1. VLBI Observations of Spacecraft
Ian Avruch*, JIVE
*On behalf of the Huygens VLBI Tracking Team
This tutorial is divided in two parts connected by the methodology – VLBI.

2. I.Avruch, 8th EVN Symposium
Team
SMART-1:
S. Pogrebenko, JIVE, NL
I. Avruch, JIVE, NL
R. Campbell, JIVE, NL
L. Gurvits, JIVE, NL
R. Oerlemans, JIVE, NL
A. Szomoru, JIVE,NL
A. Mujunen, HUT/MRO, FI
J. Ritakari, HUT/MRO, FI
J. Wagner, HUT/MRO, FI
G. Maccaferri, INAF/IRA, IT
S. Montebugnoli, INAF/IRA, IT
A. Foley, ASTRON/WSRT, NL
O. Camino, ESA/ESOC, DE
B. Foing, ESA/ESTEC, NL
K. van’t Klooster, ESA/ESTEC, NL
T. Morley, ESA/ESOC, DE
L. Petrov, NASA/GSFC, USA
With special thanks to Klaas Stuurwold, ASTRON,NL
Huygens:
JIVE ESA-ESTEC NASA-JPL NRAO
I.M.Avruch C.. van’t Klooster S.Asmar W.Brisken
H.Bignall J.-P.Lebreton W.Folkner F.Ghigo
A.Brunthaler R.A.Preston G.Langston
R.M.Campbell J.Romney
M.A.Garrett
L.I.Gurvits
S.V.Pogrebenko
ASTRON ATNF U Tasmania NICT (CRL)
A.R.Foley J.Lovell G.Cimo T.Kondo
C.Phillips S.Elingsen
U Bonn J. Reynolds B.Reid
M.Bird R.Sault.
T.Tzioumis
NAO China Helsinki University ISAS
T.An (ShAO) A.Mujunen R.Dodson
X.Hong(ShAO) J.Ritakari
S.Huang(ShAO)
D.Jiang(ShAO)
X.Liu(UAO)
I.Avruch, 8th EVN Symposium
28 Sep 2006

3. I.Avruch, 8th EVN Symposium
Spacecraft
I.Avruch, 8th EVN Symposium
28 Sep 2006

4. I.Avruch, 8th EVN Symposium
Signals
Spacecraft Spectrum
Coherent Harmonics
Carrier
I.Avruch, 8th EVN Symposium
28 Sep 2006

5. Signals Tone Purity Dynamic Spectrum of
Smart1 TX carrier line detected
by Medicina telescope at
2.235 GHz
( Frequency resolution 24 Hz)
After tracking smooth frequency deviations,
Frequency residual < 1 mHz
Velocity residual < 0.1 mm/s
Of course, this is just instrumental accuracy; short-term propagation effects and S/C LO variance still present.
I.Avruch, 8th EVN Symposium
28 Sep 2006

6. Signals (SMART-1 Occultation by Moon)
SMART-1 carrier wave voltage, power and
phase as detected by Medicina station
Post-egress “classical” diffraction pattern
and zoom on pre-egress features, like those seen around seconds 5 and 8-10
For comparison: power (red) and phase (blue)
patterns for diffraction on a flat circular screen
I.Avruch, 8th EVN Symposium
28 Sep 2006

7. Signals (SMART-1 Impact on Moon)
TIGO
Concepcion
Hobart 26m
SMART-1 last
Hobart:
05:42: (5)
03 Sep 2006 UTC
I.Avruch, 8th EVN Symposium
28 Sep 2006

8. Signals (Huygens Probe)
Incident Power (1 IF of 16MHz Bandwidth)
AGN 50mJy
Flux = 4x10-21 W/m2
Huygens Probe 3.7W in carrier line
Flux = 5x10-25 W/m2
But Spectral Density is high.
Dn ~ 20mHz
g2500Jy
I.Avruch, 8th EVN Symposium
28 Sep 2006

9. I.Avruch, 8th EVN Symposium
Signals
Low occupation number for obs. Huygens carrier
@ l 15cm 0.4 photons/m2/s
P/hυ = 20 photons/s at VLBA_MK (500 at GBT)
Dn Dt >= 1
gDt ~ 50s
There are ~1000 photons in the system, on average.
The most sensitive VLBI
Observation ever?
I.Avruch, 8th EVN Symposium
28 Sep 2006

10. VLBI and Spacecraft Navigation
DDOR “Delta Differential One-way Ranging”
i.e. Group Delay Measurement.
DOR tone &
harmonics
CCSDS CP-5060WO-1.1
carrier S n
t=Df/Dn f n
I.Avruch, 8th EVN Symposium
28 Sep 2006

11. VLBI and Spacecraft Navigation
DDOR Technique:
The s.c. carrier (S,X, or Ka band) is modulated, producing a number of harmonics.
1 hour is spent on a QSO-s.c. scan cycle, 5-10min per source.
S.c. with narrow channels (50kHz) centered on tones,
QSO with wide channels (2MHz) centered same.
Group Delay measured for both, differenced, gives s.c. position relative to QSO.
Precision: dt ~ 0.15ns g 1.5mas
I.Avruch, 8th EVN Symposium
28 Sep 2006

12. I.Avruch, 8th EVN Symposium
VLBI on Spacecraft
Phase Delay
Potential precision 1-10 ps g 15mas
(at the limit of delay model precision)
SMART-1 Correlation
Without Delay Modeling
Short term phase noise
65 milliradian (or 4.6 ps)
rms at 40 ms sampling,
Initial phase ambiguity
~ several cycles
I.Avruch, 8th EVN Symposium
28 Sep 2006

13. I.Avruch, 8th EVN Symposium
VLBI on Spacecraft
Huygens Residual
Phases
Delay model for near-field source.
Unfortunately,
delay model is wrong!
I.Avruch, 8th EVN Symposium
28 Sep 2006

14. VLBI on Spacecraft Huygens Trajectory on Titan preliminary 11:08:11
Note spread of the data points: ~ 1 km across the trajectory
09:11:10 SCET
11:08:11
I.Avruch, 8th EVN Symposium
28 Sep 2006

15. Current & Future Developments
Self-consistent VLBI Delay Model for near-zone objects
“VTD” VLBI package by L.Petrov(NASA GSFC)
ps precision for Earth-bound observers
SPICE package for spacecraft navigation
Newtonian g ms precision anywhere in the SS
Time is right for a convergence
VLBI observations from space
Applications for precise path-lengths
Plate tectonics on Europa
Dynamic gravitational lensing
GR Tests: Pioneer Anomaly
I.Avruch, 8th EVN Symposium
28 Sep 2006