Graz in Space 2008

Graz SLR System

Daniel Kucharski

IWF / SatGeo

Satellite Laser Ranging

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

SLR – geodetic technique

‘time of flight’ measurement of the laser pulses

SLR measurements

- scientific studies of the Earth / Atmosphere / Oceans systems, determination of the temporal mass redistribution, EOP

- determination of the geocentric positionof an Earth satellite (precise calibration ofradar altimeters)

- allow to determine the stations’ positions, their tectonic motion with respect to the geocenter

- support research in fundamental physics. SLRmeasurements of LAGEOS 1and 2 have measured the Lense-Thirring “drag” of the referenceframe. A third LAGEOS-type satellite has been proposed forrelativity studies.

SLR measurements

The satellites

Currently 35 objects

- active: altimetry, gravitometry, navigation

- passive: geodynamic

LAGEOS-1 i 2

426 CCRs

60 cm diameter

Mass 411 kg, 405 kg

~6000 km above the surface

Fully passive, geodesy

Ajisai

1436 CCRs + 318 mirrors

685 kg

Diameter 215 cm

1500 km above the Earth

Fully passive, geodesy

GPS-35 i 36

Panels with 32 CCRs

Navigation system,

time transfer

ERS-2, Envisat

9 CCRs

800 km above the ground

remote sensing and environmental monitoring

1200 km

altimetry, oceanography

The Moon

The Moon

SLR stations on the world

Graz SLR stationGRAZ The other

stations2 kHz 5 - 10 Hz

35 – 200 mJ

35 – 200 ps

532 nm

0.4 mJ

10 ps

532 nm

Laser pulse

Energy / puls

Puls width

Wavelength

High accuracy of the distance measurements

200 times more measurements per second -> POD

LAGEOS-1 pass

GPS 35: Average # of Pts/NP in 2004

845

357

215

155

129

95 67 62 46 32 30 30 20 18 12 7 30200400600800

1000

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Graz kHz SLR - statistics

SLR Graz: Routine - Calibrations 2003-2005;10 Hz: 500 Returns; kHz: 10 000 Returns / CAL

-4

-3

-2

-1

0

1

2

3

4

2003 2003.5 2004 2004.5 2005 2005.5

Peak

min

us M

ean

[mm

] CAL Peak minus Mean [mm]

Graz kHz SLR - calibration

Up Component: -3.53 ± 0.07 mm / year (≈100 k years until sea level)East Component: 22.15 ± 0.07 mm / yearNorth Component: 14.85 ± 0.10 mm / year

Graz station – position motion

Graz kHz SLR – new applications

Satellite spin measurementsGravity Probe – B, 650 km, 75s AJISAI, 1500 km, 2sLAGEOS – 1, 2, 6000 km, 5000s, 600sETALON –1 , 2, 19000 km, 65 s

Atmospheric seeing measurementsmonitoring the atm. condition of the way of a laser pulse

Space debris trackinghelps to monitor them, POD

Graz kHz SLR – Spin GP-BLense-Thirring “drag”

650 km

Only Graz kHz SLR station was able to measure the spin of the spacecraft

Graz kHz SLR – Spin GP-B8 CCRs, 10cm dia.

RMSLASER-OnBoard = 0.98 s

Graz kHz SLR – Spin GP-B

Graz kHz SLR – Spin AJISAI

Spectral analysis of kHz SLR data

Graz kHz SLR – Spin AJISAI

AJISAI SPIN RATE 2003/10 - 2005/06; corrected for apparent Spin 195 passes with >300 k points; ± 48 s around CA used (40 k min)

0.500

0.505

0.510

0.515

0.520

0.525

2003.8 2004.2 2004.6 2005.0 2005.4Year

Spin

Rat

e [H

z]

6-Retro

9 Retro

12 Retro

Graz kHz SLR –LAGEOS-1

T=5775 s

Graz kHz SLR – ETALON-1, 2

Real

obs.

Sim:

30 s

66 s

100 s

~70k returns/h

Graz kHz SLR – ETALON-1, 2

Spin period of the ETALONs is increasing by a value of about 0.5 s/year

RMS ~1%

Spin parameters - applicationImproving the accuracy of the perturbations’ models

The magnetic torque

( ) ( ) BBVBBVmagnetic ××′′−⋅×′=Γ ϖαϖϖα Bertotti and Iess, 1991

The gravitational torque

( )( )( )( )LnLnACLm

nalgravitatio ×⋅−−−=Γ 1cos343 2

2

2

ϑ Farinella et al., 1996

Solar radiation pressure causes a torque:

( )suncrossR

offset rscAhCI

×=Γ 0 Vokrouhlicky, 1996

Bertotti, B., and Iess, L. The rotation of LAGEOS, J. Geophys. Res., 96 (B1), 2431-2440, 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, 3079-3082, 1996

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

Graz kHz SLR – atm. 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

Graz kHz SLR – seeing

- 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

Graz – the first kHz SLR system