First Exotic Space Thruster Test Ends in Explosion

KentuckyFC writes "A NASA-funded test of an entirely new way to control orbiting satellites has ended with the prototype arcing dangerously and parts of the machine exploding. The new propulsion system is based on the Lorentz force: that a charged particle moving through a magnetic field experiences a force perpendicular to both its velocity and the field. So the plan is to ensure that a satellite passing though the Earth's magnetic field is electrically charged so as to generate a force that can be used to steer the spacecraft. The advantage of the idea is that it requires no propellant, which is a big deal since most satellites' lifespans are limited by the amount of fuel they can carry. But the first ground-based tests haven't gone entirely to plan."

Comments

Doesn't seem like a significant setback.

[Pendersempai]

Here is the story, based on my admittedly non-expert reading: To use the (very exciting) Lorentz steering technology, the sattelite has to have an electric charge. The method they used to obtain the charge is to apply a voltage to a radioactive substance and then allow solar wind to carry away the positive charge, leaving the sattelite negatively charged. The problem seemed to be that this process caused sparks to arc across the sattelite, which in turn damaged electronics and dislodged soldering.

I'm not sure why this is a big deal. Couldn't they just use a different kind of solder, or at least insulate vulnerable electronics from the charge?

Re:Doesn't seem like a significant setback.

[v1]

That's what I was working on figuring out, from the wording of the article ("explosion") it made it sound like a big deal, like when a rocket launch goes bad. (see various youtube links in this thread)

But when I got to reading, they use the word "explosion" for solder. Solder is not big. It's not like a fuel tank went up - this is a little bit of electronics. That sounds like a smaller explosion than you get with your average match when you strike it.

That's like talking about buildings and saying there was a "collapse", and if you RTFA close enough you find what they're actually referring to is the water glass on the table in the lounge tipped over.

Honest perhaps, but definitely deceptive.

Re:Doesn't seem like a significant setback.

[smaddox]

It seems like arcing shouldn't be a huge problem in a vacuum. The charge would have to be isolated from electronics, because transistors wouldn't work very well if they had a high initial base charge.

However, isolating the transistors might be harder than it seems at face value because transistors must be used to control the mechanics of the satellite. If you tried to isolate the charge to the metallic chassis, it might be able to pass through control lines into the electronics. The resulting electric field could either keep transistors from depleting, or even worse, blow the dielectric.

It seems to me that an isolated piece of metal would have to be incorporated specifically to hold the charge. In order to isolate it you would need a dielectric with a very high breakdown voltage. However, even then the isolated charge would cause electric fields to appear across the rest of the satellite.

Hmm... That is not an easy problem at all.

Re:Doesn't seem like a significant setback.

[Agripa]

It seems like arcing shouldn't be a huge problem in a vacuum.

Arcing, or at least conduction, is a huge problem in a vacuum and can even be worse in a rarefied or ionized gas where the effective resistance will be much lower and negative resistance may manifest leading to sudden destructive discharge. Vacuum tubes contain a vacuum for proper operation and the only tricky requirement is a source of electron emission. The vacuum of space conveniently provides such a source in the ultraviolet radiation from the sun which will quite handily knock electrons off of the right materials and has no problem ionizing various gas atoms in the vicinity. A flame detector for safety applications can be made using a gas filled tube somewhat like a neon bulb and they work by watching for the characteristic ultaviolet from a flame which will ionize the gas.

However, isolating the transistors might be harder than it seems at face value because transistors must be used to control the mechanics of the satellite. If you tried to isolate the charge to the metallic chassis, it might be able to pass through control lines into the electronics. The resulting electric field could either keep transistors from depleting, or even worse, blow the dielectric.

I have never designed or worked with vacuum rated electronics (except for tubes and certain other devices with a self contained vacuum) but my guess is that a conformal coating is used to insulate all conductors from the vacuum. Conformal coatings are also used in high precision circuits to prevent surface leakage. Most of my work has been at the low end of the current and voltage spectrum (less then picoamps and nanovolts) but at the high end (kilovolts, amps, and kilowatts), I have occasionally found component failure mode to be "disappearance" with attendant explosive like effects.

dependant on earth's magnetic field?

[lobiusmoop]

Will this screw up when the earths field begins fluctuating when poles being going into reversal again?

Mind you, when this begins, I suspect the last thing we would be worried about if/when this comes would be the odd satellite crashing back to earth.

Re:Heh

[vux984]

(On that point when will which ever god or other deity is responsible for our design fix the bloody faulty memory unit and start using error correcting cells?)

Perhaps its a survival mechanism that keeps you from going insane and killing yourself before you reach age 10. The ability to forget might be the only thing keeping us sane.

Or maybe its a performance optimization - keeping the dataset smaller makes retrieval faster.

Or part of a disaster recovery system, enabling you not to be permanently traumatised after seeing the goatse guy. ;)

Re:Another variant also had problems.

[Ungrounded Lightning]

"large-scale tethered orbital structures have an additional problem to be solved: Keeping the tethers intact despite kilovolts of induced voltage along the tether and the resulting arcing"

Would those same issues apply to a Space Elevator?

To a much smaller extent - at least for the skyhook/beanstalk variety. (Some of the tumbing ones might have issues.)

A skyhook is rotating with the Earth, which also means with the Earth's field lines. Or at least roughly:
  - Any waving back-and-forth in the beanstalk will induce voltages. (Climbers will cause it to wiggle, as will several kinds of weather.)
  - So will distortion of the Earth's field by bow shock (which will cause its position to vary with respect to a tide-locked beanstalk, depending on the time of day.
  - So will sudden distortions of the Earth's field by solar flares and such. (You think you get a big voltage induced in a power transmission line crossing a continent? Imagine what you get in one several times the diameter of the planet...)
  - And beyond the bow shock you're dealing with the the galactic field, which DOESN'T rotate with the earth. (I think the bow shock is beyond the Clarke orbit but I'm not sure at all.)

And of course down here where the atmosphere is thicker than a neon sign's content you have all sorts of other electrical stuff - lightning, sprites/jets, voltages from the ionosphere, etc.

So skyhooks have the issue, mitigated by moving generally with the field and by the extreme thickness of the cable but exacerbated by it's length.

Upside: Charge collectors and electron guns at various heights along the tether can be used to induce currents in segments of the tether. This can be used to damp the component of any oscillations that's at right angles to the Earth's field. (That's the big ones.) (Also: Damping oscillations means throwing energy away. So the sense of the generated voltages should be helping, rather than hurting, the powering of the dampers.)

Re:Good for them

[barzok]

Even in failure there's so much to learn from it.

I wish I knew the source of this quote:

If you haven't failed, you haven't tried hard enough

looping B field

[The Fun Guy]

From TFA:

The team tested the ability of various objects to hold a charge in a vacuum while being bombarded with plasma...Microscopic arcing was observed at voltages as low as -300 V. This arcing caused solder to explode off of the object.

In my experience, damn near everything shorts out in a plasma field if it will carry a charge.

If you want to deflect the plasma (and thereby use the resultant Lorenz force to thrust your spacecraft), you have to use microsecond pulses of surface charge, not continuous charge like you would get from a weak alpha-emitter. Continuous charge = intact plasma filament = charge lead right back to your surface. Break the filament and you still get the expansion of plasma, with the resultant force transferred to the spacecraft through the magnetic field.

Re:Explosions are an indicator of work

[iamlucky13]

Since I basically just put words into people's mouths for a laugh, I figured I'd google up some actual quotes by these people related to their work.

• MIT coworker on Percy Spencer: "Like Edison, he will cut and fit and try and throwaway and try again."
• James Watt on one of his designs: "It is very defective."
• Alfred Nobel: "If I have a thousand ideas and only one turns out to be good, I am satisfied."
• Vladimir Titov after his Soyuz rocket exploded beneath him: "We were swearing."
• Werner von Braun (memory from childhood): "Selecting half a dozen of the biggest skyrockets I could find, I strapped them to the wagon. It performed beyond my wildest dreams. The wagon careened crazily about, trailing a tail of fire like a comet. When the rockets burned out, ending their sparkling performance with a magnificent thunderclap, the wagon rolled majestically to a halt. The police who arrived late for the beginning of my experiment, but in time for the grand finale, were unappreciative."
• Yang Liwei: "I did not see the Great Wall from space."
• Yet-Ming Chiang (MIT chemist): "The unstable materials release oxygen, oxidizing other materials in the battery, which in turn produces more heat. The cycle continues in a process called "thermal runaway," which in some cases can lead to a violent explosion."
• J. Robert Oppenheimer: "It worked."

Re:Heh

[zippthorne]

Sadly, it's not nearly as useful *outside* an atmosphere, as it's principle benefit is its high thrust. Electric propulsion can achieve much higher specific impulse if you don't have to worry about launch phase.