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

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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

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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

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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

Channel data from MK5's

Unpack,Filter,Phase subtractPhase Fitting,Fringing

AIPScalibration and imaging

1 2 141516

“Standard” broad-band VLBI correlation on

calibratorsImaging 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)

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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

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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!

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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

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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