GFZ-1 is a geodetic satellite designed to improve the current knowledge of the Earth's gravity field. The satellite, a passive system with no onboard sensors or electronics, is covered with retroreflectors that reflect laser beams sent from ground stations. By measuring the round trip time of the transmitted light, the distance between the satellite and the station can be determined with approximately 1 centimetre. These measurements are used to determine variations in the rotational characteristics of the Earth and for measurement of the Earth's gravitational field. As the vehicle's orbit decays, the satellite's orbital motion will also be used calculate to atmospheric densities. Deployed from the Mir space station, GFZ-1 was the first non-Russian satellite launched from MIR. GFZ-1 was developed in under 12 months and cost approximately $700,000 (including design, fabrication, test, and launch). Data collection, distribution and evaluation is co-ordinated by the project's scientists at the Geo Forschungs Zentrum Potsdam. Spacecraft: The satellite consists of a spherical body made from brass with 60 corner cube reflectors distributed regularly over the satellite's surface. These retroreflectors are quartz prisms placed in special holders that are recessed in the satellite's body. External metallic surfaces are covered with white paint for thermal control purposes and to facilitate visual observation in space. The vehicle's size was limited by the maximum allowable dimensions of the Mir airlock (30 cm). The vehicle carries no electronics or sensors and is not attitude controlled. Payload: No payload. Science is performed using the vehicle's 60 retroreflectors. Delivered to Mir on Progress M-27 and deployed from Mir 4/19/95 .

Design Life: Approx. 4 years. Total Length: 0.2 m. Maximum Diameter: 0.2 m. Total Mass: 22 kg.

Geodetic; carried retroreflectors for ground laser ranging; delivered to Mir on Progress M-27 and deployed from Mir 4/19/95 .

Formerly known as WPLTN-1, this geodesy satellite was a copy of Potsdam's GFZ-1 satellite, a sphere covered with laser retroreflectors, with a different `Fizeau' corner cube design. It serves as a target for the Western Pacific Laser Tracking Network (WPLTN) and is a joint project of Electro Optic Systems of Queanbeyan, New South Wales, Australia, and the Russian Space Agency. Diameter is 0.24m.

• 2 - McDowell, Jonathan, The United Nations Registry of Space Objects, Harvard University, 1997. HTML when accessed: http://hea-www.harvard.edu/QEDT/jcm/space/un/un.html
• 6 - JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. HTML when accessed: http://msl.jpl.nasa.gov/home.html