OPS Forum Delta-DOR 22.04.2005


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D-DOR stands for Delta-Differential One Way Ranging. D-DOR is the measure of the difference in signal arrival time between two stations. The observable is an uncalibrated time-delay between the two antennas.

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OPS Forum Delta-DOR 22.04.2005

  1. 1. ESA Delta DOR ESOC, 22 nd April 2004
  2. 2.  DOR definitions (1) <ul><li> -DOR stands for Delta-Differential One Way Ranging </li></ul><ul><li>DOR is the measure of the difference in signal arrival time between two stations. The observable is an uncalibrated time-delay between the two antennas. </li></ul><ul><li>“ Delta” is respect to a simple DOR, and refers to quasar calibration of the S/C DOR. </li></ul><ul><li>Since the quasar signal is recorded on the same BW of the S/C channels, ideally any errors which are station or light path dependent will cancel. </li></ul>
  3. 3.  DOR definitions (2) <ul><li>The extent to which these error sources cancel depends on the angular separation of the two sources being observed. The maximum angular distance between S/C and Quasar is 15 deg. </li></ul><ul><li>Thus, one is able to evaluate a potentially error-free relative station delay, which leads to an accurate determination of the S/C position in the plane of the sky </li></ul><ul><li>The measurement accuracy is given by: </li></ul>Longer baselines, better accuracies
  4. 4.  DOR generic signal structure <ul><li>S/C signal </li></ul><ul><ul><li>Set of TM harmonics (possibly unmodulated) or dedicated DOR tones </li></ul></ul><ul><ul><li>Low order TM harmonics (and DOR tones) are typically not embedded in noise, high-order harmonics normally are </li></ul></ul><ul><ul><li>Accuracy on S/C signal time-delay determination is: </li></ul></ul><ul><li>Quasar signal </li></ul><ul><ul><li>Random noise-like signal </li></ul></ul><ul><ul><li>Quasar signal is totally embedded in antenna noise </li></ul></ul><ul><ul><li>Accuracy on Quasar signal time-delay determination is: </li></ul></ul><ul><ul><li>“ f max –f min ” is the “total spanned bandwidth”, i.e. the frequency span between the most distant tones, used in the observation. </li></ul></ul>
  5. 5. Current station architecture <ul><li>XDC output BW: 100 MHz </li></ul><ul><li>LDC output BW: 30 MHz </li></ul><ul><li>IFMS input BW: 28 MHz </li></ul><ul><li>IFMS can handle only 2 35 Mb/s sampled inputs </li></ul><ul><li>IFMS CPU and connectivity not suitable to handle the expected data rate generated by the DDOR process </li></ul>8400 – 8500 MHz X-band D/C L-band D/C 1 Switching Matrix IFMS1 C F E GDSP RHC LHC 540-640 MHz 70 MHz Each input BW: 28 MHz L-band D/C 2 GDSP Test Test UCPU Estrack LAN
  6. 6. Driving requirements (1) <ul><li>Current ESA Deep Space Missions : </li></ul><ul><ul><li>MEX, Rosetta, VEX transponders do not generate dedicated DOR Tones </li></ul></ul><ul><ul><li>Use of low and high order even TM Harmonics. </li></ul></ul><ul><ul><li>Recommended maximum spanned BW of about 15 – 20 MHz. This means using up to the 40 th harmonic (around 44 dBc). </li></ul></ul><ul><ul><li>This is within the input BW of current IFMS </li></ul></ul>
  7. 7. Driving requirements (2) <ul><li>JPL Missions : </li></ul><ul><ul><li>Current in-flight JPL missions have transponder with dedicated DOR tones at  3 MHz,  19 MHz (X-band). Maximum spanned BW: 38MHz </li></ul></ul><ul><ul><li>This is outside the maximum input BW of the IFMS (28MHz) </li></ul></ul><ul><li>Band Re-centring : </li></ul><ul><ul><li>Different parts of the spectrum have to be tuned to the current inputs of the IFMS </li></ul></ul><ul><ul><li>The relevant parts of the spectrum can be then properly processed in chunks (Band re-centring) </li></ul></ul>X-band F C 3MHz 19MHz 19MHz 3MHz 20MHz 20MHz Input 1 Input 2
  8. 8. Station configuration for Band re-centring LDC1 LDC2 IFMS1 CFE LDC3 IFMS3 FMS2 CFE CFE Input1 Input1 Input1 Input2 Input3 Input2 Input2 Input3 Input3 A B C A..B.C A B C SWITCHING MATRIX X 2 1 Y 2 1  2 1 X 1 1 Y 1 1  1 1 X 3 1 Y 3 1  3 1 X 1 2 Y 1 2 X 1 1 Y 1 1  1 1 X 2 1 Y 2 1  2 1 X 3 1 Y 3 1  3 1 X 1 2 Y 1 2 X 1 2 Y 1 2
  9. 9. Driving requirements (3) <ul><li>Ka-band </li></ul><ul><li>Future ESA Deep Space Missions (BepiColombo) : </li></ul><ul><ul><li>Transponders CCSDS compliant (DOR Tones at  4 MHz,  20 MHz in X-band, at  4 MHz,  20 MHz,  80 MHz in Ka-band, i.e. BepiColombo). </li></ul></ul><ul><ul><li>Maximum spanned BW 160 MHz (in Ka-band). </li></ul></ul><ul><ul><li>This is also outside current IFMS input BW (again, band re-centring has to be used but this will not cover the maximum spanned BW). </li></ul></ul>80MHz F C 4MHz 20MHz 20MHz 80MHz 4MHz 28MHz 28MHz Input 2 Input 1
  10. 10. Implementation approach <ul><li>All Station, IFMS, Storage Device, Link modifications are highlighted in red </li></ul>CORRELATOR D/C IFMS (EOLP GDSP) ESU DSA1 Estrack Lan D/C IFMS (EOLP GDSP) ESU DSA2 Estrack Lan
  11. 11.  DOR observation (1) Sequence <ul><li>Observation Sequence: S/C – Quasar – S/C (or vice versa) </li></ul>DOR Tone or TM Harm. F C Ch. BW (50kHz) DOR Tone or TM Harm. DOR Tone or TM Harm . DOR Tone or TM Harm. Ch. BW (50kHz) Ch. BW (50kHz) Ch. BW (50kHz) <ul><li>S/C Signal: Telemetry Harmonic (or DOR Tone) </li></ul>Ch. BW (2MHz) Ch. BW (2MHz) Ch. BW (2MHz) Ch. BW (2MHz) <ul><li>Quasar Signal: White Noise </li></ul>
  12. 12. (1) IFMS modifications <ul><li>IFMS GDSP Modifications </li></ul><ul><ul><li>4 channels with BW from 1kHz to 2 MHz </li></ul></ul><ul><ul><li>Quantization 1,2,4,8,16 bits </li></ul></ul><ul><ul><li>Synchronization of GDSPs internal clock </li></ul></ul><ul><ul><li>2 GDSPs will be modified, to allow reception of up to 8 channels </li></ul></ul><ul><li>IFMS Internal LAN </li></ul><ul><ul><li>Private VLAN for  DOR data routing (up to 36 Mbits/s) </li></ul></ul>IFMS C F E CH4 CH3 CH2 CH1 36Mbits/s GDSP2 36Mbits/s GDSP1
  13. 13. (1) Data rates and volumes <ul><li>Data Rates & Volumes (each GDSP) </li></ul><ul><ul><li>S/C Observation : </li></ul></ul><ul><ul><ul><li>Data rate: 50kHz sampling I & Q, 8 bits quantization, 4 channels = 3.2 Mbits/s. </li></ul></ul></ul><ul><ul><ul><li>Data Volume: 10 minutes observation = 0.24 GB </li></ul></ul></ul><ul><ul><li>Quasar Observation : </li></ul></ul><ul><ul><ul><li>Data rate: 2MHz sampling I & Q, 2 bits quantization, 4 channels = 32 Mbits/s. </li></ul></ul></ul><ul><ul><ul><li>Data Volume: 10 minutes observation = 2.4 GB </li></ul></ul></ul><ul><li>Need for an External Storage Unit (ESU) </li></ul>
  14. 14.  DOR observation (2) Data collection <ul><li>Redundant ESUs </li></ul><ul><li>Each ESU collects and formats data coming from any IFMS </li></ul><ul><li>ESUs are physically located in the station MER </li></ul><ul><li>Redundant connectivity between IFMSs and ESUs is provided by station LAN </li></ul>ESU1 IFMS1 GDSP1 GDSP2 IFMS2 GDSP1 GDSP2 IFMS3 GDSP1 GDSP2 ESU2 LAN Switch AER AER LAN Switch MER MER Existing station LAN (100 Mb/s)
  15. 15.  DOR observation (3) Data type <ul><li>Data type is “open loop” </li></ul><ul><ul><li>Time-tagged I and Q samples on a selected polarization collected in files (1 file per minute) </li></ul></ul><ul><ul><li>Observation configuration (fixed during observation) parameters in a Primary Header </li></ul></ul><ul><ul><li>Parameters that may vary during observation are stored in a Frame Header. The size of each frame is of 1526 bytes. </li></ul></ul>Primary Header Frame Header and Data
  16. 16.  DOR observation (4) Data transfer <ul><li>Data collected at the two station are transferred to a centralised facility (ESOC) to perform the correlation process. </li></ul><ul><li>In the worst case sequence of observation (Quasar – Spacecraft – Quasar), the data volume will be of up to 5 GB (using 4 channels), and up to 10 GB (using 8 channels). </li></ul><ul><li>Data transfer from the stations to the correlator has to be completed within 8 hours (in critical phases). </li></ul><ul><li>Link speed requirement: 10 GB / 8 hours = 2.77 Mbits/s </li></ul>
  17. 17. (4) Data transfer requirements <ul><li>CEB and NNO Deep space stations will be equipped with 2Mbit/s lines </li></ul><ul><li>Assuming a maximum operational throughput of about 1Mbit/s, the remaining 1Mbit/s can be assigned to DDOR data transfer. </li></ul><ul><li>The extra capacity (about 2Mbit/s in the worst case), during DDOR data transfer, shall come from ad-hoc leased lines. </li></ul><ul><li>The feasibility of this solution has already been assessed with OPS-ONC </li></ul>
  18. 18.  DOR observation (5) Correlator I/F <ul><li>Correlator interfaces definition </li></ul><ul><li>Station1, Station2 : open loop data </li></ul><ul><li>FD (input): orbital data to help the correlation process </li></ul><ul><li>FD (output): the final product of the correlation </li></ul><ul><li>CP: configuration parameters </li></ul><ul><li>The correlator will be implemented on a Linux workstation placed in an operational area </li></ul>Inputs Outputs FD Station 1 CP S/W Correlator Station 2 FD
  19. 19.  (5) Signal structure <ul><li>S/C signal Correlation </li></ul><ul><ul><li>Set of TM harmonics </li></ul></ul><ul><ul><li>Low order TM harmonics are typically not embedded in noise, high-order harmonics are. </li></ul></ul><ul><ul><li>Signal characteristic permits phase extraction </li></ul></ul><ul><li>Quasar signal Correlation </li></ul><ul><ul><li>Noise-like signal </li></ul></ul><ul><ul><li>Quasar signal is totally embedded in receiver noise </li></ul></ul><ul><ul><li>Signal characteristic forces to go for a direct correlation method </li></ul></ul>
  20. 20.  DOR observation (6) S/C signal correlation <ul><li>S/C signal Correlation (1) </li></ul><ul><ul><li>Phase extraction by means of a S/W frequency estimator on the lowest TM even harmonic (highest in S/N) </li></ul></ul><ul><ul><li>Update of the expected phase (produced after an input by FD), with the estimation obtained above. </li></ul></ul><ul><ul><li>Drive the phase extraction of all other tones with the model (properly Doppler-scaled) built on the lowest TM harmonic </li></ul></ul><ul><ul><li>At this point, we have the phase sequences of each TM harmonic at each Station, sufficiently corrected for phase uncertainties. </li></ul></ul><ul><ul><li>Correlation of the phase of each channel of Station 1 with the phase of the corresponding channel of Station 2 </li></ul></ul><ul><ul><li>The correlation result as such is “modulo 2  ” ambiguous </li></ul></ul>
  21. 21.  DOR observation (7) Ambiguity resolution <ul><li>S/C signal Correlation (2) </li></ul><ul><ul><li>In order to solve such ambiguity, some operation is performed on each pair of observed channels. </li></ul></ul><ul><ul><li>The right delta-delay is the one identified by the slope (S) straight line. </li></ul></ul><ul><ul><li>The S/C DOR delay (  S/C ) is then calculated as follows: </li></ul></ul>  
  22. 22.  DOR observation (8) Quasar signal correlation <ul><ul><li>Each data stream (channel) from each station is delay- and Doppler- compensated (using the model provided by FD). The delay is mostly given by Earth rotation </li></ul></ul><ul><ul><li>After delay- and Doppler- correction, each data stream of Station 1 will be correlated with the corresponding data stream of Station 2 for a range of delays (few  s) around the expected value (provided by FD) </li></ul></ul><ul><ul><li>The analysis of the observed data is split in observation periods (“accumulation periods”) of 1 s, in order to keep a tolerable level of error in Doppler compensation </li></ul></ul><ul><ul><li>Correlation is performed for a suitable integration time in order to maximise the signal-to-noise ratio </li></ul></ul><ul><ul><li>Delay resolution is improved by the use of available multi-band recordings (enlarging the total spanned bandwidth) </li></ul></ul><ul><ul><li>The result of the correlation is then added to the value given by FD </li></ul></ul><ul><ul><li>As a result, one obtains a Quasar DOR (  Q ) </li></ul></ul>
  23. 23.  DOR observation (9) Correlator final output <ul><li>The final output of the correlator is a file containing three DOR measurements (in the Table only the most important parameters are reported). </li></ul> S/C  S/C  Q
  24. 24.  DOR observation (10) Orbit determination <ul><li>To obtain a single  DOR observation the two S/C observations are linearly interpolated to the time of the single Quasar observation. Direct differencing of the observations can then be made. </li></ul><ul><li>The obtained time is used to correct FD estimation of the delay we are looking for. </li></ul><ul><li>The corrected delay is then used to calculate the angle between the orthogonal to the baseline and the S/C direction </li></ul><ul><li>Results are then calibrated for media effects </li></ul><ul><li>Overall accuracies are mainly driven by: </li></ul><ul><ul><li>Maximum spanned BW </li></ul></ul><ul><ul><li>SNR of S/C and Quasar signals </li></ul></ul>
  25. 25. Summary of the work to be done <ul><li>Use of 3 rd IFMS in ESA Deep Space facilities as primary  DOR processor </li></ul><ul><li>Modification of the IFMS internal DSPs (GDSP) </li></ul><ul><li>Availability of all IFMSs in Deep Space facilities for redundant  DOR measurements </li></ul><ul><li>Private VLAN for  DOR data routing (IFMS-ESU up to 36 Mbps) </li></ul><ul><li>Use of a PC (ESU) with a fast Hard Disk for  DOR data storage (up to 8 GB per  DOR observation) </li></ul><ul><li>Enhancement of link capacity (station-correlator) for the availability of data in near real time </li></ul><ul><li>S/W Correlator development limited to MEX, VEX, Ros support only </li></ul>
  26. 26. Validation plan <ul><li>First system tests possible during Correlator SAT. </li></ul><ul><li>Test Campaign on current ESA Deep Space missions (MEX, Rosetta).  DOR results will be compared versus standard tracking techniques (Doppler tracking and ranging). </li></ul><ul><li>Possible tests with Smart-1 (equipped with a transponder generating DOR tones at  2 and  16 MHz) </li></ul><ul><li>Comparison with JPL  DOR results (in S/C orbital reconstruction) during VEX Cruise phase </li></ul>
  27. 27. Further developments <ul><li>BepiColombo </li></ul><ul><ul><li> DOR will be needed as well for BepiColombo orbit insertion </li></ul></ul><ul><ul><li>BepiColombo will be equipped with a transponder capable of generating dedicated DOR tones in both X- and Ka-bands. </li></ul></ul><ul><ul><li>The use of a much larger spanned BW will permit better results in terms of S/C position accuracy </li></ul></ul><ul><li>JPL interoperability </li></ul><ul><ul><li>JPL is interested in interoperability with ESA since this would permit JPL to use the CEB – NNO baseline (JPL do not have any similar baseline) </li></ul></ul><ul><ul><li>Lot of work is needed to have compatible data formats (at station level). </li></ul></ul>
  28. 28. Example of error budget <ul><li>Main Parameters </li></ul>Station Geodesy Geodesy S/C Link Link Link Astronomy   S/C   Q
  29. 29. Current schedule (IFMS-EOLP) <ul><li>Kick-off IFMS-EOLP (31 January 2005); </li></ul><ul><li>Critical Design Review by Kick-off + 10 weeks (held on 13-04-05); </li></ul><ul><li>Pre-Acceptance Report by Kick-off + 4 months </li></ul><ul><li>Final acceptance of IFMS-EOLP, (all documents delivered and accepted by the Agency, Acceptance certificate issued) by Kick-off + 6 months. </li></ul><ul><li>IFMS upgrade in DSA1-DSA2 by Kick-off + 9 months </li></ul>
  30. 30. Current schedule (Correlator) <ul><li>Kick-off meeting (28 January 2005); </li></ul><ul><li>Critical Design Review by Kick-off + 12 weeks </li></ul><ul><li>End of development phase by Kick-off + 8 months </li></ul><ul><li>Final acceptance of S/W Correlator, (all documents delivered and accepted by the Agency, Acceptance certificate issued) by Kick-off + 9 months. </li></ul><ul><li> DOR Test Campaign: December 2005 </li></ul><ul><li>Venus Orbit Insertion: March 2006 </li></ul>
  31. 31.  DOR team <ul><li> DOR Team in OPS-GS is: </li></ul><ul><ul><li>Ricard Abelló </li></ul></ul><ul><ul><li>Javier De Vicente </li></ul></ul><ul><ul><li>Marco Lanucara </li></ul></ul><ul><ul><li>Roberto Maddè </li></ul></ul><ul><ul><li>Mattia Mercolino </li></ul></ul><ul><li>Many thanks to Mattia Mercolino for helping in preparing this presentation </li></ul>