Of the many news accounts of Cassini’s arrival at Saturn, few have mentioned the controversy that surrounded its launch. The mission, launched in 1997, engendered protests and concern from some. The crux of the problem was Cassini’s plutonium containing radio thermal generator, and fears that an accident at launch or flyby could release the plutonium. NASA went to great lengths to communicate their commitment to safely launching and flying the mission, overcoming a lawsuit in the process.

The same battle of space nuclear power looms on the horizon with Project Prometheus and the Jupiter Icy Moons Orbiter. The project hopes to design and use a new generation of RTGs and nuclear reactors. Moving this project forward will depend on communicating and debating risk and uncertainty.

A similar debate is also ongoing for the future of the space shuttle, a manned flight to Mars, the Hubble servicing mission, and commercial space flight. Indeed, much of NASA’s work contains small but significant factors of risk and uncertainty, factors that greatly complicate the agency’s ability to gather support for and maintain initiatives.

Successfully describing and supporting thier risk assessments will be a critical challenge to the agency, and will require sensitivity to the subjective nature of risk tolerance and the value judgements that underlie arguments for and against particular missions. Technical and scientific data will play an important role, but cannot alone overcome value based objections.