VLF Wave Experiments in Space Using a Modulated Electron Beam

A sounding-rocket payload to study the generation and emission of electromagnetic waves from a modulated electron beam was developed and successfully flown from the Poker Flat Research Range, Alaska, in March 1992 on a Black Brant 11 sounding rocket. We describe the mission objectives, 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 current up to vlf frequencies. Vehicle charging was inhibited by a gas-release system, synchronized with the beam emissions. A network of ground stations was set up to try to receive signals from the modulated beam, and low-light systems were set up to look for evidence of the beam below the payload trajectory. No evidence of beam-induced wave radiation to the ground was detected. However, strong vlf frequencies following the preset program were clearly detected by the diagnostic free flyer and the tethered daughter payload segment. The effect of the gas releases was very marked. The vehicle potential dropped from over 1 kV to about 30 V when the gas was turned on. Some evidence of the light from beam-atmosphere interactions was seen near the end of the flight, but in general, the optical results were not very informative. The launch was successful, mission operations were as planned, and good-quality onboard data were collected throughout the operational part of the flight.