ops forum delta-dor 22.04.2005
DESCRIPTION
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.TRANSCRIPT
ESOCR.Maddè, OPS-GSS
22-04-05, Slide 1
ESA Delta DOR
ESOC, 22nd April 2004
R.Maddè, OPS-GSS
22-04-05, Slide 2ESOC
DOR definitions (1)
-DOR stands for Delta-Differential One Way Ranging
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.
“Delta” is respect to a simple DOR, and refers to quasar calibration of the S/C DOR.
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.
R.Maddè, OPS-GSS
22-04-05, Slide 3ESOC
DOR definitions (2)
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.
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
The measurement accuracy is given by:
cosB
c
Longer baselines,
better accuracies
R.Maddè, OPS-GSS
22-04-05, Slide 4ESOC
DOR generic signal structure
S/C signal
– Set of TM harmonics (possibly unmodulated) or dedicated DOR tones
– Low order TM harmonics (and DOR tones) are typically not embedded in noise, high-order harmonics normally are
– Accuracy on S/C signal time-delay determination is:
Quasar signal
– Random noise-like signal
– Quasar signal is totally embedded in antenna noise
– Accuracy on Quasar signal time-delay determination is:
“fmax –fmin” is the “total spanned bandwidth”, i.e. the frequency span between the
most distant tones, used in the observation.
QSR0obsminmax
QN/ST)ff(2
2
C/S0obsminmax
C/SN/ST)ff(2
2
R.Maddè, OPS-GSS
22-04-05, Slide 5ESOC
Current station architecture
XDC output BW: 100 MHz
LDC output BW: 30 MHz
IFMS input BW: 28 MHz
IFMS can handle only 2 35 Mb/s sampled inputs
IFMS CPU and connectivity not suitable to handle the expected data rate generated by the DDOR process
8400 – 8500MHz
X-bandD/C
L-bandD/C 1
SwitchingMatrix
IFMS1
CFE
GDSP
RHC
LHC
540-640 MHz 70 MHz Each input BW: 28 MHz
L-bandD/C 2
GDSP
Test
Test
UCPU
Estrack LAN
R.Maddè, OPS-GSS
22-04-05, Slide 6ESOC
Driving requirements (1)
Current ESA Deep Space Missions:
– MEX, Rosetta, VEX transponders do not generate dedicated DOR Tones
– Use of low and high order even TM Harmonics.
– Recommended maximum spanned BW of about 15 – 20 MHz. This means using up to the 40th harmonic (around 44 dBc).
– This is within the input BW of current IFMS
R.Maddè, OPS-GSS
22-04-05, Slide 7ESOC
Driving requirements (2)
JPL Missions:
– Current in-flight JPL missions have transponder with dedicated DOR tones at 3 MHz, 19 MHz (X-band). Maximum spanned BW: 38MHz
– This is outside the maximum input BW of the IFMS (28MHz)
Band Re-centring:
– Different parts of the spectrum have to be tuned to the current inputs of the IFMS
– The relevant parts of the spectrum can be then properly processed in chunks (Band re-centring)
FC
3MHz19MHz 19MHz
3MHz
20MHz20MHz
Input 1 Input 2X-band
R.Maddè, OPS-GSS
22-04-05, Slide 8ESOC
Station configuration for Band re-centring
LDC1 LDC2
IFMS1
CFE
LDC3
IFMS3FMS2
CFE CFE
Input1 Input1Input1Input2 Input3 Input2 Input2 Input3Input3
X21 Y2
1 21X1
1 Y11 1
1 X31 Y3
1 31X1
2Y1
2
X11 Y1
1 11 X2
1 Y21 2
1 X31 Y3
1 31
A B C A..B.C A B C
X12
Y12 X1
2Y1
2
SWITCHING MATRIX
R.Maddè, OPS-GSS
22-04-05, Slide 9ESOC
Driving requirements (3)
Ka-band
80MHz
FC
4MHz20MHz 20MHz 80MHz
4MHz
28MHz28MHz
Input 2Input 1
Future ESA Deep Space Missions (BepiColombo):– 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).
– Maximum spanned BW 160 MHz (in Ka-band).
– 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).
R.Maddè, OPS-GSS
22-04-05, Slide 10ESOC
Implementation approach
All Station, IFMS, Storage Device, Link modifications are highlighted in red
CORRELATOR
D/C
IFMS(EOLP GDSP)
ESU
DSA1
Estrack Lan
D/C
IFMS(EOLP GDSP)
ESU
DSA2
Estrack Lan
R.Maddè, OPS-GSS
22-04-05, Slide 11ESOC
DOR observation (1) Sequence
Observation Sequence: S/C – Quasar – S/C (or vice versa)
DOR Tone or TM Harm.
FC
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)
S/C Signal: Telemetry Harmonic (or DOR Tone)
Ch. BW (2MHz) Ch. BW (2MHz) Ch. BW (2MHz) Ch. BW (2MHz)
Quasar Signal: White Noise
R.Maddè, OPS-GSS
22-04-05, Slide 12ESOC
(1) IFMS modifications
IFMS GDSP Modifications
– 4 channels with BW from 1kHz to 2 MHz
– Quantization 1,2,4,8,16 bits
– Synchronization of GDSPs internal clock
– 2 GDSPs will be modified, to allow reception of up to 8 channels
IFMS Internal LAN
– Private VLAN for DOR data routing (up to 36 Mbits/s)
IFMS
CFE
CH4
CH3
CH2
CH1
36Mbits/s
GDSP236Mbits/s
GDSP1
R.Maddè, OPS-GSS
22-04-05, Slide 13ESOC
(1) Data rates and volumes
Data Rates & Volumes (each GDSP)
– S/C Observation:
1. Data rate: 50kHz sampling I & Q, 8 bits quantization, 4 channels = 3.2 Mbits/s.
2. Data Volume: 10 minutes observation = 0.24 GB
– Quasar Observation:
1. Data rate: 2MHz sampling I & Q, 2 bits quantization, 4 channels = 32 Mbits/s.
2. Data Volume: 10 minutes observation = 2.4 GB
Need for an External Storage Unit (ESU)
R.Maddè, OPS-GSS
22-04-05, Slide 14ESOC
DOR observation (2) Data collection
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)
Redundant ESUs
Each ESU collects and formats data coming from any IFMS
ESUs are physically located in the station MER
Redundant connectivity between IFMSs and ESUs is provided by station LAN
R.Maddè, OPS-GSS
22-04-05, Slide 15ESOC
DOR observation (3) Data type
Data type is “open loop”
– Time-tagged I and Q samples on a selected polarization collected in files (1 file per minute)
– Observation configuration (fixed during observation) parameters in a Primary Header
– Parameters that may vary during observation are stored in a Frame Header. The size of each frame is of 1526 bytes.
<station_id> XXXX </station_id> <spacecraft_id> YYYY </spacecraft_id> <dset_kind> ZZ </dset_kind> <dap_type> TT </dap_type> <active_table> FreqDnlkCF = 10070150000 ; // Hz FreqDnlkConv = 10000000000 ; // Hz EolpSampleRate = 1000 ; // Hz EolpQuantisation = 1 ; // EolpFixedGain = Yes ; // EolpGainValue = 12 ; // dB EolpSubCCentreFreqOffs = 0. ; // Hz Eolp1SubC0FreqOffs = 0. ; // Hz Eolp1SubC1FreqOffs = 10. ; // Hz Eolp1SubC2FreqOffs = 20. ; // Hz Eolp1SubC3FreqOffs = 30. ; // Hz
Primary Header Frame Header and DataFrame Header
Data (I,Q samples)
Frame Header
Data (I,Q samples)
R.Maddè, OPS-GSS
22-04-05, Slide 16ESOC
DOR observation (4) Data transfer
Data collected at the two station are transferred to a centralised facility (ESOC) to perform the correlation process.
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).
Data transfer from the stations to the correlator has to be completed within 8 hours (in critical phases).
Link speed requirement: 10 GB / 8 hours = 2.77 Mbits/s
R.Maddè, OPS-GSS
22-04-05, Slide 17ESOC
(4) Data transfer requirements
CEB and NNO Deep space stations will be equipped with 2Mbit/s lines
Assuming a maximum operational throughput of about 1Mbit/s, the remaining 1Mbit/s can be assigned to DDOR data transfer.
The extra capacity (about 2Mbit/s in the worst case), during DDOR data transfer, shall come from ad-hoc leased lines.
The feasibility of this solution has already been assessed with OPS-ONC
R.Maddè, OPS-GSS
22-04-05, Slide 18ESOC
DOR observation (5) Correlator I/F
Correlator interfaces definition
Inputs
Outputs
Station1, Station2: open loop data
FD (input): orbital data to help the correlation process
FD (output): the final product of the correlation
CP: configuration parameters
FD
Station 1
CPS/W
Correlator
Station 2
FD
The correlator will be implemented on a Linux workstation placed in an operational area
R.Maddè, OPS-GSS
22-04-05, Slide 19ESOC
(5) Signal structure
S/C signal Correlation
– Set of TM harmonics
– Low order TM harmonics are typically not embedded in noise, high-order harmonics are.
– Signal characteristic permits phase extraction
Quasar signal Correlation
– Noise-like signal
– Quasar signal is totally embedded in receiver noise
– Signal characteristic forces to go for a direct correlation method
R.Maddè, OPS-GSS
22-04-05, Slide 20ESOC
DOR observation (6) S/C signal correlation
S/C signal Correlation (1)
– Phase extraction by means of a S/W frequency estimator on the lowest TM even harmonic (highest in S/N)
– Update of the expected phase (produced after an input by FD), with the estimation obtained above.
– Drive the phase extraction of all other tones with the model (properly Doppler-scaled) built on the lowest TM harmonic
At this point, we have the phase sequences of each TM harmonic at each Station, sufficiently corrected for phase uncertainties.
– Correlation of the phase of each channel of Station 1 with the phase of the corresponding channel of Station 2
– The correlation result as such is “modulo 2” ambiguous
CHf
R.Maddè, OPS-GSS
22-04-05, Slide 21ESOC
DOR observation (7) Ambiguity resolution
S/C signal Correlation (2)
– In order to solve such ambiguity, some operation is performed on each pair of observed channels.
– The right delta-delay is the
one identified by the slope
(S) straight line.
– The S/C DOR delay (S/C) is
then calculated as follows:
2)(2 12
12/
S
ffff
CS
R.Maddè, OPS-GSS
22-04-05, Slide 22ESOC
DOR observation (8) Quasar signal correlation
– 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
– 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)
– 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
– Correlation is performed for a suitable integration time in order to maximise the signal-to-noise ratio
– Delay resolution is improved by the use of available multi-band recordings (enlarging the total spanned bandwidth)
– The result of the correlation is then added to the value given by FD
– As a result, one obtains a Quasar DOR (Q)
R.Maddè, OPS-GSS
22-04-05, Slide 23ESOC
DOR observation (9) Correlator final output
The final output of the correlator is a file containing three DOR measurements (in the Table only the most important parameters are reported).
RECORD NUMBER {12345} | TT(1) = 0.1234567890123456D+NN | TIME TAG IN UTC = YYYY/MM/DD HH:MM:SS.SSS OBS(1) = 0.1234567890123456D+NN | S/C DOR (NS) SOBS(1) = 0.1234567890123456D+00 | DOR SIGMA (NS) FREQ(1) = 0.1234567890123456D+NN | MEAN REC.FREQ.(MHZ) RECORD NUMBER {12345} | TT(1) = 0.1234567890123456D+NN | TIME TAG IN UTC = YYYY/MM/DD HH:MM:SS.SSS OBS(1) = 0.1234567890123456D+NN | QUASAR DOR (NS) SOBS(1) = 0.1234567890123456D+00 | DOR SIGMA (NS) FREQ(1) = 0.1234567890123456D+NN | MEAN REC.FREQ.(MHZ) RECORD NUMBER {12345} | TT(1) = 0.1234567890123456D+NN | TIME TAG IN UTC = YYYY/MM/DD HH:MM:SS.SSS OBS(1) = 0.1234567890123456D+NN | S/C DOR (NS) SOBS(1) = 0.1234567890123456D+00 | DOR SIGMA (NS) FREQ(1) = 0.1234567890123456D+NN | MEAN REC.FREQ.(MHZ)
S/C
S/C
Q
R.Maddè, OPS-GSS
22-04-05, Slide 24ESOC
DOR observation (10) Orbit determination
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.
The obtained time is used to correct FD estimation of the delay we are looking for.
The corrected delay is then used to calculate the angle between the orthogonal to the baseline and the S/C direction
Results are then calibrated for media effects
Overall accuracies are mainly driven by:
– Maximum spanned BW
– SNR of S/C and Quasar signals
R.Maddè, OPS-GSS
22-04-05, Slide 25ESOC
Summary of the work to be done
Use of 3rd IFMS in ESA Deep Space facilities as primary DOR processor
Modification of the IFMS internal DSPs (GDSP)
Availability of all IFMSs in Deep Space facilities for redundant DOR measurements
Private VLAN for DOR data routing (IFMS-ESU up to 36 Mbps)
Use of a PC (ESU) with a fast Hard Disk for DOR data storage (up to 8 GB per DOR observation)
Enhancement of link capacity (station-correlator) for the availability of data in near real time
S/W Correlator development limited to MEX, VEX, Ros support only
R.Maddè, OPS-GSS
22-04-05, Slide 26ESOC
Validation plan
First system tests possible during Correlator SAT.
Test Campaign on current ESA Deep Space missions (MEX, Rosetta). DOR results will be compared versus standard tracking techniques (Doppler tracking and ranging).
Possible tests with Smart-1 (equipped with a transponder generating DOR tones at 2 and 16 MHz)
Comparison with JPL DOR results (in S/C orbital
reconstruction) during VEX Cruise phase
R.Maddè, OPS-GSS
22-04-05, Slide 27ESOC
Further developments
BepiColombo
DOR will be needed as well for BepiColombo orbit insertion
– BepiColombo will be equipped with a transponder capable of generating dedicated DOR tones in both X- and Ka-bands.
– The use of a much larger spanned BW will permit better results in terms of S/C position accuracy
JPL interoperability
– 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)
– Lot of work is needed to have compatible data formats (at station level).
R.Maddè, OPS-GSS
22-04-05, Slide 28ESOC
Example of error budget
Main ParametersParameter Value Unit
B = Baseline 11621 kmCh_bw = Channel Bandwidht (Quasar) 2.00E+06 HzCh_bw = Channel Bandwidht (S/C) 5.00E+04 HzTheta = Angular dist. between S/C and EGRS 10 degeps_quas= quasar position uncertainty 2 nradeps_stn = Station Position uncertainty 1.5 cmF = Reference Frequency 8.40E+09 Hzgamma_q = Quasar Elevation 15 degm_TM = modulation index TM 1.25 radgamma_sc = S/C Elevation 10 degN_c = Number of Channels 4R1 = Antenna 1 Radius 17.5 mR2 = Antenna 2 Radius 17.5 mro_z = Zenith Path Delay Uncertainty 2 cmRx S_No = Rx Signal to Noise 52.32 dBHzSamp = Sampling Quasar data (1,2,4,8,16) 2 bitsSc = Source Flux 0.8 JySEP = Sun-Earth-Probe Angle 50 degSub_freq = Subcarrier Frequency 2.62E+05 HzTM_deg = TM Harmonic Degree 20Tobs_q = Observation Time quasar 10 minTobs_sc = Observation Time S/C 10 min
DELAYS using TMType Value (nsec)
Clock Instability 0.004Earth Orientation 0.052
Instrumental Phase Ripple TM 0.265Ionosphere 0.088
Quasar observation accuracy 0.343Quasar Position 0.078
S/C observation accuracy 0.311Solar Plasma 0.003
Station Location 0.058Troposphere 0.447
TOTAL (RMS) 0.710
Station
Geodesy
Geodesy
S/CLink
Link
Link
Astronomy
S/C
Q
C/S0obsminmax
C/SN/ST)ff(2
2
QSR0obsminmax
QN/ST)ff(2
2
R.Maddè, OPS-GSS
22-04-05, Slide 29ESOC
Current schedule (IFMS-EOLP)
1. Kick-off IFMS-EOLP (31 January 2005);
2. Critical Design Review by Kick-off + 10 weeks (held on 13-04-05);
3. Pre-Acceptance Report by Kick-off + 4 months
4. Final acceptance of IFMS-EOLP, (all documents delivered and accepted by the Agency, Acceptance certificate issued) by Kick-off + 6 months.
5. IFMS upgrade in DSA1-DSA2 by Kick-off + 9 months
R.Maddè, OPS-GSS
22-04-05, Slide 30ESOC
Current schedule (Correlator)
1. Kick-off meeting (28 January 2005);
2. Critical Design Review by Kick-off + 12 weeks
3. End of development phase by Kick-off + 8 months
4. Final acceptance of S/W Correlator, (all documents delivered and accepted by the Agency, Acceptance certificate issued) by Kick-off + 9 months.
5. DOR Test Campaign: December 2005
6. Venus Orbit Insertion: March 2006
R.Maddè, OPS-GSS
22-04-05, Slide 31ESOC
DOR team
DOR Team in OPS-GS is:
– Ricard Abelló
– Javier De Vicente
– Marco Lanucara
– Roberto Maddè
– Mattia Mercolino
Many thanks to Mattia Mercolino for helping in preparing this presentation