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Incense and Senility

because life is stranger than fiction

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Riding a laserbeam into space
Back when I was 17, I went through the process of applying for university courses. I knew I wanted to study Physics with a specialization in a space related field, but at the time it wasn't really clear to me what the difference between "astrophysics" and "space science/technology" was. Somebody, and I confess I have sadly forgotten who, explained it to me like this:
"Think about the Hubble Space Telescope. The pictures that it takes are astrophysics. Putting it into orbit is space science."
And just like that, I was sold.

So I went to visit various universities, and I was ultimately torn between Salford and Leicester.

Salford was one of the first universities I visited, and was very excited by what I saw. Unfortunately most of the other universities didn't live up to their standard. Everything about my experience at Salford was amazing, and I was particularly impressed by one gentleman, who if my memory serves me correctly was retired but still had use of a lab at the department, which he used for all kinds of laser demonstrations. He was on a bit of a crusade to demonstrate that lasers could be used in schools (pre-uni) to help get kids excited and interested in physics - cheaply and safely. He had some wonderful little toys, and explained to me how he could listen to what was happening in a room by shining a laser at the window. It saddens me to note that Salford no longer appears to offer a specialization in spacey subjects, from what I see on their website.

However, I didn't choose Salford. I chose Leicester. I don't really remember all the reasons why, but I think it was more the city that won than an impression of the university itself. Or maybe it was the large rocket in the physics dept foyer that swung it, or perhaps the course content itself. I honestly don't recall.

Many years later, I was studying spacecraft engineering at Cranfield University where my group project was all about one of the biggest problems we face in the space industry today - space debris.

Space debris is something I've mentioned before though apparently not in much detail. Space debris is a serious threat to our current model of access to space. Every time we launch a spacecraft, tiny bits of material (from all kinds of sources like explosive bolts, flecks of paint etc) join those already in orbit. These are added to by "dead satellites", failed launches, anti-satellite weapons tests (grr) and so on. Many of these objects will not come down for a very long time, and pose a very real threat to spacecraft or astronauts. Ultimately, we have to do something about it or the debris cloud will become so dense that collisions would become common. For a satellite or astronaut, such a collision is likely to be fatal. If you're interested there's a good article on wikipedia.

So methods of safely de-orbiting satellites without producing more debris and without significantly reducing the lifetime of the satellite for economic reasons (as in the case of my project) are being looked into by many people. Methods of reducing the "junk" that's already up there are also commonly looked at, but so far nobody has come up with anything that the industry or agencies have wanted to implement.

So why this little trip down memory lane, complete with detours? The thing is, although lasers are very common in sci-fi there isn't a particularly large overlap between traditional "rocket science" and lasers- with the possible exception of that ogre of the cold war SDI. However, on Friday I came across an article talking about a study which would link space launches to lasers - and this morning I came across a paper linking lasers with space debris. It's a bit of a space laser geek fest.

First up was the beaming rockets into space article on the astrobiology magazine site. Yes, that's right, an article about launcher technology on an astrobiology site. I didn't ask why, I just read it. It talks about a study which is being conducted right now so we can't say anything about its conclusions, but what the study is looking at is really interesting. If you're anything like me, anyway.

The study is "to examine the possibility of using beamed energy propulsion for space launches". I recommend reading the article for details (I won't repeat them all here) but to summarize it would mean assembling a large array of "a few hundred" very powerful lasers, with a combined output of about 100 megawatts.

Although interesting, this all struck me as being a little bit too ambitious. Alternative launch concepts are typically forced to be ambitious by the mere nature of what they're trying to achieve, but there are just so many problems to overcome with such a proposal that I seriously doubt it could be realized ... yet. Technology is certainly moving in the direction of making this an option, so it's worth keeping an eye on it (though you should never look directly at a laser beam).

I was rather disappointed to read this though: "The system would make most economic sense if it was used for at least a few hundred launches a year." I say disappointed, because it strikes me whoever wrote it was being a bit lazy. My problem with this statement is that I feel it tries to make the economic argument for the idea sound plausible, in the same way newspapers misuse statistics to lead their readers to form whatever opinion they want them to have. What does "a few hundred launches a year" mean? In the interests of measuring reliability of the various launch systems available, Space Launch Report compiled a list of all the launches of 2009. They also provide stats by decade.

From this you can see the entire global market for space launches is currently around 70 launches per year, and it's going down. It peaked in the 70's, for obvious and less obvious reasons, at about 130 per year. So this is effectively stating that in order for such a system to be worth making, it would have to not only capture the entire global market but also increase the global demand for launches by a factor of at least 3 simultaneously, against the current trends.

The second paper, which happens to have been co-authored by a guy who was a year or two ahead of me at Leicester, strikes me as a lot more reasonable. As I mentioned above, it looks at space debris.

The idea is to use a laser in the same way as the launch system, to provide a thrust on an object by "beaming power" at it. But instead of launching an object from the ground, the idea is to simply accelerate an object that's already in orbit - in other words, changing the course of a piece of debris to avoid a collision. The methodology is very similar, and I can't help wondering if it will even feature in the final NASA study. In fact, I rather hope it will. While the launch system described above was talking about using 100,000kW of laser power, this paper talks about using just 10kW - in other words, a single laser. Although it still shares many of the other difficulties involved in such a system (such as accurate targeting), the laser segment seems very reasonable indeed.

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(Deleted comment)
It wouldn't spread anything around in the same way spreading dirt from a tidy pile across the floor would. Debris isn't stationary, it's flying around at HUGE speeds. The laser would simply change its direction slightly so that it misses another spacecraft (or even another piece of debris) instead of flying straight into it.

There have been lots of studies looking into cleaning up the debris, but it's a really difficult thing to do. You can't just go up with a hoover. The two biggest problems are:
1. the immense distances between objects. This makes it difficult for your womble to get to and clean up more pieces of debris than you added by launching it - and more expensive.
2. the huge speeds involved. We're talking about several km per second, or thousands of mph. How do you "collect" something that is capable of punching a hole straight through you like a rail gun? If you try to match speed with each object, the propellant you'd need to carry with you goes up exponentially.

Of course, cleaning it up is a much better goal - but we don't seem to be able to find a way to do it, and the laser might be a reasonable "stop gap" option until we do.

It also opens up a number of possible cleanup options. For example, if you can direct debris pieces one by one into similar orbits as each other then you might conceivably be able to create a giant "dustbin orbit" where we can "park" debris pieces safely, without endangering other spacecraft. We actually already do something similar with "dead" spacecraft which cannot be safely de-orbited.

Oh... and I know you were joking, but you also hit on a very important point. If we were to "contract out" a cleanup job to a private company, who would pay for it? It's not an easy question to answer!

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