Air-Breathing Electric Thruster Could Keep Satellites in Low Earth Orbit for Years

When it comes to the future of space exploration, one of the greatest challenges is coming up with engines that can maximize performance while also ensuring fuel efficiency. This will not only reduce the cost of individual missions, it will ensure that robotic spacecraft (and even crewed spacecraft) can operate for extended periods of time in space without having to refuel.

In recent years, this challenge has led to some truly innovative concepts, one of which was recently build and tested for the very first time by an ESA team. This engine concept consists of an electric thruster that is capable of “scooping” scarce air molecules from the tops of atmospheres and using them as propellant. This development will open the way for all kinds of satellites that can operate in very low orbits around planets for years at a time.

The concept of an air-breathing thruster (aka. Ram-Electric Propulsion) is relatively simple. In short, the engine works on the same principles as a ramscoop (where interstellar hydrogen is collected to provide fuel) and an ion engine – where collected particles are charged and ejected. Such an engine would do away with onboard propellant by taking in atmospheric molecules as it passed through the top of a planet’s atmosphere.

The test set-up for the air-breathing electric propulsion thruster recently developed by Sitael and QuinteScience in conjunction with the ESA. Credit: ESA/Sitael

The concept was the subject of a study titled “RAM Electric Propulsion for Low Earth Orbit Operation: An ESA Study“, which was presented at the 30th International Electric Propulsion Conference in 2007. The study emphasized how “Low Earth orbit satellites are subject to atmospheric drag and thus their lifetimes are limited with current propulsion technologies by the amount of propellant they can carry to compensate for it.”

The study’s authors also indicated how satellites using high specific impulse electric propulsion would be capable of compensating for drag during low altitude operation for an extended period of time. But as they conclude, such a mission would also be limited to the amount of fuel it could carry. This was certainly the case for the ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) gravity-mapper satellite,

While GOCE remained in orbit of Earth for more than four years and operated at altitudes as low as 250 km (155 mi), its mission ended the moment it exhausted its 40 kg (88 lbs) supply of xenon as propellant. As such, the concept of an electric propulsion system that an utilize atmospheric molecules as propellant has also been investigated. As Dr. Louis Walpot of the ESA explained in an ESA press release:

“This project began with a novel design to scoop up air molecules as propellant from the top of Earth’s atmosphere at around 200 km altitude with a typical speed of 7.8 km/s.”

Diagram illustrated how air-breathing electric propulsion works. Credit: ESA–A. Di Giacomo

To develop this concept, the Italian aerospace company Sitael and the Polish aerospace company QuinteScience teamed up to create a novel intake and thruster design. Whereas QuinteScience built an intake that would collect and compress incoming atmospheric particles, Sitael developed a dual-stage thruster that would charge and accelerate these particles to generate thrust.

The team then ran computer simulations to see how particles would behave across a range of intake options. But in the end, they chose to conduct a practice test to see if the combined intake and thruster would work together or not. To do this, the team tested it in a vacuum chamber at one of Sitael’s test facilities. The chamber simulated an environment at 200 km altitude while a “particle flow generator” provided the oncoming high-speed molecules.

To provide a more complete test and make sure the thruster would function in a low-pressure environment, the team began by igniting it with xenon-propellant. As Dr. Walpot explained:

“Instead of simply measuring the resulting density at the collector to check the intake design, we decided to attach an electric thruster. In this way, we proved that we could indeed collect and compress the air molecules to a level where thruster ignition could take place, and measure the actual thrust. At first we checked our thruster could be ignited repeatedly with xenon gathered from the particle beam generator.”

Fired at first using standard xenon propellant, the test thruster was then shifted to atmospheric air, proving the principle of air-breathing electric propulsion. Credit: ESA

As a next step, the team partially replace xenon with a nitrogen-oxygen air mixture to simulate Earth’s upper atmosphere. As hoped, the engine kept firing, and the only thing that changed was the color of the thrust.

“When the xenon-based blue color of the engine plume changed to purple, we knew we’d succeeded,” said Dr. Walpot. “The system was finally ignited repeatedly solely with atmospheric propellant to prove the concept’s feasibility. This result means air-breathing electric propulsion is no longer simply a theory but a tangible, working concept, ready to be developed, to serve one day as the basis of a new class of missions.”

The development of air-breathing electric thrusters could allow for an entirely new class of satellite that could operate with the fringes of Mars’, Titan’s and other bodies atmospheres for years at a time. With this kind of operational lifespan, these satellites could gather volumes of data on these bodies’ meteorological conditions, seasonal changes, and the history of their climates.

Such satellites would also be very useful when it comes to observing Earth. Since they would be able to operate at lower altitudes than previous missions, and would not be limited by the amount of propellant they could carry, satellites equipped with air-breathing thrusters could operate for extended periods of time. As a result, they could offer more in-depth analyses on Climate Change, and monitor meteorological patterns, geological changes, and natural disasters more closely.

Further Reading: ESA

Is Alpha Centauri The Best Place To Look For Aliens?

For generations, human beings have fantasized about the possibility of finding extra-terrestrial life. And with our ongoing research efforts to discover new and exciting extrasolar planets (aka. exoplanets) in distant star systems, the possibility of actually visiting one of these worlds has received a real shot in the arm. Unfortunately, given the astronomical distances involved, not to mention the cost of mounting an expedition, doing so presents numerous significant challenges.

However, Russian billionaire Yuri Milner and the Breakthrough Foundation – an international organization committed to exploration and scientific research –  is determined to mount an interstellar mission to Alpha Centauri, our closest stellar neighbor, in the coming years. With the backing of such big name sponsors as Mark Zuckerberg and Stephen Hawking, his latest initiative (named “Project Starshot“) aims to send a tiny spacecraft to the Alpha Centauri system to search for planets and signs of life.

Continue reading “Is Alpha Centauri The Best Place To Look For Aliens?”

How Could You Capture an Asteroid?

We can’t just go into space with a big butterfly net or catcher’s mitt, so how in the world could we capture an asteroid?

Ah asteroids, those dinosaur-killing, Scrooge-McDuck-moneybins from heaven.

They’re great and all, but you know what would be better? All the asteroids gathered up and put in a nice safe orbit where we harvest out all their precious sweet, juicy platinum cores.

Instead of nervously scanning the heavens, wishing we had more iridium at our disposal, we could seek out all the asteroids in the Solar System and push them somewhere we can get at them, whenever we want after we dump them into the orbital equivalent of a lazy susan.

Okay fine, instead of pushing all the asteroids around, maybe we should start with one. Get that right and we can extend our plans to the rest of the delicious space rocks we crave.

I know this sounds like just another pie in the sky “Fraser-Cain-double-plus-crazy” plan, but I’m not the only one to propose this idea. In fact, NASA has expressed plans to reach out and capture an asteroid and maybe put it into orbit around Earth.

There are many benefits to this plan. We’ll learn just how hard it is to move asteroids around, should we find one on a dangerous trajectory. We’ll learn how to land on an asteroid, and extract its precious resources. And of course, there’s the science. So much to learn from a pet asteroid. Also, if anyone ticks us off we can lop off clumps and hurl it at them. So a dinosaur killing space rock, returned safely to Earth? That sounds a little dangerous. Possibly a species-wide Darwin awards moment.

An artist's conception of a space exploration vehicle approaching an asteroid. Credit: NASA
An artist’s conception of a space exploration vehicle approaching an asteroid. Credit: NASA

How exactly does one capture an asteroid, and how could we move it back to Earth without killing us all, and more importantly will the Aliens have Darwin awards when we accidentally wipe ourselves out? This sounds like a job for BRUCE WILLIS.

As you may suspect, scientists have come up with a vast collection of clever ideas to move asteroids around. They all come down to the same challenge. You somehow need to impart a thrust to an asteroid. NASA has also informed me that involving Bruce Willis is optional, despite my insistence and extensive letter writing campaign.

One basic idea would be to fly down to the asteroid and install some kind of thruster on it. Perhaps an efficient ion engine, or a rail gun that throws off chunks of rock into space, imparting a thrust to the asteroid. The problem is that asteroids are often spinning, so you’d need to stop that rotation before you could fire up the thrusters.

Artist concept of an impactor heading towards an asteroid. Credit: ESA
Artist concept of an impactor heading towards an asteroid. Credit: ESA

Another idea would be to set off nuclear explosions nearby and just push it in the right direction with raw explosive power. By setting off the nuke close enough to the asteroid’s surface, you expel vaporized rock, which acts like a thruster. Also known as the “Ben Affleck Special”.

This one’s going to sound crazy, but scientists are serious. Airbags. You could bump a large inflated bag against the asteroid again and again to slowly nudge it in the direction you want. The rotation doesn’t really matter because the time you contact the asteroid is so brief.

Don’t like that? How about a gravity tractor? Now I’ve got your attention! You could fly a spacecraft really close to the asteroid, which would then attract it slowly, pulling it in the direction you like. As long as the spacecraft keeps thrusting away from the asteroid, you’ll keep pulling it along like a kite on a string.

These are just some of the big ideas. Scientists have proposed some sort of one sided space graffiti, painting them silver, possibly attaching solar sails, or even vaporizing rock with lasers to provide thrust.

Asteroid mining concept.  Credit: NASA/Denise Watt
Asteroid mining concept. Credit: NASA/Denise Watt

There’s another idea which deserves mention, and I’m going to warn you right now, it’s pretty terrifying. It’s called aerobraking. Instead of using energy to slow the asteroid and put it into the perfect orbit, we use the Earth’s atmosphere to help asteroids shed a tremendous amount of velocity.

By allowing an asteroid to pass briefly – briefly! – through the atmosphere of the Earth, you could decelerate it significantly. Make a few of these passes and you should be able to get it into a nice safe orbit around Earth. Of course, get it wrong and you crash an asteroid into Earth. So, there’s that. It would absolutely make a mess of our lawn, and we’d be the laughing stock of the local group.

Asteroids are precious resources, just waiting for us to reach out and harvest their minerals. Fortunately, we’ve got a range of strategies we can use to move them around. One of them has got to work… right?

Which idea for moving an asteroid do you like the best? Which one really freaks you out?