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Space Elevators Are Possible

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Re: Space Elevators Are Possible

#21

Post by bduerst »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

The benefit with space elevators is that you can use mechanical energy to move payloads up the gravity well, as opposed to the chemical energy we use now. What do you think of rail guns, which use electrical energy?

Re: Space Elevators Are Possible

#22

Post by atgm »

ars wrote: post #10
mehwoot wrote: post #8

What happens if something hits the cable and it breaks? Does the whole thing drift off into space?

Depends where it hits. On the tether there is a "zero" point. Below that point things fall toward the Earth, above that point things "fall" away from the Earth. So it depends on where it broke and how much weight there is above vs below that point. (To keep the tether in the air they put lots of weight above the point, which falls away from the Earth and pulls the tether taught.) If I were making one of these I'd mak…

> If I were making one of these I'd make several tethers, spaced such that a single object can not break more than one at once.

What I'd worry about is security, honestly.

What if some nation decides that the space elevator existing isn't in the best interest of their national security, or some paramilitary group wants to make a point?

Bombing the base station would hurt the elevator. But of course, we should expect that to be secured. That still leaves the entire length of cable running up and down the elevator -- that's a huge volume of space to secure against anything explosive or fragmentary.

Re: Space Elevators Are Possible

#23

Post by ghayes »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

Couldn't the elevation of the satellite be at a specific elevation that no other satellite is allowed to orbit at? I.e. using the z-axis to your advantage?

Re: Space Elevators Are Possible

#25

Post by avmich »

ghayes wrote: post #23
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

Couldn't the elevation of the satellite be at a specific elevation that no other satellite is allowed to orbit at? I.e. using the z-axis to your advantage?

No. The elevator's tether is a continuous object of length at least 36 000 km, from atmosphere to geostationary orbit. Practically all satellites are flying within that range of heights.

Re: Space Elevators Are Possible

#26

Post by bsamuels »

bduerst wrote: post #21
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

The benefit with space elevators is that you can use mechanical energy to move payloads up the gravity well, as opposed to the chemical energy we use now. What do you think of rail guns, which use electrical energy?

You would never make it through the atmosphere. At the speeds required to achieve orbit from a surface launch, the projectile leaving the apparatus and hitting the atmosphere would be like smashing it into an ocean of water. Even on a very tall mountain the air density is still enough to stop any projectile-based solution in its tracks.

Re: Space Elevators Are Possible

#28

Post by cgrubb »

kornork wrote: post #2

Great! What does the paper say about overcoming some of the problems that seem to make it tough, like the radiation that humans will receive riding up, or avoiding space debris? I'm assuming problems like building a rope strong enough to hold its own weight will be overcome, as well as developing the technology to climb the elevator.

Early in the book:

    The first few years will enable 20ton payloads without humans [radiation
    tolerance an issue for the two week trip]...
From Finding 7-5:

    Radiation is not a problem for tether climbers, as the designers will
    incorporate this threat into the design requirements and ensure operational
    success through any radiation environment.  Historic precedence supports this
    conclusion as the space community runs spacecraft in all regions where the
    space elevator will be operating.  However, when people are included in the
    tether climb [after some years of robotic success], the radiation problem
    becomes an order of magnitude more difficult.  There are many ways to reduce
    the radiation and shorten the trip, which will have to be incorporated when
    the human element is added.
Although the authors envision eventually using the elevator for transporting humans, I don't see any discussion about how to speed up the trip or increase the shielding.

There is a fairly long section on debris. The authors note that significant debris only exists in low earth orbit. They think the chance of collision is small, but large enough that the situation needs to be monitored. They think debris can be tracked and that if a collision were forecast, the cable could be moved. Also, they think space faring nations should be tasked with removing some of their junk from orbit.

Re: Space Elevators Are Possible

#29

Post by sgt »

"The rotation keeps the cable taut, to counter the gravitational pull as robotic, electric “climbers” ride the line up into space carrying the payload. Boom."

Let's just hope he didn't mean that literally. But early attempts may include some disasters, as often is the case.

Re: Space Elevators Are Possible

#30

Post by beloch »

bsamuels wrote: post #26
bduerst wrote: post #21

Earlier quoted context omitted.

The benefit with space elevators is that you can use mechanical energy to move payloads up the gravity well, as opposed to the chemical energy we use now. What do you think of rail guns, which use electrical energy?

You would never make it through the atmosphere. At the speeds required to achieve orbit from a surface launch, the projectile leaving the apparatus and hitting the atmosphere would be like smashing it into an ocean of water. Even on a very tall mountain the air density is still enough to stop any projectile-based solution in its tracks.

http://en.wikipedia.org/wiki/Project_Babylon

Iraq (with a Canadian scientist) almost made an artillery piece capable of putting material into orbit. Obviously, international sanctions gummed up the project a tad and it was basically over when the scientist was assassinated. Still, it was within the realm of possibility. Only recently have rail-guns started to usurp chemically propelled artillery in some roles, so it's not out of the question that rail-guns could put material into orbit. Even if the associated forces are too extreme for most equipment to survive, it could provide a way of getting raw materials into orbit at the very least.

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