2009

Alternative Determination of Density of the Titan Atmosphere

An alternative has been developed to direct measurement for determining the density of the atmosphere of the Saturn moon Titan as a function of altitude. The basic idea is to deduce the density versus altitude from telemetric data indicative of the effects of aerodynamic torques on the attitude of the Cassini Saturn orbiter spacecraft as it flies past Titan at various altitudes. The Cassini onboard attitudecontrol software includes a component that can estimate three external per-axis torques exerted on the spacecraft. These estimates are available via telemetry.

The atmospheric torque vector is the product of (1) a drag coefficient (which is known from ground-based experiment and analysis), (2) the Titan atmospheric density that one seeks to determine, (3) the square of the Titan-relative spacecraft speed (which is known from navigation monitoring), and (4) the projected area of the spacecraft and the offset distance between the center of pressure and center of mass, both of which are known functions of the attitude of the spacecraft relative to the known velocity through the atmosphere. Hence, the atmospheric density is the only unknown and can be determined from the other quantities, which are known.

This work was done by Allan Lee, Jay Brown, Antonette Feldman, Scott Peer, and Eric Wang of Caltech for NASA’s Jet Propulsion Laboratory.

For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. NPO-44606

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