Until recently, planetary geologists had only a handful of subjects to study. The discovery of exoplanets has changed all that, however. The number of known planets orbiting other stars now approaches 500 and few astronomers seriously doubt that an Earth-like body will turn up somewhere soon.

When that happens, we’ll want to study it in unprecedented detail. We’ll want to know it’s mass, temperature, atmospheric composition, it’s colour, whether it has seas and continents and if so whether these support life, perhaps even of the intelligent kind. But above all we’ll want to know whether we can visit this place.

Such a trip will not be easy but it may not be entirely impossible. In fact, rocket scientists have dreamed up various plans for interplanetary probes. One of the more famous was Project Daedalus, a 1970s plan by the British Interplanetary Society for a nuclear-powered spacecraft capable of visiting Barnard’s Star some 6 light years away within a human lifetime.

Today, the British Interplanetary Society and another organisation called the Tau Zero Foundation have posted plans on the arXiv to redesign Daedalus in the light of the 30 years of advances that have taken place since the original. The new plan is called Project Icarus. (In Greek mythology, Icarus was the son of Daedalus who died after flying too close to the Sun and melting the wax that held his wings together.)

What’s interesting about Icarus is that it could be an interesting measure of the progress in nuclear propulsion technology in the 30 years since Daedalus was conceived.

Back then the idea was to fuse deuterium and helium-3 in small pellets by heating them with a powerful electron beam. The resulting explosion, repeated 250 times a second, should accelerate the craft to 12 per cent of the speed of light giving a journey time of 50 years.

The challenges with such a scheme are manifold. Building a propulsion system that would work for 50 years in these extreme conditions isn’t entirely straightforward, the fuel for such a journey would have to be mined from the atmospheres of the gas giants and then there is the problem of slowing down at the other end, which the Daedalus team solved by making the mission a flyby.

The Icarus team plan to revisit all these problems to determine whether they are any more achievable than they were 30 years ago.

One of the important design limitation that Daedalus sought to meet was that the flight time should be less than a human lifetime: which they arguably met with a 50-year journey time.

But an equally important goal is to ensure that the design challenges are addressable within the working lifetime of the scientists and engineers on the project. That’s a limitation that Daedalus obviously failed to meet.

Can Icarus be conceived with such a criteria in place? If not, it is little more than science fiction: who would pay for a project they know they can’t finish?

But if it can, it’s just possible that we’ll send a probe to an Earth-like planet in the foreseeable future. When and if we find one.

Ref: arxiv.org/abs/1005.3833: PROJECT ICARUS: Son of Daedalus Flying Closer to Another Star