VLF WAVE EXPERIMENTS IN-SPACE USING A MODULATED ELECTRON-BEAM

A sounding-rocket payload to study the generation and emission of elec tromagnetic waves from a modulated electron beam was developed and suc cessfully flown from the Poker Flat Research Range, Alaska, in March 1 992 on a Black Brant 11 sounding rocket, We describe the mission objec tives, the instrumentation, flight operations, and preliminary results from the flight, The payload contained a modulated electron gun with a triode arrangement of electrodes allowing modulation of the beam cur rent up to vlf frequencies, Vehicle charging was inhibited by a gas-re lease system, synchronized with the beam emissions, A network of groun d stations was set up to try to receive signals from the modulated bea m, and tow-light systems were set up to look for evidence of the beam below the payload trajectory, No evidence of beam-induced wave radiati on to the ground was detected, However, strong vlf frequencies followi ng the preset program were clearly detected by the diagnostic free fly er and the tethered daughter payload segment, The effect of the gas re leases was very marked, The vehicle potential dropped from over 1 kV t o about 30 V when the gas was turned on, Some evidence of the light fr om beam-atmosphere interactions was seen near the end of the Eight, bu t in general, the optical results were not very informative, The launc h was successful, mission operations were as planned, and good quality onboard data were collected throughout the operational part of the fl ight.