Description of the ISEE satellite-to-satellite kilometric wavelength interferometer system

The International Sun-Earth Explorer (ISEE) spacecraft 1 and 2 carry receivers for detecting electromagnetic waves with kilometric wavelengths. For selected receiver frequencies from 30 kHz to 2 MHz, a 10-kHz bandwidth channel is single-sideband mixed down to baseband. These analog data and a reference frequency, which is a submultiple of the local oscillator frequency, are transmitted to ground stations and tape recorded along with the precise time and frequency information. Cross correlation of these tape recorded signals constitutes a satellite-to-satellite interferometer with a fringe spacing of 0.4 to 41 arcmin (at a range of 10,000 to 100 km spacing between spacecraft for 250 kHz in frequency) and with a time-delay resolution of 32 microsec for a 10-kHz bandwidth, which gives an angular resolution of 3 min to 6 deg of arc. For kilometric radiation at earth, sources in the size range of 25 to 2500 km can be identified (from 20 earth radii) and located in relative position ranging from 0.02 to 2 earth radii, depending on spacecraft spacing. Reception and analysis of solar and Jovian bursts may also be possible.