Fast forward to Mars

High-power electric propulsion technologies that could help realise the dream of a manned mission to Mars are to receive $7m (£4m) of funding from NASA.

The space agency has announced the launch of a three-year advanced electric propulsion technologies programme that it believes could enable robotic and human exploration of more distant parts of the solar system. The project involves two separate teams, one from Princeton University in New Jersey and the other from US rocket manufacturer Northrop Grumman.

One of the main reasons for the interest in high-power electric propulsion systems is that they could significantly reduce the fuel payload required to travel long distances through space. Indeed, SMART-1, ESA’s lunar probe, is now predicted to get to the moon sooner than expected, thanks to the fuel savings made possible by its solar-electric ion propulsion system. This new initiative forms part of NASA’s Prometheus project, a long-term effort to increase the power and range of spacecraft.

Northrop Grumman has received $3m (£1.5m) to research the development of a thruster where electric energy from a nuclear-electric reactor is used to energise the propellant. Company spokesperson Sally Koris explained that the Pulsed Inductive Thruster (PIT) will use this nuclear-electric system to magnetically accelerate rings of plasma. This could result in higher exhaust velocities than is possible from thrusters that rely on chemical reactions.

Koris said that this thruster, which is designed for long-duration, deep-space missions would be much more powerful but just as efficient as existing ion thrusters. Today’s ion thrusters typically operate at a power level of 10-20kW with 60-70 per cent efficiency. This thruster will demonstrate efficiencies of just above 70 per cent. She added that the thruster will be capable of sustained operation at 200kW while retaining a specific impulse range of 3,000-10,000 seconds. Specific impulse is a measure of change in momentum per unit weight – the higher the specific impulse the less fuel a rocket needs to reach a certain velocity.

To put this into perspective, Boeing’s space shuttle main engine (SSME) – which uses a mixture of liquid hydrogen and liquid oxygen as a propellant – has a specific impulse of around 452 seconds, making it both slower and more expensive to run.

Meanwhile, the team at Princeton University is to receive $4m (£2m) to work on development of a form of electromagnetic propulsion system in which an ionised propellant gas is accelerated by the application of both electric and magnetic fields. This type of thruster, able to work at relatively low power levels, is known as a magnetoplasmadynamic (MPD) system.

MPDs have actually been under development since the 1960s, but the Princeton team is working on a thruster that uses vaporised lithium as a propellant. Lithium thrusters, expected to operate at 240kW, with efficiencies greater than 60 per cent and a specific impulse of 6,200 seconds, are expected to provide significant advantages over existing state-of-the art MPD systems.