Three months to Mars: British invent space tug with thermonuclear propulsion

British startup Pulsar Fusion has unveiled the concept of the Sunbird space tug powered by fusion. A small rocket powered by a direct fusion linear drive will be able to deliver cargo very quickly within the solar system. Space testing of the fusion engine concept is planned for 2027. With sufficient funding, a prototype tug will be built by 2030. The source of funding has not yet been determined.

Image source: Pulsar Fusion

Today, all space agencies and a number of companies are developing rocket engines with nuclear propulsion. Using the energy of nuclear fission (decay), it is proposed to either generate electricity to power ion rocket engines, or to evaporate the working fluid – for example, water – to create a jet thrust. In any case, nuclear engines provide a significantly longer cycle of continuous operation with less fuel consumption than rockets with chemical fuel.

Thermonuclear fusion reactions release four times more energy than nuclear fission reactions. Thanks to this, thermonuclear rockets will be able to accelerate to impressive speeds – up to 800,000 km/h, using a minimum amount of fuel. A rocket with such an engine can reach Mars in two to three months, and the path to Saturn or Jupiter will be shortened to a couple of years.

In its vision of the future, Pulsar Fusion envisions a network of refueling stations in the solar system, where fusion tugs would periodically dock. They would then grab conventional rockets and move them around the system. Closer to their destination, the rockets would detach from the tugs, fire their chemical engines, and complete the flight on their own.

The UK Space Agency is funding the development of the Sunbird fusion tug concept. This year, Pulsar Fusion plans to send components of the rocket’s future electronics into space to ensure it can operate in zero gravity. The direct fusion drive (DFD) components are planned for launch in 2027. The developer notes that fusion is “natural” for a vacuum, but not for Earth. In any case, unlike fusion reactors on Earth designed to generate electricity, a fusion reactor at the heart of a rocket engine should be much simpler.

A rocket thermonuclear engine will not require long-term plasma containment – all fusion products will immediately be converted into a jet stream and leave the engine, creating thrust. This will significantly simplify the engine design, which is still technically difficult for tokamaks and stellators. In addition, the rocket engine will have a linear working chamber, which simplifies the magnetic field configuration to keep the plasma at a distance from the chamber walls. Finally, for a thermonuclear rocket engine to operate, it is not necessary to achieve a positive energy yield of the thermonuclear reaction – any reaction, even with an energy deficit, can be used to create thrust.

Pulsar Fusion is considering using deuterium and helium-3 as fuel. The fusion process will produce protons instead of neutrons, as in the case of reactions at thermonuclear power plants on Earth. Protons allow for more powerful thrust, while creating virtually no radioactive waste.