Etalon-1 and -2
Etalon-1 and -2
Etalon is a geodetic passive satellite family of two identical spacecraft of Russia (former USSR). Objectives of the project: Etalon is dedicated entirely to satellite laser ranging (SLR) to permit solid Earth studies: geodynamic processes, development of high accuracy global references, long-period disturbances, geopotential modelling, etc. 1) 2) 3) 4) 5) 6)
The spacecraft structure is a sphere with a diameter of 1.294 m, mass = 1415 kg. The diameter of the sphere touching the corner cube reflector (CCR) faces is 1.284 m (the difference does not cause any masking). There are a total of 2140 fused quartz CCRs (304 arrays 7 CCRs each and 2 arrays 6 CCR's each) plus 6 germanium CCRs. Each CCR has the same dimensions and is made of the same material. The germanium CCRs are intended for potential future infrared interferometric measurements. The two Etalon spacecraft were built by the United Space Device Corporation, Moscow, Russia.
Figure 1: Photo of the Etalon-1 satellite (image credit: FAS)
Launch: Etalon-1 was launched on January 10, 1989 from the Baikonur Cosmodrome together with two GLONASS satellites (GLONASS-40 and -41; Etalon-1 is also known as Cosmos 1989).
Launch: Etalon-2 (identical S/C) was launched on May 31, 1989 (Cosmos 2034) from Baikonur, Kazakhstan, along with two GLONASS satellites (GLONASS-42 and -43).
Orbit of Etalon-1: Near-circular MEO (Medium Earth Orbit), 19,095 km x 19,156 km, eccentricity = 0.00061, inclination = 64.9º, period = 676 min (11.25 h).
Orbit of Etalon-2: Near-circular MEO, 19,097 km x 19,146 km, eccentricity = 0.00066, inclination = 65.5º, period = 675 min (11.25 h).
Table 1: Main parameters of the Etalon-1 and -2 spacecraft (Ref. 2)
The expected orbital life is hundreds (even thousands) of years for each of the Etalon satellites. The high-altitude MEO orbits and the massive spheres were selected to enhance several specific goals:
• The development of a high-accuracy global reference coordinate system and determination of the Earth's rotation parameters
• Determination of lengths of long baselines
• Improvement of the Earth's gravitational field parameters
• Improvement of the selenocentric gravitational constant.
Initially, there were three satellite laser ranging stations in Russia (at Ternopol,Yevpatoria, and Maydanak) to provide the tracking services. In addition, a network of 10 sites outside Russia are performing ranging measurements. GFZ of Potsdam, Germany, is the data collection and distribution center for Etalon laser measurements in Europe. Naturally, SLR tracking is also provided by the global ILRS (International Laser Ranging Service) community.
1) S. K. Tatevian,A. N. Zakharov, “The Geodynamical Satellite Etalon,” CSTG Bulletin No. 11, Title: New Satellite Missions for Solid Earth Studies, 1989, pp. 3-9
5) N. T. Mironov, A. I. Emetz, A. N. Zaharov, V. E. Tchebotarev, ”ETALON-1, -2 Center of Mass Correction and Array Reflectivity”, Proceedings of the 8th International Workshop on Laser Ranging Instrumentation, Annapolis, MD, USA, May 18-22, 1992, NASA Conference Publication 3214, pp. 6-9, 1992, URL: http://ilrs.gsfc.nasa.gov/docs/ilrw8_section06.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.