Earth surface features like clouds, oceans, deserts and mountains reflect sunlight back into the atmosphere. Variations in reflectivity affect SSBUV's measurements of the total ozone above the different surface features. "Today's studies give atmospheric scientists a tool for adjusting their ozone models," explained an SSBUV team member. France's Solar Spectrum (SOLSPEC) experiment is making more readings of solar radiation scattered back from Earth. Though its primary objective is measuring the spectral radiation of the sun, SOLSPEC's Earth views will be compared with its solar results to determine the amount of ozone in the atmosphere. The data also can be compared with that being made by SSBUV, whose primary assignment is to track ozone concentrations by comparing ultraviolet radiation backscattered from the Earth with solar ultraviolet radiation. The mission's final solar observation period will begin at about 1 a.m. Sunday. The four ATLAS 3 solar instruments will operate during daylight portions of five orbits, cool for one entire orbit, then take measurements for an additional four orbits.