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Using the VLBA for Spacecraft Navigation

Using the VLBA for Spacecraft Navigation. Jonathan Romney National Radio Astronomy Observatory VLBA 10 th Anniversary 2003 June 9 – 12. Collaborators. John Benson Walter Brisken Vivek Dhawan Craig Walker. Overview. Basic Concept Initial Tests Proposed Pilot Project

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Using the VLBA for Spacecraft Navigation

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  1. Using the VLBA forSpacecraft Navigation Jonathan Romney National Radio Astronomy Observatory VLBA 10th Anniversary 2003 June 9 – 12

  2. Collaborators • John Benson • Walter Brisken • Vivek Dhawan • Craig Walker VLBA 10th Anniversary

  3. Overview • Basic Concept • Initial Tests • Proposed Pilot Project • Implementation Phase VLBA 10th Anniversary

  4. Basic Concept • Precision Differential Astrometry • Use well-established VLBA phase-referencing technique. • Image spacecraft downlink transmitter; • measure (time-dependent) offset, relative to suitable reference sources. • Close Analog • Observations of maser sources, referenced to continuum calibrators. • Primary difference: source moves relative to references. VLBA 10th Anniversary

  5. Basic Concept • Conventional Spacecraft Navigation • Primarily based on range, measured as integrated velocity. • Supplemented by single-baseline VLBI technique. • Bandwidth-synthesis-like side tones required to resolve fringe ambiguity. • Yields delay as fundamental observable. • VLBA Multi-Baseline Technique • 45-baseline observation eliminates fringe ambiguity, as in normal imaging. • Provides absolute celestial coordinates directly. VLBA 10th Anniversary

  6. Basic Concept • Synthesis • Precise two-dimensional celestial coordinates can enhance range-based navigation substantially. • Overall 3-dimensional navigation capability could be simultaneously more precise, less expensive, and operationally simpler. VLBA 10th Anniversary

  7. Overview • Basic Concept • Initial Tests • Proposed Pilot Project • Implementation Phase VLBA 10th Anniversary

  8. Initial Tests August – December 2002 • Experimental Target • Stardust. • Mission to sample and return dust from Comet Wild 2: 2004 January 2. • (Successful close flyby of Asteroid Annefrank: 2002 November 2.) • Test Observations • October – December 2002. • Imaged Stardust with ~5 mas resolution, 100:1 dynamic range. • Phase referencing only partially successful. • Stardust was in far southern Ecliptic, at -22 degrees declination. • Reference sources 2 – 6 degrees distant. • Successfully measured position offset once, ~12 mas relative to predicted orbit. VLBA 10th Anniversary

  9. Initial Tests • Experimental Modifications to VLBA • Schedules kluged to point to Stardust. • Downlink schedule transmitted by fax. • Correlator software modified to add moving source coordinates. • NAIF/SPICE system previously used for moving station in Space VLBI correlation. • But: best ephemeris expected is equivalent to SVLBI “predicted orbit”; “reconstructed orbit” would require same input we aim to provide. • Near-field correction, already implemented in correlator model server, tested for first time. • (VLBA’s near field extends to ~100 AU at X-band!) VLBA 10th Anniversary

  10. Overview • Basic Concept • Initial Tests • Proposed Pilot Project • Implementation Phase VLBA 10th Anniversary

  11. Proposed Pilot Project • Study Goals – Feasibility • Evaluate feasibility of VLBA spacecraft navigation. • Achievable angular precision, under various observing conditions, for various spacecraft characteristics. Goal: 0.5 nano-radian. • Enhancement of overall spacecraft navigation resulting from addition of VLBA angular position measurements. • Determine optimal observing strategy. • Required instrumental sensitivity and density of reference sources. • Estimate impact on VLBA observing load. • (Expected to be possible to interleave with ongoing observations, with minor impact.) VLBA 10th Anniversary

  12. Proposed Pilot Project • Study Goals – Implementation: Plans / budgets for … • New equipment. • 33-GHz receiver systems: new spacecraft downlink band. • Wideband Mark 5 recording systems: essential for sufficiently dense catalog of reference sources. • Replacement for correlator PBI: current bandwidth bottleneck. • Software upgrades. • Scheduling & pointing. • Rapid bandwidth switching. • Correlation & model accountability. • New operational procedures. • Scheduling. • Shipping. VLBA 10th Anniversary

  13. Proposed Pilot Project • Status • Discussions with NASA began in January 2003. • NRAO proposal positively received. • Anticipating NASA will fund Pilot Project in near future … • but details of how it will work still being worked out. VLBA 10th Anniversary

  14. Overview • Basic Concept • Initial Tests • Proposed Pilot Project • Implementation Phase VLBA 10th Anniversary

  15. Implementation Phase • Assuming Successful Outcome of Pilot Project: • NRAO will propose implementation phase. • Two-year duration planned. • Implementation Project Would Include: • New equipment: 3 GHz / new PBI / Mark 5. • Software upgrades. • Development of new operational procedures. • Compilation of 33-GHz reference catalog. VLBA 10th Anniversary

  16. Thank You! • For exploiting the VLBA’s many capabilities … • to achieve all the great science reported in these four days; • … • And for coming to our Anniversary Party! VLBA 10th Anniversary

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