NASA Wants To Zap Space Junk With Lasers

Hugh Pickens writes "MIT Technology Review reports that various ideas have been floated for removing space junk, most of them hugely expensive, but now James Mason at NASA Ames Research Center has come up with the much cheaper option of zapping individual pieces of junk with a ground-based laser, to slow them down so that they eventually de-orbit. Mason estimates that a device to test the reversal of the Kessler syndrome could be put together for a million dollars, which would have to be shared by many space-faring nations, to avoid the inevitable legal issues that using such a device would raise. 'The scheme requires launching nothing into space — except photons (PDF) — and requires no on-orbit interaction — except photon pressure. It is thus less likely to create additional debris risk in comparison to most debris removal schemes,' writes Mason. 'Eventually the concept may lead to an operational international system for shielding satellites and large debris objects from a majority of collisions as well as providing high accuracy debris tracking data and propellant-less station keeping for smallsats.'"

Comments

Added bonus:

[olsmeister]

Ability to blind and de-orbit enemy satellites in wartime.

Re:Added bonus:

[blair1q]

Ability to blind populations on the ground in peacetime.

This laser would have to be powerful.

Satellites are irregularly-shaped and have flat reflective surfaces.

See where I'm going with this?

Not for long.

Re:Added bonus:

[interkin3tic]

Ability to blind populations on the ground in peacetime. This laser would have to be powerful. Satellites are irregularly-shaped and have flat reflective surfaces. See where I'm going with this?

Are you suggesting that governments will blind, say, protesters or peaceful people they don't like who happen to be staring at the lasers or at sattelites, which will reflect the beams into their eyes? Wow, that WOULD be a nightmare scenario, those evil bastards! So much wasted tax money! They should really stick to the low-tech grabbing them, putting them in a van, and burying them in an unmarked grave. It's SO much more efficient.

Re:Added bonus:

[natehoy]

There are already websites that track what are called "Iridium Flares" where the sun reflects off one of the boxy, shiny AT&T Iridium satellites. Focus the beam a little more and you could accomplish some fairly serious eye damage. However, aiming such a thing at a specific target for any length of time would be damned near impossible.

If you wanted to truly permanently blind a populace, issue each of your people a 1kw aiming laser for their rifles. If you want to temporarily blind them, set up a couple of powerful spotlights on a tall building or helicopter. It's a lot cheaper and more reliable.

Re:Added bonus:

[rgbatduke]

What? You insist on doing arithmetic? Something like P = I/c (within a factor of 2) for the radiation pressure exerted by light? So that if we make a very generous assumption of a kilowatt in a single square centimeter, we have 10^3/3x10^8 \approx 3 x 10^-6 Pa. We multiply by 10^-4 square meters (one square centimeter) and get 3 x 10^-10 Newtons. Take into account attenuation in the atmosphere and the fact that the beam is wiggling all over the place because of atmospheric thermal ripple and lensing, and you would be lucky to exert 10^-11 Newtons per kilowatt per square centimeter of laser beam.

If our supposed space junk is travelling in an actual low orbit, it is travelling at roughly 7 km/sec. Let's assume that it has a mere 10 kg of mass -- if it is much smaller just finding it from Earth will be difficult, let alone hitting it. Lessee, F=ma, so we can give it a maximum relative acceleration of a whopping 10^-12 m/sec^2! A year, on the other hand, has a mere \pi x 10^7 seconds, and of course we can shine our laser on the object at most a few hours a day -- again, a duty cycle of 10^7 seconds/year would be enormously generous.

This means that we can -- over a whole year -- change the velocity of the junk by 10^-5 meters/second! That's right folks, you heard it here first -- ten microns per second per year of thrust with a 1 KW laser beam 1 cm across, and downhill from there in nearly every direction.

Of course this is still wildly optimistic. The problem is that we are exerting the thrust on the object from underneath. This is more or less at right angles to the direction of motion, and hence does very little to speed it up or slow it down. In fact, pretty much nothing. If we wait until it is directly overhead to hit it, we get the cosine of a nearly right angle as a transverse component and can only fire on half of the overhead pass before we are hitting it from the rear and speeding it up again. If we fire at an oblique angle, to get a good dot product cosine with the direction of thrust and direction of motion, we have to go through an equally oblique layer of atmosphere that both bends the laser beam (making it effectively impossible to hit the target) and attenuates the kilowatt still further (reducing efficiency at about the same rate the dot product improves).

If the material were highly ablative, and if we could hold the beam steady enough to actually heat the object to where it boils, we could get some real thrust. Even a thin layer of actual reaction mass being boiled off of the surface would exert orders of magnitude more force than a perfectly reflected laser beam. But even orders of magnitude more thrust would almost certainly not suffice to slow the object enough to in any possible drug-addled, hallucinatory Universe make this an economically feasible, intelligent idea.

Now I know who was using the cocaine found at NASA today. Whoever it was that dreamed this one up.

rgb

Re:Added bonus:

[Flere Imsaho]

Do not look at satellite with remaining eye

Re:Added bonus:

[MozeeToby]

The idea is not to blast debris out of the sky. The idea is to change the orbit ever so slightly using photon pressure. The laser is fired as the object comes over the horizon until the object is at the zenith. This has two effects. The obvious, since the laser is only fired until the object is at zenith it pushes against the object's orbital motion, effectively lowering it's orbital velocity. Less obvious, it pushes the satellite 'up' away from the earth. Since you aren't actually increasing orbital velocity all that this does is increase the eccentricity of the orbit. The two effects combined cause the sattelite's Perigee to be close enough to the atmosphere of the Earth that drag does the rest and de-orbits the debris.

All with a relatively low power, and now focused laser beam.

Re:Added bonus:

[KeensMustard]

It's safe to assume that if the US possesses such a weapon, then in a war so will the enemy - if you can build it, so can they. Doesn't sound like a winning strategy.

Re:Added bonus:

[Lluc]

Satellites are irregularly-shaped and have flat reflective surfaces.

How is this not +5 Insightful already? Does anyone really think we can split or stop metal parts by shining light on them? It was a slightly less retarded idea when all they wanted to do was burn a tiny little hole into aircraft and nukes, but this is ridiculous.

Since when does NASA take their knowledge of physics from Star Trek?

Ever heard of a CO2 Laser?? They use them all the time to cut and weld metal. It doesn't take Star Trek technology to melt metal at large distances. http://en.wikipedia.org/wiki/Carbon_dioxide_laser

Let's face it...

[Anonymous Coward]

...everyone wants to zap space junk with lasers. NASA just happens to be in a better position than most to get the job done.

Shields at maximum!

[Thraxy]

Fire photon torpedoes!

Re:Lasers

[f8l_0e]

To answer your question, there is a reason the signs outside laser labs say "Do not stare at laser with remaining eye."

FPS game!!

[nowen2dot]

Oooh! Can they set up a web interface and charge money for us to shoot them!!!?

Who wants high score??

James Mason Continues...

[Ancantus]

To avoid legal incidents we will be mounting the lasers in international waters. We will be subsidizing costs by using existing biological life-forms, mainly sharks, as the key base for the laser installation. Aiming the devices will also utilize the shark's keen sense of smell to identify and destroy decaying orbital installations.

Ah, the possibilities...

[fuzzyfuzzyfungus]

There are some very pricey earth-facing CCDs, behind sophisticated optics, in earth orbit. Be a pity if any of them were to catch fire...

Recycled from 2000

[Bamfarooni]

NASA Hopes Laser Broom Will Help Clean Up Space Debris
http://www.spacedaily.com/news/debris-00a.html

Re:Recycled from 2000

[Daniel Dvorkin]

What TFA is talking about is the same as the laser broom in the same way a street-sweeping machine is the same as a guy with a pushbroom. The goal is similar, but there's a vast difference in scale.

oblig.

[memnock]

Are sharks space worthy?

Re:Lasers

[Nadaka]

That is a problem that lasers can fix, you will eventually run out of remaining eyes.

Prior art

[inviolet]

but now James Mason at NASA Ames Research Center has come up with the much cheaper option of zapping individual pieces of junk with a ground-based laser

Pfah, this is an old idea: it's called a laser broom.

NASA was even talking about this a decade ago, though it had a $200M price tag at the time: SpaceDaily article from 2000.

Re:Prior art

[BattleApple]

The breakthrough is that these are the first lasers that actually make a pewpew sound.

Re:Lasers

[Nidi62]

That's why you use that other universal fixer. Just cover said "remaining eye" with duct tape.

Re:Insert shark joke here...

[natehoy]

(tap tap tap)
"Candygram!"

Not about de-orbiting anything

[PSaltyDS]

In reply comments at the bottom of TFA you see they are NOT talking about de-orbiting things this way, only making minute changes in orbit to avoid collisions.

Perhaps preventing collisions allows natural decay to remove debris faster than it accumulates, but other than that, their plan was not about de-orbit of debris.

Enormously stupid idea...

[rgbatduke]

I commented elsewhere on the actual numbers, which show quite clearly that even a 5 kw laser would exert at most completely irrelevant forces on any object large enough to actually see from earth and hence target -- accelerations on a good day of 10s of microns per second per year of radiation pressure. Having RTFA and noted all of the corrections by the authors (of the idea, if I understand things correctly) it is still an enormously stupid idea. What part of piconewton scale forces is difficult to understand?

I give this one as an assignment for my intro physics classes -- suppose you have a megawatt laser with a beam 1 cm^2 across and mount it on the rear of your spaceship to use as a drive. Wow, a whole million watts of power! Surely that will provide the ship with all kinds of thrust!

Sure, if all kinds of thrust is a few micronewtons.

You'd get more thrust -- and probably more net delta-vee for any acceleration time you are willing to wait -- if you simply took the laser to the door of your capsule and threw it, as hard as you can, away.

rgb