Explorer 20

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Explorer 20
Explorer-20 IE-A.jpg
Explorer 20.
Mission typeEarth science
COSPAR ID1964-051A
SATCAT no.870
Spacecraft properties
ManufacturerLangley Research Center
Launch mass44.5 kilograms (98 lb)
Start of mission
Launch dateAugust 25, 1964, 13:43 (1964-08-25UTC13:43Z) UTC
RocketScout X-4
Launch siteVandenberg SLC-5[1][2]
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Semi-major axis7,304 kilometers (4,538 mi)
Perigee altitude864 kilometers (537 mi)
Apogee altitude1,025 kilometers (637 mi)
Period104 minutes
Epoch25 August 1964

Explorer 20, also known Ionosphere Explorer IE-A, Ionosphere 2, Science S-48, Topside-sounder TOPSI and Beacon Explorer BE-A, was an American satellite launched as part of Explorers program.

Explorer 20 was designed to measure electron distribution, ion density, and temperature, and to estimate cosmic noise levels between 2 MHz and 7 MHz. The satellite was a small ionospheric observatory instrumented with a six-frequency ionospheric sounder and an ion probe. A cosmic noise experiment used the noise signal from the sounder receivers. The satellite consisted of a short cylinder terminated on either end by truncated cones. The ion probe, mounted on a short boom, extended from the upper cone. The six sounding antennas (three dipoles) extended from the satellite equator. One pair of 18.28 m (60.0 ft) antennas formed the dipole used for the low frequencies, and the other two dipoles consisted of four 9.14 m (30.0 ft) antennas. The satellite was spin stabilized at 1.53 rpm just after antenna extension, with the spin axis initially very close to the orbit plane.

At the end of one year, the spin had slowed to 0.45 rpm. Since there was no tape recorder, data were received only in the vicinity of telemetry stations. Telemetry stations were located to provide primary data coverage near 80° W plus areas near Hawaii (U.S.), Singapore, United Kingdom, Australia, and Africa. Data were recorded for periods of 1/2 hour to over 4 hours per day depending upon available power. Even though there were problems with telemetry and interference, the experiments operated satisfactorily for about 16 months. A large spacecraft plasma sheath prevented the ion probe data from being useful in spite of attempts to compensate. For this spacecraft, the one-year automatic satellite turnoff was disconnected just prior to launch. The satellite responses to command signals were not dependable after December 20, 1965, and the satellite transmitter, which was often spuriously turned on, did not respond to a turnoff command.[3]



  1. ^ "IE". Encyclopedia Astronautica. Mark Wade. Retrieved June 9, 2018.
  2. ^ "Letter dated 12 October 1964 from the Permanent Representative of the United States of America addressed to the Secretary-General". COMMITTEE ON THE PEACEFUL USES OF OUTER SPACE. Retrieved June 9, 2018.
  3. ^ "IE-A". NSSDC Master Catalog. Retrieved 9 June 2018. This article incorporates text from this source, which is in the public domain.