Project Title:

Rarefied Gas Aerodynamic Bridging Procedures

02.07-8581
Rarefied Gas Aerodynamic Bridging Procedures
Remtech, Inc.
3304 Westmill Drive
Huntsville, AL 35805
E. C. Knox  (205-536-8581)
MSFC -- NAS8-37635

Abstract:

	 Shuttle flight data have shown that the "bridging" relations used to predict the
Shuttle reentry aerodynamics in the rarefied-gas portion of its trajectory were inadequate
in that twice the predicted body-flap deflection was required to trim the vehicle.
Fortunately, there was sufficient margin built into the Shuttle; however, providing
such margins on future vehicle designs may render them not viable. For example, the
next generation of spaceflight vehicles, such as the Aero-Assisted Flight Experiment
(AFE) currently being designed, will require more precise predictions of the vehicle
aerodynamics in the transitional flow regime in order to reduce the allowance for
propellants in favor of increased payload. 
	In Phase I the bridging techniques and formulas used to connect the continuum with
the free-molecular flow regime in predicting the aerodynamic characteristics of vehicles
designed to fly in the rarefied gas regime were revisited. Results from the Phase
I study show that some improvements can be made in the bridging techniques, but that
further work is needed to account for real-gas effects and molecular-surface interactions.
Failure to account for the molecular-surface interactions can cause the drag on a
typical vehicle operating in this regime to be in error by as much as 25 percent.

Potential Commercial Application:

Potential Commercial Application: Applications would be for spacecraft operating
between the continuum region near the earth and the free-molecular regime of space.