back to article Cubesats to go interplanetary with tiny plasma drives

Cube satellites – the current craze among space researchers with more ideas than money – could take a step farther out into deep space, if the University of Michigan has its way. UoM researcher Benjamin Longmier, assistant professor of aerospace engineering and a propulsion specialist in the university's Plasmadynamics and …

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Just out of interest, how do they steer these things? If the nozzle is directable does it put the whole thing in a spin? Clearly, I am no rocket scientist.

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Boffin

steering

The nozzle is a magnetic field (see the Kickstarter page) so I suppose the exhaust could be directed by changing the shape of the field, the same way the electron beams are steered in CRT tubes. The kickstarter page talks about using permanent magnets for generating the nozzle, but maybe they add some smaller electric magnets for steering.

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Re: steering

More likely they would orient the spacecraft to put the thrust vector in the required direction. In near-earth orbits this can be done by magnetic reaction against the earth's field. Reaction wheels could be used further out in space.

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Typically you steer a spacecraft by changing it's orientation so that the nozzle is now pointing in a different drection. In a traditional plasma driven spacecraft, there are a series of nozzles. You can vary the force from the different nozzles to generate a torque to change your orientation. Modern spacecraft also tend to be internally stabilised using reaction wheels or control momentum gyros. By changing wheel speed and/or rotating the wheel axis, you generate a torque that reorients the spacecraft.

I don't suppose they'll have the space/mass to do that on their cubesat, but thought I'd share it with you. I tried to read the kickstarter page, but only in text on a mobile connection it didn't tell me much.

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Could it carry anything useful and if so how would it phone home with the results or information?

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I was wondering something similar, given the size of dishes etc that probes which have gone before seem to need, plus the apparatus and thrusters needed to align it back toward mother Earth to send a signal back.

But then again I suppose it could be a proof-of-concept test bed for the plasma engine etc, but I thought that was basically proven technology at this point anyway?

Or is this a solution looking for a problem again, or just something to use up NASA funding, with the definition of "deep space" being slightly beyond Earth's magnetosphere (or any distance further than you could get out and walk home).

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I was wondering about the communication problem as well.

Generally speaking, it would have to be a dish style communications method, as it's much more efficient to only transmit in the direction you want it to be received in. However the smaller the dish (generally the tighter the "beam" as a result and the lower tolerances) the more accurate the direction needs to be to hit the target. I believe this is similar to the problem where smaller consumer satellite dishes have to be more accurately aligned.

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Happy

@Nick Ryan

"Generally speaking, it would have to be a dish style communications method, "

No. AMSAT have quite a lot of history doing radio relay using ribbon aerials, essentially multiple steel tape measures unrolling in orbit. With minimal loads on them they can unroll to 10m easily. Operating in the 2GHz band you can get substantial gain from such a design.

"However the smaller the dish (generally the tighter the "beam" as a result and the lower tolerances) the more accurate the direction needs to be to hit the target"

No. Bigger the dish, tighter the beam. Smoother the dish above the transmission wavelength the better, but strictly it's how accurately it fits the curve that matters.

"I believe this is similar to the problem where smaller consumer satellite dishes have to be more accurately aligned."

True.

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Re: @Nick Ryan

Thanks. I'm obviously rather behind the times on satellite transmission comms like ribbon aerials, but I have no need other than an interest to be up to date on these things. And a ribbon aerial (now I've looked them up) would fit nicely with the cube sat scheme.

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Where does the energy for plasma generation come from?

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Joke

It's either got an internal combustion engine, or hamsters in wheels.

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Leaving orbit?

Won't they have to start from a much higher orbit than cubesats usually get to, in order to get out of the Earth's gravity? I can't see a micro plasma engine being able to accelerate to escape velocity.

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Re: Leaving orbit?

Not a rocket scientist, but at the altitude cubesats are normally released, drag should be minimal enough to boost out of orbit even with something as weak as a mini plasma drive.

Starting a little higher would add a good deal of effective delta V though, so a good idea if possible.

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Re: Leaving orbit?

Drag? It;'s gravity that I'm thinking of. You need somewhere around 11km/s velocity to escape from the earth, and a satellite in low-earth orbit will only have about 80% of that. Can a weak plasma engine give it the addition 2/3 km/s it needs?

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Re: Leaving orbit?

Drag is what is important. If the thrust from your drive is greater than your drag then you accelerate. Accelerate long enough and you will reach escape velocity. So any orbit where the atmospheric drag is less than the thrust is a workable starting point. It may take months or years to escape, but with enough fuel it can be done

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Beware the nanoprobes!

Tiny cube seed today, Borg Cube tomorrow!

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Re: Beware the nanoprobes!

We are Festival. Entertain us (or else)!

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Anonymous Coward

eco friendly

I'm all for this type of research. But once its fuel cells are depleted it looks like it will become space junk orbiting the Sun. And if they are successful it will pave the way for more cheap and accessible projects to proliferate. So it is incumbent on them to set an example and have the craft safely destroyed once its mission is completed - like firing it into the Sun.

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Re: eco friendly

The delta-V to get it into the sun would be enormous. Probably easier to head for a gas giant. If they have the capability to generate enough delta-V, then they could do a Pioneer & get out into the Galaxy.

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Re: eco friendly

"But once its fuel cells are depleted it looks like it will become space junk orbiting the Sun"

It's not as if there's a dearth of natural space junk already doing just that. Apollo asteroids spring to mind.

LEO junk is a problem because there's so much of it in a very limited plane.

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I'll have a go at some of those questions.

Being so tiny the power level is 10W, not 10Kw and the thrust is 2mn, with a 20mn "burst" mode.

The design is actually a 3 cubesat unit, which allows space for swing out solar panels. IIRC the current record for these is 43% but at huge expense. That would be around 670W at Earths orbit,

This is a proof of concept for JPL so part of the experiment is what level of comms can you put on a 3U cubesat and get a decent data rate. JPL spent a lot of effort developing much smaller RF telemetry for things like their DS1 probe. Others have used the guts of mobile phones.

Steering could use electro magnets to re-shape the field and deflect the plasma but that's likely to be expensive. At this size you can change the attitude of the whole probe, using things like magnotorquers interacting with the Earths magnetic field (or later the Suns field), or Control Moment Gyros (if you can get them small enough) which are spun up on Earth (high power) and only need low power to deflect their access (exerting a counter force that shifts the probe axis)

As regard experiments well studying deep space conditions in terms of radiation, solar wind etc. If they fly in formation you can start to map fields over larger areas with more accuracy. Gamma ray sensors have been used to identify elements on the surface and map water deposit.

If this comes up you could change the way JPL does exploration totally. If it works instead of 1 launch a decade they could be looking at 1 JPL launch per commercial launch, because with an engine, once it's in orbit it can start to change orbit. Instead of one bet-the-budget launch of a new probe multiple launches can carry multiple copies for better map building of phenomena. Designs can be refined with a 1 instrument on 1 cubesat philosophy. If it's ready it launches, if not it does not.

It may be a light step, but it's a bold step.

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Earth's upper atmosphere as fuel?

Could they stay in low Earth orbit and scoop up the thin upper atmosphere to use as fuel? That way they could achieve a highly eccentric ellipse for no fuel cost, ideal if they wanted to use it to de-orbit space junk rather than speed off into outer space.

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Re: Earth's upper atmosphere as fuel?

Ooh - a mini Bussard. Lovely idea.

Perhaps with an electrotether to help with iniital accelaration?

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Alien

Optional

"Pledge $100 or more... Your message ... laster etched onto gold plated spacecraft panel."

"Come and have a go if you think you're hard enough!"

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If theyre planning to head out of the solar system couldn't they use sails for the bulk of the journey only needing the plasma drive when there is no solar wind of when they cant manipulate the sails enough to get the movement in the direction they want to go?

Also, isn't there a method of transport being examined that uses electro magnets to collect the scarce particles in space and then propel them through a tube as a means of propulsion thereby reducing the requirement for actual fuel on board as electricity can be derived by solar power

Forms of travel that in whatever form use the scarce matter of space itself would surely be the best options to explore for any seriously long range exploration

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