L.I. Gurvits, S.V. Pogrebenko, L.I. Gurvits, S.V. Pogrebenko, I.M. Avruch I.M. Avruch Joint Institute for VLBI in Europe Joint Institute for VLBI in Europe Dwingeloo, The Netherlands Dwingeloo, The Netherlands and and PRIDE team PRIDE team Space horizons of Space horizons of radio astronomy and radio astronomy and the world’s largest the world’s largest radio telescope radio telescope Frontiers of Astronomy with the World’s Largest Radio Telescope Washington DC, 12-13 September 2007
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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.
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L.I. Gurvits, S.V. Pogrebenko, I.M. AvruchL.I. Gurvits, S.V. Pogrebenko, I.M. AvruchJoint Institute for VLBI in EuropeJoint Institute for VLBI in Europe
Dwingeloo, The NetherlandsDwingeloo, The Netherlandsandand
PRIDE teamPRIDE team
Space horizons of radio Space horizons of radio astronomy and the world’s astronomy and the world’s
largest radio telescope largest radio telescope
Frontiers of Astronomy with the World’s Largest Radio Telescope Washington DC, 12-13 September 2007
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
LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C. 3
Titan, 14 January 2005
Huygens signal paths
Cassini S/C
TCXO TCXO
TCXORUSO
TCXOTUSO
Ch. B: 2097 MHz
Ch. A: 2040 MHz
“Channel C” – eavesdropping on Channel A carrier
Huygens Data
HuygensReceivers
HuygensProbe
LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C. 5
VLBI tracking of Huygens, 14 January 2005
09:30 UTC 16:00 UTC
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Algorithm of VLBI processing…
Correlator
Station Units and DDU
MK5/MK4 UNITS
CCCDDD
EEE
T-Base 10/100/1000 LAN
LinuxCluster
Control and Visualisation Workstation
Celestial Model from CCC
Phase corrections from AIPS
Ephemerids and Navigation dataon Titan/Huygens from JPL
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)
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?
REFERENCE SOURCE
TARGET
CORRELATORand
POSTPROCESSING
Phase Distortions
Telescope positionand LO errors
Apparent group delay
Measure the apparent group delayon reference source, compare withpredicted according to the knownmodel, derive corrections, applythem to the signal from a target.
Resulting accuracy depends on SNRfor ref.source and its distance fromthe target (isoplanaticity ).
Need for strong enough and compact reference source within primary beam!
Huygens
Reference
Huygens
Reference110 11070 70
Time
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Huygens Field
MERLIN 5 GHz70 mJy
MERLIN 5 GHz10.4 mJy
VLA 5 GHz1.3 mJy
VLA 8 GHz7.2 mJyTitan
10 arcmin
Prime reference J0744+2120
Primarybeam
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 (B2/λ >> 1 AU)
Improves a-priori VLBI geometrical
model comparing to the
“standard” CALC-10 software
package (now better than 1 ps)
Antenna temperature for Mauna Kea Ta=~100 K, with SNR=70
Line width B=20 mHz,
Total power P=k*Ta*B,
hυhυhυhυ
hυ
Huygens’Signal power captured by
Mauna Kea antenna:
20 photons per second,Photon Rate = P / hυ
“Pulsar-style” folding
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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 Arguably the most sensitive radio astronomical detection ever
Single dish detected power Fringes on baselines
Exploring the Quantum Frontiers of VLBI
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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
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Utilisation of Doppler data (probe’s motion)
T = 8÷10 sΔV = 0.22 m/sA ≈ 0.6 m
Data available for analysis!Data available for analysis!
LIG 12 Sep 2007Frontiers of radio astronomy, Washington D.C. 14
Doppler residual analysis
Parks “after-landing” phase
Green Bank “parachuting” phase
Perfectly consistent withtheoretical value 1.6 cm/s
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Titan atmosphere turbulence signature
Characteristic velocity Characteristic time
GBT parachute phase (smooth) 11.0 cm/s 12.9 s
Parkes parachute phase 7.2 cm/s 8.5 s
Parkes after landing 1.6 ± 0.2 cm/s 5.7 ± 0.4 s
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
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 appearsmany seconds before the direct signalbeams 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
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
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Favorable configuration
X-band, 4 cm estimates
VLBI across Solar System: pushing the limits
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Generic PRIDE configuration
Venus
Earth VLBINetwork andTwo-way tracking stations
Orbiter
MicroLander
Balloon
Backgroundradio sources
Planet-target
PRIDE utilises and enhances generic instrumental configuration
of [any planetary] mission
Planetary Radio Interferometry and Doppler Experiment (PRIDE)
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PRIDE-X vs Huygens VLBI – without and with Arecibo
Huygens PRIDE-X Resolution gain
Radio link frequency 2 GHz 2/8/32 GHz 1/4/16
Distance 8 AU ~8 AU 1
VLBI “fringe” SNR:
- “Huygens network”
- Arecibo + GBT + …
10 - 30 30 - 100
100 - 300
~3
~10
Linear resolution (1σ):
- “Huygens network”
- Arecibo + GBT + …
1 km 360/80/20 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
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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