Graz in Space Graz SLR System. Daniel Kucharski. IWF / SatGeo

Transcription

1 Graz in Space 2008 Graz SLR System Daniel Kucharski IWF / SatGeo

2 Satellite Laser Ranging Range measurements to the satellites - time of flight of the ultrashort laser pulses - mm precision station-satellite - for: POD, science

3 SLR geodetic technique time of flight measurement of the laser pulses

4 SLR measurements - scientific studies of the Earth / Atmosphere / Oceans systems, determination of the temporal mass redistribution, EOP - determination of the geocentric position of an Earth satellite (precise calibration of radar altimeters)

5 SLR measurements - allow to determine the stations positions, their tectonic motion with respect to the geocenter - support research in fundamental physics. SLR measurements of LAGEOS 1 and 2 have measured the Lense- Thirring drag of the reference frame. A third LAGEOS-type satellite has been proposed for relativity studies.

6 The satellites Currently 35 objects - active: altimetry, gravitometry, navigation - passive: geodynamic

7 LAGEOS-1 i CCRs 60 cm diameter Mass 411 kg, 405 kg ~6000 km above the surface Fully passive, geodesy

8 Ajisai 1436 CCRs mirrors 685 kg Diameter 215 cm 1500 km above the Earth Fully passive, geodesy

9 GPS-35 i 36 Panels with 32 CCRs Navigation system, time transfer

10 ERS-2, Envisat 9 CCRs 800 km above the ground remote sensing and environmental monitoring 1200 km altimetry, oceanography

11 The Moon

12 The Moon

13 SLR stations on the world

14 Graz SLR station Laser pulse GRAZ The other stations 2 khz 5-10 Hz Energy / puls Puls width Wavelength 0.4 mj 10 ps 532 nm mj ps 532 nm High accuracy of the distance measurements 200 times more measurements per second -> POD

15 LAGEOS-1 pass

16 GPS 35: Average # of Pts/NP in 2004 Potsdam Graz Matera Grasse Riyadh Monument Wettzell Koganei Mt Stromlo McDonald Herstmonceu Yarragadee Zimmerwald Maidanak 1 Simosato Changchun Beijing Graz khz SLR - statistics

17 Graz khz SLR - calibration SLR Graz: Routine - Calibrations ; 10 Hz: 500 Returns; khz: Returns / CAL 4 Peak minus Mean [mm] CAL Peak minus Mean [mm]

18 Graz station position motion Up Component: ± 0.07 mm / year ( 100 k years until sea level) East Component: ± 0.07 mm / year North Component: ± 0.10 mm / year

19 Graz khz SLR new applications Satellite spin measurements Gravity Probe B, 650 km, 75s AJISAI, 1500 km, 2s LAGEOS 1, 2, 6000 km, 5000s, 600s ETALON 1, 2, km, 65 s Atmospheric seeing measurements monitoring the atm. condition of the way of a laser pulse Space debris tracking helps to monitor them, POD

20 Graz khz SLR Spin GP-B Lense-Thirring drag 650 km Only Graz khz SLR station was able to measure the spin of the spacecraft

21 Graz khz SLR Spin GP-B 8 CCRs, 10cm dia.

22 Graz khz SLR Spin GP-B RMS LASER-OnBoard = 0.98 s

23 Graz khz SLR Spin AJISAI Spectral analysis of khz SLR data

24 Graz khz SLR Spin AJISAI AJISAI SPIN RATE 2003/ /06; corrected for apparent Spin 195 passes with >300 k points; ± 48 s around CA used (40 k min) Spin Rate [Hz] Retro 9 Retro 12 Retro Year

25 Graz khz SLR LAGEOS-1 T=5775 s

26 Graz khz SLR ETALON-1, 2 Real obs. Sim: 30 s ~70k returns/h 66 s 100 s

27 Graz khz SLR ETALON-1, 2 Spin period of the ETALONs is increasing by a value of about 0.5 s/year RMS ~1%

28 Spin parameters - application Improving the accuracy of the perturbations models The magnetic torque ( ϖ B) Vα ( B ϖ ) B Γmagnetic = Vα ϖ B Bertotti and Iess, 1991 The gravitational torque m Γ nal = L ( C A)( 3cos ϑ )( n L)( n L) gravitatio Farinella et al., 1996 Solar radiation pressure causes a torque: I hc A c ( s r ) 0 R cross Vokrouhlicky, 1996 Γoffset = sun Bertotti, B., and Iess, L. The rotation of LAGEOS, J. Geophys. Res., 96 (B1), , 1991 Farinella, P., Vokrouhlicky, D., Barlier F. The rotation of LAGEOS and ist long-term semimajor axis decay, J. Geophys. Res., 101 (B8), 17,861-17,892, 1996 Vokrouhlicky, D. Non-gravitational effects on LAGEOS rotation. Geophys. Res. Lett., 23, , 1996

29 Graz khz SLR LAGEOS-2 Full 15 years spin period history, Only Graz khz system can measure L2 spin of more than 100s Study of various perturbations and RE

30 Graz khz SLR atm. seeing

31 Graz khz SLR seeing Laser Beam Backscatter is monitored by ISIT; => into PC; Real Time Image Processing: Determine Peak of Laser Beam; At 25 fps: Store peak coordinates in file; Post Processing: Get Area of Coordinates; FWHM of this area => Astr. Seeing (arc secs) Calibrate with standard astronomical methods

32 Graz the first khz SLR system - more accurate range measurements = improvement of POD (navigation systems HEO, LEO) - much more scientific data: spin determination of various sat. - khz SLR allows to investigate the values of the SP and their changes, that gives an unique possibility to study the tiny petrurbating forces (RE) - more information about the atmospheric conditions: seeing measurements over the station