Last November Dr George Schmidt was made manager of NASA’s Propulsion Research Centre — the kind of job that would turn many engineers green with envy. Based at the Marshall Space Flight Centre in Huntsville, Alabama, Schmidt leads the organisation’s R&D into advanced propulsion technology that will power future missions to the moon, Mars and beyond.
Following work for companies including Boeing, Schmidt joined NASA in 1989 to work on the development of propulsion systems and hardware. After holding a number of posts, he served as programme executive for Nuclear Power Systems at the agency’s Science Mission Directorate in Washington. Before being appointed to his current role he led the development of radioisotope-based nuclear power flight systems and advanced power conversion technologies for NASA’s Project Prometheus, developing propulsion systems for exploration throughout the solar system.
If the most recent US budget proposals are agreed, Schmidt may have considerably more money to work with than his predecessors. For 2006 President Bush has requested $16.5bn (around £9bn) for NASA, a 2.4 per cent increase over the previous year. Of this $858m (£457m) has been set aside for robotic missions to Mars and the Moon. However, the challenges facing his department are numerous, and Schmidt knows he must spend his windfall wisely.
‘No one propulsion system will fit all our needs. We have to produce a solution tailored for each,’ he said. ‘The time frame extends to 2030 and even beyond. By the end of this decade and the start of the next we should be into our first phase, Spiral 1, where we are using mostly existing technologies to send science missions to the Moon.’
The next stage, Spiral II, will see a crew return to the Moon by 2020 at the latest. This means that those anticipating the early adoption of revolutionary nuclear or solar sail-powered craft are likely to be disappointed. ‘Spiral II needs some development of technology, but due to the ambitious timeline we will have to keep to the systems we know,’ said Schmidt.
Some new technologies may come online by Spiral III when a long-term base will be established on the Moon. But at first these will only be used for unmanned vehicles, refuting criticisms that robotic missions will be shelved to make way for a new emphasis on human exploration.
‘The Mars Spirit mission has shown that you can’t ignore how important robots are,’ claimed Schmidt. ‘Robots are great for reconnaissance. You can take greater risks and you don’t need as much redundancy and back-up in your spacecraft. But they can’t do everything. Information from them is very linear: you get data, analyse it and send back a command. This takes time. People are able to act on their own initiative.’
Reducing the impact of travel beyond Earth on the human body is central to the selection of an ideal propulsion system. ‘Space is filled with solar and cosmic ray radiation. Any human transportation needs to minimise the time spent there to reduce exposure for the crew. If there is no crew we can afford to take more time using more efficient but slower systems. When it comes to the point where we are sending infrastructure to the Moon and we are not so concerned with trip times we can start to use high-performance propulsion such as solar electric systems.’
Beyond spiral III the timeline becomes less certain. But once NASA enters Spirals IV and V, which will culminate in the first manned mission to Mars, Schmidt claimed that the design of manned space vehicles will have changed dramatically.
‘We really need new technologies for this. It opens up a whole load of propulsion options.’ But choosing which is best will not be easy, he admitted. ‘Nuclear thermal propulsion is more attractive than chemical systems in terms of trip time. Nuclear systems were looked at in conjunction with the Apollo programme. They are very complex, though — a monopropellant like hydrogen is run through a reactor to expand it, then pushed through a nozzle. The exhaust velocity is much greater than for liquid oxygen or hydrogen. The only problem is that liquid hydrogen is not very dense so you need large tanks for storage. The jury is still out on whether chemical or nuclear thermal propulsion makes most sense, but we have to look into nuclear systems to make sure we are making the right choice.’
Schmidt’s remit also includes propellant-less systems such as solar sails, which could be used to maintain non-equilibrium orbits for satellites that would provide any Moon base with early warning of radiation surges caused by solar flares. Other promising technologies include momentum exchange tethers, which rely on a spinning payload being released, reducing the amount of energy used, and captive aero-braking. This involves reducing the velocity of a spacecraft by skimming through sections of the atmosphere, rather than using propellant for reverse thrust. Once man moves beyond the Moon, these may be vital.
‘The distance between Mars and the Sun means solar-powered craft would be less efficient at transporting infrastructure. As man ventures further into the solar system we would have to rely on nuclear systems or something else,’ he said. ‘Many advanced technologies look promising but aren’t viable for the first five Spirals. This doesn’t mean we shouldn’t invest in them, especially if we want to send a crew beyond the asteroid belt. For a robotic mission nuclear electric systems are fine, but if you are sending a crew you need to think about antimatter or fusion-powered spacecraft.’
Research on such systems is still at an early stage. While scientists at CERN have produced small quantities of anti-hydrogen, any NASA propulsion system would have to make antiprotons or anti-hydrogen molecules efficiently, without using too much energy, then store them. ‘People think that if you just mix antimatter with regular matter it creates a reaction, but it’s not that simple,’ conceded Schmidt. ‘We need to research the reaction mechanism now if we want to use it in several decades’ time.’
NASA is currently looking for a way around these issues, using antimatter as a trigger for fusion instead of basing the entire power system around it. However, this is not the sole focus of research. Schmidt and his team are investigating the use of bismuth to replace xenon in experimental ion thrusters as bismuth is cheaper, easier to store and performs better. They are also looking at improving the performance of materials used in the core of nuclear drives to allow them to operate at higher temperatures, improving efficiency and exhaust velocity without risking a meltdown.
A proof-of-principle demonstration of a plasmoid thruster, which uses electric and magnetic forces to accelerate the vehicle, is likely to occur within two years. Using pulsed fusion or fission to create thrust is also being probed.
With so much to accomplish Schmidt knows that spreading staff and money across each project will be hard. ‘We really have a lot of challenges and the trick lies in balancing the portfolio,’ he said. The future of NASA’s ambitions depends on it.