1. 10th Inkaba yeAfrica/!Khure Africa (AEON) Conference/Workshop
Lord Milner Hotel, Matjiesfontein - Karoo
29 September – 3 October 2014
Development of an integrated timing and photon detection system for the HartRAO Lunar Laser Ranger
C. Munghemezulu1,3, L. Combrinck2,3, J. Botai3 1,3Hartebeesthoek Radio Astronomy Observatory (HartRAO), PO Box 443, Krugersdorp 1740, South Africa, 2,3Hartebeesthoek Radio Astronomy Observatory (HartRAO), PO Box 443, Krugersdorp 1740, South Africa, 3Department of Geography, Geoinformatics and Meteorology, University of Pretoria, South Africa,

2. OUTLINE
Introduction
System designs (timing and photon detection systems)
Specifications and analysis
Conclusion

3. Introduction S/LLR control room Ex-OCA telescope
The new S/LLR station requires timing and
photon detection systems of high accuracy.
Both systems need to be integrated and
characterised to increase systems
performance.
We present timing and photon detection
system designs for the new LLR station.
Re-furbished ex-OCA telescope at HartRAO

4. Introduction Project aim: millimetre ranging precision and accuracy.
Global Geodetic Observing Systems (GGOS): cm  mm measurement accuracy and precision (
To do this: pointing model (Prof Combrinck), thermal distortions (Mr Tsela), laser (Mr Botha + Mr Ndlovu), optics (Ms Nkosi), timing reference signals, single-photon detection systems, etc., must be integrated to increase system performance (e.g. increasing number of return photons, high laser power, etc.).
Why such stringent requirement (mm ranging precision and accuracy)?
Detailed understanding of the Earth-Moon System
Geodynamics of the Moon
(Williams et al., 2004). Further tests?
Accurate orbit determination parameters (e.g., for future Moon missions, launching of satellites)
Earth Orientation Parameters (EOP’s)

5. Introduction
Courtesy John Vig

6. System design (timing system)
Caesium and Hydrogen MASERS are very expensive.
Crystal oscillators such as OCXO are affordable and most of them are of good quality.

7. Long and short term stabilities
Credit: Microsemi
Credit: Microsemi

8. System design (single-photon detection system)
Telescope model: credit to Miss Nkosi.

9. Specifications and analysis
Phase noise and jitter for 10 MHz OCXO
(from Microsemi)
Single-photon detection system (from Panek et al., 2010)
Statistical Error Source
RMS Error (ps)
One-way Error (mm)
Laser pulse
<30
4.5
Start detectors 1
0.15
HQE*
<<200 30
SPAD#
<20 3
NPET
<1
LLR total*
<232
<34.8
SLR total#
<52
<7.8
0.22 ps RMS jitter
OCXO: Allan deviation of 4 x at 1 second and a drift rate of 1 x per 24 hours.
Sub-centimetre ranging precision depends on many factors such as pointing model for the telescope, Lunar librations, astronomical seeing conditions, etc., and electronic systems for the telescope (jitter).
The current system design and consideration of electronic components permit sub-centimetre for SLR and centimetre for LLR ranging precision.

10. Thank you all Conclusion & next step
The timing system design and specifications meet our S/LLR requirements (low jitter of 0.22 ps RMS).
Single-photon detection system contributes <200 ps RMS and < 50 ps RMS for LLR and SLR respectively.
The SPAD-HQE has high jitter (<200 ps RMS) for LLR, resulting in ~3 cm range. This limits our gaol of millimetre ranging for LLR applications.
More options will still be investigated to enhance system performance.
Procurement process: Timing system, almost completed.
Photon detection system, different options still to be investigated.
Project completion:
Thank you all

11. Acknowledgments
The authors would like to thank Inkaba yeAfrica, DST, NRF, HartRAO and also OCA and NASA for supporting this project.