Slashdot Mirror
Highlift Systems' Space Elevator In The News Again
Kris_J writes "Highlift Systems may have found a second location for the anchor of their space elevator -- Perth, Western Australia. Apparently we have the calm waters and international airport that it needs, amongst other things. Slashdot has covered this company's efforts before: Oct 9, 2002 and, earlier, August 13, 2002, but it's worth discussing again since '[recent funding] has been given momentum by the Columbia shuttle disaster.'"
.. only under great circumstances do any modern marvels come to full attrition. Unless there is an actual need, be it military or economic, this project will never "take off the ground"
Basically, it would take some sort of War or space race with China for this to even be the slightest possiblity. Tax payers will not vote for a 17 billion dollar project unless it was under dire circumstances or felt threatened [alla China]
Think about all the previous advances in the human culture. So many were spawned from war. For instance, I doubt the common 747 jet airliner would be such a popular mode of transportation today if the Nazi's weren't looking for a plane that could run circles around the allied air force.
This post is going off in a tangent. I guess what I'm trying to say is that with war comes advancement in technology. Without war, technology is backed by monetary gain. What is to gain by building a space elevator? Unless they can mine diamonds or gold from the upper atmosphere...
Live web cams
What happened to Sri Lanka? I thought the goal was to get as close to the equator as practical.
The Earth has a much thicker atmosphere than Mars, and atmospheric drag would be sufficiently large to vaporize all of the cable falling from more than 25 km or so. This effectively sets the distance you need to be from the shore in order to guarantee that the cable won't fall on someone in case of an accident.
"Obviously, there has to be a pretty good anchor in the ground for it not to go flying into space."
Question: The article mentions having a cable some 100,000 kms long. Uh, wouldn't that lap the planet a few times? What would keep (or cause) a Gary Larsonesque tragedy from occuring?
Granted I'm being leight hearted with my question, but in light of the recent shuttle tragedy one has to weigh the potential risk of something like this happening.
OK, so I'm not a physicist or a geographer, but... don't these things had to be positioned at (or near) to the equator (like a geo-synchronous satellite)? Otherwise they would sway and stretch because the orbit would not match the ground.
By my recollection, geosynchronous satellites are at ~22,000 miles / ~35 km up. In this orbit, obviously, centrifugal acceleration exactly counterbalances gravity. (Else the thing would rise or sink to a different orbit). Objects in higher orbits travel more slowly (they are further away, and therefore fight against less gravity). As I understand it, the space elevator will be geosynchronous, with an elevation far beyond the "force-balanced" geosynchronous orbit point 35 K up. Any geosynchronous object more than 35K up (i.e., the top of the elevator) will be travelling far faster than necessary to maintain its orbit; in fact, it will be fighting like hell to escape to a higher orbit (trading its kinetic energy for gravitational potential energy). The problem is similar to that of many carnival rides -- keeping tethered to the center. I don't think current nanotube manufacturing processes are sufficient to handle these forces. I could be wrong -- I haven't found good public descriptions on nanotube manufacturing.
wired recently ran an article on this. One key quote is ""Technically it's feasible," said Robert Cassanova, director of the NASA Institute for Advanced Concepts. "
a little further on the cost benefits are addressed, "a space elevator could transport materials into the cosmos for about $100 a kilogram. He estimated that sending materials on a shuttle costs $10,000 to $40,000 per kilogram. "
How would the structure stand up to the ravages of time? Has anyone modelled a nano structure to see what the effects of entropy are?
Do you need a website upgrade?
a rocket gets launched trailing a reel of carbon nanotubes. This original cable is very small, almost useless but it will hold enough weight for a small car to go up it laying down a reinforcing layer. Every three days another car goes up and every three days the cable gets thicker, stronger, and capable of sustaining more weight. Eventually, the entire thing is ready to go and what's the first thing they're going to launch? Reels of full sized space elevator cable so when the original inevitably breaks, it'll take just a few days to reel the replacement down at a negligible cost.
The ease of replacement, more than anything, is what is going to keep the thing off any terrorist's a-list of targets.
Warning: Spoiler if you're planning to read Kim Stanley Robinson's 'Mars' trilogy.
Something like this happens in 'Red Mars' - the cable snaps after the end-point in space is blown up, and wraps itself aroung the planet, with huge destructive force, making a giant trench. KSR prides himself on being as scientifically accurate as possible, is this an error?
...or am I missing something?
I don't understand how they can base it so far from the equator. If you start the counterweight south of the equator, above Perth, it will be way north of the equator 12 hours later.
In more detail:
In a reference frame rotating with the Earth, the counterweight has three forces on it:
Gravity: G m M_earth / r^2
towards the center of the earth
'Centrifugal' force (because we are in a rotating frame): v^2 / r cos l (l = latitude) directed perpendicular to and away from the earth's axis
Tension on the cable.
We want these three forces to cancel out, so that the counterweight is stationary (in the rotating frame.) The problem is that the gravity force has a north/south component unless the counterweight is on the equator. The centrifugal force can't have a north/south component, so the balancing force has to come from the cable tension.
The cable will have be at a small angle to vertical, and the north/south component of the tension is proportional to the sine of this angle, so that component can't be big.
Aha! I think I have the solution.I was thinking of the counterweight being above the tether point.
In the 1st approximation, put the counterweight in geostationary orbit (i.e. on the equator). Run the cable to it.
If the cable had no tension, we would done - but it does. The major component of the tension is towards the earth. We compensate for this by moving the counterweight into a higher orbit. (Decreases gravity, increases centrifugal force, to balance the tension.) There is nothing new here - the Highlift Systems website talks about this.
If the cable was anchored south of the equator, it will have a slight angle to vertical, which will give a southwards force component. If we now modify the orbit of the counterweight to be slightly south of the equator, there will be a northward component to the gravity vector. We can adjust to balance.
From the point of view of the tether point, the cable (if it is straight) will be pointing almost towards the geostationary point. From 30 degrees south, that would be a point about 3000 km north and about 35 km up, so it would be about 5 degrees off vertical.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Carbon nanotubes may have a longitudinal tensile strength of 200 Gigapascals, but what about the strength of the transverse bonds connecting one carbon tube to the tube next to it? Those transverse bonds may not need to withstand 200 Gigapascals of force, but they still have to be damn strong. A split in a wooden board can travel the length of the entire board. Would a split in the space elevator ribbon cause the whole ribbon to become a series of parallel threads?
The section of their FAQ that discusses the problem of large electrical currents generated by long space tethers was really interesting...
Would it be feasible to create a tether to low-earth orbit for the express purpose of generating electricity? I wonder how the cost would compare over the long-term to other low-cost sources like wind and nuclear.
I don't get it either. But as some of the other posts have mentioned, it wouldn't be orbiting, it would be getting 'swung' around by the earth.
Would a physicist please correct the following?!
I picture a tether at the equator going out at 90 degrees. If you move down to Perth, the tether will still go out at 90 degrees to the axis of rotation wouldn't it? That is, it would go out parallel to the tether at the equator. See diagram.
X
XX
XXX
XXXX
XXXX---------O equator
XXX
XX---------O perth
X
So, does that mean that it wouldn't be vertical at perth but would go out at an apparent 31 degrees?
Also, does that mean that the thing actually goes over all of the airspace between 31 degrees and just south of the equator? That is, because of the angle, would it actually go over, say, Indonesia's airspace.
Parts of Indonesia are nearly 10 degrees south. Does a line drawn vertically from Indonesia intersect with the ribbon?
it should wait until we have enough in the way of manned orbital stations to justify the cost
Transportation systems come first, then comes money making. If we wated to have a global system of communications satellites before launching rockets, we wouldnt have any system. In the rainforest, roads come first then the settlers and lumberjacks. If you ever fly across america you can see little strings of towns founded along sometimes now extinct railroad lines. Urban sprawl is a result of increased roadbuilding and major interstates. When the first interstates were built they were mostly empty. Theres a story i heard about some family that was lost on the Washington DC beltway and just made a U-turn in the middle of it because there was no traffic. Try that today. Transportation systems are the ultimate "if you build it, they will come" phenomenon. Private companies wont pay for it, private companies want a 5 year break even with a 30% rate of return. Good luck on even getting the thing built in 5 years, let alone getting it to break even. There are some things only govt can do because buisness is always looking at next quarters bottom line and not the bottom line 10 years from now.
I have some friends that work on creating large (long) carbon nanotubes. As of about 2 years ago, they were unable to make tubes longer than about 1 cm. Things may have improved somewhat in the last couple years, but basically we're about 8 orders of magnitude short of the length needed for a space elevator.
It sounds like you might need at least a little review also. An object, any object, at the right distance from the Earth will naturally fall around the Earth (assuming the right initial conditions so it is above a point on the equator and its velocity vector is perpendicular to its displacement and contained in the equatorial plane) and remain above the same point at all times. If it is too close then the acceleration of gravity will force it to advance slowly while if it is too far away it will move slower than the rotation of the Earth under it. All this involves no cable at all and is absolutely routine for many communications satellites.
Attaching a cable to these two points that do not move relative to each other is some other engineering challenge. Analyzing it could probably start from considering a satellite dragging a long cable and examining what forces would need to be used to cause it to extend straight down to the Earth's surface. I don't believe Newton examined anything like this in the Principia. Since he did describe gravitation and dynamics mathematically I suppose you could glibly indicate that the needed results follow but I believe you have left a considerable exercise for the reader.
Cost of a space elevator: 17 billion dollar Cost of a shuttle launch: .5 billion dollar
Project implementation timeframe: 20 to 30 years
Cost per year = 17 / 25 = .68 billion dollar = 1.36 shuttle launches per year
-- Contradictions only exist in thought - not in reality.