The US space agency (Nasa) has issued the first contracts to develop a new generation of space craft to explore deep space that will herald a revolution in the exploration of the outer Solar System.
By Dr David Whitehouse
BBC News Online science editor
As part of the newly established Project Prometheus, the aerospace company Lockheed Martin has been given a $6m (£4m) contract for a design study of the proposed Jupiter Icy Moons Orbiter (Jimo).
All these worlds are within reach...
Project Prometheus is part of Nasa's Nuclear Systems Initiative to develop nuclear propulsion technology for the exploration of the Solar System.
The nuclear-powered Jimo mission will allow for the first time a single space craft to reach the Jupiter system with a large complement of scientific equipment along with the propulsive power to visit each of Jupiter's moons in turn for a sustained study.
Currently, the limiting factor in the exploration of the outer Solar System is the lack of power available for a space craft to travel to the region and manoeuvre when it gets there.
For example, one mission uppermost in the minds of most planetary scientists is a space craft to orbit Europa, the ice-crusted moon of Jupiter under which there may reside primitive forms of life. At the moment, engineers can develop a space craft to fly past Europa but they have not got the technology to enter orbit.
To get to the outer Solar System, space craft have used the time-consuming technique of gravitational flybys, whereby space craft gather velocity by flying close to a planet and receiving a gravitational impulse. The technique has severe limitations on what space craft can do when they reach the outer planets.
Operating energy for the few craft that have ventured that far out has been provided by nuclear power - in which heat from a decaying radioactive source provides a trickle of energy. Conventional solar panels are inefficient beyond the orbit of Mars because sunlight is too weak.
All this means that astronomers need a new generation of technology if they are to truly explore what lies in the cold, outer reaches of the Solar System.
Science otherwise unachievable
To overcome these problems and develop a new generation of deep space explorers, Nasa is planning to develop new nuclear power sources for use where solar energy is too weak, as well as the new fission reactor power sources for much higher power requirements.
The study phase of Project Prometheus will evaluate many different technologies for the reactor, power conversion, electric propulsion, and other aspects of the Jimo spacecraft and follow-on missions. Once the technologies are identified and selected, the next stage will be to prepare more advanced designs.
Nuclear power allows new missions
With new power technology it will at last be possible to achieve the appealing scientific objectives of orbiting the three icy moons of Jupiter - Callisto, Ganymede, and Europa.
The Jimo mission would be able to observe each of the moons for long periods then move to the next having unprecedented electrical power available to its sensors.
From such a space craft, it would be possible to determine whether the moons do indeed have sub-surface oceans. It would also be possible to map the location of organic compounds and other chemicals of biological interest, determine the thicknesses of ice layers, with emphasis on locating potential future landing sites.