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Mission Photos:

Courtesy of EOS

Mission Objectives:

At the Western Pacific Laser Tracking Network (WPLTN) Executive meeting in Moscow on 2 December 1995, it was announced that Electro Optic Systems (EOS) had entered into a joint project with the Russian Space Agency (RSA) to construct and launch a new SLR satellite (WESTPAC-1, formely known as WPLTN-1) designed to overcome the limitations of all present targets in relation to millimeter geodesy. The satellite has a very similar in design to GFZ-1.

The main immediate purpose of the satellite is to provide the best possible target for the WPLTN stations and, by implication, the Keystone Project constructed by Communications Research Laboratory (CRL) of the Japanese Ministry of Posts and Telecommunications.

More detailed information on the WESTPAC satellite can be found in the WESTPAC Satellite Scientific-Technical Note for User document developed by The Russian Institute for Space Device Engineering and The Science Research Institute for Precision Device Engineering.

The WESTPAC satellite is covered with recessed retroreflectors of the Russian Fizeau design to permit only one retroreflector to contribute to the return. On average, 0.7 corner cubes contribute to the return, and therefore the return signal fades in and out as different reflectors come into view. The satellite is well-suited for advanced two color ranging experiments.

Mission Instrumentation:

WESTPAC is a passive satellite where the only instrumentation onboard is the retroreflector array.

Mission Parameters:
Sponsor: Western Pacific Laser Tracking Network
Expected Life: decades
Primary Applications: geodetic and retroreflector technology
COSPAR ID: 9804301
SIC Code: 8801
Satellite Catalog (NORAD) Number: 25394*
Launch Date: 10 July 1998
RRA Diameter: 24 cm
RRA Shape: circular
Reflectors: 60 corner cubes
Orbit: circular, sun synchronous
Inclination: 98 degrees
Eccentricity: 0.0
Perigee: 835 km
Period: 101 minutes
Weight: 23 kg

*Note: Some confusion in the COSPAR and Satellite Catalog (NORAD) numbers of the payloads occurred shortly after launch. NORAD eventuall assigned the COSPAR/NORAD combination of 9804301/25394 to the WESTPAC payload. Unfortunately, NORAD later changed the NORAD number 25394 to 25398. Since the ILRS had begun using 25394 in tracking, we have elected to keep this designation in the ILRS records.

Additional Information:

Web sites:


  • Burmistrov, V.B., Parkhomenko, N.N., Pliev, L.F., Shargorodsky, V.D., Soyuzova, N.M. and Vasiliev, V.P., "The WESTPAC Satellite: Design Features and First Results of Return Signal Analysis", Proc. of the 11th International Workshop on Laser Ranging, Deggendorf, Germany, September 21-25, p. 297, 1998.
  • Glotov, V., Mitrikas, V., Revnivych, S., and Parchomenko, N., "WESTPAC Satellite Orbital Parameters and Measurements Accuracy", Proc. of the 11th International Workshop on Laser Ranging, Deggendorf, Germany, September 21-25, p. 50, 1998.
  • Rutkowska, M., "Satellite WESTPAC influence of the gravity field on the accuracy of orbit estimation", Artificial Satellites 38, 97-104, 2003.
  • Rutkowska, M., and Noomen, R., "SLR system characteristics in WESTPAC, LAGEOS-1 and LAGEOS-2 observations", Presentation to 12th International Workshop on Laser Ranging, Matera, Italy, November 13-17, 2000.