The future of space travel is steam

Imagine a spacecraft powered by steam instead of fuel, able to hop from space rock to space rock and extract enough water to power its flight – theoretically forever. 

This space-age steam power sounds like it belongs in a Jules Verne novel, but US scientists have made it into a modern reality. 

A collaboration between the University of Central Florida (UCF) and Pasadena-based private space company Honeybee Robotics has just successfully tested a steam-powered spacecraft. 

Dubbed the World Is Not Enough (WINE), this small exploratory vehicle is designed to extract water from asteroids or other planetary bodies and use it to generate enough steam to propel it to its next target.

“We could potentially use this technology to hop on the moon, Ceres, Europa, Titan, Pluto, the poles of Mercury, asteroids — anywhere there is water and sufficiently low gravity,” says Phil Metzger, UCF planetary researcher. “These spacecraft will be explorers.”

Fuel is a big challenge for every space mission. It is bulky and heavy, and craft must carry their own limited supply. But if a vehicle could make use of existing space resources, every asteroid could be a potential pit-stop and the possibilities for space exploration explode.

“The WINE-like spacecrafts have the potential to change how we explore the universe,” says Honeybee vice president Kris Zacny.

“We know there is a lot of water sequestered away in asteroids and on the moon, and we know it can be converted into rocket fuel,” Metzger says. “But it will be even simpler and therefore a smaller step to take if we just use that water for steam propulsion instead.”

The project is funded by NASA as part of its Small Business Technology Transfer program. Metzger put in the hard yards to develop the necessary computer modelling and simulations for the spacecraft, verifying that the steam-propulsion process would work off-screen. Then Honeybee Robotics – with the help of researchers at Embry-Riddle Aeronautical University in Florida – built a microwave-sized prototype.

On the last day of 2018, the spacecraft was put to the test in a vacuum tank filled with simulated asteroid soil. 

The demonstration, according to Metzger, was “awesome”.

“WINE successfully mined the soil, made rocket propellant, and launched itself on a jet of steam extracted from the simulant.”

The water extraction is a simple enough process – the craft drills down into the soil, the heats it until water rises as vapour, which is then captured and frozen. 

Solar panels provide energy for the heating process.  For targets further from the sun, WINE could use small radioisotopic decay units.

But while steam propulsion does provide a high amount of thrust, it is not the most effective propellant. 

For long-haul missions, steam would likely have to be augmented with a higher-efficiency, lower thrust system or a solar sail. This would allow the spacecraft to achieve greater velocities, while the steam propulsion system would allow it to manoeuvre around and land on the target body.

Another challenge is that WINE is highly reliant on its environment, and not every space rock contains water. If a steam-powered spacecraft landed on a parched asteroid, that could spell the end of the mission. 

Luckily, Metzger says, “we already have a pretty good idea which asteroids have water just by looking through telescopes at the light that reflects from their surfaces, and as the prospecting proceeds we will become better experts at finding the ‘wet’ ones and avoiding the ‘dry’ ones”.

In theory, with well-chosen pit stops, WINE could travel onwards forever – or at least until the hardware breaks or it runs out of its radioisotope energy source. This is a stark contrast to current spacecraft, which have a limited lifespan based on their fuel supply. 

“Each time we lose our tremendous investment in time and money that we spent building and sending the spacecraft to its target,” Metzger says. “WINE was designed to never run out of propellant so exploration will be less expensive. It also allows us to explore in a shorter amount of time, since we don’t have to wait for years as a new spacecraft travels from Earth each time.”

The team is currently seeking partners to continue developing the project, as well as simultaneously working on related technologies.

Metzger concludes: “There are many ways to use the resources of space, and this future in space is exciting.”

Related reading: Reaching for the stars: the top ideas in space travel