1. System Operations Eastbourne, October 2005 Towards the 1-mm: -A realistic goal ? -A vision ? -A myth ? -???

2. System Operations: Accuracy Eastbourne, October 2005  How to reach the 1 mm ACCURACY ? Is it possible ?  How to reach the 1 mm STABILITY ? Is it possible ?  Which developments are necessary ? Recommended ?  Is the 1 mm a realistic / achievable goal ?  Simple answer:  Yes, but we do not know WHEN

3. Eastbourne, October 2005 1 mm: What we need …  Good LASER: SSDPL (Solid State Diode Pumped)  Short Pulse Duration:  10 ps  Good Event Timer:  A032-ET (Riga): < 10 ps RMS, < 2 ps nonlinearity, kHz...  Dassault Modules (Graz E.T.): < 3 ps RMS, < 2 ps nonlinearity  Good detector: C-SPAD, Time Walk Compensated;  Good satellites:  ZERO Signature; PLUS strong return signal !  Grace A, Grace B, Champ: No sat signature, good signal  LARET-C: Zero signature, but weak signal

4. Eastbourne, October 2005 1 mm: Needs a good laser …  UPGRADE THE LASER:  Switch to Solid State Lasers (e.g. kHz);  Excellent Pulse uniformity;  Excellent Stability (shot-to-shot, day-by-day);  Short Pulses (10 ps in Graz) => better accuracy;  We do not see any disadvantage...  Change from „TUBES“ to „SOLID STATE“ !!!

5. October 2005 1 mm: Needs strong signals …  With a 10-ps laser, good ET, strong-signal /  zero signature sat.:  2 – 3 mm Single Shot RMS precision;  With VERY strong returns (> 300 pe / return): 1 mm SS RMS  Measure Return Signal Strength of EACH return:  C-SPAD: Use Time Difference Comp. / Uncomp. Output  Select returns with > 300 pe only  1 mm RMS  In CALs to 4 km Retro Target: Routinely achieved;  Current project ongoing in Graz; results in Canberra expected

6. Eastbourne, October 2005 CAL RMS: From 10 Hz to kHz

7. Eastbourne, October 2005 CAL P-M: From 10 Hz to kHz

8. Eastbourne, October 2005 1 mm with flash lamp laser ?  Old 10-Hz-Laser system in Graz (but with E.T. etc.):  Peak-minus-Mean: about ± 2 mm variations;  Too big; => difficult to reach the 1 mm goal !!!  With new Solid State Laser (kHz):  Peak-minus-Mean: MUCH better, very stable !!!  about ± 0.3 mm variations only...

9. Eastbourne, October 2005 1 mm: Needs a good satellite …  Use Retros / panels WITHOUT satellite signatures !!! GRACE-A GRACE-B CHAMP ??? 2-3 mm SS RMS

10. Eastbourne, October 2005 1 mm Accuracy / Stability  All previous comparisons:  From 10 Hz Flash Lamp to 2 kHz Solid State Laser  All other Equipment: Same...  Event Timer (Graz E.T. / Dassault Modules)  Same C-SPAD; same other equipment....  Conclusion again: Change from „TUBES“ to „SOLID STATE“ !!!

11. Eastbourne, October 2005 Laser Pulse Width and Accuracy  Wide range of pulse widths used in SLR:  10 ps: Graz / kHz / Solid State Laser;  35 –50 ps: Standard Lasers; Flash Lamp Pumped;  110 ps: e.g. Herstmonceux Flash Lamp Pumped;  300 ps: SLR 2000  Any other ?  What is the „best“/„optimum“/„desired“ pulse width ?

12. Eastbourne, October 2005 Laser Pulse Width Selection  10 ps: Present optimum; no reason for shorter pulses …  No significant contribution to overall systematics anymore;  Excellent for Single-Photon-Detectors;  Allowa to see – and to handle - Single Retros ….  300 ps: Can be eye-safe at e.g. 50 cm dia, if < 150 µJ / pulse  Relatively big contribution to overall systematics;  1mm goal for Lageos => difficult with SPE signals<  Satellite signature problem slightly increasing;  Less problems with LEOs / MultiPhoton Detection

13. Eastbourne, October 2005 Measuring Laser Pulse Width  I have no idea how to measure it...  But Jerry Wiant is doing it