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Instrument Information
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INSTRUMENT_ID |
TVS
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INSTRUMENT_NAME |
TELEVISION SYSTEM
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INSTRUMENT_TYPE |
CCD CAMERA
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INSTRUMENT_HOST_ID |
VEGA1
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INSTRUMENT_DESC |
Instrument Overview
===================
The television system consists of two telescopes,
one narrow-angle camera (TVY) for high-resolution
imaging of the nucleus, and one large-angle camera
(TDN) for detecting and tracking the comet. The
TVY optics have a reflecting objective with a focal
length of 1200 mm and a detector which yields an
average angular resolution of 3 arcsec, i.e. a
spatial resolution of the order of 150 m at the
nominal flyby distance of 10 000 km. The maximum
angular dimension of the nucleus and its near
environment is expected to be 5 arcmin at closest
approach, and the pointing error is estimated to be
+/- 5 arcmin. The field of view of the TVY must
therefore be not less than 15 arcmin.
The TDN has a refractory objective with a focal
length of 150 mm. It is characterised by an
angular resolution of 0.5 arcmin, required for
early acquisition of the comet and its nucleus, and
a 2deg field of view imposed by the constraints
associated with control of the pointing platform.
The light collected by each telescope is divided
into two paths by a beam splitter, 0ne channel is
fitted with a fixed filter, the other has a set of
eight filters mounted on a rotating wheel, to yield
a spectral analysis of the signal. The images are
forms on area CCDs cooled by a passive radiator
regulated by a Peltier plate. The commutable
filters of the TDN have an additional function,
namely to adjust the amount of light collected by
the detector. This channel is operated
autonomously and performs an independent analysis
of the video signal, thus providing redunant
information to the platform pointing system for the
sake of reliability. The signals delivered by the
three other TDN and TVY channels are handled by the
same microprocessor system which analyses the
images and generates the commands that control the
motion of the platform. The TVS electronics
include a 816 kbit memory to store both data and
programs, The main characteristics of the TVS are
given below.
-------------------------------------------------------------------------
Table . Television System characteristics
Camera system High resolution Low resolution
-------------------------------------------------------------------------
Objective Reflector Refractor
Focal distance 1200 mm 150 mm
Aperture 240 mm 50 mm
Relative aperture 1:5, effective 1:6.5 1:3
Channel Multispectral Integral Multispectral Integral
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Spectral range, micro m 0.4-1.1 0.63-0.76 (1) 0.4-1.1 0.63-0.76
(2)0.63-0.76
-------------------------------------------------------------------------
Number of filters 8 1 Range (1):1 1
Range (2):7
-------------------------------------------------------------------------
Field of view 26.4'x39.6' 211'x316' 211'x158'
Resolution 3.1inx4.1in 24.75inx33in 99inx132in
-------------------------------------------------------------------------
Shutter Mechanical Electronic
-------------------------------------------------------------------------
Exposure time range 0.01-163 s 6-800 ms
-------------------------------------------------------------------------
Detector area 5l2x512 pixels 512x256 pixels
-------------------------------------------------------------------------
Data compression Floating window of 128 X 128 pixels Full image
around brightest point of 128x128
pixels
after
integration
of 4x2 pixels
-------------------------------------------------------------------------
The resolution of the images was a trade-off.
Scientists wanted nucleus images with the highest
possible resolution, but that was limited by weight
considerations and by selecting a trajectory for
the spacecraft which was far enough away from the
nucleus to guarantee a high survival probability.
The compromise solution was to use a
Ritchey-Chretien type telescope for scientific
imaging with a focal length of 1200 mm, an
effective aperture of f/6.5, and a field of view of
26.4x39.6 arcmin. It was immediately obvious that
the field of view of this narrow angle camera (NAC)
was too small to find the nucleus autonomously. It
was also not possible to steer the telescope from
the ground because the position of the nucleus in
the coma was not well enough known. Therefore, a
wide angle scanning camera (WAC) had to be added to
the payload.
A major concern was the target definition, namely
what should the pointing system be aimed at. The
sensors could identify only the centre of
brightness, but it obviously was not identical to
the centre of the nucleus. This was partly due to
partial illumination of the nucleus by the Sun
(comparable to the phases of the Moon) and partly
due to jet activity. The pointing system might
well have locked on to a bright dust jet and be
steered away from the nucleus. As we found no way
to define an offset reliably, we decided simply to
aim at the centre of brightness. This targeting
strategy worked well for Vega.
The main navigation system for the platform was the
imaging system itself. However, as a backup an
eight-segmented light sensitive sensor was mounted
on the pointing platform. Its working principle
was extremely simple: if the centre of light from
the comet would move away from the centre of the
sensor, a change of the platform orientation would
have been initiated to compensate for this offset.
Fairly sophisticated computer simulations proved
that this backup was reliable, but fortunately, it
never had to be used.
To have many backups was a major element in our
design philosophy. A third navigational backup,
which used analog signals from a completely
independent CCD sensor, was added to the TV system.
The output signal was processed in a similar way to
the eight segmented light sensitive sensor but with
much higher precision.
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REFERENCE_DESCRIPTION |
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Abergel, A. and J.L. Bertaux, Le Noyau de la Comete de Halley de la Cometede Halley d'Apres les Images Transmises par les Sondes Vega, Journeesd'Etude de de l'ATP Planetologie, Besancon, Mai 1988, 183-186, 1988.
Abergel, A. and J.L. Bertaux, Surface Features and the Rotation State ofComet-Halley, Annales Geophysicae, 7, 129-140, 1989.
Abergel, A. and J.L. Bertaux, Rotation States of the Nucleus of CometHalley Compatible with Spacecraft Images, Icarus, 86, 21-29, 1990.
Abergel, A., Traitment et Analyses des Images Transmises Lors des Surols dela Comete de Halley par les Sondes Vega, Thesis of the University of Paris,1987.
Abergel, A., L'imagerie Numerique Appliquee a la Technique Spaciale, Revuedu Palais de la Decouverrte, 17, 14-31, 1988.
Abergel, A., J.L. Bertaux, and F. Dimarellis, Image Processing on VegaPictures, Proceedings of the Symposium on the Diversity and Similarity ofComets, Bruxelles, Belgique 6-9 April 1987, ESA SP-278, 689-694, 1987.
Abergel, A., J.L. Bertaux, G.A. Avanesov, V.I. Tarnopolsky, and B.S.Zhukov, Photometric Characteristics of the Vega 1 and Vega 2 CCD Camerasfor the Observations of Comet Halley, Applied Optics, 26, 4457-4468, 1987.
Abergel, A., J.L. Bertaux, and E. Dimarellis, La Decouverte du Noyau de laComete de Halley, PIXIM 88, Paris, Octobre 1988, 425-444, 1988.
Bertaux, J.L. and A. Abergel, Some Physical Characteristics of Halley'sNucleus as Inferred from Vega and Giotto Pictures, Proceedings of the 20thESLAB Symposium on the Exploration of Halley's Comet, Heidelberg, 27-31,Octobre 1986, ESA SP-250, Vol II, 341-345, 1986.
Danz, M., G. Elter, T. Mangoldt, D. Mohlmann, B. Rubbert, and U. Weidlich,Processing for the Vega-Mission to Comet Halley, Computer Analysis ofImages and Patterns, Proceedings of the II.INT.CONF CAIP '87 on AutomaticProcessing Held in Wismar 1987, Mathematical Research Series, Vol 40, L.P.Yaroslavskii, A. Rosenfeld, and W. Wilhelmi (eds.), Akademie-Verlag Berlin,222-226, 1987.
Dimarellis, E., J.L. Bertaux, and A. Abergel, Restoration of Vega-1Pictures of Comet Halley's Nucleus: A New Method Revealing Clear Contoursand Jets, Astronomy and Astrophysics, 208, 327-330, 1989.
Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', EuropeanSpace Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986.
Foldy, L., K. Szego, and I. Toth, On the Rotation of Comet Halley, PreprintKFKI-1990-26/C.
Horanyi, M., K. Kecskemety, T.I. Gombosi, K. Szego, T. Cravens, and A.F.Nagy, The Sponge Model of Cometry Nucleus, Proceedings of the InternationalConference on Cometary Exploration, Budapest, 1982, Vol I, 59, 1982.
Horanyi, M., T.I. Gombosi, T.E. Cravens, A. Korosmezey, K. Kecskemety, A.F.Nagy, and K. Szego, The Friable Sponge Model of a Cometary Nucleus, TheAstrophysical Journal, 278, 449-455, 1984.
Kondor, A., Destripping of the Vega-1 TV Images, MPAE-W-100-90-04, 1990.
Kondor, A., Noise Supression Version of the Method of Convergent Weights,MPAE-W-100-90-05, 1990.
Merenyi, E., L. Foldy, K. Szego, I. Toth, and A. Kondor, The Landscape ofComet Halley, Icarus, 86, 9-20, 1990.
Mohlmann, D., H. Borner, M. Danz, G. Elter, T. Mangoldt, B. Rubbert, U.Weidlich, Physical Properties of P/Halley-Derived from Vega-Images,Proceedings of the 20th ESLAB Symposium on the Exploration of Halley'sComet, Heidelberg, Germany, 1986, SP-250, Vol II, 339-340, 1986.
Mohlmann, D., M. Danz, G. Elter, T. Mangoldt, B. Rubbert, U. Weidlich, H.Lorenz, and G. Richter, Image Processing of Vega-TV Observations,Proceedings of the 20th ESLAB Symposium on the Exploration of Halley'sComet, Heidelberg, Germany, 1986, ESA SP-250, Vol I, 313-315, 1986.
Mohlmann, D., M. Danz, and H. Borner, Properties of the Nucleus ofP/Halley, Symposium on the Diversity and Similarity of Comets, ESA SP-278,487-492, 1987.
Richter, A.K., P.W. Daly, M.I. Verigin, K.I. Gringauz, G. Erdos, K.Kecskemety, A.J. Somogyi, K. Szego, A. Varga, and S. McKenna-Lawlor,Quasi-Periodic Variations, of Cometary Ion Fluxes at Large Distances fromComet Halley, Annales Geophysicae, 7, 115-120, 1989.
Sagdeev, R.Z., and K. Szego, Near Nuclear Region of Comet Halley Based onthe Imaging Results of the Vega Mission, KFKI Preprint, KFKI-1987-35/C.
Sagdeev, R.Z., G.A. Avanesov, I.V. Barinov, A.I. Debabov, V.A. Krasikov,V.I. Moroz, V.A. Shamis, V.I. Tarnopolski, D.A. Usikov, YA.L. Ziman, B.S.Zhukov, F. Szabo, K. Szego, A. Kondor, E. Merenyi, B.A. Smith, S. Larson,P. Cruvellier, A. Abergel, J.L. Bertaux, J. Blamont, M. Danz, D. Mohlmann,H. Stiller, and H.P. Zapfe, Comet Halley: Nucleus and Jets (Results of theVega Mission), Advances of Space Research, 5, 95-104, 1986.
Sagdeev, R.Z., G.A. Avanesov, I.V. Barinov, V.I. Kostenko, V.A. Krasikov,V.A. Shamis, K.G. Sukhanov, V.I. Tarnopolski, YU.K. Zaiko, S.I. Zatsepin,YA.L. Ziman, B.S. Zhukov, F. Szabo, L. Szabo, K. Szego, A. Balazs, G.Endroczi, M. Gardos, M. Kanyo, Z. Nyitrai, I. Renyi, P. Rusznyak, B. Smith,S. Szalai, I. Toth, L. Varhalmi, M. Zsenei, P. Cruvellier, M. Detaille, T.Nguyen-Trong, A. Abergel, J.L. Bertaux, J. Blamont, E. Dimarellis, G.N.Dulnev, G. Tsukanova, and B.I. Valnicek, TV Experiment in Vega Mission:Strategy, Hardware, Software, Proceedings of the 20th ESLAB Symposium, ESASP-250, Vol II, 289, 1986.
Sagdeev, R.Z., G.A. Avanesov, V.A. Krasikov, V.A. Shamis, V.A. Tarnopolski,YA.L. Ziman, A.A. Kuzmin, K. Szego, E. Merenyi, and B.A. Smith, TVExperiment in Vega Mission: Image Processing Technique and some Results,Proceedings of the 20th ESLAB Symposium, ESA SP-250, Vol II, 295, 1986.
Sagdeev, R.Z., J. Blamont, A.A. Galeev, V.I. Moroz, V.D. Shapiro, V.I.Shevchenko, K. Szego, Vega Spacecraft Encounters with Comet Halley, Nature,321, 259-262, 1986.
Sagdeev, R.Z., V.A. Krasikov, V.A. Shamis, V.I. Tarnopolski, K. Szego, I.Toth, B. Smith, S. Larson, and E. Merenyi, Rotation Period and Spin Axis ofComet Halley, Proceedings of the 20th ESLAB Symposium, ESA SP-250, Vol II,335, 1986.
Sagdeev, R.Z., F. Szabo, G.A. Avanesov, P. Cruvellier, L. Szabo, K. Szego,A. Abergel, A. Balazs, I.V. Barinov, J.L. Bertaux, J. Blamont, M. Detaille,E. Dimarellis, G.N. Dulnev, G. Krasikov, T. Nguyen-Trong, Z. Nyitrai, I.Renyi, P. Rusznyak, V.A. Shamis, B. Smith, K.G. Sukhanov, S. Szalai, V.I.Tarnopolski, I. Toth, G. Tsukanova, B.I. Valnicek, L. Varhalmi, YU.K.Zaiko, S.I. Zatsepin, YA.L. Ziman, M. Zsenei, and B.S. Zhukov, TelevisionObservations of Comet Halley from Vega Spacecraft, Nature, 321, 262-265,1986.
Sagdeev, R.Z., YA.L. Ziman, G.A. Avanesov, V.A. Tarnopolski, V.A. Krasikov,D.A. Usikov, A.S. Debabov, K.G. Sukhanov, A.Yu. Kogan, V.N. Kheifets, andK. Szego, TV Experiment in Vega Mission: Nucleus Shape Reconstruction andComa Tomography, Methods and Preliminary Results, Proceedings of the 20thESLAB Symposium, ESA SP-250, Vol II, 307, 1986.
Sagdeev, R.Z., V.D. Shapiro, V.I. Shevchenko, and K. Szego, Jet Formationin Comets, Astrophysical Letters, 25, 247, 1987.
Sagdeev, R.Z., K. Szego, B.A. Smith, S. Larson, E. Merenyi, A. Kondor, andI. Toth, The Rotation of P/Halley, The Astronomical Journal, 97, 546-551,1989.
Smith, B., K. Szego, S. Larson, E. Merenyi, I. Toth, R.Z. Sagdeev, G.A.Avanesov, V.A. Krasikov, V.A. Shamis, and V.I. Tarnopolski, The SpacialDistribution of Dust Jets Seen at Vega-2 Fly-By, Proceedings of the 20thESLAB Symposium, ESA SP-250, Vol II, 327, 1986.
Smith, B.A., K. Szego, R.Z. Sagdeev, and S. Larson, Rejection of a Proposed7.4-Day Rotation Period of the Comet Halley Nucleus, Nature, 326, 573,1987.
Szego, K., Modeling a Cometary Nucleus, Astrophysics and Space Science,144, 439-449, 1988.
Szego, K., The Nucleus of Comet Halley, Acta Physics, Hungary, 64, 267-275,1988.
Szego, K., What Do We Know About the Nucleus of Comet Halley?,Bioastronomy-The Next Steps, Marx, G. (ed.), Kluwer Academic Publisher,31-37, 1988.
Szego, K., P/Halley, the Model Comet, in View of the Imaging ExperimentOnboard the Vega Spacecraft, Comets in the Post-Halley Era, Newburn, R.L.,et al (eds.), Kluwer Academic Publisher, Netherlands, Vol 2, 713, 1991.
Szego, K., A. Kondor, I. Toth, R.Z. Sagdeev, K. Wilhelm, and H.U. Keller,Reconstruction of the Orientation and Shape of the Nucleus of Comet Halley,Proceedings on Diversity and Similarity of Comets, Brussels, Belgium, ESASP-278, 463, 1987.
Szego, K., A. Kondor, S. Larson, E. Merenyi, R.Z. Sagdeev, B.A. Smith, andI. Toth, Analysis of the Rotation of Comet Halley, Advances in SpaceResearch, 9, 73-76, 1989.
Szego, K., E. Merenyi, A. Kondor, B.A. Smith, I. Toth, and L. Foldy,Surface and Dust Features Seen on the Nucleus of Comet Halley, Advances inSpace Research, 9, 85-88, 1989.
Szego, K., I. Toth, Z. Szatmary, B.A. Smith, A. Kondor, and E. Merenyi,Dust Photometry in the Near Nucleus of Comet Halley, Advances in SpaceResearch, 9, 89-92, 1989.
Toth, I., K. Szego, and A. Kondor, Dust Photometry in the Near NucleusRegion of Comet Halley from Vega-2 Observations, Proceedings on Diversityand Similarity of Comets, Brussels, Belgium, ESA SP-278, 343, 1987.
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