Thursday, October 27, 2011

Space Junk? Meet Lasers

"Back in the 60's, I had a weather changing machine that was, in essence, a sophisticated heat beam which we called a 'laser.' Using these 'lasers,' we punch a hole in the protective layer around the Earth, which we scientists call the 'Ozone Layer.' Slowly but surely, ultraviolet rays would pour in, increasing the risk of skin cancer. That is unless the world pays us a hefty ransom."

Perhaps I should have titled this post the Alan Parsons Project?

Anyway, I was looking for a specific article I had seen written up in Wired Science and my cursor would not allow me to scroll further than an article about frying space junk with lasers. Smart cursor.

As with everywhere else we've been we leave stuff behind. Space is no exception. Over the past 35 years we have created several hundred thousand pieces of space debris larger than 1cm in the 400-2000km altitude low Earth orbit (LEO) band, their density reaching a peak in the 800-1,000km altitude range. Small, untracked debris is hazardous to space vehicles, and although larger debris are less numerous and trackable they are also dangerous. Not to mention that what goes up may eventually come down. Recent events with a falling satellite have illustrated that. As someone who lives on the down area I may have cause to be concerned. But what do do about it?

A new paper published Oct. 17 on arxiv suggests a solution. First, categorize the debris into threat categories. The authors present an equation that calculates the interval between collisions because while the debris growth rate is reduced by removing large objects that, when hit, produce small objects and the small objects are a greater threat numerically.

Next, create a method to get rid of said debris. Up to now many methods have been proposed to rid LEO of space junk including grappling the objects, attaching deorbiting kits, deploying nets to capture objects, attaching an electrodynamic tether and deploying clouds of frozen mist, gas or blocks of aerogel in the debris path to slow it. The problems with these techniques are the expense (costing about 27 million dollars per large object!), the accuracy, and the difficulty.  So what do you do? Lasers!

Laser-based methods can be divided into three categories: (1) low laser intensity which doesn't destroy but instead divert the debris, (2) higher laser intensity which heats to ablation with continuous (CW) lasers, and (3) pulsed laser orbital debris removal (LODR) which uses a mirror to focus a repetitively pulsed, high intensity laser on an object. The first method is less efficient, its effects are comparable to the uncertain effects of space weather and sunlight, and it does not address the debris growth problem. The second method involves slow heating of tumbling debris which gives an ablation jet whose momentum contribution cancels itself out, and the heating causes a messy melt ejection that adds to the debris problem. Therefore the authors recommend the third method.

If you read the entire 37 page paper then you will see that the authors make a good case for the pulsed laser space junk removal system. Overall, it costs the least per object, can deal with both small and large objects, can handle tumbling objects, can prevent collisions, and the target access is at the speed of light, redundant and agile. Not to mention that it will require international cooperation to build and operate, and the authors make the point that this cooperation will "avoid concerns that it is a weapon system." So I guess it has that forcing everyone to play nice factor going for it.

Summary: Lasers disintegrating space junk = Really cool.

Here's the paper:
Phipps, Claude R. (2011) Removing orbital debris with lasers. (arxiv:1110.3835)

And here is the Wired Science Story:
Space Junk Crisis: Time to Bring in the Lasers

Also check out:
Space Junk Problem Reaches 'Tipping Point' from Discovery News

"Mini Me, stop humping the 'laser'. Honest to God! Why don't you and the giant 'laser' get a fricken room for God's sakes"

Sorry, couldn't help it; I just had to throw in one last Dr. Evil quote.
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