Thruster for Mars Mission Breaks Records

A side shot of the X3 firing at 50 kilowatts. (Credit: NASA)

ANN ARBOR, Mich. (University of Michigan PR) — An advanced space engine in the running to propel humans to Mars has broken the records for operating current, power and thrust for a device of its kind, known as a Hall thruster.

The development of the thruster was led by Alec Gallimore, University of Michigan professor of aerospace engineering and the Robert J. Vlasic Dean of Engineering.

Hall thrusters offer exceptionally efficient plasma-based spacecraft propulsion by accelerating small amounts of propellant very quickly using electric and magnetic fields. They can achieve top speeds with a tiny fraction of the fuel required in a chemical rocket.

“Mars missions are just on the horizon, and we already know that Hall thrusters work well in space,” Gallimore said. “They can be optimized either for carrying equipment with minimal energy and propellant over the course of a year or so, or for speed—carrying the crew to Mars much more quickly.”

The challenge is to make them larger and more powerful. The X3, a Hall thruster designed by researchers at U-M, NASA and the U.S. Air Force, shattered the previous thrust record set by a Hall thruster, coming in at 5.4 newtons of force compared with 3.3 newtons. The improvement in thrust is especially important for crewed mission—it means faster acceleration and shorter travel times. The X3 also more than doubled the operating current record (250 amperes vs. 112 amperes) and ran at a slightly higher power (102 kilowatts vs. 98 kilowatts).

Scott Hall makes some final adjustments on the thruster before the test begins. (Credit: NASA)

The X3 is one of three prototype “Mars engines” to be turned into a full propulsion system with funding from NASA. Scott Hall, a doctoral student in aerospace engineering at U-M, carried out the tests at the NASA Glenn Research Center in Cleveland, along with Hani Kamhawi, a NASA Glenn research scientist who has been heavily involved in the development of the X3. The experiments were the culmination of more than five years of building, testing and improving the thruster.

NASA Glenn, which specializes in solar electric propulsion, is currently home to the only vacuum chamber in the U.S. that can handle the X3 thruster. The thruster produces so much exhaust that vacuum pumps at other chambers can’t keep up. Then, xenon that has been shot out the back of the engine can drift back into the plasma plume, muddying the results. But as of January 2018, an upgrade of the vacuum chamber in Gallimore’s lab will enable X3 testing right at U-M.

For now, the X3 team snagged a test window from late July through August this year, starting with four weeks to set up the thrust stand, mount the thruster and connect the thruster with xenon and electrical power supplies. Hall had built a custom thrust stand to bear the X3’s 500-pound weight and withstand its force, as existing stands would collapse under it. Throughout the process, Hall and Kamhawi were supported by NASA researchers, engineers and technicians.

“The big moment is when you close the door and pump down the chamber,” Hall said.

After the 20 hours of pumping to achieve a space-like vacuum, Hall and Kamhawi spent 12-hour days testing the X3.

Even small breakages feel like big problems when it takes days to gradually bring air back into the chamber, get in to make the repair and pump the air back out again. But in spite of the challenges, Hall and Kamhawi brought the X3 up to its record-breaking power, current and thrust over the 25 days of testing.

Looking ahead, the X3 will at last be integrated with the power supplies under development by Aerojet Rocketdyne, a rocket and missile propulsion manufacturer and lead on the propulsion system grant from NASA. In spring 2018, Hall expects to be back at NASA Glenn running a 100-hour test of the X3 with Aerojet Rocketdyne’s power processing system.

The project is funded through NASA’s Next Space Technologies for Exploration Partnership, which supports not just propulsion systems but also habitat systems and in-space manufacturing.

Gallimore is also the Richard F. and Eleanor A. Towner Professor, an Arthur F. Thurnau Professor and a professor of applied physics. Kamhawi is also Hall’s NASA mentor as part of the NASA Space Technology Research Fellowship. The $1 million upgrade of the test facility in Gallimore’s lab is funded in part by the Air Force Office of Scientific Research, with additional support from NASA’s Jet Propulsion Laboratory and U-M.

  • Jacob Samorodin

    Hall-Effect thrusters have been experimented with since the 1960’s. And many of the same issues that presented technical obstacles then are still with us now: erosion of the grids for example.
    And the Hall-Effect thrusters , like VASIMR, have limits set by the simple physics equation: KE = 1/2MV^2. Simply put, if you want to double the Isp (and the exhaust velocity) you have to increase the electric power input by a factor of four; if you want to treble the Isp, you have to increase the electric power input by nine and so on and so forth. We’re talking about power levels required to be measured in megawatts for any useful thrust.

  • Andrew Tubbiolo

    I’d rather go into interplanetary space with a few 10’s to 100’s of megawatts at my disposal instead of a few 100 k watts any day. Yes you can cross the ocean in a sailboat, but I’d rather go in a missile cruiser if I have the option.

  • Jacob Samorodin

    And that usually means nuclear reactor. I’m OK with that, just as long as your returned vehicle is parked in HEO.

  • Andrew Tubbiolo

    For 10’s of megawatts or more yes, you need nuclear. I agree such systems should be limited to HEO. So long as you don’t operate in atmosphere, large gossamer structures of solar collectors will get you into the megawatt range with solar.

  • voronwae

    “Hall had built a custom thrust stand to bear the X3’s 500-pound weight and withstand its force, as existing stands would collapse under it.”

    5.4 Newtons! Great Scott! Why…that’s over a pound of thrust! 🙂

    I have a feeling that the writer of the U-M press release wasn’t clear on just what a Newton represents. But give this little thruster time and propellant, and it can get the job done. Hopefully, at some point NASA will be funded to build 200KW thrusters, which I believe would yield about 8 Newtons. They’re not great for human transportation, but they’re a boon for transporting cargo.

  • I don’t think there are any grids with a Hall thruster. That’s the big advantage over gridded ion thrusters. There is some channel erosion, but IIRC there’s been some recent cleverness on that front.

  • I love that the picture caption has Scott Hall working on a Hall thruster.

  • Jeff2Space

    The problem is that NASA isn’t currently developing any nuclear reactors for manned Mars missions. All this hype about VASIMR is hollow without an actual, quite large, power source.

  • That’s why Ad Astra is spending so much time working on 200 kW systems. That’s a reasonable size for a near-term SEP system.

    Specific power for solar power systems is almost always better than a comparable nuke system, by well more than an order of magnitude. There are solar systems in development that will get close to 300 W/kg. In contrast megawatt-class nuclear electric systems barely get 5 W/kg. It’s all about the radiator mass with nukes. With solar, it’s a matter of how much area you can deploy, which is constrained more by fairing size and deployment complexity–both problems that are likely to get a lot better in the next 10 years.

    Nukes are only necessary for missions out past 3 AU, where the spacecraft/habitation will be in shadow for long periods, or where the mission duration without resupply is so long that the solar panels degrade.

  • Vladislaw

    collapse under a 500 pound weight? LOL

  • Vladislaw

    and if you adapt muliti-junction cells or not.

  • passinglurker

    Or set up a beamed power infrastructure.

    There is no telling what the future holds. nuclear might seem the best/only way to push into deep space “now” but there is a lot more development going into solar both on the ground and in space presently whereas nuclear systems are progressing at a developmental crawl if not stand still.

  • Michael Vaicaitis

    Liquid fuelled nuclear research and development is vibrant. There are several projects targeting the early to mid 2020’s for proof of concept working reactors that will lead to commercialisation before 2030. These reactors will undercut wind/solar and coal. How well and how long it might take to transition designs for space travel is not yet clear, but interplanetary EP is not likely to gain a significant foothold this side of 2050 so there is plenty of time to mature nuclear (and solar of course) for in space use.

    Beamed power is hugely inefficient nonsense, IMO.

  • redneck

    Unless you have looked into propulsion for multiple spacecraft of course.

  • windbourne

    Ion thrusters for medium to large crafts is likely not that useful other than controls.

    I read once, fairly recently, but have not found it again, where shotwell stated that they have an ongoing nuke engine project, but coming up with nuke fuel is the hard part. However, I have not found that article again.

    If this is true, then we have a fast way to get to Mars and beyond.

  • duheagle

    Beamed power is just a really big phased array radar.

  • duheagle

    Yes. We know how touchy your nation is about errant nuclear reactors in space. Not that you don’t have good reason to be.