Solar Electric Propulsion Makes NASA’s Psyche Spacecraft Go


NASA’s Psyche spacecraft is photographed in July 2021

NASA’s Psyche spacecraft is photographed in July 2021 during the mission’s assembly, test, and launch operations phase at JPL. Hall thrusters – two of which are visible beneath red round protective covers – will propel the spacecraft to its target in the main asteroid belt.Credits: NASA/JPL-Caltech

Meet asteroid Psyche

Psyche spacecraft chassis arrives at JPL

Futuristic electric thrusters emitting a cool blue glow will guide the Psyche spacecraft through deep space to a metal-rich asteroid.

When it comes time for NASA’s Psyche spacecraft to power itself through deep space, it’ll be more brain than brawn that does the work. Once the stuff of science fiction, the efficient and quiet power of electric propulsion will provide the force that propels the Psyche spacecraft all the way to the main asteroid belt between Mars and Jupiter. The orbiter’s target: a metal-rich asteroid also called Psyche.

The spacecraft will launch in August 2022 and travel about 1.5 billion miles (2.4 billion kilometers) over three and a half years to get to the asteroid, which scientists believe may be part of the core of a planetesimal, the building block of an early rocky planet. Once in orbit, the mission team will use the payload of science instruments to investigate what this unique target can reveal about the formation of rocky planets like Earth.

Engineers at NASA’s Jet Propulsion Laboratory

Engineers at NASA’s Jet Propulsion Laboratory work to integrate Hall thrusters into the agency’s Psyche spacecraft in July 2021. One of the thrusters is visible on the side of the spacecraft underneath a red protective cover.Credits: NASA/JPL-Caltech

The spacecraft will rely on the large chemical rocket engines of the Falcon Heavy launch vehicle to blast off the launchpad and to escape Earth’s gravity. But the rest of the journey, once Psyche separates from the launch vehicle, will rely on solar electric propulsion. This form of propulsion starts with large solar arrays that convert sunlight into electricity, providing the power source for the spacecraft’s thrusters. They’re known as Hall thrusters, and the Psyche spacecraft will be the first to use them beyond the orbit of our Moon.

For propellant, Psyche will carry tanks full of xenon, the same neutral gas used in car headlights and plasma TVs. The spacecraft’s four thrusters will use electromagnetic fields to accelerate and expel charged atoms, or ions, of that xenon. As those ions are expelled, they create thrust that gently propels Psyche through space, emitting blue beams of ionized xenon.   

Engineers prepare to integrate four Hall thrusters

At NASA’s Jet Propulsion Laboratory, engineers prepare to integrate four Hall thrusters (beneath the red protective covers) onto the agency’s Psyche spacecraft. The thrusters will propel Psyche to its target in the main asteroid belt.Credits: NASA/JPL-Caltech

In fact, the thrust is so gentle, it exerts about the same amount of pressure you’d feel holding three quarters in your hand. But it’s enough to accelerate Psyche through deep space. With no atmospheric drag to hold it back, the spacecraft eventually will accelerate to speeds of up to 200,000 miles per hour (320,000 kilometers per hour).

Because they’re so efficient, Psyche’s Hall thrusters could operate nearly nonstop for years without running out of fuel. Psyche will carry 2,030 pounds (922 kilograms) of xenon in its tanks; engineers estimate that the mission would burn through about five times that amount of propellant if it had to use traditional chemical thrusters.  

“Even in the beginning, when we were first designing the mission in 2012, we were talking about solar electric propulsion as part of the plan. Without it, we wouldn’t have the Psyche mission,” said Arizona State University’s Lindy Elkins-Tanton, who as principal investigator leads the mission. “And it’s become part of the character of the mission. It takes a specialized team to calculate trajectories and orbits using solar electric propulsion.”

Illustration depicts NASA’s Psyche spacecraft

This illustration depicts NASA’s Psyche spacecraft, set to launch in August 2022.Credits: NASA/JPL-Caltech/ASU

A Gentle Maneuver

Psyche will launch from the historic Pad 39A at NASA’s Kennedy Space Center. The Falcon Heavy will place the spacecraft on a trajectory to fly by Mars for a gravity assist seven months later, in May 2023. In early 2026, the thrusters will do the delicate work of getting the spacecraft into orbit around asteroid Psyche, using a bit of ballet to back into orbit around its target.

That task will be especially tricky because of how little scientists know about the asteroid, which appears as only a tiny dot of light in telescopes. Ground-based radar suggests it’s about 140 miles (226 kilometers) wide and potato-shaped, which means that scientists won’t know until they get there how exactly its gravity field works. As the mission conducts its science investigation over 21 months, navigation engineers will use the electric propulsion thrusters to fly the spacecraft through a progression of orbits that gradually bring the spacecraft closer and closer to Psyche.

NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission, used a similar propulsion system with the agency’s Deep Space 1, which launched in 1998 and flew by an asteroid and a comet before the mission ended in 2001. Next came Dawn, which used solar electric propulsion to travel to and orbit the asteroid Vesta and then the protoplanet Ceres. The first spacecraft ever to orbit two extraterrestrial targets, the Dawn mission lasted 11 years, ending in 2018 when it used up the last of the hydrazine propellant used to maintain its orientation.

At left, xenon plasma emits a blue glow from an electric Hall thruster

At left, xenon plasma emits a blue glow from an electric Hall thruster identical to those that will propel NASA’s Psyche spacecraft to the main asteroid belt. On the right is a similar non-operating thruster.Credits: NASA/JPL-Caltech

Partners in Propulsion  

Maxar Technologies has been using solar electric propulsion to power commercial communications satellites for decades. But for Psyche, they needed to adapt the superefficient Hall thrusters to fly in deep space, and that’s where JPL engineers came in. Both teams hope that Psyche, by using Hall thrusters for the first time beyond lunar orbit, will help push the limits of solar electric propulsion.

“Solar electric propulsion technology delivers the right mix of cost savings, efficiency, and power and could play an important role in supporting future science missions to Mars and beyond,” said Steven Scott, Maxar’s Psyche program manager.

Along with supplying the thrusters, Maxar’s team in Palo Alto, California, was responsible for building the spacecraft’s van-size chassis, which houses the electrical system, the propulsion systems, the thermal system, and the guidance and navigation system. When fully assembled, Psyche will move into JPL’s huge thermal vacuum chamber for testing that simulates the environment of deep space. By next spring, the spacecraft will ship from JPL to Cape Canaveral for launch.

More About the Mission

ASU leads the mission. JPL is responsible for the mission’s overall management, system engineering, integration and testing, and mission operations. Psyche is the 14th mission selected as part of NASA’s Discovery Program.

For more information about NASA’s Psyche mission go to:

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dodgy geezer
September 20, 2021 10:07 pm

Solar power, eh? Bet the activists are already lobbying for the next satellite to use wind power…..

Reply to  dodgy geezer
September 21, 2021 4:52 pm

The solar wind? an interesting idea!

Joe Dun
Reply to  mcswelll
September 21, 2021 7:13 pm

You are talking about a solar sail. There have been a few orbital tests. The first US mission to really use them is the Near Earth Asteroid (NEA) Scout mission, which is scheduled to launch later this year.

Reply to  Joe Dun
September 21, 2021 7:15 pm

I confess I meant it partly as a joke. Do you know whether the orbital tests *really* worked? My impression was that they were pretty equivocal, but I could be wrong.

Reply to  dodgy geezer
September 21, 2021 6:52 pm

You mean solar sails, I hope. That would be interesting. I wonder how long before they were shredded to tatters with no backup.

Bill E
Reply to  dodgy geezer
September 24, 2021 4:34 pm

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is a Japan Aerospace Exploration Agency (JAXA) experimental spacecraft. The spacecraft was launched on 20 May 2010 …

September 20, 2021 10:11 pm

Exciting climate news… not. But hey, if you run out of ideas and have no spark of inspiration, just go mainstream.

Timo V
Reply to  E. Schaffer
September 21, 2021 12:53 am

Read the “About”-page:

Watts Up With That? News and commentary on puzzling things in life, nature, science, weather, climate change, technology, and recent news by Anthony Watts.”

It’s been like this from beginning, and i think it’s great.

Reply to  E. Schaffer
September 21, 2021 3:20 am

Or you could just leave, go spew your greentarded stupidity at cnn.

Reply to  E. Schaffer
September 21, 2021 6:00 am

Running low on things to complain about again?

Reply to  E. Schaffer
September 21, 2021 6:08 am

On this morning’s front page, I count 23 articles about climate and renewable energy, and 1 article about space.
In the last few months, there have been several articles about Mars and space sciences.
Nothing at all unusual going on.

September 20, 2021 10:43 pm

There’s not much sunlight way out at the Asteroid Belt (only about 10% of what we get in Earth’s orbit), so this seems like a good application for a Pu238-powered nuclear RTG. Did they use solar, instead, because of the shortage of Pu238?

Tom Abbott
Reply to  Dave Burton
September 21, 2021 8:00 am

The Russians claim they are going to build a nuclear-powered orbital transfer vehicle in the not-so-distant future.

Reply to  Tom Abbott
September 21, 2021 12:17 pm

Hopefully they succeed and prove to us American’s that we were idiots to abandon nuclear propulsion last century.

Last edited 10 months ago by leowaj
Tsk Tsk
Reply to  Dave Burton
September 21, 2021 3:25 pm

It’s not like an RTG produces all that much power either.

Reply to  Dave Burton
September 21, 2021 5:02 pm

I was going to say your math is a little off, but for Psyche it’s close. The Belt is roughly 2.2 — 3.2 AU, so the sunlight would be between 2.2^2 = 4.8 and 3.2^2 = 10 less. So for the further side, yes, 10%, but on the near side like 20%. Psyche’s orbit is 2.5 — 3.3 AU, so between 6 and 11 times less sunlight.

So why did they use solar? I guess because it’s good enough, even at that distance.

September 21, 2021 12:08 am

So they’re going to use solar power to get it into space ?. Suspect 99.999999% + of the energy required will come from fossil fuels, the solar panel powered xenon thrusters are just for minor adjustments to trajectory.

Reply to  Sparko
September 21, 2021 10:48 am

No, after Earth escape velocity (about 95,000 mph) the ion thrusters will continue accelerating Psyche to about 200,000 mph, as they said.

My wife and I (and three others) designed a solar-powered interplanetary ion-thruster spacecraft at Rocketdyne back in 1960. Much tougher with 60’s technology, but I bet my wife’s powered-flight orbital mechanics equations haven’t changed much.

Hope to live to see it reach Psyche Asteroid sixty-six years later! LOL

Reply to  hiskorr
September 21, 2021 11:20 am

I worked on Deep Space – 1, which was the first spacecraft to use Ions as propulsion and not just station keeping. It’s a great technology for certain applications. I’m still not sure why they went with solar instead of RTGs.

Reply to  hiskorr
September 21, 2021 1:51 pm

I expect the energy used to make those solar panels and xenon thrusters, was also fossil fueled.

Reply to  hiskorr
September 21, 2021 2:01 pm

You aren’t including the energy used to lift the probe, and most of the rocket out of earth’s gravity well.

Tsk Tsk
Reply to  hiskorr
September 21, 2021 3:26 pm

Much tougher with 60’s technology,

Not really considering this isn’t much changed from when it was invented in the 50s and 60s.

Peter Fraser
Reply to  hiskorr
September 21, 2021 3:59 pm

“No, after escape velocity ( about 95,000 mph) the ion thrusters …”
In my youth before a moon landing was even contemplated escape velocity was given as 25,000 mph. Has something changed?

Reply to  Peter Fraser
September 21, 2021 6:49 pm

I see that going to Mars is about 75,000 mph. As you keep climbing out a gravity well, you keep slowing. To the Moon, we swapped to the Moon’s gravity well. We didn’t break free so much as entered the Moon’s well. It was efficient. We could have probably gone slower and been more efficient with fuel.

Joe Dun
Reply to  Peter Fraser
September 21, 2021 6:58 pm

I suspect that the 95,000 mph is deliberately much more than needed to excape orbit, to give it an extra kick on its way.

Reply to  Peter Fraser
September 22, 2021 5:36 am

Change reference system! After leaving the Earth’s gravity “well” Psyche is tooling along in Earth’s orbit at about 67,000 mph. Then it keeps accelerating (gaining energy) to climb to the asteroid’s orbit. “200,000 mph” is just the integrated F=Ma, not that it is “going 200,000 mph relative to” something. You want it to end up going zero mph relative to the asteroid.

Last edited 10 months ago by hiskorr
Reply to  Sparko
September 21, 2021 6:41 pm

Chemical cannot get you to 200,000 mph. New Horizons did about 36,000 mph. Some say it was the fastest ever. Keep adding fuel to go faster is a losing game. You gain in saving the weight of the fuel by using less mass for more thrust. This is the future.

September 21, 2021 12:54 am

The destination of this satellite is asteroid 16 Psyche which seems to be comprised of nickel and various other metals (including gold and silver) with an estimated worth of $10,000 quadrillion….

I think this asteroid is a major reason private sector companies are taking their first baby steps in space flight to develop the necessary technologies to eventually make space mining a viable business.

Peta of Newark
September 21, 2021 12:57 am

What a contrived way of doing things.
All that’s happening is Newton’s Law of action & reaction = throwing one obeject in one direction pushes the ‘thrower’ in the opposite.
All they needed to do was keep the Xenon in a pressurised tank (how could it already be inside anything else) and release little blasts of the stuff to nudge the Sputnik along and push it around

Where the Hall drive (presumably the ‘Hall’ guy from the Hall Effect) would be in accelerating to the huuuuuuge speeds you might want for Inter-Stellar voyaging = an electric Rail Gun for atoms
Solar Panels are gonna do you One Bigge Phatt Lotta Goode in interstellar space methinks

Why are we told that the thing is ‘quiet’?
Considering the complexity of it, I can not believe it to be ‘efficient’ – apart from the fact that Sputnik needn’t be carrying any oxidant for its ‘fuel’

(OMG!!! – Its because they’ve closed the fertiliser factories in the UK – they make nitrate – The Original and Genuine Oxidant. Boris Johnson, you are a Terminal Muppet, Just Look At The <expletive> Grief You’re Causing everybody)

In the Grand Scheme of things, it is NOT emitting ions. If it only pushed out, what would be, positively charged particles, Sputnik would finish up carrying a very large negative charge.

How can The Geniuses that understand the GHGE not realise that +ve and -ve attract. The cloud of emitted ions will come chasing after Sputink while it hankers to be in the midst of said cloud – net result being Sputnik going Precisely Nowhere.
(Oh Nooooo, its because nobody, not even computers, understands ‘clouds‘ – how could I be soooo dumb)

Thus, no matter how blue it might be glowing or quiet it might be, quietness will be its undoing.
We all know how cookies crumble…
In space, no-one can hear you scre….”

In all probabbility, the boulder they’re visiting will contain Iron, why not just glue a small bit of Neodymium to Sputnik’s nose?
That was where we came in, Hall was a guy who was seriously interested in Magnetism

<Einstein quote>

Reply to  Peta of Newark
September 21, 2021 5:54 am

This way a ‘mission scientist’ can have a job for life.

Reply to  Peta of Newark
September 21, 2021 7:43 am

How can The Geniuses that understand the GHGE not realise that +ve and -ve attract. The cloud of emitted ions will come chasing after Sputink while it hankers to be in the midst of said cloud – net result being Sputnik going Precisely Nowhere.

Jesus H Christ, at least read the wikipedia page for the Hall thrusters before you write stupidities.

Reply to  nyolci
September 21, 2021 5:19 pm

Exactly, but I’ll quote the relevant sentence here so Peta doesn’t think he won: “Upon exiting, however, the ions pull an equal number of electrons with them, creating a plasma plume with no net charge.” So Hall Effect thrusters are perfectly capable of accelerating spacecraft, and have done so for many spacecraft since 1971 (when the Soviets launched their Meteor spacecraft).

Alan Watt, Climate Denialist Level 7
Reply to  Peta of Newark
September 21, 2021 8:00 am

You are reacting negatively because the title says “solar electric propulsion” and all things solar must be bad. Hall thrusters have been used in spacecraft since the early 1970’s. Solar-electric krypton-fueled Hall thrusters are used in the new SpaceX Starlink constellation.

What appears to be new with the Psyche mission is the distance that will be travelled,

I had the same question as several other posters regarding just how much solar power you can get that far from the sun. I suspect the Psyche probe also carries some chemical thrusters for final maneuvering near the asteroid, and the Hall effect thrusters are just the most efficient way to get it there.

Reply to  Alan Watt, Climate Denialist Level 7
September 21, 2021 12:17 pm

What appears to be new with the Psyche mission is the distance that will be travelled,

Exactly. Most missions use a few tens of kg of propellant, here we have almost 1 ton.

Reply to  Peta of Newark
September 21, 2021 11:04 am

Oh, please! Did your high school physics not at least tell you that F=MV^2? Ions can be accelerated to many times the velocity of chemical propellants– and then you square it !!

Tsk Tsk
Reply to  hiskorr
September 21, 2021 3:30 pm

No, F=d(mv)=ma=m*vdot. POWER(energy) goes as the square. In this case it’s power because the mass flow rate.

Reply to  Tsk Tsk
September 22, 2021 5:48 am

Sorry, should have edited E instead of F.

September 21, 2021 3:35 am

Solar power outside the Earth’s atmosphere, where it actually makes sense. As a first step in asteroid mining getting to the target is something we have already achieved, at least crashing into it. The real test is a craft capable of altering the orbit of the target sufficiently to get it into an orbit close enough to Earth to make using it feasible. Baby steps, folks, are necessary till you can take man sized strides.

Reply to  2hotel9
September 21, 2021 9:11 am

They tried extension cords, but airplanes kept knocking them down.

Reply to  2hotel9
September 21, 2021 5:35 pm

This is not the first spacecraft to orbit an asteroid. Shoemaker orbited Eros in 2000 (and later landed). Dawn orbited Vesta and later Ceres (using its ion engines to make the trip).

Reply to  mcswelll
September 22, 2021 3:32 am

Yes, baby steps, glad to see you get it.

Ron Long
September 21, 2021 3:39 am

Great pictures of Psyche spacecraft, great in that they show all of that gold that will be launched into space and lost, and someone, like a Gold Exploration Geologist, will have to find more to replace it.

September 21, 2021 4:59 am

It’s a long game

The trade-off for the high top speeds of ion thrusters is low thrust (or low acceleration). 

To compensate for low thrust, an ion thruster must be operated for a long time for the spacecraft to reach its top speed. Acceleration continues throughout the flight, however, so tiny, constant amounts of thrust over a long time add up to much shorter travel times and much less fuel used if the destination is far away.

NASA – Ion Propulsion: Farther, Faster, Cheaper

I thought the idea was to get to warp speed?

Tom in Florida
Reply to  fretslider
September 21, 2021 6:09 am

The real question is what is their definition of “a long time”?

Reply to  fretslider
September 21, 2021 7:45 am


NASA lost its way and has just become one big bureaucratic organization.

True innovation can best be accomplished by the private sector where the world’s best minds, physicists, mathematicians, programmers and rocket scientists are recruited and paid large salaries and given big budgets providing they can show results and beat the completion.

Now that the largest corporations in human history are involved in the new space race, I expect some really amazing innovations will emerge at a fast pace.

Tom Abbott
Reply to  SAMURAI
September 21, 2021 8:08 am

Yes, the private sector space activity is picking up nicely.

NASA just needs to keep facilitating these types of activities, which they are doing, to their credit.

Reply to  SAMURAI
September 21, 2021 7:00 pm

I tend to agree about NASA in general, and about getting things to low Earth orbit–and probably the Moon–in specific. What I usually say is that’s no longer rocket science, it’s become rocket engineering. But trips to other planets, asteroids and comets are still, I think, the province of NASA. It will be at least decades before anything further out becomes economically feasible (unless Elon finds a way to make trips to Mars pay). And the research into non-chemical propulsion systems, which will be needed to make such planetary scale voyages practical, is unlikely to pay off any time soon–it really is rocket science. Unless of course someone invents the Epstein Drive or the Cochrane Drive…

Reply to  fretslider
September 21, 2021 9:12 am

Patience young padawan, that’s the next step.

George V
September 21, 2021 5:05 am

I get a kick out of reading this because waaaaayyyy back when I was a undergrad student in Aerospace engineering the senior year satellite design project the class selected was an asteroid belt survey powered by ion thrusters using solar cells for the electricity. The thrusters boosted the satellite to a much greater distance while using a smaller booster rocket.

September 21, 2021 5:58 am

It takes a specialized team to plot the trajectories????

They use the same equations they always have. Just the size and duration of the thrust have been changed.

Joao Martins
Reply to  MarkW
September 21, 2021 10:46 am

Are you sure? I suspect (did not confirm) that the diversity committee in its report stated that the old FORTRAN code was much tinted with white supremacy and suggested the substitution of more than half of the modules with Python subroutines and some Javascript to make displays easier (although not as accurate than the numerical outputs)…

Reply to  MarkW
September 21, 2021 7:09 pm

Traveling through hyperspace ain’t like dusting crops, boy! Without precise calculations we could fly right through a star or bounce too close to a supernova and that’d end your trip real quick, wouldn’t it?”

Ok, all seriousness aside: the Halls Thrusters (IIUC) are variable thrust engines, so there are tradeoffs like using more thrust and running out of propellant faster vs. carrying more propellant and being more massive; being at the right speed when you get to your destination to achieve orbit, using gravity assist flybys, and interpreting the telemetry you get from your probe plus the tracking information derived from the pointing of the antennas on Earth, and so forth. Yes, the equations are the same for each one of those, but there are lots of optimizations to consider.

Plus you don’t want some simple mistake to mess up your $500 million dollar project, so it’s wise to have someone check the way you’re doing the calculations and the numbers going into them. What kind of a mistake, you ask? I dunno, maybe mixing up newton-seconds and pound-seconds, except of course nobody would ever do that.

Tom Abbott
September 21, 2021 8:29 am

It will be fascinating if it turns out 16 Psyche is the core of a larger planet.

I bet there are a couple of geologists around here that would love to inspect it. 🙂

Bill Parsons
September 21, 2021 9:43 am

The Japanese and Australians have been working for a few years on a plasma-burst satellite to clear space junk out of orbit. This is obviously a long-term mission, so maybe this type of satellite is suited to it. Maybe a better use of the technology than studying the heavy-metal components of the asteroid belt?

Reply to  Bill Parsons
September 21, 2021 7:14 pm

I’m pretty sure they can make more than one spacecraft using this technology. Also, I’m not sure how well the current Hall Thrusters would do for maneuvering a satellite deep inside the Earth’s gravity well; you might have to wait a long time to get from one piece of junk to the next–and there are lots of pieces of junk out there. Whereas this probe has a single target a long ways away, and the trip is going to take a long time anyway, so the low thrust works for you.

To bed B
September 21, 2021 1:21 pm

“Your mission has shown the world that space is for all of us and that everyday people can make extraordinary impacts in the world around them,”
Kris Young of Space X

I’m pretty sure a trip more than 100 km from home will be what most people dream of before I die.

Keith Van Ausdal
September 23, 2021 8:49 pm

Go Sun Devils!

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