OPS Forum Delta-DOR 22.04.2005

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


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


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


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


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



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


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



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


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


DOR observation (1) Sequence

Observation Sequence: S/C – Quasar – S/C (or vice versa)

DOR Tone or TM Harm.

FC

Ch. BW (50kHz)




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


(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


(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


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


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


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


(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


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


(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


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


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


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


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


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


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


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


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


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


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


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


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

Technology

OPS Forum Delta-DOR 22.04.2005