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My understanding is that the ISS provides 75-90 kWatts of power, so enough power for a 1 second Megawatt pulse for zapping debris in about 15 seconds.

Question is: is this right, have I over looked something? And if so, what is in the way of them deploying such a system?

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    $\begingroup$ What is in the way? That you're essentially weaponizing an orbital research facility. It will never happen while there's I in ISS. $\endgroup$ – TildalWave Mar 2 '15 at 15:50
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    $\begingroup$ The ISS would be a terrible weapons platform as it is almost completely unable to maneuver and thus vulnerable to any space-faring nation. I think a laser on the ISS would not be that much of a threat really. It is a good point though. $\endgroup$ – Mike Wise Mar 2 '15 at 16:13
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    $\begingroup$ If you can zap defunct satellites or larger debris out of orbit than that qualifies as an anti-satellite weapon. It's not as easy as you probably imagine even in legal terms. Even orbital debris has ownership rights, obligations and liabilities. See Outer Space Treaty and Liability Convention over at UNOOSA. BTW another point re your maths is efficiency. You'd be lucky to get somewhere close to 50% system power efficiency. And then there's target reflectivity,... you might find masers or phased array microwave a better choice than lasers. $\endgroup$ – TildalWave Mar 2 '15 at 16:17
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    $\begingroup$ Why a megawatt - Just a nice round number? Would you be able to do useful work with a smaller ie 40KW laser? Are megawatt lasers even available? $\endgroup$ – Hugh Bothwell Mar 2 '15 at 19:29
  • $\begingroup$ Yeah, because it was an easy number to type and say I suppose. But the US Navy is working on a "Free Election Laser" in the Megawatt class to shoot down the swarms of UAVs it thinks it might need to cope with someday. popsci.com/technology/article/2011-01/… - I thought that was a reasonable starting point seeing I know nothing about how much damage a laser does given its energy... $\endgroup$ – Mike Wise Mar 2 '15 at 21:36
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Obviously the reason they have that amount of power on station is to use it to run the station. So the first obvious math hour is that you cannot have all the power for 15 seconds.

Conversely the notion of using extra power that is unconsumed is valid. The Ad Astra guys with VASIMR plan to scavenge extra power to charge the batteries for their engine so they can run reasonable tests of 15 minutes of their 200kW engine. So not out of the question in principle.

Of course, once VASIMR is on station, if it happens, then that spare power is spoken for.

Better question, is a 1 Megawatt laser enough to matter to debris? Two approaches:

  1. Small stuff vaporize it.
  2. Larger stuff, let the emitted burst of gases act to slow it down, drop orbit, hoping it is enough for it to reenter.
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    $\begingroup$ Where'd you dump extra heat? $\endgroup$ – Deer Hunter Mar 2 '15 at 17:15
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    $\begingroup$ @DeerHunter Radiators in the station's shadow $\endgroup$ – Rikki-Tikki-Tavi Mar 2 '15 at 17:28
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    $\begingroup$ @Rikki-Tikki-Tavi The point Deer Hunter is making is that while there may be excess power available, there may not be excess cooling available when needed. A laser or VASIMR will store power over a long period of time, then discharge it much quicker. Which would imply a longer heat load, that that Station might not have the capacity to handle. $\endgroup$ – geoffc Mar 2 '15 at 17:31
  • $\begingroup$ @geoffc Well, the answer is still the same, isn't it? $\endgroup$ – Rikki-Tikki-Tavi Mar 2 '15 at 17:36
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    $\begingroup$ @Rikki-Tikki-Tavi No the answer is not the same. I did not account for the excess heat. Only focused on the power source instead of dealing with the side affects. He raises an excellent point to which I do not know the answer. $\endgroup$ – geoffc Mar 2 '15 at 17:37
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Several things, actually

1: Power

  • As others have said, you need to power this monster. Lasers are very power hungry and inefficient weapons. For every watt of heat you put towards vaporizing your target, you're going to need twenty to both power the thing AND run the cooling system to keep it from melting.

2: Heat

  • Not only are they power inefficient, but lasers also generate huge amounts of waste-heat. On earth this makes them impractical, but since space is a near-perfect insulator they're downright dangerous. Again, expect to use most of your mass and power for a cooling system instead of the actual laser.

3: Targeting

  • Believe it or not, tracking a tiny object at vast distances and incredible speeds with erratic doppler readings by radar is quite a tall order. In addition to cooling and weapon power, we're now doing to need a large, complicated, and delicate sensor array to track debris. It's going to be extremely difficult getting targeting data that's accurate enough for your pinpoint-accurate laser to strike a pinpoint-sized target.

4: Targeting II: Turret Actuation Boogaloo

  • Once you've solved all the other problems, you still have to point your laser in the right direction. Even with perfect targeting data, you can still miss because your turret/control moment gyros have errors in either their manufacturing or programming. Tolerances can only be made so tight.

So yeah, you're trying to hit a gnat with a scalpel, at night, from a thousand miles distance, while said gnat is traveling faster than an SR-71. It's not impossible but the engineering is going to be deeply impressive.

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  • $\begingroup$ Good comments. I actually think getting rid of heat in space is a lot harder too, since you don't have convection or conduction available, the heat has to be radiated away. $\endgroup$ – Mike Wise Aug 23 '16 at 20:08
  • $\begingroup$ Some lasers have better than 70% efficiency (admittedly, not ones with enough power to do the job), so I think your assertion that ~5% of power goes toward the actual beam needs to be backed up; it's not clear why it would be that low. $\endgroup$ – Nathan Tuggy Oct 8 '16 at 21:39
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The one thing you would not want to do is blast something apart and create more space debris. So I would think you would need to have to have a way to determine if the target was small enough to be completely vaporized, and restrict it's use to those objects.

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