The International Comet Halley campaign

TIMELINE: 1984-1985

During the 1970s there was mounting interest in the coming apparition in 1986 of the famous Comet Halley. The US was developing various plans for intercepting the comet at close range. The fledgling European Space Agency was considering doing the same. And the very small and academically oriented Japanese Institute for Space and AstronauLical Science had decided to send two small spacecraft equipped with plasma instrumentation.

At the start of the 1980s the USSR began to develop a large balloon mission for Venus with the French. But with the development of the mission advancing well the Soviets became interested in Comet Halley when they realized it would be possible for a spacecraft to use a Venus flyby to redirect itself towards the comet. The two missions were partially combined, and in an unprecedented move the Soviets issued an international call for instruments to fly on their spacecraft to Halley. As a result, their planetary exploration program suddenly became international outside the Iron Curtain. Not even the US had opened its more public space exploration program to such extensive international cooperation.

The spacecraft for this Venus-Halley (Vega) mission was very similar to a flyby Venera, but with an instrument scan platform added to track Halley. But instead of a large balloon consuming essentially the entire mass limit for the entry system, it was decided to carry a lander and augment this with a smaller balloon package. The balloon package would be released from the Lop portion of the entry sphere and the lander from the bottom portion. The balloon was to be inflated after release and then float at an altitude of about 50 km with a battery life of about 50 hours. The lander would be of the standard configuration.

Launched in December 1984, both of the Vega spacecraft performed well. Their landers and balloons were successful, the balloons drifting thousands of kilometers from the night-side to the day-side after more than 40 hours of flight. The spacecraft proceeded to encounter Halley, imaging the nucleus, taking data on the surrounding

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer Praxis Hooks 1, DOl 10.1007/978-1-4419-7898-1 18,

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environment, and supporting the rest of the Halley ‘armada5 that comprised the two Soviet spacecraft, two Japanese spacecraft at far encounter, and the European Giotto spacecraft which, with navigational assistance from the Vega missions, was able to refine its trajectory to achieve a very close approach to the nucleus of the comet. The US was notably absent from the armada having failed, in a major embarrassment, to fund a mission to the comet.