# Would ablation be an effective way to redirect objects in space?

So I'm writing a story set in the close(ish) future(say 2130), and space debris is starting to be a real problem. Stations in orbit are constantly having to maneuver out of the paths of orbital debris, at least a few satellites have been taken out, and it's just a big hassle all around.

So (space organization) gets a few meetings together and they decide that a reasonable solution would be to launch a few lightsail craft equipped with high power pulse lasers to maneuver space debris using ablation to deorbit it. The lightsail craft would be maneuvered with the help of a laser array on the surface of the Earth, and they would deorbit debris by ablating the debris in the opposite direction of its flight, hopefully slowing it down enough to make its trajectory intersect the atmosphere.

But is this really an effective solution? What are some ways to make it more effective? Bonus points if you can tell me the math required to calculate how much power the laser would have to draw to ablate steel in 1/60th of a second or shorter.

The answer is actually "yes", and the proposed system is sometimes referred to as a "laser broom".

The general idea is to use laser energy (in most proposals, from mountain top laser batteries) to deposit energy on a piece of space debris. The material on that side will eventually vaporize and propel the object into a different orbit via Newton's Third Law. In effect, you have made part of the object into a rocket engine.

This idea is ramped up to "11" when discussing asteroid deflection. Some proposals substitute a nuclear device for the laser, and unlike the movies, the device is set off away from the asteroid. The intense pulse of X-ray radiation from the device vapourizes a portion of the surface of the asteroid, which once again acts like a rocket motor and moves the object onto a new path.

Now there are a lot of variables to the idea. A rocket impulse requires a lot of energy to be deposited onto the body in a small area and generally in a short time frame. Lower energy might not do the trick unless it becomes enough to create a plume of vapour to drive the "rocket" impulse. A series of short impulses that are powerful enough to vapourize the surface of the body might work better than a long continuous beam. And of course the body needs to be understood, so things like the material it is made of, the orbital path and even the centre of rotation are identified and taken into account. A wildly tumbling body might need to be stabilized by hitting it multiple times with the laser broom until it is spinning in a predictable manner, so the final impulse is controlled and the path the body will take becomes predictable.

Wired Magazine ran a good introduction several years ago: http://www.wired.com/2011/10/space-junk-laser/

• en.wikipedia.org/wiki/Laser_broom "Using a laser guide star and adaptive optics, a sufficiently large ground based laser (1 megajoule pulsed HF laser) can deorbit dozens of objects per day at reasonable cost." It's nice, but not really going to be a game changer, especially if the debris situation is worse than today. Apr 20, 2016 at 12:37
• There can be dozens of laser brooms set on mountaintops around the world, so several hundred targets a day could be serviced, if needed. Apr 20, 2016 at 19:08

# No

This is personal opinion. Until a working anti-spacetrash system is deployed it's theoretical problem that's still being developed.

The problem here is not that ablation won't redirect debris (it will, and has been considered as an asteroid defense) but that if debris are an issue, they will be of such quantity, small size and spread over such a vast area that a laser system will not be able to make a serious dent.

I suggest you read up on https://en.wikipedia.org/wiki/Space_debris

As of July 2013, there are over 170 million debris smaller than 1 cm (0.4 in). From one to ten cm at ~670,000, larger debris at 29,000.[1] As of 2009, 19,000 debris over 5 cm (2 in) are tracked.[2]

As of 2014, there were about 2,000 commercial and government satellites orbiting the Earth.[4] It is estimated that there are 300,000 pieces of space junk ranging from 1 cm to 25 cm, and on average one satellite is destroyed each year.[4]

• Both of those Wikipedia quotes cannot possibly be correct. Given that the first claims that debris of size 1-10 cm number at 670k in 2013, and the second claims that debris of size 1-25 cm (a larger set) number at 300k in 2014, and that we didn't send a large vacuum cleaner into orbit in the interim, logically at least one of the claims must be inaccurate.
– user
Apr 20, 2016 at 11:28
• @MichaelKjörling: Well, it is normal that debris in LEO is decelerated through atmospheric resistance and eventually ends up burning on reentry. So the numbers could go down without a giant space vacuum cleaner. ;) I agree however, that such a huge decline is rather unlikely. Apr 20, 2016 at 13:33
• @fgysin If we were looking at anywhere near that magnitude figures being deorbited due to atmospheric drag, I doubt orbital debris would be a huge issue even long term. :) We'd just need to stop sending more stuff into orbit for 1-2 years and the problem would take care of itself. Not likely to be the case, and Wikipedia does aim to describe the real world.
– user
Apr 20, 2016 at 13:41
• @MichaelKjörling: I could be that the largest portion of this debris was created in a single crash at very low altitude, resulting in short-lived orbits and fast reentry. Or, of course, you are right and Wikipedia is indeed wrong. o.0 ;) Apr 20, 2016 at 13:52
• @fgysin Verifiability, not truth. Both claims are cited. I just haven't bothered to evaluate the source material. :)
– user
Apr 20, 2016 at 13:55