Incoherent scatter measurements of exhaust injections into the ionosphere during space shuttle flight sts-86 and sts-93

When the Space Shuttle Orbiting Maneuver Subsystem (OMS) engines burn in the ionosphere, two types of processes are produced. First, charge exchange between the exhaust molecules and the ambient Onions yields molecular ions beams that excite plasma turbulence. Second, the ions eventually recombine with electrons to yield a plasma hole. The ion-beam interactions and the evolution of artificial plasma holes in the ionosphere have be studied with ground based, incoherent-scatter radars (ISR's) during the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) series of experiments. The SIMPLEX I experiment occurred over Jicamarca, Peru in the afternoon on 4 October 1997 during the Shuttle Mission STS-86. An electron density depression was produced at 359-km altitude on the mid-point of a magnetic field line. The filling-in of the artificial hole occurred much more rapidly than can be explained with current ionospheric models. Another experiment took place in late July 1999 during the STS-93 flight of the Space Shuttle Columbia. This SIMPLEX II experiment used controlled ion injections over the incoherent scatter radar (ISR) facilities located at Arecibo, Puerto Rico to excite unusual radar signatures. After charge exchange between the exhaust and the ambient plasma, pick-up ions were produced with energies of about 10 eV with a retrograde orientation of the OMS engines relative to the vehicle orbit. These ions were unstable and quickly generated plasma waves that changed their distribution. The rapid of the ion beam distribution with recorded in the radar spectra. On these missions, the first radar observations ionospheric recovery from a localized disturbance near the equator were recorded and the first ISR spectra were measured by reflection from electrons in the presence of the high-speed ions. These observations open up the possibility of conducting a new series of experiments for (1) validation of ionospheric space weather models and (2) studying ionbeam instabilities occur naturally at high latitudes.