141–150 of 304 posts
I don't understand how a space elevator would be advantageous in terms of the energy required to get something to space. The load still has to reach orbital velocity. Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage? Wouldn't the load going up the elevator pull the tether to one side?
I don't understand how a space elevator would be advantageous in terms of the energy required to get something to space. The load still has to reach orbital velocity. Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage? Wouldn't the load going up the elevator pull the tether to one side?
The tyranny of the rocket equation! The energy use of a rocket isn't just "how much energy is needed to have that kinetic energy and that potential energy", but also includes the energy needed to lift and accelerate the fuel used to provide that energy, as well as the fuel needed to provide that energy, as well as the ... and so on.
Earlier quoted context omitted.
Perhaps unless you decide to detach the cable at the earth end? You might be able to react to a break faster than the cable can fall.
Even if you could react and cut the cable in 1 ms, if the counterweight is disconnected, the rest of the cable is coming down to Earth.
The cars would travel at up to 200kph and arrive at the space station eight days after departure from Earth. These early cable experiments are important, but someone should also be working on the composing an 8 day Elevator Muzak score that won't drive you insane.
I think copyright won't apply after the first half hour.
> "...six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, ... eight days ...." Whooooa. Let's think about this for a second. Eight days means people need to sleep (and not just sitting up in a chair, no matter how comfy). At 1m x 2m per bed that would be a 15m x 4m space even without aisles to walk between the beds or down the middle or any sort of privacy separators. Also, a bathroom and actual washin…
You forget this is Japan, where tons of people sleep on trains almost every day - often on their feet.
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Is humor against HN rules? I regularly see such posts being downvoted and it doesn't make sense to me.
Most humor can be categorized as "insubstantive comments" and those are discouraged. It is possible to crack a joke here and get it upvoted, but it's hard to pull it off. I even once had a joke upvoted by quite a lot,* like 50 points or something, but most jokes are downvoted not because humor is forbidden, but because insubstantive comments are discouraged. Some humor is downvoted for being uncivil because a lot of…
Earlier quoted context omitted.
Most humor can be categorized as "insubstantive comments" and those are discouraged. It is possible to crack a joke here and get it upvoted, but it's hard to pull it off. I even once had a joke upvoted by quite a lot,* like 50 points or something, but most jokes are downvoted not because humor is forbidden, but because insubstantive comments are discouraged. Some humor is downvoted for being uncivil because a lot of…
Can I ask why you retired your previous handle?
> using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people Hmmm...is that 30 people/car or 30 people/6 cars? You will be enclosed with them on 18m x 7.2m, that's 120m², for 8 days! The former case would sound like torture, in the latter case it could be done comfortably, though, but it would still require some good nerves by the travellers...
I don't understand how a space elevator would be advantageous in terms of the energy required to get something to space. The load still has to reach orbital velocity. Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage? Wouldn't the load going up the elevator pull the tether to one side?
The advantage of going up by pulling oneself up on a space elevator over pushing oneself up with a rocket, is that one doesn't have to push oneself up with a rocket. The tyranny of the rocket equation! The energy use of a rocket isn't just "how much energy is needed to have that kinetic energy and that potential energy", but also includes the energy needed to lift and accelerate the fuel used to provide that energy,…
I don't understand how a space elevator would be advantageous in terms of the energy required to get something to space. The load still has to reach orbital velocity. Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage? Wouldn't the load going up the elevator pull the tether to one side?
Since rockets lack infinite thrust, they take a finite amount of time to reach space. While they're doing so, they need to fight gravity -- ~all the thrust that's directed downwards, as opposed to horizontally, is wasted energy. There are more reasons to build a space elevator, but that's a big one. It really would be far more energetically efficient.
To get near 100% efficiency, it follows from the kinetic energy formula and conservation of momentum the body you're pushing against must have a much larger mass than you[1].
So discounted exotic phenomena, the only way to travel efficiently through space is to push off a very large mass, departing at full velocity, or in the case of near-Earth travel, simply push Earth.
The space elevator is essentially an elaborate staircase. It is in a stable equilibrium, and climbing it doesn't steal energy from the counterweight (which in fact doesn't move in fact because it is in constant tension); you're just pushing Earth away.
In the grand scheme of things the very low efficiency of maybe 10% (in my guesstimation) to LEO isn't so bad (not even the maybe ~5% interplanetary efficiency); especially considering the costs of space systems in general in comparisson to fuel cost. This small fuel cost makes reusable rockets quite an attractive option near term (as noted by SpaceX).
But long term, that's quite a steep inefficiency. If we were to endeavor large scale colonization or exploration of exoplanetary resources it seems to me either a kinetic launch system or at least a space elevator variant would be a necessity.
[1] Derivation: M1 v1=M2 v2 => v1^2 = (M2/M1)^2 v2^2; M1 v1^2 + M2 v2^2 = E => M2^2/M1 v2^2 + M2 v2^2 = E; M2 v2^2 (1+M2/M1) = E => K2 = E/(1+M2/M1).
As M1->infinity, all the kinetic energy goes to K2 and none to K1 (which is why you don't give Earth any meaningful energy by walking).