A team of researchers from the University of Central Florida (UCF) and Honeybee Robotics in California has developed a prototype steam-powered space probe. This may seem like a great leap backwards, but by using water as a propellant, the World Is Not Enough (WINE) spacecraft can operate indefinitely by topping off on ice gathered while visiting asteroids and other bodies to fuel future travels.

Deep space exploration has made great strides in the past 60 years with every planet and quite a few minor ones visited, plus a number of moons, comets and asteroids. Humanity's efforts have sent probes as far away as 13.5 billion miles (21.7 billion km) and counting, but our robotic marvels are ultimately limited by one inflexible factor – propellant.

To travel over interplanetary distances, spacecraft must use propellant. This can either be in the form of chemical rockets that fire briefly and with great power, or through ion drives that fire for months on end with a thrust that is about that of the weight of a coin. In addition, propellant are used in the thrusters that make course corrections or maintain the attitude of the craft.

But however a propellant is used, there is one iron rule. Once it runs out, the mission is over. The craft's trajectory is entirely at the mercy of Newton's laws of motion and its attitude can only be held so long as the gyros, if any, hold out. This was true of the first V-2 rocket enter space in 1942 and it is true of the New Horizons probe speeding through the Kuiper Belt.

That may change one day if the system conceived by UCF proves viable. Rather than depending on supplies of fuel carried along from Earth, the WINE spacecraft can scavenge fuel as it goes by visiting low-gravity worlds like the Moon, Mercury, Pluto, the asteroids, or comets, extracting water from their surfaces, then using it to generate steam for propulsion.

Honeybee, in partnership with the Embry-Riddle Aeronautical University created a prototype probe to test the idea. This relied on computer models and simulations created by UCF planetary research scientist Phil Metzger, and UCF provided simulated asteroid materials. On December 31, 2018, WINE made its first demonstration.

WINE is about the size of a domestic microwave oven. It is designed to use solar panels to power it in the inner Solar System and nuclear radio-thermal generators (RTG) in the outer system where the sunlight is too weak. With an energy supply limit that is effectively that of the life of the probe, WINE would be able to operate indefinitely as it refuels at each stop using a variety of scenarios based on the host planet's gravity.

The team says that not only would this greatly extend mission times, but it would bring down the costs of space exploration.

"Each time we lose our tremendous investment in time and money that we spent building and sending the spacecraft to its target," says Metzger. "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."

Developed as part of NASA's Small Business Technology Transfer program, the WINE project is currently seeking partners to produce a flightworthy craft to test in space.

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