Robert H. Tolson

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The structure of the upper atmosphere of Mars (above ∼100 km) has been probed in situ mainly using spacecraft accelerometers during the aerobraking phases of 3 Mars or-biters. In a similar manner, the Mars Atmosphere and Volatile Evolution (MAVEN) Ac-celerometer Experiment (ACC) will also use atmospheric drag accelerations sensed by iner-tial measurement(More)
The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above(More)
Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere,(More)
Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office is operated by Langley Research Center, the lead center for NASAÕs scientific and technical information.(More)
Radio tracking data from the Viking lander have been used to determine the lander position and the orientation of the spin axis of Mars. The areocentric coordinates of the lander are 22.27 degrees N, 48.00 degrees W, and 3389.5 kilometers from the center of mass; the spin axis orientation, referred to Earth's mean equator and equinox of 1950.0, is 317.35(More)
During the last 2 weeks of February 1977, an intensive scientific investigation of the martian satellite Phobos was conducted by the Viking Orbiter-1 (VO-1) spacecraft. More than 125 television pictures were obtained during this period and infrared observations were made. About 80 percent of the illuminated hemisphere was imaged at a resolution of about 30(More)
With the recent Mars Odyssey 2001 Accelerometer Experiment measurements of the upper atmosphere, insitu measurements have finally been extended from pole to pole. The Mars Odyssey 2001 (M01) Spacecraft was placed into a near polar orbit about Mars in September 2001. Aerobraking was performed from then until January 2002 to circularize the M01 orbit. The(More)
Atmospheric drag measurements obtained from the study of the orbital decay of Pioneer Venus 1 indicate that atomic oxygen predominates in the Venus atmosphere above 160 kilometers. Drag measurements give evidence that conditions characteristic of a planetary thermosphere disappear near sundown, with inferred exospheric temperatures sharply dropping from(More)