Imagine a near-future where a spacecraft the size of a SpaceX Starship is setting out on a mission to Mars. Under current plans, that would mean a rendezvous with multiple rockets ferrying fuel from Earth to tank up the Mars ship for the year-long journey to the Red Planet.

However, things are different now. Instead of tankers, small, black, polygonal modules leave a stick-like space station. They dock with the stern of the Mars ship and, once in position, their exhausts glow blue, then violet as the ship accelerates faster and faster, the self-contained nuclear fusion engines burning longer and with more power than anything seen before as the ship slips into a transfer orbit that will see it reach Mars in record time.

Science fiction? Maybe not.

Founded in 2013, Pulsar Fusion has been on our radar for sometime and it's been the cause of much head scratching at New Atlas editorial meetings. On the one hand, it seemed to be a very serious company producing a solid line of electric space propulsion systems as well as a hybrid liquid/solid rocket engine and space-based nuclear fission reactors, along with getting some serious development money from the British government. On the other hand, it was also making noises about a nuclear engine project that sounded so crazy that it seemed like it had to be vaporware put out for publicity.

Called Sunbird, we now have more details on the nuclear fusion rocket project that is so far along that the company expects to demonstrate it later this year and begin orbital tests in 2027.

What made Sunbird seem impossible when we first heard about it was that it was based on a fusion rocket engine. If anyone has followed the attempts to build practical commercial fusion reactors, they'll be aware that the goal is right where it was back in the 1950s – always 20 years in the future. If that's the case, how could Pulsar Fusion be claiming to be building something that would make SpaceX's Starship look like a horse-drawn Zeppelin?

According to Richard Dinan, CEO of Pulsar Fusion, the answer is that Sunbird uses a completely different kind of fusion to what you find in a tokamak reactor – one with a completely different purpose in a completely different environment where weaknesses become strengths

In a tokamak reactor, fusion is based on Deuterium-Deuterium (D-D) or Deuterium-Tritium (D-T) reactions, where the hydrogen isotopes deuterium and tritium are subjected in confinement to immense pressures and temperatures until a reaction is set off that fuses the hydrogen atoms into helium, releasing energy and neutrons.

Since a tokamak has to run continuously and the energy is collected as heat to generate steam to run a turbine, the reactor has to be built on a gargantuan scale with giant magnetic coils, cryogenic coolant systems, heavily armored containment vessels, and lots of radiation shielding to deal with neutron erosion.