Cassini's progress

Henry Joy McCracken considers the reaction to the latest space probe leaving Earth

Despite the best efforts of Grandmothers for Peace and a variety of other activist organisations, NASA's Cassini probe left Earth on 15 October 1997 to begin its seven-year journey to Saturn. It took with it all of the 72 pounds of plutonium which had caused consternation among many of Florida's anti-nuclear campaigners as well as a diverse collection of individuals from around the world. They feared that a mishap at launch would spread radioactive material along the Florida coast and perhaps even contaminate Mickey Mouse himself, fifty miles north in Orlando.

The plutonium is used to generate Cassini's electricity supply; near Saturn the Sun is much too far away to power solar panels. The plutonium was encased in an extremely hard ceramic compound and further wrapped in several layers of iridium making it resistant to impacts or pulverisation. If that weren't enough, the radiation from plutonium can only travel a few millimetres in air anyway, so the only way in which to sustain a lethal dose would be to inhale it. The resilience of the shielding has already been tested - in 1968 a US weather satellite re-entered the Earth's atmosphere and plunged into the Pacific ocean. Engineers were able to retrieve the undamaged energy source, dust it off, and put it into another satellite. Cassini's plutonium payload wouldn't be much use in a nuclear reactor, or in a bomb - it is not weapons-grade - a fact which the protesters tended to ignore, preferring instead to cry "nukes in space!".

Cassini was the culmination of a decade of planning and preparation, and will probably be the last large interplanetary mission launched for a long time. This is thanks to the insistence on 'faster, cheaper, better' modes of space travel, the pursuit of which is currently the only way scientific adventures can hope to survive in today's economic climate.

The attitude of the demonstrators is hardly surprising when viewed in the wider context of space missions over the past few years. Space is a frontier - and exploring frontiers is by nature a risky business. Over the past year we have watched the spectacle of the Mir space station breaking down every other week. At every turn the press called for it to be evacuated, as if they had only just realised that space is a lethal environment where mistakes can be fatal. Exactly what is drummed into every aspect of astronaut's training.

Certainty is something which does not exist in science and certainly does not exist when exploring the furthest recesses of the Solar System. The fears surrounding the extremely negligible danger of a release of radioactive material from Cassini perfectly articulate the attitude of a society retreating from innovation and exploration in favour of a pointless quest for safety and avoidance of risk which are impossible to attain - especially when you're attempting something of this magnitude.

Henry Joy McCracken has written the Futures feature in the forthcoming LM105 'Why have we still not walked on Mars?'. Excerpts from LM 105 go online on Thursday 30 October