NADIR: Neutral Atmosphere Density

Interdisciplinary Research

A Multidisciplinary University Research Initiative (MURI)

Sponsored by the Air Force Office of Scientific Research

August 2007 - August 2012








The objective of NADIR is to significantly advance understanding of drag forces on satellites, including density, winds, and factors affecting the drag coefficient. We seek a level of understanding that will enable specification and prediction at the “next level” of performance.

The specific goals are to:

  • Understand the physical processes driving the variability of neutral atmospheric density

  • Determine the relationship between neutral density structure and satellite drag

  • Improve forecasts of the drivers of the system including wave activity from the middle and lower atmosphere, geomagnetic/magnetospheric forcing, and solar EUV

  • Provide the information to improve empirical models of neutral density

  • Determine the most valuable dataset required to specify and forecast the system state

  • Improve estimates of drag in the re-entry regime (100-200 km)



NORAD has the responsibility for keeping track of objects that are in orbit around the Earth down to a certain critical size. Following major magnetic storm activity, the atmosphere heats and expands, exerting an increased drag on satellites, and changing their orbits. NORAD has to re-identify hundreds of objects and record their new orbits after a large magnetic storm event. This figure shows the number of satellites lost in connection with the March 13-14, 1989 storm. During this event, for example, the SMM (Solar Maximum Mission) spacecraft was reported to have "dropped as if it hit a brick wall" due to the increased atmospheric drag. (Image courtesy of Air Force Space Command)






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Last updated: 10/03/07.