1. L.I. Gurvits, S.V. Pogrebenko, I.M. Avruch Joint Institute for VLBI in Europe Dwingeloo, The Netherlands and PRIDE team Space horizons of radio astronomy and the world’s largest radio telescope Frontiers of Astronomy with the World’s Largest Radio Telescope Washington DC, 12-13 September 2007

2. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.2 Space exploration & radio astronomy: 50 years together Glorious start: first sputnik and 76-m Jodrell Bank (now Lovell) telescope, 4 October 1957 Parkes receives the first TV images of N. Armostrong on the Moon, July 1969 VEGA Balloons & VEGA/Giotto Pathfinder, 1984-86 (Sagdeev et al., 1992) Discovery of variability of extragalactic radio sources using deeps space communication antenna by G.B. Sholomitsky, 1965 Arecibo radio telescope as a “pathfinder” for planetary science and exploration

3. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.3 Titan, 14 January 2005

4. Huygens signal paths Cassini S/C TCXO RUSO TCXO TUSO Ch. B: 2097 MHz Ch. A: 2040 MHz “Channel C” – eavesdropping on Channel A carrier Huygens Data Huygens Receivers Huygens Probe

5. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.5 VLBI tracking of Huygens, 14 January 2005 09:30 UTC16:00 UTC

6. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.6 Algorithm of VLBI processing… “Standard” broad-band VLBI correlation on calibrators Imaging of calibrators and calibration definition Extraction of narrow-band probe’s Signal from Mk5 to HSC Application of calibration corrections to the narrow-band data Iterative search for monocromatic (carrier) signal; Common Mode defined Phase-lock to Common Mode, narrowing down search window Iterative imaging (trajectory reconstruction)

7. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.7 70 s gaps in radio data Phase-referencing duty-cycle 70-110 s: two telescopes, PT and OV were on Huygens continuously: no detections so far in direct Doppler measurements (cf. Folkner et al. 2006, JGR) Can in-beam (no nodding) phase-referencing help? Need for strong enough and compact reference source within primary beam! Huygens Reference Huygens Reference 110 70 Time

8. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.8 Huygens Field MERLIN 5 GHz 70 mJy MERLIN 5 GHz 10.4 mJy VLA 5 GHz 1.3 mJy VLA 8 GHz 7.2 mJy Titan 10 arcmin Prime reference J0744+2120 Primary beam

9. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.9 VLBI Theoretical Delay (VTD): a tool for S/C VLBI tracking Developed by L.Petrov (NASA GSFC) Accounts for various fine-tuning effects (general relativity propagation, telescope mechanics, geo-tectonics, atmospheric and ocean tides – mm-level shift of baricenter, etc.) Takes into account “near field” effects (B 2 /λ >> 1 AU) Improves a-priori VLBI geometrical model comparing to the “standard” CALC-10 software package (now better than 1 ps)

10. Antenna temperature for Mauna Kea Ta=~100 K, with SNR=70 Line width B=20 mHz, Total power P=k*Ta*B, hυhυhυhυhυhυhυhυhυhυ Huygens’ Signal power captured by Mauna Kea antenna: 20 photons per second, Photon Rate = P / hυ “Pulsar-style” folding

11. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.11 Stochastic delay noise ~ 20 picoseconds The Huygens probe signal delay detections are based on cross-correlation of ~ 20 photons per second from 20 -25m antennas with ~ 600 photons per second from GBT @ λ=15cm and energy flux of 0.2 - 0.4 photon per second per square meter Arguably the most sensitive radio astronomical detection ever Single dish detected powerFringes on baselines Exploring the Quantum Frontiers of VLBI

12. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.12 Huygens VLBI-DTWG descent trajectory Based on VLBI “picture plane” measurements and in-situ altitude data Utilises 7 telescopes only (GBT + VLBA, 6 baselines only) Titan-centric accuracy limited by the J2000 accuracy of Titan (~10 mas  60 km) Permits parallel shift for ±40 km Further improvement underway

13. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.13 Utilisation of Doppler data (probe’s motion) T = 8÷10 s ΔV = 0.22 m/s A ≈ 0.6 m Data available for analysis!

14. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.14 Doppler residual analysis Parks “after-landing” phaseGreen Bank “parachuting” phase Perfectly consistent with theoretical value 1.6 cm/s

15. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.15 Titan atmosphere turbulence signature Characteristic velocityCharacteristic time GBT parachute phase (smooth)11.0 cm/s12.9 s Parkes parachute phase7.2 cm/s8.5 s Parkes after landing1.6 ± 0.2 cm/s5.7 ± 0.4 s

16. Medicina 32-m VLBI antenna Metsähovi 14-m VLBI antenna Westerbork synthesis radio telescope, single 25-m antenna is used for tracking experiments Computational core, Board and chip of the 50 Tflops EVN Mk5 Correlator at JIVE “Old” hardware setup on which JIVE/Huygens software correlator was developed “New” S/C VLBI tracking hardware setup at JIVE SMART-1 demonstration

17. Dynamic spectra of S/C signal as observed by Medicina (left) and Metsähovi (right) during the spacecraft’s egress from an occultation “Mouse tails” at the bottom represent diffracted signal which appears many seconds before the direct signal beams into receiving antennas. Frequency detections: Medicina – circles, Metsähovi - diamonds Frequency scales for both stations are cross-calibrated to sub-milliHz level with “clock-search” data on calibrator source

18. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.18 Smart-1 as a text-book demo for classical optics For comparison: power (red) and phase (blue) patterns for diffraction on a flat circular screen Post-egress “classical” diffraction pattern and zoom on pre-egress high beamed features, seen around seconds 5 and 8-10

19. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.19 Favorable configuration X-band,  4 cm estimates VLBI across Solar System: pushing the limits

20. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.20 Generic PRIDE configuration Planet-target PRIDE utilises and enhances generic instrumental configuration of [any planetary] mission Planetary Radio Interferometry and Doppler Experiment (PRIDE)

21. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.21 PRIDE-X vs Huygens VLBI – without and with Arecibo HuygensPRIDE-XResolution gain Radio link frequency2 GHz2/8/32 GHz1/4/16 Distance8 AU~8 AU1 VLBI “fringe” SNR: - “Huygens network” - Arecibo + GBT + … 10 - 3030 - 100 100 - 300 ~3 ~10 Linear resolution (1σ): - “Huygens network” - Arecibo + GBT + … 1 km360/80/20 m 120/30/- m ~3/12/50 ~10/30/- Conservative estimate, today’s technology; No special requirements for the on-board instrumentation In-beam “Orbiter-Probe” calibration can improve SNR further

22. LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C.22 Arecibo as a PRIDE facility? Numerous planetary science and exploration missions call for “Huygens-style” VLBI support (PRIDE) Arecibo offers at least factor of 3 gain in sensitivity for “Huygens- style” VLBI experiment over GBT S-band communication “probe – orbiter” is likely to remain operational Plus: a “free” bonus: Data rate of direct receipt of Huygens-style (~10 W) probe signal on Earth with Arecibo is possible at 3-10 bps