When discussing meaningful space flight, the vastness of space compared with the relatively low speeds of our propulsion technologies has limited our ability to explore. Even a modest goal – modest in space terms, that is – such as sending humans to Mars, is especially challenging due to the length of the journey, and the logistics of propulsion.
Using currently technology, a one-way trip to Mars would take eight or nine months, and space agencies are hesitant to undertake such a trip without justification in the form of serious and extended exploration on the Mars surface. This in turn means more food, more supplies, and more energy to be accounted for.
Current propulsion technology uses “chemical propulsion,” which makes use of chemical fuels such as liquid or solid nitrogen, and thrust is generated by combustion. To create the combustion, the chemical fuel generally needs an oxidizer as well. A major obstacle to planning a meaningful and not merely symbolic Mars mission has been how to transport enough fuel for the round trip. A related issue has been the length of the trip and the need to keep astronauts healthy, physically and mentally, for two nine-month space flights and an undetermined period of time on Mars.
But what if the trip itself could be made much shorter?
NASA has developed the X3 thruster in collaboration with researchers at the University of Michigan and the US Air Force. The X3 uses Hall thruster architecture, named after Dr. Edwin Hall, in which a stream of ions generated from gases such as xenon and krypton propels the craft.
A rocket using chemical propulsion has a top speed of around five kilometers per second (1.85 miles per second). The X3, on the other hand, can reach speeds of up to 40 kilometers per second (25 miles per second). It is exactly this kind of increase that is critical to developing long-distance space travel such as a voyage to Mars, or even to the outer planets. Team leaders of the X3 project have predicted that ion propulsion technology could make a manned mission to Mars logistically possible within the next 20 years.
In addition to the speed benefits of ion engines, they are also considerably more efficient than their chemical-powered predecessors.
“We have shown that X3 can operate at over 100 kW of power,” said Alec Gallimore, project lead and dean of engineering at the University of Michigan, in an interview with space.com. “It operated at a huge range of power from 5 kW to 102 kW, with electrical current of up to 260 amperes. It generated 5.4 Newtons of thrust, which is the highest level of thrust achieved by any plasma thruster to date.” The previous record was 3.3 Newtons.
Some limitations still need to be addressed. Although the technology offers considerable improvements in speed, and is capable of generating far more thrust than previous ion rockets, ion technology still generates far less thrust compared to chemical rockets. Unless that problem is solved, the engine would have to operate for a very long time to achieve the same acceleration as a chemical system, consequently requiring shielding to prevent plasma from damaging the walls of the thruster.
Several other challenges, including the compactness of the thruster itself, need to be addressed, but scientists are optimistic about being able to solve these issues and expect to position the X3 as the near-term solution for long-distance space exploration within the solar system.