The group, from Glasgow University and Oles Honchar Dnipro National University in Ukraine claim to have built, fired, and throttled up and down a so-called ‘autophage’ engine which they claim could be used to put small satellites in orbit more easily.
Today, most rockets use tanks to store their propellant as they climb, and the weight of the tanks is usually many times greater than the weight of the useful payload. This reduces the efficiency of the launch vehicle, and contributes to the problem of space debris.
However, a launch vehicle powered by an autophage engine would consume its own structure during ascent, so more cargo capacity could be freed-up and less debris would enter orbit.
Described in a paper published in the Journal of Spacecraft and Rockets, the engine consumes a propellant rod which has solid fuel on the outside and oxidiser on the inside. The solid fuel is a strong plastic, such as polyethylene, so the rod is effectively a pipe full of powdered oxidiser. By driving the rod into a hot engine, the fuel and oxidiser can be vaporised into gases that flow into the combustion chamber. This produces thrust, as well as the heat required to vaporise the next section of propellant.
Dr Patrick Harkness, who is leading Glasgow’s work on the project said: “Launch vehicles tend to be large because you need a large amount of propellant to reach space. If you try to scale down, the volume of propellant falls more quickly than the mass of the structure, so there is a limit to how small you can go. You will be left with a vehicle that is smaller but, proportionately, too heavy to reach an orbital speed. A rocket powered by an autophage engine would be different. The propellant rod itself would make up the body of the rocket, and as the vehicle climbed the engine would work its way up, consuming the body from base to tip.”
Harkness added that the technology opens the possibility of actually sizing launch vehicles to match small satellites, thereby offering more rapid and more targeted access to space.
The researchers have shown that the engine can be throttled simply by varying the speed at which the rod is driven into the engine, and have sustained rocket operations for 60 seconds at a time in their lab tests. The next stage, said Harkness, is to secure further funding to investigate how the engine could be incorporated into a launch vehicle.