Space Activity

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The Vega Mission to Comet hlly1.gif Halley

 The Vega mission comprised two identical spacecraft, Vega-1 and Vega-2. The name of the mission VEGA is formed from the Russian words Venera (Venus) and Gallei (Halley). The mission was headed by the USSR with a number of other countries within the framework of Intercosmos. Each Vega spacecraft comprised a Halley flyby probe and a Venus descent module.

The two spacecraft were launched by Proton rockets from the Baikonur cosmodrome on 15 and 21 December 1984, respectively. On 11 and 15 June 1985, the two spacecraft successfully delivered the balloons into the Venusian atmosphere. After Venus gravity assist flyby the two spacecrafts encountered comet Halley on 6 and 9 March 1986, respectively.

The Vega spacraft weighted about 4.5 t at launch, it was three-axis stabilised with a wingspan. It carried 14 experiments, among them a TV system (TVS) for tracking and imaging the inner coma and the comet nucleus.

Imaging the comet during the flyby at relative velocity close to 80 km/s from a three-axis stabilised spacecraft required a steerable platform. This platform had a mass of 82 kg and carried 64 kg of payload. The telemetry system consisted of a high-data-rate channel of 65 536 b/s and a low-data-rate channel of 3 072 b/s. The high-data-rate channel was used for real-time scientific data transmission only, while the housekeeping data were transmitted via low-data-rate channel. Scientific data could also be stored on-board on a magnetic tape recorder with 5 Mbit capacity and subsequently telemetred.

Imaging Television System (TVS) for the Vega spacecraft

The TVS of the Vega 1 and Vega 2 observed the comet Halley in 1986. It was placed on a pointing platform, and consisted of a narrow-angle camera, a wide-angle camera, and a digital processor unit (DPU). The DPU had two computers. One of them controlled the imaging, maintained communication with the Earth (download information and process the uplink commands). The task of the second computer was to recognize the comet and to track it by controlling the platform motion. This was the first time in the history of space research that real-time autonomous control was realized through onboard picture processing. The most sensitive and critical components of both computers (memory, clock generator) had warm redundancy. In addition, the DPU contained back-up systems for the tracking and for the communication functions. They were designed on different technological bases for the same function, so that any systematic error in the design or manufacture could affect only the subsystem in question, but not the functionality of the whole system.

Optical parts of the TVS was built partly by French and partly by Russian scientist. The TVS transmitted 1500 images to the Earth, the nucleus of Halley's comet was observed for the first time in history. Its shape, surface features and activity mechanism were derived. Cometary nuclei are considered to belong to the oldest, most primitive population of solar system bodies, thus their investigation contributes to understanding the formation of the solar system.


TÜNDE instrument for the Vega spacecraft

The TÜNDE energetic particle experiment was planned and built by KFKI RMKI. The instrument measured the ions from halley comet, to determinate their energy distribution between 20 keV and 650 keV. Additionally it performed continuous measurements of the cosmic ray radiation of the Sun between 3 MeV and 13 MeV of charged particles.

A new mechanism of particle acceleration has been discovered in the region sunward of the bow shock separating supersonic and subsonic streaming. Intense fluxes of energetic heavy ions with energies above 80 keV were seen by the TÜNDE instrument as far as 107 km from the nucleus of the comet. The very nearly time variation of those fluxes was attributed to the modulation of the emission of neutral particles by the rotation of the nucleus. However, neutral ionized in interplanetary space had to undergo a substantial acceleration in order to be detected at the observed energies. Turbulence in the foreshick region is thus more intense then previously thought.


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