GFZ Potsdam contributions to ELT

Transcription

1 Aces workshop, Zürich, Switzerland, 29th 30th June GFZ Potsdam contributions to ELT S. Bauer 1, L. Grunwaldt 1, E.D. Hoffman 2 1 GFZ Potsdam, Brandenburg, Germany. 2 NASA GSFC, Greenbelt, Maryland, USA.

2 Slide 01 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Content Two-way and one-way ranging to ELT/ACES GFZ Laser Retro Reflector (LRR) for ELT/ACES Calibration of the total, transmit (Tx) and the receive (Rx) delay Ground to space Time Transfer (TT) from GFZ SLR station to ELT/ACES GFZ SLR station accuracy and stability Summary

3 Slide 02 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Two- and one-way ranging to ELT/ACES GFZ Potsdam SLR station ranging to ELT/ACES. ISS & Columbus module GFZ LRR ACES &ELT t Tof + t Tof t ReceiveTime t RxDelay ELT performance from Schlicht et al. (2011). ELT performance Accuracy GTS TT: 50 ps GTG TT: 50 ps Stability/Precision 4 ps over 300 s 7 ps over 10 days t TxDelay Tx Rx t RxDelay t FireTime t ReceiveTime Equation: t FireTime + t TxDelay + t Tof + t Tof + t RxDelay = t ReceiveTime Two-way: station station station station One-way: station station ELT ELT Frequently calibrated at SLR stations t TotalDelay =t TxDelay +t RxDelay

4 Slide 03 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June GFZ LRR for ELT/ACES Originally the GFZ Laser Retroreflector (LRR) was developed for CHAMP, same design was also used on GRACE, SWARM and TSX & TDX LRR developed, tested and manufactured by GFZ, prisms by Zeiss since SWARM Two-way ranging and GPS receiver calibration Small (100x100x48 mm), lightweight (400 gr) and passive Small number of prisms and with that reflections when ranging to the LRR which allows for a small signal precision (< 1 cm) Far field diffraction pattern is corrected for the velocity aberration of light GFZ LRR for ELT/ACES. GFZ LRR being mounted on the CHAMP satellite.

5 Slide 04 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Two-way ranging to a satellite GFZ Potsdam SLR station two-way ranging to a target. t SDTx Tx IRP Rx t RxDe t ToF = t ET Stop t ET Start t Total SD ET De Laser t SDET t DeET Two-way ranging of the GFZ SLR station to a satellite Due to multistatic setup of the telescope, our Invariant Reference Point (IRP), to which the ranges are referenced, is in free space

6 Slide 05 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Total delay calibration GFZ Potsdam SLR station performing calibration of the total system delay. t TxRx t Total = t ET Stop t ET Start t TxRx t SDTx Tx IRP Rx t RxDe t Total = t SDET + t SDTx + t RxDe + t DeET t Total = t Tx + t Rx SD ET De Laser t SDET t DeET Calibration of total system delay: pointing Tx&Rx on each other This covers all involved delays and references the measurements to the IRP Optical path is roughly constant but there are variations in the equipment and the cables Accuracy of the calibration depends on the used detector

7 Slide 06 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Tx and Rx delay calibration GFZ Potsdam SLR station performing calibration of the transmit and receive system delay. Tx t TxRx t TxPD PD Rx t TotalPD = t ET Stop t ET Start t TotalPD = t SDET + t SDTx + t TxPD + t PDET t SDTx SD ET t PDET De t RxDe t TotalPD = t Tx + t TxPD + t PDET t Tx = t TotalPD t TxPD t PDET Laser t SDET t DeET t Rx = t Total t Tx t TxRx Calibration of Tx delay with a Photo Diode (PD) at the IRP and calibrated cables and calculation of Rx delay The accuracy and precision of the measurement is defined by the detector, the cable calibration and the position knowledge Application: ground to space TT to ELT/ACES and multistatic ranging to space debris

8 Slide 07 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June TT from GFZ SLR station to ELT/ACES GFZ SLR station has a GPS receiver and a cesium Check the difference of our epochs to UTC via ELT/ACES Idea: connecting GFZ SLR station and PTB via a fiber optical link Distance is 200 km, links were demonstrated over 1400 km Two options Forwarding frequency and creating time locally Forwarding both frequency and time For time, all delays in the fiber link would need to be known Ongoing discussion about: Realization of link (provider, path and delay calibration) Hardware Costs Would it be valuable for ACES and the community?

9 Slide 08 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June GFZ Potsdam SLR station accuracy Hardware wise the accuracy of the ranges is defined by the accuracy and precision of the calibration Calibration is carried out frequently (max. 2 hours) Total station delay is affected by Detector precision (PMT: 48 ps - 16 mm; SPAD: 18 ps - 6 mm) Change of laser amplitude ( 24 ps 8 mm directly after switch on)

10 Slide 09 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June GFZ Potsdam SLR station accuracy Hardware wise the accuracy of the ranges is defined by the accuracy and precision of the calibration Calibration is carried out frequently (max. 2 hours) Total station delay is affected by Detector precision (PMT: 48 ps - 16 mm; SPAD: 18 ps - 6 mm) Change of laser amplitude ( 24 ps 8 mm directly after switch on) Change of temperature ( 40 ps 13 mm over DOY 148 in 2017) Overall station accuracy is 10 mm ± 1 mm/h one-way Calibration of GFZ SLR station total system delay with the PMT. Detail during DOY 140 to 150 during A change of 40 ps can be observed during DOY 148.

11 Slide 10 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June GFZ Potsdam SLR station stability Stability (TDEV) estimated from a calibration run over 2 hours Prochazka et al. (2010) shows the stability of the ELT SPAD recorded with the Graz 2 khz and the WETL 10 Hz laser system GFZ SLR and Graz station stability are in agreement GFZ SLR station meets the ELT detector performance ( 1 ps after 300 s) Prochazka et al. (2010). POT3 station system stability recorded with the PMT. Time deviation (TDEV) is given in seconds.

12 Slide 11 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Summary Flight proven GFZ LRR will provide two-way ranges with a precision of better than 1 cm Two-way ranges enable the optical ground to space and ground to ground TT via ELT/ACES Calibration of the GFZ SLR station Tx delay Idea: transfer PTB frequency and time to GFZ SLR station via fiber optical link for transferring it to ELT/ACES Station range accuracy is 10 mm ± 1 mm/h one-way ( 30 ps ± 3 ps/h) and stability 1 ps after 300 s GFZ SLR station meets the ELT detector performance (50 ps ground to space TT and a stability of 4 ps after 300 s Schlicht et al., 2011)

13 S. Bauer et al. GFZ Potsdam contributions to ELT Aces workshop, Zürich, Switzerland, 29th 30th June Thank you for your attention! Literature Prochazka, I., et al., Development of the European Laser Timing instrumentation for the ACES time transfer using laser pulses. Proceedings of the EFTF th European Frequency and Time Forum, 13th-16th April, Noordwijk, Netherlands. Schlicht, A., et al., The European Laser Timing Experiment and Data Center. Proceedings of the 17th ILRS workshop, 16th-20th May, Bad Kötzting, Germany. Acknowledgements Thanks to Jens Steinborn and Andre Kloth from DiGOS Potsdam for software support.