Giotto experiments all working well

Press, 14 December 1985, Page 18

Giotto experiments all working well

All 10 experiments on board the British-built Giotto spacecraft heading for a rendezvous with Halley’s Comet are now switched on and working well, the United Kingdom Science and Engineering Research Council has reported. The first rehearsals for the encounter with the comet next March were held in October at the European space operations centre, at Darmstadt in Federal Germany. These were to check that all the Brocedures will run smoothly as le spacecraft is guided in to make the closest encounter of several craft being flown towards the comet. The instruments on board will measure the nature and composition of neutral and ionised matter in interplanetary space as well as close to the comet. Investigators from the Mullard Space Science Laboratory of University College London and the University of Kent at Canterbury, supported by staff from the Science and Engineering Research Council’s Rutherford Appleton Laboratory, are co-investi-gators in two of the key experiments — a positive ion analyser and a dust-particle impact detector.

The positive ion analyser was

provided by a consortium from Britain, Federal Germany, Italy, Sweden, and the United States, led by the Mullard Space Science Laboratory. Scientists from University College Cardiff in Wales are also involved in this experiment, which consists of a fast-ion sensor and implanted-ion sensor. The Rutherford Appleton Laboratory contributed the high-volt-age generator for the fast-ion sensor and is now taking part with the other groups in the operation of the experiment and analysis of its results. The instrument has been operating since September 8 collecting solar-wind data. The fast-ion sensor is now making frequent, high resolution measurements of the highly-variable solar wind stream which is travelling at average speeds of 450 km/s. The implanted-ion sensor separates and identifies the less common heavy ions from the predominant protons and alpha particles. A detailed survey of the solar wind is essential to gain a proper understanding of the formation of the comet’s coma and tail. These visible cometary features are the result of the interaction between the solar wind and the dust and gases (neutral and ionised) origin-

ating from the surface of the comet’s nucleus. When close to the comet, the detector will measure the distribution of energetic ions in the coma.

The dust impact detector system, provided jointly by the principal investigator at the University of Kent and the Rutherford Appleton Laboratory, will investigate the distribution and density of dust particles. The system detects the impact of solid particles on the spacecraft’s protection shield using small microphones and other sensors. The prime function of the shield — a two-piece aluminium and Kevlar fabrication — is to protect the spacecraft from damage by the particles striking at a speed of 68 km/s, the closing speed of the spacecraft and comet. A particle penetrating the first aluminium plate, one millimetre thick, vapourises and produces an expanding plasma stream which is then absorbed over a wide area of the second, 30mm-thick Kevlar plate spaced 25cm away. The impact sensors have been calibrated in order to produce a dust-particle distribution profile along the track of the encounter. — London Press Service.