OPS Forum ESA Delta DOR 16.03.2007

ESOCR.Maddè, T. Morley

16-03-07, Slide 1

ESA Delta DOR: from implementation to operation

R. Maddè, T. Morley

ESOC, 16th March 2007

R.Maddè, T. Morley

16-03-07, Slide 2ESOC

R.Maddè, T. Morley


Summary

DOR definitions and system requirements System integration

– Receiver modifications and storage unit installation

– Communication links between DSAs and ESOC

– Correlator development Validation with MEX VEX operational campaign

– Results and comparison with JPL results Rosetta operational campaign

– Results and comparison with JPL results Current developments and the future

– Interoperability with other space agencies (JPL, JAXA)

– Use for GAIA, BepiColombo and other future ESA missions

– Support to Phoenix (next JPL mission to Mars)

R.Maddè, T. Morley


DOR definitions (1)

≤10°

Ionosphere

Troposphere

Baseline

-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 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 path dependent will cancel

R.Maddè, T. Morley


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 should not exceed 10 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, T. Morley


Observation Sequence: S/C – Quasar – S/C (or Q-S-Q)

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 (embedded in the receiver noise)

DOR definitions (3)

R.Maddè, T. Morley


Driving requirements

Capability of simultaneous multiple channel (up to 8) open loop recording in the receiver (IFMS)

Timetag synchronisation among channels better than 1 nanosecond

Capability to format and store huge amount of data (tens of GB)

Raw data transfer and processing within 24 hours from acquisition– Fast data transfer

– Fast correlation process

System to be developed, tested, deployed and validated in 10 months

Delta-DOR overall accuracy: 1 nanosecond

R.Maddè, T. Morley


Implementation approach

Modifications to implement Delta-DOR capabilities:

– Receiver (IFMS) modification to record in open loop up to eight channels simultaneously

– Installation of an External Storage Unit (ESU) for fast formatting and storage of the data

– Upgrade of the communication links between DSAs and ESOC to transfer up to 5.5 GB of data in 10 hours

– Development of a S/W correlator for Delta-DOR raw data processing

R.Maddè, T. Morley


IFMS/ESU modifications

IFMS GDSP Modifications

– 4 channels per GDSP with BW from 1kHz to 4MHz (depending on quantisation)

– Quantisation 1,2,4,8,16 bits (normally 8-bit for S/C acquisitions and 2-bit for quasar acquisitions)

– Synchronisation of GDSPs internal clock to a level better than 1 nanosecond

– 2 GDSPs per IFMS modified, to allow reception of up to 8 channels

Installation of two ESUs

– Release the IFMS from storage burden

DOR data fast formatting and storage

CH

4

CH

3

CH

2

CH

1

36Mbits/s

36Mbits/s

GDSP2

GDSP1

CFE

External Storage Unit (ESU)

IFMS

R.Maddè, T. Morley


Need for an ad-hoc data transfer strategy

– Use of the direct link between the DSA and ESOC

– Use of an indirect link between the DSA, a nearby antenna (Perth for NNO and Vilspa for CEB), and ESOC

– Optimized stacks and algorithms

Communication links

Data volumes to be transferred from each station

– S/C observation: 0.25 GB– Quasar observation 2.6 GB– Worst case (Q-S-Q sequence): 5.5 GB– Requirement: data to be transferred

and processed within 24 hours from acquisition

R.Maddè, T. Morley


DOR Correlator (1)I/F definitions

Correlator interfaces Inputs

Outputs

Station1, Station2: open loop data

FD (input): orbital data to help the correlation

FD (output): the final product of the correlation

CP: configuration parameters

FD

Station 1

CP S/WCorrelator

Station 2

FD

S/C signal correlation– Set of TM harmonics: signal characteristic permits phase extraction

Quasar signal correlation– Noise-like signal totally embedded in receiver noise: signal characteristic

forces to go for a direct correlation method

R.Maddè, T. Morley


Spectrum of the TM harmonics (up to the 14th) of the Rosetta

transponder

Spectra (over 1 second data) of the four 50kHz channels recorded

during one of the passes

DOR correlator (2) S/C signal structure

R.Maddè, T. Morley


DOR correlator (3) S/C signal correlation

Phase extraction by means of a S/W frequency estimator on the carrier and the lowest order TM even harmonic (highest in S/N)

Drive the phase extraction of all other tones with the model (properly Doppler-scaled) built on the lowest order TM harmonic

Multiplication of the extracted phasor with a phasor computed using the FD model At this point, we have the phase sequences of each TM harmonic at each Station, sufficiently corrected for phase uncertainties

The correlation result as such is “modulo 2” ambiguous After an ambiguity resolution process a S/C DOR delay (S/C) is obtained

Correlation of the phase of each channel of Station 1 with the phase of the corresponding channel of Station 2

CHf

R.Maddè, T. Morley


Spectra (over 1 second data) of the four 2MHz channels recorded

during one of the passes

Quasar signal– Random noise-like signal

– Quasar signal is totally embedded in antenna noise

– Need for a wider channel BW to accumulate enough Signal-to-noise

DOR correlator (4) Quasar signal structure

R.Maddè, T. Morley


DOR correlator (5) 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 due to 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 typically 1 s, in order to keep a tolerable level of error in Doppler compensation

Correlation is performed for a suitable integration time (typically 10 min) 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: “bandwidth synthesis”)

The result of the correlation is then added to the value given by FD model

As a result, one obtains a Quasar DOR (Q)

R.Maddè, T. Morley


DOR correlator (6) Correlator 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, T. Morley


Orbit determination

To obtain a DOR observation, the two S/C observations are linearly interpolated to the time of one 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 line 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, T. Morley


Example of error budget

Main ParametersB = 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 1 nradeps_stn = Station Position uncertainty 2 cmF = Reference Frequency 8.40E+09 Hzgamma_q = Quasar Elevation 15 degm_TM = modulation index TM 1.25 radgamma_sc = S/C Elevation 12 degN_c = Number of Channels 4R1 = Antenna 1 Radius 17.5 mR2 = Antenna 2 Radius 17.5 mro_z = Zenith Path Delay Uncertainty 5 cmRx S_No = Rx Signal to Noise 50 dBHzSamp = Sampling Quasar data (1,2,4,8,16) 2 bitsSc = Source Flux 0.7 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 6 min

DELAYS using TMType Value (nsec)

Clock Instability 0.000Earth Orientation 0.052

Instrumental Phase Ripple TM 0.053Ionosphere 0.006

Quasar observation accuracy 0.297Quasar Position 0.039

S/C observation accuracy 0.401Solar Plasma 0.000

Station Location 0.058Troposphere 0.252

TOTAL (RMS) 0.569

S/C

Q

C/S0obsminmax

C/SN/ST)ff(2

2

QSR0obsminmax

QN/ST)ff(2

2

Station

Geodesy

Geodesy

S/CLink

Link

Link

Astronomy

R.Maddè, T. Morley


System Validation and tracking

campaign results

R.Maddè, T. Morley


DOR system validation with MEX

Quasar1 – Quasar2 – Quasar1 trackings

– A series of Quasar-Quasar tracking was performed during December 2005 in order to validate the Quasar correlator

System validation with Mars Express

– Orbiting S/C with an a-priori trajectory known with an accuracy of 200 m

– Mars ephemeris known with an accuracy of the same order of magnitude

0.905

1.169

0.488

0.488

1.169

0.533

1σ (ns)

-0.114

-0.421

0.168

0.196

-0.679

-0.041

Post fit residual (ns)

-0.977

-0.978

13:18:56.90

13:40:39.90S678SQSQS7/Mar

0.312

0.312

0.312

0.310

13:21:50.90

13:42:19.90

14:06:42.90

14:42:15.90

S072 and

S088SQSQSQSQS29/Jan

Δtime (μs)DDOR time

Hh:mm:ss.msQOrder

Date

(DD/MM)

RMS post-fit residuals 0.3 ns

R.Maddè, T. Morley


VEX operational campaign (1)

= ESA NNO-CEB Baseline (both 35m antennas)

= DSN GOL-MAD Baseline (two 70m antennas) = DSN GOL-CAN Baseline (two 70m antennas)

= DSN GOL-MAD Baseline (at least one 34m antenna) = DSN GOL-CAN Baseline (at least one 34m antenna)

R.Maddè, T. Morley


45 JPL DOR data points

– Overall JPL data RMS post-fit residual = 0.8 ns

– JPL data RMS (34-metre antenna only) = 1 ns

15 ESA DOR data points (in 5 DOR sessions)

– ESA data RMS post-fit residual = 1.2 ns (data weighted with 1/ of the measurement – with 0.4 < < 2.1 ns )

– 35-metre antennas only

– Smaller total spanned BW with respect to JPL

– All JPL data weighted either using = 0.25 or = 0.35 ns

Both JPL and ESA results are below expectations because of probable mismodelling of S/C accelerations

VEX operational campaign (2)

R.Maddè, T. Morley


Test with Smart-1

Smart-1 is (was) the only ESA spacecraft equipped with a transponder capable of generating dedicated DOR tones (placed at ±2 and ±16 MHz)

– Higher signal-to-noise on the spacecraft signal

– Wider total spanned bandwidth (better accuracy)

Date(DD/

MM)Order Q

Timetaghh:mm:ss.m

s

1σ (ns

)

Pre-fit residual (ns)

Plane of the sky (m)

8/Jul QSQS S48419:24:20.90 19:46:23.00

0.50.5

3.753.481

3734

10/Aug SQSQSQS S60521:53:11.7022:22:28.7022:40:44.00

0.50.50.5

2.4584.0452.107

22.436.919.2

Only pre-fit residuals available

Pre-fit plane of the sky residuals (RMS = 30m) < uncertainty in orbit determination (150m)

R.Maddè, T. Morley


Rosetta operational campaign (1)

R.Maddè, T. Morley


46 JPL DOR data points – Overall JPL data RMS post-fit residual = 0.16 ns

31 ESA DOR data points (in 16 DOR sessions) – ESA data RMS post-fit residual = 0.53 ns (data weighted with 1/ of the

measurement – with 0.4 < < 3 ns ), all JPL data weighted either using = 0.25

– 35-metre antennas only (some of JPL DOR performed using 70-metre antennas)

– Smaller total spanned BW with respect to JPL (ESA 9 MHz, JPL 15 MHz)

– Smaller channel bandwidth used for quasar tracking (ESA 2 MHz, JPL 4MHz)

– Two DOR performed with quasars having very low flux (< 0.1 Jy)

– Two DOR acquisitions were with the Rosetta transponder in self-lock status (dramatic degradation of signal quality). This never happened during JPL acquisitions

– Discarding these 4 DOR ESA data RMS post-fit residuals = 0.34 ns

ESA results are well within the required accuracy (1 ns) but could possibly give better accuracies. This needs further investigations (ongoing)

Rosetta operational campaign (2)

R.Maddè, T. Morley


On going developments and the future

R.Maddè, T. Morley


Current activities (1)

Development of a data translator – Being able to process data coming from other Agencies, ESA would be

capable to provide

• Tracking support + data translation to the desired data format

• Tracking support + data correlation

R.Maddè, T. Morley


Current activities (2)

Enhancement of S/W correlator capabilities– The first version of the S/W correlator was able to support

only a limited number of quantisation schemes and sampling rates (i.e. 50kHz with 8-bit for the S/C signal and 2MHz with2-bit for the quasar signal)

– The maximum number of channels to be processed was fixed to 4

– The new S/W correlator will be capable to process data with all sampling rates and quantisation schemes possible with the IFMS

– The maximum number of channels to be processed will be up to 8

– New operational modes will also be added

R.Maddè, T. Morley


DOR future (1) - Interoperability

Interoperability with other Agencies

– With JPL: ESA baseline CEB-NNO is almost perfectly orthogonal to JPL baseline Goldstone-Canberra, thus providing complementary information for OD

– With JAXA: NNO is almost in a North-South direction with Japanese stations (and declination is the coordinate which is worse determined by Doppler and ranging only solutions). CEB would provide a very long baseline when in conjunction with one Japanese antenna

Why interoperability with VLBI network

– Being able to process data coming from other stations than ESA would enlarge the number of usable baselines

– It would also reduce the operational load on ESA stations when necessary

On which missions

– First opportunity would JPL mission Phoenix (launch in August 2007, arrival at Mars in April 2008)

– All interplanetary missions

R.Maddè, T. Morley


DOR future (2) – JPL Cross support

ESA DOR support to Phoenix– Phoenix has extremely stringent navigation requirement (requirement for JPL

DOR is of 60 ps accuracy)

– It is equipped with a transponder capable to generate DOR tones at ±19MHz at X-band only

– JPL plan to get down to the desired level of accuracy is to use the second harmonic of the DOR tone (so to have a total spanned BW of 76 MHz). The theoretical uncertainty in this case would be of 80 ps with quasars having flux of 0.7 Jy

– ESA cannot use the same BW JPL is using. Limitation to 28MHz BW

– The use of this BW would anyway guarantee accuracies down to 0.22 ns with quasars having flux of 0.7 Jy

– ESA baseline is almost perfectly orthogonal to the Goldstone – Canberra, thus providing the complementary information for orbit determination

– We are currently developing a plan to demonstrate the feasibility of its support to Phoenix

R.Maddè, T. Morley


Roadmap for JPL cross support (1)

Currently, the interoperability has been tested in only one direction (ESA spacecraft tracked by JPL antennas and correlation results provided to ESA OD team by JPL)

Progressive steps of interoperability validation are:1. “calibration step”: ESA planetary orbiting S/C simultaneously tracked by 2

ESA and 2 JPL antennas. Independent correlation processes performed by JPL and ESA. Final DDOR results validation by ESA OD team step completed

2. ESA S/C tracked by one JPL antenna and one ESA antenna. Exchange of raw data and correlation performed at both ESA and JPL. DDOR data analysis by ESA OD team on going

3. JPL S/C tracked by two ESA antennas, correlation results and OD provided by ESA to JPL ready for Phoenix support

4. JPL S/C tracked by one JPL antenna and one ESA antenna. Exchange of raw data and correlation performed at both JPL and ESA. DDOR data analysis by JPL OD team

5. JPL S/C tracked by two ESA antennas, correlation results and OD provided by ESA to JPL

R.Maddè, T. Morley


Roadmap for JPL cross support (2)

Step 2 would need an ESA orbiting S/C to be tracked using the four stations:

- CEB (ESA)

- NNO (ESA)

- Robledo (JPL)

- Goldstone (JPL)

The tracking should be structured as follows:– Simultaneous tracking from CEB-NNO and

Robledo

– Simultaneous tracking from Goldstone-Robledo and CEB

This step would validate the ESA data translator and correlator with JPL correlator

R.Maddè, T. Morley


Roadmap for Jaxa cross support

Jaxa would like to use K5 raw data format

This is a VLBI compatible data format (very similar to Mk5 format)

The translator under development will be able to treat the Mk5 format

An agreement for the formalisation of cooperation on delta-DOR has been reached in January 2007

Definition of interfaces on going Future steps:

– Definition of level of cooperation– Identification of suitable missions, for cooperation demonstration– Preparation of a suitable test campaign

R.Maddè, T. Morley


Example of JPL and JAXA cross support

R.Maddè, T. Morley


DOR future (3) – Inside ESA

DOR with Kourou

– Kourou has been recently upgraded with Hydrogen Masers and IFMS/ESU. The station is potentially ready to support DOR

BepiColombo DOR will be needed as well for BepiColombo navigation during critical

phases (Venus fly-bys) and Mercury orbit insertion

– BepiColombo will be equipped with a transponder capable of generating dedicated DOR tones in both X- (total spanned bandwidth of 40 MHz) and Ka- (total spanned bandwidth of 160 MHz) bands.

– The use of a much larger spanned BW will permit better results in terms of S/C position accuracy (estimation below 100 ps in Ka-band)

GAIA

– GAIA has very stringent navigation requirements when orbiting in L2, making this mission a perfect potential user of DOR

EXO MARS, LISA-Pathfinder, LISA, Don Quijote, SOLO

R.Maddè, T. Morley


DOR future (4) – Related techniques

Station location DOR could be used to check the position of ESA stations

– This would be done using for each observation one ESA and one VLBI station which position is already well known

Phase referencing

– Phase referencing is a powerful interferometric technique to get absolute differential phase measurements

– It was used to get a-posteriori results for the descent orbit of Huygens

Same Beam Interferometry (SBI)

– SBI is another interferometric technique that makes use of a planetary orbiting S/C to precisely locate another S/C which is in the same antenna beam

– The technique could be used at Mars, where there are several S/C already orbiting

R.Maddè, T. Morley


Conclusions

A lot of work has been done in the last 2 ½ years Much more work is going to come Currently ESA is the only place investing on cross-support Such (moderate) investment will allow ESA to be in a favourite position for the years

to come

However, the current activities are only marginally improving the quality of our service, in terms of end-to-end performance

In order to improve in performance, we need to invest more on the following areas:– Troposphere calibration techniques (a very simplified model is used today)

– Ionosphere calibration techniques (we currently depend on JPL for that)

– We need to develop a wider band receiver (IFMS limitations)

R.Maddè, T. Morley


Acknowledgments

Delta-DOR Team

– OPS-GS

• Mattia Mercolino

• Marco Lanucara

• Ricard Abelló

• Gunther Sessler

• Javier De Vicente

– OPS-GF

• F. Budnik

• N. Schlecht

– OPS-ECT

• M. Bertelsmeier

• G. Buscemi

Technology

OPS Forum ESA Delta DOR 16.03.2007