X3 Hall thruster sets records at NASA Glenn
GLENN RESEARCH CENTER, Ohio — Researchers at the University of Michigan, in Ann Arbor, and the NASA Glenn Research Center in Cleveland, Ohio, have completed a round of important tests on a new ion thruster system that may one day provide propulsion for materials and crews on future missions to Mars.
The unit tested was the X3 Hall thruster, which is one of a number of ion thruster designs currently under development by NASA. An ion thruster is a system that uses electricity to ionize atoms of a propellant, in this case, xenon. These ions are then expelled by a strong electric field out the back of the spacecraft, producing thrust. The Hall-effect (ion) thruster – the term is based on the discovery by Edwin Hall – is also referred to as a Hall thruster or a Hall-current thruster.
The recent test of the X3 Hall thruster set new records for the technology. The thruster ran at 102 kW of power, besting the previous record of 98 kW. It managed an operating current of 250 amps, more than twice that of the previous record. Most importantly, the thruster produced 5.4 newtons of thrust, far out-performing the previous record of 3.3 newtons.
The testing on the X3 was conducted over a 25-day period between July and August of this year (2017) in NASA Glenn’s large VF-5 vacuum chamber. A special stand had to be built for the large thruster, as it weighed more than 500 pounds (227 kg). The X3 is a joint project of NASA, the University of Michigan, and the Air Force, and is funded under NASA’s Next Space Technologies for Explorations Partnership (NextSTEP).
“The X3 is a three-channeled nested Hall thruster,” Hani Kamhawi, senior research engineer at NASA Glenn’s electric propulsion systems branch, told Spaceflight Insider. “There are two channels that are nested inside a larger channel. It is a high-powered device that can go up to 200 kW. The reason why we nest Hall thrusters is because we have this high power requirement. We want to process a lot of power so we can use it to get higher thrusts from the device. We can achieve that at higher efficiency because they are nested. It improves the power density of the device. Instead of having three separate thrusters, we put them all together in one device that has a lot of common components among those thrusters. This optimizes the mass for the device.”
Aptly named UM graduate student Scott Hall and UM Professor Alec Gallimore did preliminary testing on the X3 thruster in the vacuum chamber facility at UM. Their tests ran the thruster up to about 30 kW. It became obvious, however, that for them to test the thruster at higher power levels, they had to come to NASA Glenn. The primary reason for the move was to use the vacuum chamber facility at NASA Glenn, which features a much higher pumping speed to keep the chamber at vacuum conditions much closer to what the thruster will experience in space.
Placing the thruster in the larger VF-5 chamber at NASA Glenn provided them with the opportunity to test the X3 at the record-breaking levels it reached.
“You need a large chamber for that,” Kamhawi said. “You need high pumping speed to maintain spaceflight vacuum levels.”
The X3 is scheduled for further testing early next year, but it is uncertain exactly when and where that next battery of tests will take place.
“We’re going through a major update of our vacuum chamber to make it somewhat equivalent in capability to the one that NASA (Glenn) has,” Gallimore told Spaceflight Insider. “We don’t think these updates will be ready by January of 2018. So what we might do is some testing of the facility first to see if it performs the way we think it will perform in terms of pumping speed. Then based on that we can have a discussion with NASA if it makes sense to do the X3 thruster work all at the U of M, or at NASA (Glenn). Right now, I would say we are baselining at least part of the test to be done at NASA Glenn.”
Ion thruster technology could play a crucial role in any future architecture for getting humans to Mars. Much of the equipment, supplies, and other hardware that would go to Mars in advance of a first landing of humans on the planet is expected to make the trip using ion thruster technology. The coupling of solar array technology with ion thruster technology is the basis of NASA’s efforts to produce higher efficiency solar electric propulsion (SEP). Solar arrays produce the electricity to power the ion thruster technology and its resultant propulsion. Today, SEP is used to keep over 100 geosynchronous Earth-orbit satellites in their locations, a process called station keeping.
The greatest example of the propulsion system currently in use is the Dawn mission, launched in 2007 atop a United Launch Alliance Delta II rocket from Cape Canaveral Air Force Station in Florida, the spacecraft has traveled to the giant asteroid Vesta, and the dwarf planet Ceres, where it currently orbits.
Dawn was the first spacecraft to go into orbit around two extraterrestrial bodies – a feat that was achieved primarily through the use of SEP and its ion thruster technology. If the mission had used chemical rockets, it would have required a much heavier spacecraft and a tremendous amount of fuel to achieve the mission’s goals.
This reduction in mass and the efficiency of the fuel are the factors that drive the effort to make the X3 Hall thruster, as well as other components of SEP, ready for future missions to Mars and beyond.
This article was updated at 10:05 EST on November 10, 2017.
Michael Cole is a life-long space flight enthusiast and author of some 36 educational books on space flight and astronomy for Enslow Publishers. He lives in Findlay, Ohio, not far from Neil Armstrong’s birthplace of Wapakoneta. His interest in space, and his background in journalism and public relations suit him for his focus on research and development activities at NASA Glenn Research Center, and its Plum Brook Station testing facility, both in northeastern Ohio. Cole reached out to SpaceFlight Insider and asked to join SFI as the first member of the organization’s “Team Glenn.”