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TOPO 1, the U.S. Army Topographic Command's first satellite, was launched from the Western Test Range (WTR) on April 8, 1970, piggyback with the Nimbus 4 meteorological satellite. Approximately 1 hr and 41 min after launch, the satellite was ejected from the final stage of the launch vehicle into a near-circular, near-polar orbit. The objectives of the spacecraft were (1) to study new techniques for accurate real-time determination of positions on the earth's surface involving a triangulation technique using satellite transponders and ground-based tracking facilities, (2) to test relay and one-way ranging techniques used by the Defense Navigation Satellite System, and (3) to obtain information about ionospheric effects on satellite geodetic surveys. The 18.14-kg satellite was shaped like a rectangular box (0.36 m by 0.30 m by 0.23 m). It was equipped with modified SECOR components including (1) a transponder that retransmitted the 136.84-MHz telemetry signals received from three ground stations whose locations were determined from satellite ranging measurements using phase comparison techniques and (2) a 590-KHz high-resolution ranging channel to obtain an ionospheric correction factor. Power was supplied by solar cells mounted on the satellite's exterior recharing onboard batteries. The telemetry transmissions were made by flexible metal tape antennas that were wound around the satellite's structure and deployed after orbital injection. The satellite obtained excellent data for a 6-month period (May 1970 to October 1970). Owing to a lack of funding, however, further tracking was discontinued and, as of January 14, 1972, the satellite was orbiting in an operational off mode.

Image from Corliss, 1967

Alternate Names

  • TOPO-A
  • 04363
  • TOPO1

Facts in Brief

Launch Date: 1970-04-08
Launch Vehicle: Thor-Agena
Launch Site: Cape Canaveral, United States
Mass: 21.8 kg

Funding Agencies

  • National Aeronautics and Space Administration (United States)
  • Department of Defense-Department of the Army (United States)


  • Navigation/Global Positioning
  • Engineering

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Mr. F. VarnumProject ManagerUS Army Topographical Command

Selected References

  • Corliss, W. R., Scientific satellites, NASA, SP-133, Wash., D.C., 1967.
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