25 Years of ionospheric modification with Space Shuttle OMS burns

The Space Shuttle Orbital Maneuver Subsystem (OMS) is the largest engine to be fired in the F-region ionosphere. The OMS thruster provides 10 kg/s of exhaust materials exiting at a speed of 3 km/s. The OMS nozzle can be pointed in the ram, wake or out-of-plane relative to the Space Shuttle orbit. The vector addition of the exhaust velocity and the orbit velocity provides possible injections speeds of between 4.7 and 10.7 km/s. When the exhaust impacts the ionosphere, neutral-ion collisions and ion-molecule charge exchange yields ions moving at hyper-acoustic speeds. A ten second burn of two OMS engines deposits over 1 Giga-Joule of energy into the upper atmosphere. The ionosphere reacts to an OMS burn by exciting a large number of plasma wave modes including the whistler, fast and slow MHD, Alfven, ion acoustic, lower hybrid, and ion Bernstein waves. These waves have been detected by both radar scatter and in situ electric field plasma probes. Field aligned irregularities are produced by the exhaust interactions. The exhaust pickup ions eventually thermalize with the background atmosphere and they recombine with ambient electrons leaving an electron hole. All these phenomena were obtained first in July 1985 during STS-51F and were detected for the next 25 years through STS-129 with 18 flights of the Space Shuttle. These experiments have demonstrated the (1) Space Shuttle OMS burns can change the HF radio propagation characteristics of the F-layer, (2) artificial ionospheric holes may be used to trigger plasma instabilities that scatter radar and possibly affect GPS propagation, (3) space based electric field sensors can detect OMS burns in the ionosphere for ranges over 400 km, and (4) optical emissions are produced as the pickup ions recombine with F-region electrons. This type of ionospheric modification has been studied with computer models that employ direct simulation Monte Carlo (DSMC) techniques for the neutral exhaust expansion, plasma fluid theory for the p- - lasma density effects and kinetic theory with Maxwell´s equations for the plasma wave generation.