The glow of the plasma from the H9 MUSCLE Hall thruster during a test with krypton propellant. Credit: Plasmadynamic and Electric Propulsion Laboratory
It has been believed that Hall thrusters, an efficient kind of electric propulsion widely used in orbit, must be large to produce a lot of thrust. Now, a new study from the University of Michigan suggests that smaller Hall thrusters can generate much more thrust—potentially making them candidates for interplanetary missions.
“People had previously thought that you could only push a certain amount of current through a thruster area, which in turn translates directly into how much force or thrust you can generate per unit area,” said Benjamin Jorns, U-M associate professor of aerospace engineering who led the new Hall thruster study to be presented at the AIAA SciTech Forum in National Harbor, Maryland, today.
His team challenged this limit by running a 9 kilowatt Hall thruster up to 45 kilowatts, maintaining roughly 80% of its nominal efficiency. This increased the amount of force generated per unit area by almost a factor of 10.
Whether we call it a plasma thruster or an ion drive, electric propulsion is our best bet for interplanetary travel—but science is at a crossroads. While Hall thrusters are a well-proven technology, an alternative concept, known as a magnetoplasmadynamic thruster, promises to pack much more power into smaller engines. However, they are yet unproven in many ways, including lifetime.
Hall thrusters were believed to be unable to compete because of the way they operate. The propellant, typically a noble gas like xenon, moves through a cylindrical channel where it is accelerated by a powerful electric field. It generates thrust in the forward direction as it departs out the back. But before the propellant can be accelerated, it needs to lose some electrons to give it a positive charge.
Electrons accelerated by a magnetic field to run in a ring around that channel—described as a “buzz saw” by Jorns—knock electrons off the propellant atoms and turn them into positively charged ions. However, calculations suggested that if a Hall thruster tried to drive more propellant through the engine, the electrons whizzing in a ring would get knocked out of the formation, breaking down that “buzz saw” function.
“It’s like trying to bite off more than you can chew,” Jorns said. “The buzz saw can’t work its way through that much material.”
In addition, the engine would become extremely hot. Jorns’ team put these beliefs to the test.
“We named our thruster the H9 MUSCLE because essentially, we took the H9 thruster and made a muscle car out of it by turning it up to ’11’—really up to a hundred, if we’re going by accurate scaling,” said Leanne Su, a doctoral student in aerospace engineering who will present the study.
They tackled the heat problem by cooling it with water, which let them see how big a problem the buzz saw breakdown was going to be. Turns out, it wasn’t much trouble. Running with xenon, the conventional propellant, the H9 MUSCLE ran up to 37.5 kilowatts, with an overall efficiency of about 49%, not far off the 62% efficiency at its design power of 9 kilowatts.
Running with krypton, a lighter gas, they maxed out their power supply at 45 kilowatts. At an overall efficiency of 51%, they achieved their maximum thrust of about 1.8 Newtons, on par with the much larger 100-kilowatt-class X3 Hall thruster.
Ph.D student Will Hurley leaves the chamber where the new Hall plasma thruster is tested at the PEPL lab. Credit: Marcin Szczepanski/Michigan Engineering
“This is kind of a crazy result because typically, krypton performs a lot worse than xenon on Hall thrusters. So it’s very cool and an interesting path forward to see that we can actually improve krypton’s performance relative to xenon by increasing the thruster current density,” Su said.
Nested Hall thrusters like the X3—also developed in part by U-M—have been explored for interplanetary cargo transport, but they are much larger and heavier, making it difficult for them to transport humans. Now, ordinary Hall thrusters are back on the table for crewed journeys.
Jorns says that the cooling problem would need a space-worthy solution if Hall thrusters are to run at these high powers. Still, he is optimistic that individual thrusters could run at 100 to 200 kilowatts, arranged into arrays that provide a megawatt’s worth of thrust. This could enable crewed missions to reach Mars even on the far side of the sun, traveling a distance of 250 million miles.
The team hopes to pursue the cooling problem as well as challenges in developing both Hall thrusters and magnetoplasmadynamic thrusters on Earth, where few facilities can test Mars-mission-level thrusters. The amount of propellant exhausting from the thruster comes too fast for the vacuum pumps to keep the conditions inside the testing chamber space-like.
More information:
Leanne L. Su et al, Operation and Performance of a Magnetically Shielded Hall Thruster at Ultrahigh Current Densities, AIAA SCITECH 2023 Forum (2023). DOI: 10.2514/6.2023-0842
Citation:
Plasma thrusters used on satellites could be much more powerful than previously believed (2023, January 24)
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NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
