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Topo 1 (S70-3)

SECOR (Topo 1 similar) [US Army]

TOPO 1, the U.S. Army Topographic Command's first satellite, was launched from the Western Test Range (WTR) on 8 April 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.

TOPO I was used primarily for research and development in determining the ultimate accuracy of SECOR when using transponders with ultra-stable oscillators. The objectives of the spacecraft were:

  • 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,
  • to test relay and one-way ranging techniques used by the Defense Navigation Satellite System, and
  • to obtain information about ionospheric effects on satellite geodetic surveys.

The 18.14 kg satellite was based on the SECOR Type II satellite and 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:

  • 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
  • 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 14 January 1972, the satellite was orbiting in an operational off mode.

Nation: USA
Type / Application: Geodesy
Operator: U.S. Army Topographic Command
Contractors: Cubic Corporation ?
Equipment: MAT SECOR transponder
Configuration: cube
Propulsion: ?
Mass: 18 kg
Satellite COSPAR Date LS Launch Vehicle Remarks
Topo 1 (S70-3) 1970-025B 08.04.1970 Va SLC-2E Thorad-SLV2G Agena-D with Nimbus 4


Further STP missions: