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OPS Forum ESA Delta DOR: from implementation to operation 16.03.2007
 

OPS Forum ESA Delta DOR: from implementation to operation 16.03.2007

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The presentation will report on experiences gained during the past year of delta-DOR at ESA. The system was deployed and validated in ESA deep space stations, provided substantial support to VEX orbit ...

The presentation will report on experiences gained during the past year of delta-DOR at ESA. The system was deployed and validated in ESA deep space stations, provided substantial support to VEX orbit insertion, was handed over to Operations and was essential for support during the Rosetta Mars swing-by. The presentation will also give an overview of the current and foreseen developments, with the strategic view of providing cross-support to other Agencies.

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    OPS Forum ESA Delta DOR: from implementation to operation 16.03.2007 OPS Forum ESA Delta DOR: from implementation to operation 16.03.2007 Presentation Transcript

    • ESOC Introduction to ∆DOR T. Morley OPS/GFI OPS-G Forum: ∆DOR System 22 April 2005
    • Contents ESOC ❒ What is ∆DOR? ❒ Why ∆DOR? ❒ Why ESA ∆DOR now? ❒ ∆DOR accuracy. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 2 / 11
    • What is ∆DOR ? ESOC ❒ ∆DOR stands for Delta Differential One-way Range. ❒ ∆DOR is a radiometric (tracking) data type that complements conventional Doppler and range measurements for deep space missions; - main use is during heliocentric cruise at large geocentric distance. ❒ ∆DOR is a kind of Very Long Baseline Interferometry (VLBI) for spacecraft, with an extra-galactic radio source (quasar) used for calibration. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 3 / 11
    • Differential One-way Range Measurements ESOC Measure differential one-way delay of spacecraft signal. Measure differential one-way delay of near-by quasar signal. Subtract differences - cancels errors, e.g. media, clocks, instrumentation.. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 4 / 11
    • ∆DOR Features ESOC ❒ Observables are the differential delay (τ) for s/c and quasar: - “delta” conversion to ∆DOR is done within the orbit determination. ❒ Basic equations: cτ c sin θ = ---- , - δθ = --------------- δτ - B B cos θ - angular error inversely proportional to length of baseline! - long baseline means low elevation at mutual station visibility. ❒ Quasar direction known precisely (best < 2 nanoradians error). ❒ Quasar chosen so that direction close to spacecraft (< 15 ° ): - similar spacecraft and quasar signal paths through atmosphere. ❒ Same frequency channels recorded for spacecraft and quasar: - no frequency-dependent differential effects. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 5 / 11
    • Why ∆DOR ? (1) ESOC ❒ Range and Doppler are line-of-sight measurements: - range gives accurate information on only 1 component of position; - Doppler gives accurate information on only 1 component of velocity; - direction information is obtained only indirectly thanks to Earth rotation but the accuracy is limited even after many passes; - poor accuracy in declination when s/c near the equator; - (in planetary orbit, fast-changing dynamics gives direction). ❒ A single ∆DOR data point gives one direction angle: - nearly instantaneous measure (less than 1 hour); - very accurate measurement; - need ∆DOR data points from 2 baselines for full direction. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 6 / 11
    • Why ∆DOR ? (2) ESOC ❒ Improves orbit determination (OD) accuracy: - saves fuel ! ❒ Independent confirmation of conventional OD solutions: - improves robustness ! ❒ Needed when critical reliance on navigation accuracy: - planetary swing-by (except Earth), e.g. Rosetta/Mars, Bepi Colombo; - planetary orbit insertion, e.g. MEX, VEX, Bepi Colombo; - landing on a planet, e.g. Beagle 2. ❒ Fast recovery of orbit knowledge after unknown ∆V: - e.g. MEX or VEX safe mode entry with unbalanced thrusters. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 7 / 11
    • Why ESA ∆DOR now ? ESOC ❒ 2 ESA Deep Space antennas will be operational in 2005. ❒ To meet needs of current and future deep space missions without being dependent upon NASA/DSN: - MEX: used DSN ∆DOR measurements; - VEX: both ESA and DSN ∆DOR being planned; - Rosetta: Mars swing-by in February 2007; - Bepi Colombo: navigation absolutely needs ∆DOR. ❒ Complementary to DSN ∆DOR (and other VLBI systems): - Cebreros - New Norcia is a new baseline orientation; - future use of 1 ESA + 1 DSN station could be foreseen; - possibilities with other stations, e.g. 70 m. antenna at Evpatoria. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 8 / 11
    • Station Baselines and Visibility for ∆DOR ESOC 80. NASA/DSN ESA 70. 60. 50. 40. MADRID GOLDSTONE CEBREROS 30. 20. 10. 0. -10. -20. -30. NEW NORCIA -40. CANBERRA YELLOW REGIONS OF SUBSATELLITE POINT SHOW -50. MUTUAL VISIBILITY ABOVE 10 DEGREES ELEVATION -60. -70. -80. 140. 160. 180. 200. 220. 240. 260. 280. 300. 320. 340. 360. 380. 400. 420. 440. 460. 480. 500. 0. 20. 40. 60. 80. 100. 120. 140. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 9 / 11
    • ∆DOR Accuracy ESOC ❒ ESA system initial target accuracy of 1 nanosecond for τ: - for 10 000 km baseline, angular accuracy = 30 nanoradians; - 30 nanoradians at 1 AU (150 million km) = 4.5 km. ❒ Comparison with MEX NASA/DSN ∆DOR: - expected accuracy before launch of ~0.5 ns; - assumed RMS error during cruise was usually 0.25 ns; - overall RMS error value from navigation analysis ~0.17 ns; - less than 1 km for MEX arrival at Mars. OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 10 / 11
    • MEX B-plane estimates on 23 December 2003 ESOC 3-SIGMA ERROR ELLIPSES 1200 DOPPLER ONLY 263.0 X 66.5 KM 1100 DOPPLER + RANGE 87.9 X 5.6 KM B-R - KM 1000 TARGET 900 DOPPLER, RANGE + DELTA-DOR 800 12.8 X 1.9 KM 7600 7700 7800 7900 B-T (PROJECTION OF MARS EQUATOR) - KM OPS/G Forum: ∆DOR System T. Morley OPS/GFI 22-04-05, Slide 11 / 11