Ivan Procházka presented at : seminart Institute of Astronomical and Physical Geodesy, Technische Univ.Muenchen, Germany October 27, 2008 Czech Technical University in Prague, Czech Republic Photon counting detectors for picosecond time transfer ground to space ACES mission

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Key question #1 ACRONYM n 3 (?) letter abbreviation characterising the experiment n Existing T2L2 Time Transfer by Laser Link (CNES) LTT Laser Time Transfer (China) n OCC Optical Clock Comparison n TLSTime Synchronisation by Laser n ETTEuropean Time Transfer n ???

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Key questions # 2 n GENERAL requirements - resolution single shot.. ps - stability.. ps n TECHNICAL requirement - detector resolution single shot.. ps - detector timing stability.. ps / K - system resolution.. ps - system stability.. ps / K / hr n DETECTOR operating conditions - operating temperature.. C - temperature stability +/-.. C

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Fast photon counting detectors for the Time Transfer by Laser Light space missions n Already approved / operated in (deep) space missions MARS 92/96 (Russia) NASA Mars Polar Lander (USA) Laser Time Transfer LTT China - operational since 2007 T2L2 time transfer, CNES, operational since 2008 n Three detector configurations - operation modes n single phot. only1 photon onlyLTT China n single multiple ooo phot. SLR worldwide n multiple10-10 ooo phot.T2L2 France n low mass, power, bias voltage n high radiation in-sensitivity (> 10 years in space) n hightemperature range n extremeoptical damage threshold (full Solar flux)

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Optical signal strength Ground - ACES Standard Satellite Laser Ranging system, 532 nm, ps pulses Laser20 mJ, 200’’0.2 mJ, 20’’ Range 540 km540 km Photons / m 2 3 * * Aperture 1 mm3 * * um10 ooo10 ooo 25 um200 phot.200 phot. The worst case estimate

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Background photon flux - ACES Solar flux 0.2W/m 2 /0.1 nm ~ phot/s/m 2 /0.1 nm Earth albedo 0.1 Field of View ~1 radian, ~ 400 km altitude 1. Direct Sun light> 1 * ph / s on detector photon counting not possible, no damage 2. Daylight – Earth albedo in entire footprint 1 mm 3 * ph / s / 10 nm 200 um 1 * ph / s / 10 nm 25 um 2 * 10 9 ph / s / 10 nm 3. Night time in entire footprint (estimate < daylight) 1 mm < 3 * 10 9 ph / s / 10 nm 200 um < 1 * 10 8 ph / s / 10 nm 25 um < 2 * 10 6 ph / s / 10 nm The worst case estimate

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Proposed detector configuration #1 n K14 SPAD dual detector package (LTT China analogy) n Active aperture 25 um n Coincidence option on sw level on-board n Gated operation mode, synchronous with local 10 pps n Blocking glass filter 10 nm, aperture limited FOV n Additional neutral density filter (glass) n MAIN PARAMETERS - timing resolution 50 ps / shot - timing stability~ +/- 10 ps & temperature - power / mass 0.1 us daylight > 20 us night time LTT China

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Proposed detector configuration # 2 n K14 SPAD dual detector package n Active aperture 200 um, TE cooled in vaccum n Active temp. control (chip & PCB) +/- 0.5 K n Coincidence option on sw level on-board n Gated operation mode, sync. with local 10 pps n Interference filter 1 nm, aperture limited FOV n Rough glass / geometry attenuation 10 4 x n MAIN PARAMETERS - timing resolution 30 ps / shot - timing stability~ +/- 2 ps - power / mass 0.1 us daylight > 20 us night time

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Satellite laser ranging chain stability including Optical Detector Ground target calibration runs K.G.Kirchner, SLR Graz, private communication, Sept entire system stability ~ 0.8 mm / 5 ps year

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Proposed detector features n POSITIVE - based on proven technology - extremely simple, rugged, easy to adjust - low power, low mass - acceptable timing resolution, stability, reproducibility - operates day (some SLR) and night time (~ all SLR) - overload resistant, long lifetime in space - ground HW & operation compatible with other missions n NEGATIVE - synchronous operation required (100 ns /10 us) - small additional HW required for some ground SLR (prototype is existing in our labs) - downlink data rate ~ 400 bits/s (may be reduced by scheduling strategy and optionally by coincidence )

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Level of Technological maturity n Retroreflector assembly (Potsdam) - operated on board of several missions (Grace, …) - small modifications needed (central hole to host the optical detector) n Optical receiver - operated in SLR network worldwide > 10yrs OK - launched on MARS 92/96, NASA Mars Polar Lander98 - operating on Compass M1, > 18 months OK - operating on Jason-2, > 4 monthsOK

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Specific accomodation requirements # 1 n Field of view of the optical assembly (retro + receiver) + / - 60 degrees from nadir un-obscured view n Detector temperature range - IDEAL caseany temperature C, stable +/- 2 C - the WORST caserange -50…+50 C n Cooling of optical receiver - total heat generated 0.15 W to 5 W depends on configuration - amount of heat depends on detector temperature range (the excess heat is used to temp.stabilize the receiver, if needed) n

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Specific accomodation requirements # 2 n Functions needed to be added to ACES MWL - Gate pulse10 or 100 pps signal sync.to locat time base in ideal case selectable 10 or 100 pps - time tagging of the detector output versus local time base resolution 50 ps n Data handling / downlink services - downlink of the detected time tags - ~ 40 bits / event, => 400 bits/s or 4 kbit/s for 10 or 100pps resp. - data volume may be reduced by scheduling ~ 10 x “on demand~ 100 x coincidence? TDB n On ground data processing - computing of the clock differences, near real – time => www page

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Optical detector design and construction n Definition of goals fall 2008 n Laboratory sample3- 6 months Prague + indoor breadboard tests n Technology Demonstrator TD3 - 6 monthsPrague n TD tests vers,. SLR system6 monthsWettzell n TD construction corrections3 monthsPrague / Wettzell n Optical detector FM construction……Astrium ? n Integration into Retro……?

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Gaining confidence – Breadboard demo, Prague n The entire Time transfer experiment may be carried out in our lab to demonstrate the feasibility of the proposed project n GROUND segment u LaserHamamatsu diode, 42 ps, 10 Hz, 778 nm u SLR detectorSPAD standard detector package u SLR timing HP5370B, 50 ps resolution u Time base GPS timing system, 10 MHz, 10pps n SPACE segment u Satellite retroplastic retroreflector, range m u Optical receiverSPAD standard detector package u Timing Event timing 150 ps resolution u Time basestandard quartz oscillator 10MHz n RESULTS u Satellite range u Space / ground time base difference u Demonstration of basic principles

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Breadboard demo, Prague - setup n SPACE SEGMENT n Optical detector package+electronics n Retro-reflector array n Optical detector input aperture n Space segment motion range n GROUND SEGMENT n Laser transmitter / diode n Ranging optics and detector package

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Breadboard demo, Prague – Resuls # 1 Laser ranging Range shift +16o mm / ns Data stability & reproducibility & consistency 10 psec Series meas. each RMS ~ 100 ps 20 Hz rate, data yield ~ 5% Ranging data histogram Note the high photon flux background

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Breadboard demo, Prague – Resuls # 2 Time comparison “Ground” “Space” equal frequency on both terminals Series 150 meas. each RMS ~ 500 ps 20 Hz rate, data yield 5%~ 12% Result impaired by limited Resolution and stability of event timing On “space segment”

I.Prochazka, Tech.Univ.Munich, Germany.October 27, 2008 Breadboard demo, Prague Results Summary n The Laser Time Time transfer experiment was demonstrated in a indoor environment to demonstrate the feasibility of the proposed project n For demo purposes, modest performance epoch timing device was used for time transfer n DEMONSTRATED u Laser ranging resolution, consistency & stability better than 10 ps, u Ranging performed for different ranges u Time comparison using laser pulses u Frequency comparison using laser pulses n SUMMARY & CONCLUSION 1. Performance of the indoor time & frequency transfer corresponds to the components involved 2. The precision and accuracy of ~ 10 ps of the LTT is achievable using proposed solution for ACES upgrade