THE EARTH'S van Allen radiation belts are more dynamic than previously thought, according to data returned from the Space Technology Research Vehicles STRV 1A and 1B, launched in June 1994.

These satellites, built by the UK's Defense Research Agency (DRA) at Farnborough, were expected to survive only for a year, as a result of massive doses of radiation encountered in their highly elliptical, 200 x 36,000km geostationary transfer orbits.

They have not been subjected to the constantly high levels of radiation predicted by internationally accepted scientific models, says the DRA. "We feared an early degradation of the [STRV] solar arrays," says Nigel Wells, mission manager. The satellites have shown up major variations. "The Earth's radiation belts are, far from being constant or static, very dynamic," adds Wells. The peak regions of the belts - which were discovered by an instrument aboard the USA's first satellite, the Explorer 1, in 1958 - move "...dramatically in and out. There is a correlation with the 27-day rotation of the Sun linked to its active region," says Wells.

The 55kg STRV spacecraft carry 14 experiments in a unique collaboration between the UK's Ministry of Defence, the European Space Agency and the USA's Ballistic Missile Defense Organization to measure the space environment and demonstrate new technologies. The DRA is misusing a follow-on mission with Europe and the USA with a target date of 1988.

Source: Flight International