Junking the Space Elevator

I think a space elevator is a really cool idea. Unfortunately, cool is not the same as practical. While I am certain that we will eventually be able to make cables of such strength they could theoretically be suspended from orbit, I'm far from sure we can make a space elevator cable that will be able to withstand the inevitable damage it will sustain.

Any cable that is put under tension stores up energy. If a steel cable that is being used to tow a truck snaps, it can whip around with enough force to kill someone. The cable of a space elevator will be under incredible tension. If a single fibre breaks the shockwave of energy released could destroy adjacent fibres and set off a chain reaction that snaps the entire cable. The easiest way to avoid this problem might be to use a "mesh bag" design in which one strand breaking won't propagate enough energy to other strands to destroy them.  There are people who think this design will work.  I have no idea if they are right. But even if we can make a cable robust enough to survive if one fibre snaps, it might not take long for it to be severely damaged or destroyed by impacts with space junk or meteorites.

A space elevator cable can be moved to avoid collisions with larger objects that can be tracked by radar. However there is no way to avoid the many smaller pieces of junk ranging from centimetres across down to particles the size of a speck of dust. Dangerous impacts don’t happen all the time, otherwise satellites wouldn’t last as long as they do, however the space shuttle suffers numerous impacts with tiny pieces of space junk and tiny meteorites on every mission, which typically lasts less than two weeks. Space shuttle windows are replaced on average every other mission as a result of impacts. One impact left a hole about half a centimetre deep. If the space shuttle windows which are only about a couple of square meters in area are hit so often, then a space elevator cable, which in one design will be a a thin ribbon about a metre across, can expect to be hit often as well.

Although only about 2,000 kilometres of cable will pass through areas with significant space junk, a square meter of cable can expect to be hit more often and with particles travelling at greater velocities than a square meter of space shuttle. This is because the space shuttle and space junk all orbit from east to west, even objects in high latitude orbits. When the space shuttle orbits there will also be a portion of space junk that will be in a similar orbit and so will have a low relative velocity. However, only the part of the space elevator cable at 36,000 km will actually be in orbit. In lower orbit, the cable will almost be standing still compared to the space junk, and many pieces will collide with it at speeds in excess of 10,000 kilometres per hour (2.8 kilometres per second). These impact speeds are fast enough to pit or chip diamond, although I am unsure of what the exact effects would be, as I lack a small bore rifle with which to take pot shots at my store of diamonds.

If we can’t make a cable that won’t destroy itself if even one fibre breaks, then it won’t be possible to build a space elevator. Impacts would soon destroy it even if it could be deployed intact. A ribbon like, meter wide cable could receive an impact like the one that put a half centimetre deep hole in the space shuttle window every couple of days. A significantly larger impact could be expected every month and so on.

So if we can build a a cable that can survive multiple minor impacts for an extended period of time, then it will need to be either regularly repaired or replaced as a result of damage from these impacts. If it is to be replaced that will greatly increase the cost of using space elevators. Repair would be difficult unless we had robot climbers that could manipulate carbon molecules in such a way as to perform flawless repairs in material under incredible amounts of tension. However, if we had robots that could do that, we probably wouldn’t need a space elevator to haul cargos up from earth as robots with such brilliant ability to manipulate matter could probably make whatever we want from materials found in space.

Shields Up - Spam Defenses Activated

You know, I've got a feeling that not everybody out there on the internet is entirely honest.

A couple of days ago when I started this blog I had only just put up my second post when someone wrote a comment saying that my blog was really creative and that they would definately bookmark it. This was interesting as my two posts consisted of the sentences, "This is a test," and, "This is another test." I shudder to think what a boring life he must lead to think that was really creative. Oh, and he also wanted me to buy land in New Orleans or something.

The second comment I received was from someone who seemed to want me to send money to help the plight of poverty stricken young women with large busts who apparently couldn't afford adequate clothing. There was a link with pictures and everything. Although I felt for these women, I decided that there are people in the developing world who would benefit from my charity more.

So to protect my readers from purchasing real estate that is now technically part of the continental shelf, and from feeling depressed at the sight of sad, yet compelling images of poor young women who have lost everything, including the shirts off their backs, I have activated word verification for comments.

Intelligent Design - Flipping Wrong

Supporters of Intelligent Design often say that the probability of complex life coming about by random chance is almost impossible. They are right. But complex life didn't come about by random chance, it came about by natural selection, but in their arguments many ID supporters continually speak and write as if natural selection doesn't exist. They don't seem to understand the rules of the game.

Imagine a (boring) game where the object is to get a line of one hundred coins all showing tails to show all heads. The only rule is that the only way you are allowed to change the coins is by flipping them. ID supporters immediately start trying to flip all one hundred coins at once. They start to loudly complain that it is almost impossible for all the coins to come up heads, that the odds against it happening are astronomical. Indeed, they say the only way it could ever happen is if some Godlike powerful entity intervened to make it happen.

At the other end of the room someone who understands natural selection starts playing the game with another row of one hundred coins that are currently all tails. She flips one coin until it comes up heads and then moves onto the next coin, flips it until it comes up heads and so on. Eventually, after about quater of an hour, she is finished and all the coins are heads up. Then, instead of looking sheepish and saying, "Well, why didn't I think of that?" the ID supporters start loudly complaining that the rules insist that all one hundred coins be flipped at once, when actually the rules say no such thing.

The ID supporters where operating on the random chance model, while the person who understood natural selection was making small changes and keeping those that helped succeed in the game, just as small changes that help organisms survive in the game of life are kept.

Undigested Red Meat

Just the other decade I was watching a movie in which a character stated that the average male has four pounds of undigested red meat in his bowels at all times. Now this got me thinking. Why is the meat undigested? And why does the body set aside four pounds of it not to digest? How does it keep it fresh? Is it stored in a special meat sack for emergencies, like when your significant other goes on a weird vegetarian diet and you end up eating dinners consisting of bean sprouts on a bed of sawdust and carbon nanotubles? I think I'll have to send an e-mail to P.Z. Myers, the biologist. He's an expert on squids and pirates, so if anyone could explain the mysteries of the meat sack to me it would be him.

Of course, Australian researchers have long known about the existence of the carrot sack, which can store carrots for years after you've eaten them.

Stupid maths shortcut #1 - Volume of a sphere

I'm afraid I'm not very good at maths. Never have been. Back when other kids were learning their multiplication tables I was daydreaming about dinosaurs or being an astronaut, or a dinosaur astronaut. However, my friends all think I am good at maths simply because I can do fairly difficult arithmetic quickly in my head. But the only reason I ever learnt to do this is because I am bad at maths. Because I never paid attention in class I had to develop all kinds of mental tricks to cover up the fact that I didn't know what I was doing.

Most of my shortcuts probably won't make much sense to anyone but me, such as turning numbers into dates and subtracting the Wall Street Crash from the Boxer Rebellion, but I guess there are a few that might help other people.

One lazy shortcut I had was for finding the volume of a sphere. Rather than remembering pi and the correct formula, I would just find the volume of a square of the same diameter as the sphere, which is easy (the diameter cubed, or simply diameter by diameter by diameter), and cut the result in half and round up to get a quick approximate answer. To be more precise, a sphere will have 52% of the volume of a cube of the same diameter. (Or to be really precise, 52.35988%, but this is supposed to be a short cut.)

Perhaps the more mathematically gifted are laughing at me right now, but I hope this is of help to someone, particularly students.

Robot Climbers – What we do when we can’t do what needs to be done.

Apparently there is a contest to see who can make the best robotic climber for a space elevator. It sounds like the sort of project that would be a lot of fun to work on. However, call me picky, but isn’t this a bit premature? I realize I probably sound like a killjoy here, but there doesn’t seem to be much point in building a robotic climber unless we know we can manufacture the ultra-strong cable a space elevator requires. We don’t even know if it is possible to make a material that is strong enough, can survive prolonged exposure to space, and which will be economical to use. The climbers seem like a straight-forward engineering challenge. Surely work on them could have waited the first samples of material suitable to build the cable were produced in a lab? Perhaps I’m just hopelessly cynical but it seems a little bit suspicious to me. The contest looks designed so that someone can say, “Look! We’ve already perfected the climber and the energy beaming system! We’re halfway there! Now just give us funding to complete the next step.” Unfortunately we currently don’t know if the next step will ever be feasible.

Having a contest to develop a suitable cable material first seems a lot more logical.

Hello

Hi. Welcome to my blog. I'll be posting my ideas on a variety of subjects here in the hope that you might find them helpful or amusing. I'll probably use my first few posts to throw out some ideas I have on technology, but I imagine I'll get around to writing on a wider variety of subjects soon enough. I'll also try to get some of my more creative friends to post.