The UK’s Defence and Security Accelerator (DASA), an agency of the country’s Ministry of Defence, has committed £90 000 (about R1.92-million) to support the development of a potentially revolutionary ‘autophage’ rocket engine. Autophage literally means self-eating, and the rocket is being developed by the James Watt School of Engineering at the University of Glasgow, with support from London’s Kingston University.
The autophage rocket would not only burn its propellant, it would also burn up its own structure. In this process it would both increase its thrust and reduce its mass as it climbed into space. The idea is that such a rocket would be used to launch small satellites into low Earth orbit.
The research team in Glasgow has already test-fired autophage engines which used entirely solid propellants. (Rockets normally used either solid or liquid propellants, the latter providing more energy but the former being much simpler to design and construct.) The DASA funding will be used to create a hybrid autophage engine, with a tube of solid fuel containing a liquid oxidiser. This hybrid system will provide more energy than a purely solid-fuel engine would.
“We’re thrilled to have DASA in support of the autophage programme,” affirmed James Watt School of Engineering senior academic Dr Patrick Harkness. “The new propellants will take us closer to viability, because they contain enough energy to reach orbit in a smaller launch vehicle. The specific payloads we are targeting include the small satellites for which Glasgow is becoming increasingly well-known. At the moment it often takes a long time to launch these, because they need to be grouped for a flight on a larger rocket, and that rocket is often launched from sites in the US or Kazakhstan. It can take years.”
Hitherto, the problem with smaller rockets has been that the required scaling down of the design reduces the mass of the propellant more than it reduces the mass of rest of the rocket (including the propellant tanks). That has imposed a minimum size on rockets intended to launch spacecraft, even small satellites into low Earth orbit. Harkness described this size/mass limit as a ‘wall’.
“The autophage concept is simple: burn the tanks as well,” he explained. “That saves excess mass, and it means that we can miniaturise the vehicle without hitting this wall. The body of the hybrid autophage rocket will be a tube of solid fuel, containing a liquid oxidiser. “The entire assembly will be consumed, from the bottom up, by an engine which will vaporise the fuel tube, add the oxidiser, and burn the mixture to create thrust. The engine will have consumed the entire body of the rocket by the time the assembly reaches orbit, and only the payload will be left. It is a much more mass-efficient process.”
“The engine has to run hot enough to vaporise the fuel tube, but at the same time not destroy itself in service,” highlighted engineer Krzystof Bzdyk, who is responsible for the technical development of the engine. “We will use the cold fuel tube coming into the engine as a means of controlling temperature, in a process called regenerative cooling. But even so, the test article will have to be made of exotic materials, like tungsten and graphite, at least until we fully understand the temperatures inside.”
The engine will be test fired next year at Kingston University’s new rocket laboratory at its dedicated engineering campus at Roehampton Vale in south-west London (near Wimbledon). The ambition is that the autophage rocket will be operated from the spaceports now being developed in the UK. The value of the low Earth orbit small satellite launch business could reach £100-million (roughly R2.1-billion) by the mid-2020s. Britain has the strategic aim of securing 10% of the global space business by 2030. “Smaller rockets like this, which could be launched from sites here in Britain, could be the key to unlocking that market,” pointed out Harkness.