| DESCRIPTION |
Mission Overview
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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
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Vega 1 Vega 2
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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
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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.
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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
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Collaborating institutes
Acronym Experiment Collaborating institutes
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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
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