Instrument Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument:tvs.vega2::1.0 |
NAME |
TELEVISION SYSTEM |
TYPE |
IMAGER |
DESCRIPTION |
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 ------------------------------------------------------------------------- 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 Full image of 128 X 128 pixels 128x128 pixels around brightest point 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. |
MODEL IDENTIFIER | |
NAIF INSTRUMENT IDENTIFIER |
not applicable |
SERIAL NUMBER |
not applicable |
REFERENCES |
Abergel, A. and J.L. Bertaux, Evolution of Comet Halley in Early March 1986 as
Observed from Vega Pictures, Astronomy and Astrophysics, 187, 829-834, 1987. Abergel, A. and J.L. Bertaux, Le Noyau de la Comete de Halley de la Comete de Halley d'Apres les Images Transmises par les Sondes Vega, Journees d'Etude de de l'ATP Planetologie, Besancon, Mai 1988, 183-186, 1988. Abergel, A. and J.L. Bertaux, Surface Features and the Rotation State of Comet-Halley, Annales Geophysicae, 7, 129-140, 1989. Abergel, A. and J.L. Bertaux, Rotation States of the Nucleus of Comet Halley Compatible with Spacecraft Images, Icarus, 86, 21-29, 1990. Abergel, A., Traitment et Analyses des Images Transmises Lors des Surols de la Comete de Halley par les Sondes Vega, Thesis of the University of Paris, 1987. Abergel, A., L'imagerie Numerique Appliquee a la Technique Spaciale, Revue du Palais de la Decouverrte, 17, 14-31, 1988. Abergel, A., J.L. Bertaux, and F. Dimarellis, Image Processing on Vega Pictures, Proceedings of the Symposium on the Diversity and Similarity of Comets, 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 Cameras for the Observations of Comet Halley, Applied Optics, 26, 4457-4468, 1987. Abergel, A., J.L. Bertaux, and E. Dimarellis, La Decouverte du Noyau de la Comete de Halley, PIXIM 88, Paris, Octobre 1988, 425-444, 1988. Bertaux, J.L. and A. Abergel, Some Physical Characteristics of Halley's Nucleus as Inferred from Vega and Giotto Pictures, Proceedings of the 20th ESLAB 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 of Images and Patterns, Proceedings of the II.INT.CONF CAIP '87 on Automatic Processing 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-1 Pictures of Comet Halley's Nucleus: A New Method Revealing Clear Contours and Jets, Astronomy and Astrophysics, 208, 327-330, 1989. Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', European Space Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986. Foldy, L., K. Szego, and I. Toth, On the Rotation of Comet Halley, Preprint KFKI-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 International Conference 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, The Astrophysical 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 of Comet 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's Comet, 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's Comet, Heidelberg, Germany, 1986, ESA SP-250, Vol I, 313-315, 1986. Mohlmann, D., M. Danz, and H. Borner, Properties of the Nucleus of P/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 from Comet Halley, Annales Geophysicae, 7, 115-120, 1989. Sagdeev, R.Z., and K. Szego, Near Nuclear Region of Comet Halley Based on the 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 the Vega 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, ESA SP-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, TV Experiment 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 of Comet 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, Television Observations 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, and K. Szego, TV Experiment in Vega Mission: Nucleus Shape Reconstruction and Coma Tomography, Methods and Preliminary Results, Proceedings of the 20th ESLAB Symposium, ESA SP-250, Vol II, 307, 1986. Sagdeev, R.Z., V.D. Shapiro, V.I. Shevchenko, and K. Szego, Jet Formation in Comets, Astrophysical Letters, 25, 247, 1987. Sagdeev, R.Z., K. Szego, B.A. Smith, S. Larson, E. Merenyi, A. Kondor, and I. 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 Spacial Distribution of Dust Jets Seen at Vega-2 Fly-By, Proceedings of the 20th ESLAB Symposium, ESA SP-250, Vol II, 327, 1986. Smith, B.A., K. Szego, R.Z. Sagdeev, and S. Larson, Rejection of a Proposed 7.4-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 Experiment Onboard 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, ESA SP-278, 463, 1987. Szego, K., A. Kondor, S. Larson, E. Merenyi, R.Z. Sagdeev, B.A. Smith, and I. Toth, Analysis of the Rotation of Comet Halley, Advances in Space Research, 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 in Space 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 Space Research, 9, 89-92, 1989. Toth, I., K. Szego, and A. Kondor, Dust Photometry in the Near Nucleus Region of Comet Halley from Vega-2 Observations, Proceedings on Diversity and Similarity of Comets, Brussels, Belgium, ESA SP-278, 343, 1987. |