1. Laser Retro-reflector Arrays on the Compass Satellites Chen WanZhen, Yang FuMin, Wang YuanMing, Li Pu Shanghai Observatory, Chinese Academy of Sciences Yangfm@shao.ac.cn

2. “COMPASS” (or “BeiDou”) is the regional satellite navigation system in China, which will cover the most areas of the East Asia region, and expect to be operational by 2011. The Compass constellation will consist of 12 satellites all equipped with LRA: GEO5 IGSO3 MEO4

3. Drawing of COMPASS-M1 Navigation Satellite

4. LRA Location of the LRA on COMPASS-M1

5. The LRA on Compass-M1 (MEO) Size 31.6  28 cm Diameter of corner cube 33mm Number42 Reflective area360cm 2 Materialfused silica Weight2.45 kg The corner cubes are uncoated both front and back surfaces

6. The LRA on Compass GEO/IGSO Size 49  43cm Diameter of corner cube 33mm Number90 Reflective area770cm 2 MaterialFused silica Weight5.0 kg The corner cubes are uncoated both front and back surfaces

7. Testing of LRA’s optical performance with ZYGO interferometer

8. Environment testing of LRA

9. Cross section, range and signal for different satellites By David Arnold* Sat.Cross section Range (0 deg.) Range** 4 Signal strength Range (45 deg.) Range** 4 Signal strength Lageos 155.811.0006.811.000 Etalon 5519.0115.03220.582.044 GPS 1920.0141.00921.5100.012 GIOVE-A 4523.9288.01025.4195.015 Glonass 8019.0115.04620.582.065 Compass 8021.0189.02823.0131.041 ETS-8 14036.01484.006337.6935.010 * Private communication

10. Parameters of LRA on satellites* SatelliteCube Number Diameter (inch) CoatingDihedral Offset Vendor Lageos14221.5uncoat1.25Perkin- Elmer Lageos24221.5uncoat1.25Zygo Etalon21401.06coat-IPIE GPS321.06coat-IPIE GIOVE-A761.06coat-IPIE Glonass1321.06coat-IPIE Compass421.3uncoat0.6SHAO ETS-8361.6uncoat0.5ITE * From David Arnold, private communication

11. Manufacturer of LRAs ITE ITE, Inc., Laurel, MD, USA ZYGO Zygo Corp., Middlefield, CT, USA IPIE Institute for Precision Instrument Engineering, Russia Perkin-Elmer Headquarters-- Waltham, MA, USA SHAO Shanghai Astronomical Observatory, China. The fused silica was made by the Shanghai LengGuang Co., China

12. New Laser and Transmitter for Compass-M1 ranging at Changchun The new laser was loaned from the NCRIEO in Beijing The new laser was loaned from the NCRIEO in Beijing - Active-active mode locked Nd:YAG laser - Active-active mode locked Nd:YAG laser - 100-150mJ in 532nm, 250ps, 20Hz - 100-150mJ in 532nm, 250ps, 20Hz - 10ns firing jitter - 10ns firing jitter New Coude mirrors New Coude mirrors New 210mm diameter transmitting telescope New 210mm diameter transmitting telescope 10 aresec laser beam divergency 10 aresec laser beam divergency

13. Real-time display for Compass-M1 tracking

14. Range residuals of Compass-M1 on Sept. 5, 2007

15. Range residuals after data fitting

16. Conclusions The parameters of 12 sets of COMPASS LRA arrays are introduced in this paper The performance of the Compass M1 LRA is excellent. It is shown in the ranging experiment that the returned signal strength from the Compass-M1 LRA is much stronger than those from GPS-35/36 and GIOVE-A The uncoated corner cubes are fine for high orbit satellites

17. Thank you

18. Active-active mode-locked Nd:YAG laser 100-150mJ (532nm), 250ps,20Hz

19. Changchun SLR Telescope

20. Changchun SLR Control Room