PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "NULL" OBJECT = MISSION MISSION_NAME = "VEGA 1" OBJECT = MISSION_INFORMATION MISSION_START_DATE = 1984-12-15 MISSION_STOP_DATE = 1986-04 MISSION_ALIAS_NAME = "N/A" MISSION_DESC = " Mission Overview ================ In the late 1970s it was realised that the return of Halley's comet in 1985/86 would provide a unique opportunity to combine a mission to explore Venus, (which had already been planned) with a mission to Halley by employing a two-element space vehicle consisting of a Venus lander (and balloon) and a Halley flyby probe. The mission was called Vega, a contraction of the Russian words `Venera' (Venus) and `Gallei' (Halley) and was conducted by the USSR with a number of other countries within the framework of Intercosmos. The Vega mission comprised two identical spacecraft, Vega 1 and Vega 2. This was a standard approach in the USSR, aimed primarily at increasing the overall reliability of the mission. In addition, if both flybys were successful there would be a significant increase in the scientific return, which was particularly valuable in the case of the Halley flybys considering the variability of the cometary activity. The Vega project was truly international. While the spacecraft themselves were controlled by Soviet agencies, the scientific programme and payload were coordinated by the International Science and Technical Committee (CIST), representing scientific institutions and space agencies from nine countries. The CIST designed the Vega mission to be complementary to the European Giotto and the Japanese Suisei cometary missions. The two spacecraft were launched by Proton rockets from the cosmoport Baikonur on 15 and 21 December 1984, respectively. On 11 and 15 June 1985, the two spacecraft successfully delivered the first balloons into the Venus atmosphere. After deltaV- Venus gravity assist flybys, Vega 1 and Vega 2 encountered comet Halley on 6 and 9 March 1986, respectively. The interplanetary orbit of Vega 1 from launch to Halley flyby was entirely in the ecliptic. The orbit of Vega 2 was almost identical except for slightly different flyby dates. The plane of Halley's orbit was inclined at 17.8 degrees with respect to the ecliptic. Halley was above the ecliptic from the ascending to the descending node. The flyby speeds were extremely high because Halley's orbit sense was retrograde, that is, directed opposite to that of the Earth and thus of the spacecraft. During the encounter dust particles impacted on the spacecraft at ~ 80 km/s and caused damage to some experiments and the unprotected solar panels. The flight operations centre was located in Evpatoria (Crimea), but during the flybys most investigators were in Moscow at the Space Research Institute, where they were able to obtain all the data in real time. Deep space antennas in Evpatoria (70 m) and Medvezy Ozera (64m), near Moscow, received the telemetry. During the cruise phase the pointing platform was clamped. The clamping mechanism was released on Vega 1 on 14 February 1986 and on Vega 2 on 18 February 1986, and the operation of the TVS and the pointing platform was checked by observing Jupiter and Saturn. The cameras were found to be fully functional. Two days before the Halley encounters the cameras were oriented towards Halley and switched on for two hours. At last, on 6 March 1986, a few minutes before 7:20 UT, for the first time in the history of mankind, the nucleus of comet Halley unveiled itself to the human eye. The second encounter took place almost exactly three days later. (The most important parameters of both flybys are summarised in the Table below.) Key data of the Vega mission ----------------------------------------------------------------- Vega 1 Vega 2 ----------------------------------------------------------------- launch 15.12.1984 21.12.1984 time of closest approach (UT) 7:20:06 7:20:00 6.3.1986 9.3.1986 closest approach to the nucleus (km) 8.890 8.030 encounter velocity (km/s) 79.2 76.8 distance of the encounter point from the Sun (AU) 0.7923 0.8341 ----------------------------------------------------------------- Vega mission operations were discontinued a few weeks after the encounters. The general condition of the spacecraft would have allowed further operation. The solar panels were partially damaged by dust impact but could still have provided enough power. The camera performance was tested by observing Jupiter and no essential degradation was registered. Even the amount of fuel onboard was considerable. However, after extensive searches and debates, no interesting object was identified for a possible second encounter. -------------------------------------------------------------- VEGA scientific payload Direct Recorded Acronym Experiment Mass Power telemetry telemetry (kg) (W) (bit/s) (bit/20min) TVS Television 32 50 32768 System IKS Infrared l8 18 2048 4320 Spectrometer TKS Three-Channel 14 30 12288 Spectrometer PHOTON Shield Pene- 2 4 108 tration Detector DUCMA Dust Particle 3 2 100 100 Detector SP-2 Dust Particle 4 4 1024 2160 Detector SP-1 Dust Particle 2 l 150 2160 Detector PUMA Dust Mass 19 31 10240 Spectrometer ING Neutral Gas 7 8 1024 1080 Mass Spectro- meter PM-1 Plasma Energy 9 8 2048 15120 Analyser TN-M Energetic Par- 5 6 512 6480 ticle Analyzer MISCHA Magnetometer 4 6 512 2160 APV-N Wave and 5 8 2048 28080 Plasma Analyser APV-V Wave and 3 2 512 15120 Plasma Analyser ----------------------------------------------------------- -------------------------------------------------------------- Collaborating institutes Acronym Experiment Collaborating institutes -------------------------------------------------------------- TVS Television LAS, Marseille, France (P. Cruvellier) System Central Research Inst for Physics, Budapest, Hungary (L. Szabo) IKI, Moscow, USSR (G. Avanesov) IKS Infrared Observatoire de Meudon, France(M. Combes) Spectrometer IKI, Moscow, USSR TKS Three-Channel Observatoire de Besancon, France (G. Moreels) Spectrometer IKI, Moscow, USSR (V. Krasnopolskii) Bulgaria (M. Gogoshev) PHOTON Shield Pene- USSR tration Detector DUCMA Dust Particle University of Chicago, USA (I. Simpson) Detector MPI, Lindau, W. Germany IKI, Moscow, USSR Central Research Institute for Physics, Budapest SP-2 Dust Particle IKI, Leningrad, USSR (E. Mazets) Detector SP-1 Dust Particle IKI, Moscow, USSR (O. Vaisberg) Detector PUMA Dust Mass MPI, Heidelberg, W. Germany (J. Kissel) Spectrometer Service d'Aeronomie, Verrieres, France (I.Lertarnsl11(1, Moscow, USSR (R. Sagdeev) ING Neutral Gas MPI, Lindau, W. Germany (E. Keppler) Mass Spectro- Central Research Institute for Physics, meter Budapest, IKI, Moscow, USSR University of Arizona, USA PM-1 Plasma Energy IKI, Moscow, USSR (K. Gringauz) Analyser Central Research Institute for Physics, Budapest, MPI, Lindau, W. Germany ESA Space Science Dept., ESTEC, Netherlands TN-M Energetic Par- Central Research Institute for Physics, ticle Analyzer Budapest, Hungary (A. Somogyi) IKI, Moscow, USSR MPI, Lindau, W. Germany ESA Space Science Dept., ESTEC, Netherlands Nuclear Research Institute, Moscow, USSR MISCHA Magnetometer Space Research Institute, Graz, Austria (W.Redler) Izmiran, Troitsk, USSR APV-N Wave and IKI, Moscow, USSR, (S. IClimov) Plasma Analyser Aviation Institute, Warsaw, Poland Geophysical Scientific Institute, Prague APV-V Wave and ESA Space Science Dept., ESTEC (R. Grard) Plasma Analyser LPCE, Orleans, France Izmiran, Troitsk, USSR ---------------------------------------------------------------------" MISSION_OBJECTIVES_SUMMARY = " Mission Objectives Overview =========================== One of the Vega program's aims was the exploration of Comet Halley. The scientific objectives of the Vega cometary investigation are: (i) determination of the physical parameters of the nucleus: dimensions, shape, temperature and surface properties (ii) study of the structure and dynamics of the coma around the nucleus (iii) definition of the gas composition in the close vicinity of the nucleus and the nature of the parent molecules (iv) study of the dust particles' composition and mass distribution as functions of the distance to the nucleus, and (v) study of the interaction of the solar wind with the atmosphere and ionosphere of the comet. The Vega mission to Halley's comet was not only scientifically highly successful, it also helped to forge international cooperation in space science at an unprecedented level, both within the Vega Project and in the worldwide cooperation with the other major space organisations. In fact, it led to the formation of the Inter-Agency Consultative Group for Space Science (IACG) which from 1981-86 coordinated the six Halley space missions from its four member agencies: Intercosmos, NASA, ESA, and the Japanese ISAS. Since 1986 the IACG has been coordinating a number of projects from the four space agencies in solar-terrestrial science. The in-situ observations by the various experiments onboard the flyby spacecraft were complemented by a large number of remote observations from space and from the ground, the latter being coordinated by the International Halley Watch (IHW). The IACG and its counterpart on the ground, the IHW, formed the cornerstones of a global effort to explore Halley's comet as completely as possible during its 1985/86 apparition. By the end of the 1980's when Halley disappeared again into the outer Solar System, it was the most thoroughly studied comet ever with more data having been collected on it than on all other comets put together. The cameras onboard the Vega spacecraft made the most important observation of all: the discovery of the nucleus of comet Halley." END_OBJECT = MISSION_INFORMATION OBJECT = MISSION_HOST INSTRUMENT_HOST_ID = "VEGA1" OBJECT = MISSION_TARGET TARGET_NAME = "1P/HALLEY 1 (1682 Q1)" END_OBJECT = MISSION_TARGET OBJECT = MISSION_TARGET TARGET_NAME = "HALLEY" END_OBJECT = MISSION_TARGET END_OBJECT = MISSION_HOST OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ESA-SP1066" END_OBJECT = MISSION_REFERENCE_INFORMATION END_OBJECT = MISSION END