The sentence "SpaceShipOne is on it's way to the Smithsonian National Air and Space Museum in Washington DC." seems a bit inaccurate. A friend of mine who was there a week or so ago said that SpaceShipOne is already there, albeit under a tarp. Doent's seem like there is much traveling left for her to do. Naturally, a throng of people (including my friend) were there looking at the tarp, and probably taking pictures too to show to their kiddies/grandkiddies.
It's an interesting read, but I think that the "rational geometry" isn't as fundamental a change as the author claims.
I would say that it is a lot like switching between polar and rectangular coordinates. Some things are easier to do in one system, some things are easier to do in the other.
The author makes an excellent point that when working with quadrance and spread, trigonometry and spread become easy. So if I am working with a triangle, I can do everything with rational numbers. However, it often happens to me that I want to do things like add two angles. In the new parametrization, this often useful operation becomes a lot less trivial. I can't just add spreads. Also, if I want to know the distance between two points A and B on a line, and I happen to know the distances from both A and B to an intermediate point C, then my life will be simpler if I use distances.
I'm happy for the insight that working with distance squared and spread (which is just sine squared) can make some computations simpler. But I wouldn't see this as more than a change of coordinate systems. You win something and you loose something. In any given problem, you still should pick the coordinate system that is most suitable.
Same reason a wire strung between two poles has to sag in the middle. That's the quick version. For the details, check out my paper referenced in the previous post.
Actually, the page an non-equatorial elevators you are looking at is a bit out of date. There is much more recent material in the paper I presented at the 3rd annual space elevator conference. The slides are also available here.
The paper should give you a quantitative idea of what the situation is.
To put into perspective what the previous post says. Moving a bit off the equator is possible and costs nearly nothing. On the other hand, if you want to place the Space Elevator in the continental USA, you are going to have to significantly increase the tension at the base of the space elevator, for a given payload.
The reason for this increase in tension is that as you move further away from the equatorial plane, the elevator ribbon starts being inclined at the anchor. The vertical component of the tension needs to be able to lift the desired payload, so the total tension in the ribbon is greater. This gets really bad as the inclination of the ribbon nears 90 degrees (at a latitude of about 48 degrees for the standard Edwards ribbon parameters).
Will people accept to let their car drive for itself, or do they enjoy the pleasure of driving themselves too much? I think it is just a question of what you have been brought up to expect. For example, in Fnance, nearly all cars are stick shifts. In North America, the norm is to have automatic transmission. A French person will tell you he wants that extra bit of control, so that he can get the maximum power of his engine right when he wants it. In North America people will ask you why the hell you would want to worry about changing gears when automatic transmissions are so good. It's all in what people are used to. Give them automatic cars, and some will adapt to it and wonder how you could even dream of wanting to drive yourself. Others may be harder to adapt. I thought that the movie I Robot played this theme quite well...
In this experiment, the errors were only left in the encyclopedia for 5 days. I wonder how many people actually looked at the modified articles in those 5 days. Ten? A hundred? How many of them read with enough attention for the subtle facts that were changed to even register with them. I wouldn't expect these subtle changes to be noticed within such a short time span. I think it would be interesting to do a much longer experiment in which the debugging process would have a chance to occur. How long would it take for those errors to be found? A month? A year? Forover?
"Thirdly, 60000 miles? Geosynchronous orbit is at
42000km from the centre of earth, how the hell are
they going to keep the "weight" where it's
supposed to be? Rockets? Unless they manage to
keep the centre of mass at 42000 km I don't think
it's possible, and you'll end up with 60000 miles
of expensive ribbon wrapped around earth (2.5
rounds) and a small crater where the "weight" met
earth."
People commonly believe that the center of mass of the elevator has to be at geosynchronous altitude because it is rotating synchronously with the Earth. This idea is simply wrong. For example, most Slashdot readers are currently rotating synchronously with the Earth. Not one of them is at geosynchronous altitude.
In the case of the Slashdot reader, he (she?) does not need to be at GEO simply because he is not in orbit. His chair is pushing him up. The elevator, also, is not in orbit, as it is attached on one end to the ground. In the case of the elevator, the ground will be pulling down on the elevator (this is necessary if you want to be able to climb up the elevator into space). So the elevator is not in orbit, there is no reason to expect its center of mass to be at GEO.
But in fact, the idea of its center of mass being at GEO is even wronger than that. Indeed, suppose that the elevator was not attached to the ground. In that case, the elevator would be in orbit, but it would certainly not be a point mass. Therefore, the orbital rules that most people are familiar with (Kepler's laws, etc) do not apply. Because Earth's gravity decreases slower and slower with altitude (it is a convex function), the center of mass would have to be beyond GEO for a geosynchronous orbit. I've got a little more detail on this on my web page.
> The thinnest part, most likely to fail I'd think, > if it were to fail, would leave it hovering just > above the ground waiting to be duct taped back in > place.
This is not true, the base of the elevator has to be in tension so if you try to climb the elevator the elevator pull you up, rather than you pulling you down. Therefore, if the base of the elevator breaks, the base will go snapping upwards.
If you compare the mass per mile of the space elevator ribbon with the mass per mile of the pipeline, you will get a better idea of the difference. I estimate that the elevator ribbon will be about 25kg/mile. The pipeline certainly weighs many tons per mile, I'd say at least 10. So the material costs per mile are a lot less for the elevator than for the pipeline, even if the ribbon material costs an order of magnitude more than the steel for the pipeline.
Next, you clearly haven't looked at how they intend to build up the elevator. They will start by deploying a thin initial ribbon; this is the only part that has to be flown up with rockets. All the rest of the ribbon mass will be built up by sending spools of ribbon material up along the elevator on "climbers". They will build up the ribbon cross-section as they go. The labor costs will be minimal compared with pipeline laying. Also, there won't be any terrain difficulties to overcome, unlike pipeline construction. No mountains, marshes, etc...
I remember from a few days I spent touring Moscow that they have 3 ruble coins there (or at least they did in the early 90s). I was rather clueless about the coins so I would let the merchants help me pick out the coins I was supposed to give them. For some reason, they never took the 3 ruble coins. For the same reason, I don't think that the strange denomination coins in the article would get used very much.
I thought that capitalism was supposed to work best under the assumption of perfect information (in particular price information). Wouldn't making price collecting illegal be un-capitalistic?
Thrusting at 1g for 6 days simply isn't practical. Assume an engine that ejects propellant at 100000m/s (this is more than 10x what is practical with the best ion drives). Your delta velocity over 6 days at 1g will be 9.8*86400*6=5 million m/s (typical missions are in the thousands of m/s, generally). That means that your initial mass to payload mass will be exp(5e6/1e5)=exp(50)=5.18e21. So for a payload weighing one ton, you would need a mass of propellant equal to the mass of the earth!
Fortunately, there is a much more practical way to provide astronauts with gravity: rotation. You can put them in a spinning ring, as in 2001, or you can have a ship and a counterweight tethered together, and spinning around each other. And this won't cost you any propellant at all (except to get things started).
I discovered Stephen Baxter recently thanks to a book that he coauthored with Arthur C Clarke.
Baxter tends to have novels that spane the lifetime of the universe, and that consider humanity's place in such an immensity of space and time. He is often also quite critical of NASA (at least in the part of the book that takes place near enough to the present for NASA still to be in existence).
Slashdot Mirror
The sentence "SpaceShipOne is on it's way to the Smithsonian National Air and Space Museum in Washington DC." seems a bit inaccurate. A friend of mine who was there a week or so ago said that SpaceShipOne is already there, albeit under a tarp. Doent's seem like there is much traveling left for her to do. Naturally, a throng of people (including my friend) were there looking at the tarp, and probably taking pictures too to show to their kiddies/grandkiddies.
It's an interesting read, but I think that the "rational geometry" isn't as fundamental a change as the author claims.
I would say that it is a lot like switching between polar and rectangular coordinates. Some things are easier to do in one system, some things are easier to do in the other.
The author makes an excellent point that when working with quadrance and spread, trigonometry and spread become easy. So if I am working with a triangle, I can do everything with rational numbers. However, it often happens to me that I want to do things like add two angles. In the new parametrization, this often useful operation becomes a lot less trivial. I can't just add spreads. Also, if I want to know the distance between two points A and B on a line, and I happen to know the distances from both A and B to an intermediate point C, then my life will be simpler if I use distances.
I'm happy for the insight that working with distance squared and spread (which is just sine squared) can make some computations simpler. But I wouldn't see this as more than a change of coordinate systems. You win something and you loose something. In any given problem, you still should pick the coordinate system that is most suitable.
Same reason a wire strung between two poles has to sag in the middle. That's the quick version. For the details, check out my paper referenced in the previous post.
Actually, the page an non-equatorial elevators you are looking at is a bit out of date. There is much more recent material in the paper I presented at the 3rd annual space elevator conference. The slides are also available here. The paper should give you a quantitative idea of what the situation is.
To put into perspective what the previous post says. Moving a bit off the equator is possible and costs nearly nothing. On the other hand, if you want to place the Space Elevator in the continental USA, you are going to have to significantly increase the tension at the base of the space elevator, for a given payload.
The reason for this increase in tension is that as you move further away from the equatorial plane, the elevator ribbon starts being inclined at the anchor. The vertical component of the tension needs to be able to lift the desired payload, so the total tension in the ribbon is greater. This gets really bad as the inclination of the ribbon nears 90 degrees (at a latitude of about 48 degrees for the standard Edwards ribbon parameters).
Will people accept to let their car drive for itself, or do they enjoy the pleasure of driving themselves too much? I think it is just a question of what you have been brought up to expect. For example, in Fnance, nearly all cars are stick shifts. In North America, the norm is to have automatic transmission. A French person will tell you he wants that extra bit of control, so that he can get the maximum power of his engine right when he wants it. In North America people will ask you why the hell you would want to worry about changing gears when automatic transmissions are so good. It's all in what people are used to. Give them automatic cars, and some will adapt to it and wonder how you could even dream of wanting to drive yourself. Others may be harder to adapt. I thought that the movie I Robot played this theme quite well...
In this experiment, the errors were only left in the encyclopedia for 5 days. I wonder how many people actually looked at the modified articles in those 5 days. Ten? A hundred? How many of them read with enough attention for the subtle facts that were changed to even register with them. I wouldn't expect these subtle changes to be noticed within such a short time span. I think it would be interesting to do a much longer experiment in which the debugging process would have a chance to occur. How long would it take for those errors to be found? A month? A year? Forover?
"Thirdly, 60000 miles? Geosynchronous orbit is at 42000km from the centre of earth, how the hell are they going to keep the "weight" where it's supposed to be? Rockets? Unless they manage to keep the centre of mass at 42000 km I don't think it's possible, and you'll end up with 60000 miles of expensive ribbon wrapped around earth (2.5 rounds) and a small crater where the "weight" met earth."
People commonly believe that the center of mass of the elevator has to be at geosynchronous altitude because it is rotating synchronously with the Earth. This idea is simply wrong. For example, most Slashdot readers are currently rotating synchronously with the Earth. Not one of them is at geosynchronous altitude. In the case of the Slashdot reader, he (she?) does not need to be at GEO simply because he is not in orbit. His chair is pushing him up. The elevator, also, is not in orbit, as it is attached on one end to the ground. In the case of the elevator, the ground will be pulling down on the elevator (this is necessary if you want to be able to climb up the elevator into space). So the elevator is not in orbit, there is no reason to expect its center of mass to be at GEO.
But in fact, the idea of its center of mass being at GEO is even wronger than that. Indeed, suppose that the elevator was not attached to the ground. In that case, the elevator would be in orbit, but it would certainly not be a point mass. Therefore, the orbital rules that most people are familiar with (Kepler's laws, etc) do not apply. Because Earth's gravity decreases slower and slower with altitude (it is a convex function), the center of mass would have to be beyond GEO for a geosynchronous orbit. I've got a little more detail on this on my web page.
> The thinnest part, most likely to fail I'd think,
> if it were to fail, would leave it hovering just
> above the ground waiting to be duct taped back in > place.
This is not true, the base of the elevator has to be in tension so if you try to climb the elevator the elevator pull you up, rather than you pulling you down. Therefore, if the base of the elevator breaks, the base will go snapping upwards.
If you compare the mass per mile of the space elevator ribbon with the mass per mile of the pipeline, you will get a better idea of the difference. I estimate that the elevator ribbon will be about 25kg/mile. The pipeline certainly weighs many tons per mile, I'd say at least 10. So the material costs per mile are a lot less for the elevator than for the pipeline, even if the ribbon material costs an order of magnitude more than the steel for the pipeline.
Next, you clearly haven't looked at how they intend to build up the elevator. They will start by deploying a thin initial ribbon; this is the only part that has to be flown up with rockets. All the rest of the ribbon mass will be built up by sending spools of ribbon material up along the elevator on "climbers". They will build up the ribbon cross-section as they go. The labor costs will be minimal compared with pipeline laying. Also, there won't be any terrain difficulties to overcome, unlike pipeline construction. No mountains, marshes, etc...
Actually, last time I tried, VMware wouldn't run in VMware. Maybe they have changed this in more recent versions, though.
I remember from a few days I spent touring Moscow that they have 3 ruble coins there (or at least they did in the early 90s). I was rather clueless about the coins so I would let the merchants help me pick out the coins I was supposed to give them. For some reason, they never took the 3 ruble coins. For the same reason, I don't think that the strange denomination coins in the article would get used very much.
I thought that capitalism was supposed to work best under the assumption of perfect information (in particular price information). Wouldn't making price collecting illegal be un-capitalistic?
Thrusting at 1g for 6 days simply isn't practical. Assume an engine that ejects propellant at 100000m/s (this is more than 10x what is practical with the best ion drives). Your delta velocity over 6 days at 1g will be 9.8*86400*6=5 million m/s (typical missions are in the thousands of m/s, generally). That means that your initial mass to payload mass will be exp(5e6/1e5)=exp(50)=5.18e21. So for a payload weighing one ton, you would need a mass of propellant equal to the mass of the earth!
Fortunately, there is a much more practical way to provide astronauts with gravity: rotation. You can put them in a spinning ring, as in 2001, or you can have a ship and a counterweight tethered together, and spinning around each other. And this won't cost you any propellant at all (except to get things started).
A lot of small experimental languages target the JVM. That way they get all kinds bytecode tools for free.
One example I got to work with a few years ago is Nice. A nice (no pun intended) combination of functional programming and java.
I discovered Stephen Baxter recently thanks to a book that he coauthored with Arthur C Clarke. Baxter tends to have novels that spane the lifetime of the universe, and that consider humanity's place in such an immensity of space and time. He is often also quite critical of NASA (at least in the part of the book that takes place near enough to the present for NASA still to be in existence).