Horizon Science Experiment for Mars Global Surveyor

T.Z. Martin (JPL/Caltech)

The Mars Horizon Sensor Assembly on the MGS orbiter monitors the orientation of the spacecraft relative to the limb by sensing atmospheric emission in the 15 tex2html_wrap_inline12 m CO tex2html_wrap_inline14 band. These data are used to maintain nadir pointing for the remote sensing instrument suite. The set of 5.5 tex2html_wrap_inline16 tall triangular fields of view normally straddle the limb, and cover quadrants 90 tex2html_wrap_inline16 apart around the limb.

As an engineering device, the MHSA benefits from Mars' atmosphere being spatially bland at 15 tex2html_wrap_inline12 m. However, these data will carry information about the thermal state of the atmosphere, which is subject to diurnal, seasonal, latitudinal, and dust-storm related variations, as well as possible wave effects. The Mariner 7 IRS, Mariner 9 IRIS, and Viking IRTM all demonstrated such variability.

The Horizon Science Experiment (HORSE) is intended to glean new insight into atmospheric variation from the MGS horizon sensors, with continuous data flow to the Earth in the engineering stream, and a rapid buildup of spatial coverage. MHSA data will also be used to monitor atmospheric thermal behavior during the aerobraking of MGS in late 1997.