back to article RF pulses from dust collisions could be killing satellites

Space scientists have long known that impacts too small to pierce a craft's skin can still damage the electronics inside, by creating electromagnetic pulses. Why those pulses happen, however, is still not well understood. Alex Fletcher of Boston University and MIT, and Sigrid Close of Stanford University reckon they've cracked …

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Impact --> dense plasma --> charge separation due to differential velocity--> RF pulse

Strong enough to kill some satellites.

OK the process seems reasonable but the shear strength of the effect is astonishing.

It's like that DARPA man portable X-ray machine that basically uses static electricity to generate the high voltage.

But then that's the thing about hypervelocity impacts.

No one sees them coming.

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Re: Impact --> dense plasma --> charge separation due to differential velocity--> RF pulse

you can actually unroll a reel of sellotape in a vacuum to get X-rays, without DARPA

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"you can actually unroll a reel of sellotape in a vacuum to get X-rays, without DARPA"

Essentially DARPA paid to have that core process turned into a disposable package you can use on the battlefield.

I understand this has been known for decades but it was DARPA that provided the funding to turn it from a lab curiosity into a practical device. I think it's had a Register write up. It's certainly been mentioned in comments.

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Anonymous Coward

Re: "you can actually unroll a reel of sellotape in a vacuum to get X-rays, without DARPA"

"Essentially DARPA paid to have that core process turned into a disposable package you can use on the battlefield."

It must go through an awful lot of sellotape.

Hope they don't use the cheap stuff. It'd be a pain in the arse if it kept tearing and you had to find the end of the roll during a death ray battle.

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I'm Relieved...

the lighter electrons move faster. I though the laws of physics were being broken as I read electrons all have the same mass.

I think I understand that they mean that the electrons are less massive than the ionized nuclei and therefore move faster.

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Unhappy

"I though the laws of physics were being broken as I read electrons all have the same mass."

Not strictly true.

In a vacuum they do. Inside a crystal lattice you get into ideas around the "virtual mass" of the electron (and holes viewed as "positive electrons"). You also get into the idea of rest mass and changes in momentum so the question then becomes what voltage have you accelerated it through?

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the VNIIEF January 1952 andrei sakharov emp grenade-generator, where he used tnt to blow apart a single loop of coppery/plasma with circulating high current was similar to this? basically back-emf EMP as an electromagnet turned to scattering dust. the small mass of the particle in the satellite case has rather a lot more momentum than a hundred grams of exothermic chemical, but would the overall energies be similar!

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See also a recent news item from the Cassini project about why and how they use a high frequency radio receiver to detect and measure microparticular impacts during Saturnian ring plane crossings.

Sorry: no URL. I heard the report on BBC Radio 4 this morning.

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+1

I heard too, came to post it and to remark how astonishing it was to hear an actual physicist (the Fields & Particles PI no less) being interviewed on Today by an actual adult who didn't keep stopping to ask the interviewee astonishingly ignorant questions that would embarrass a 13 year old.

(I still remember James Naughtie on a piece about the ISS nearly falling off his chair in astonishment when told that you could see it pass overhead from the UK. "What -- you mean you can actually see it move?!??)

The piece is at 08:20, here: http://www.bbc.co.uk/programmes/b08njv5y (should work outside the UK, too )

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Slow

5-10km/s? Come /on/ people, I know that's an attainable lab speed, but admit it, it's really slow. "Most" orbital impacts are going to be 10-14km/s, and get some Perseid particles involved and it's 67 or something.

ICON: Mine's the one with the 20 year old space debris conference proceedings in it.>>>

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Re: Slow

but admit it, it's really slow.

From my well defended position on the Heights of Ignorance, I'll happily admit it.

But what's the real world significance of all this? A few satellites have failed for a whole range of reasons, but what is the actual attrition rate for satellites, and how many are due to micro-meteorites and the like?

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Boffin

Re: Slow

but what is the actual attrition rate for satellites

Hrm. Another question: How much international carnage could a tinpot dictator with an orbit-capable rocket and a few sacks of flour cause?

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Re: Slow

@nagyeger: "...'Most' orbital impacts are going to be 10-14km/s..."

Low-earth orbital speed is 8 km/s, relative to the earth's center. Most satellites, and therefore I assume most dust, is in lower/medium-inclination orbits, about 30 degrees for US launches, about 50 for launches from the former USSR, etc. All that stuff will indeed be moving, relative to each other, a bit slower. (Though if you're headed across the equator going south in a 30 degree inclination orbit, and hit a speck coming north from a similar orbit, 8 * (2 * sin(30)) = 8 km/s.)

Anyway. You raise an interesting point: satellites in higher (polar and near-polar) inclination orbits, such as some recon and communication satellites, ought to hit dust particles, on average, a little faster. Therefore, they ought to see these unexplained electrical failures more often.

On the other hand... since not as much stuff is in those orbits, they'll spend a good chunk of time going over the poles, in areas where the dust is less common. That'll work in the other direction, making them _less_ likely to fail.

However, when they _do_ fail, it should be more likely to happen at lower latitudes. If an analysis of failures showed that tendency, it would support this theory that dust impacts matter. I was going to suggest checking the frequency of failures in still higher orbits, but those are above the Van Allen belts, are in sunlight almost all the time instead of a bit over half the time, and therefore have other factors that wouldn't be easy to consider.

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Re: Slow

How much international carnage could a tinpot dictator with an orbit-capable rocket and a few sacks of flour cause?

Well, loss of military surveillance wouldn't stop the enthusiastic and sometimes random bombing of foreigners by the US, so no real impact there: just the regular "Carnage as a Service".

More problematic, fuckwit drivers in developed nations would be totally unable to function without their satnav: A bit inconvenient for the rest of us when they reverse round roundabouts because they missed the last sign. Hardly carnage.

Sky: Interruption to their satellite TV drivel. From a personal perspective, not a problem. And since Sky would continue billing their customers regardless, no financial carnage for them (sadly).

Pornosat (various): Grumble lovers all round the globe would find that they were no longer able to receive satellite broadcasts of slickly made US and Europorn. Now for some that would be carnage.

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Re: Slow

OK, I recant my bit about "most" impacts, as measured per hit. But I stand by my argument regarding plasma, since I'm pretty sure that's far more prevalent in higher velocity impacts, and so for real velocity you want to look at plasma-creating dust, not so much debris.

@Bill Gray "Low-earth orbital speed is 8 km/s, relative to the earth's center. Most satellites, and therefore I assume most dust, is in lower/medium-inclination orbits,"

Urm, to me (out of the field for a few decades, I admit) Dust=natural, debris=paint flakes, dropped zips, ASAT tests, and of course impact ejecta.

Dust, by the time it's dropped down the gravity well can be prograde or retrograde, at any inclination, and (back when I was studying this stuff) is/was considered a significant source.

Hmm... looked it up. Dust impacts on the space face of NASA's 69 month LDEF experiment consistent with the natural flux at an average impact velocity of 15km/s. So, 15km/s average, with a random inclination, and you're going 7.8km/s or there-abouts, in LEO circular orbit, faster for elliptical orbits, of course.

I'll leave the calculation about if we can or can't just average the max & min (15 +/- 7.8km/s) because of the "running into the rain effect" as an exercise to the student. I know it's spawned papers....

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