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Japan starts space elevator experiments

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Re: Japan starts space elevator experiments

#191

Post by ridgeguy »

WtfRuSerious wrote: post #181
ridgeguy wrote: post #179

I'm curious about space elevator phenomena related to lateral ∆V. At Earth's equator (zero altitude - i.e., on the ground), an object moves spinward at about 0.46 km/sec. In geosynchronous orbit, an object has to move at about 3.07 km/sec. A space elevator car ascending from stationary on the equator to a terminal at geo altitude would require a tangential (lateral) ∆V of 2.61 km/sec. This is in addition to the energ…

What about at the poles? Seems like that would negate the lateral problems, but maybe I'm just introducing a twisting one instead...?

I think it would be the same ∆V requirement (for geosynchronous orbital altitude). But it's not possible to have a geo orbital plane (so the subsatellite point is stationary on the Earth) that is out of the equatorial plane.

Re: Japan starts space elevator experiments

#192

Post by dang »

yters wrote: post #186
dang wrote: post #183

Earlier quoted context omitted.

Maybe so, but can you please not post unsubstantive comments to HN?

It's substantive, pointing out there are many major tech projects these days based on pipe dreams born of sci fi books. The fact there are so many means either our tech leaders are not very smart, are scamming the government funds, and/or are out of good ideas. Which leads to the bigger question, what has happened to our vision for the future?

I believe you that you had those words in mind, but they're not what you posted.

Re: Japan starts space elevator experiments

#193

Post by jessaustin »

bencompanion wrote: post #122
curiousgal wrote: post #45

Earlier quoted context omitted.

How much space would they get on the ISS either ways? It'd be a good practice.

The end of this cable would be 36000km up, compared to the ISS's 400km. The first space elevator would primarily be used to shift stuff, rather than people at first - there's no point having convenient transit for people if they've got nowhere to go at the other end.

That's where the end of the cable is, but there's no rule that that's where anyone has to get off the elevator.

Re: Japan starts space elevator experiments

#194

Post by jessaustin »

BurningFrog wrote: post #158
curiousgal wrote: post #45

Earlier quoted context omitted.

How much space would they get on the ISS either ways? It'd be a good practice.

There is - and I don't mean to pun - plenty of space in space. Space stations could be quite roomy.

They'll be roomy just as soon as it isn't exorbitantly expensive to transport material to space. So, possibly sometime after this elevator is operational...

Re: Japan starts space elevator experiments

#195

Post by djsumdog »

ghaff wrote: post #30

For those looking for a popular culture examination of space elevators--albeit from a number of decades back--check out Arthur C. Clarke's The Fountains of Paradise. It also deals with some of the engineering issues, though again it's quite old.

Also the Mars Trilogy (Red Mars, Green Mars, Blue Mars) by Kim Stanley Robinson.

Honestly that's my favorite Sci-Fi novel series of all time. Just give Red Mars a try and I prosome you won't be able to put it down.

Re: Japan starts space elevator experiments

#196

Post by jessaustin »

mvilim wrote: post #170
stretchwithme wrote: post #133

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?

There are two types of energy at play here: the gravitational potential energy and the kinetic energy of the orbiting object (necessary to maintain an orbit). As you climb the cable, the force of gravity pulling you back to earth decreases, and the centrifugal force pulling you away from earth increases. The difference between these two is the force you need to provide to climb the cable. I believe you are correct fo…

Geosynchronous orbit is 42 km from the center of the earth while the ISS orbits 7k km from the center of the earth.

  s/center/surface/g
...although I'm not sure that's right either. The point is that anything 42 km from the center is still very much inside the earth.

Re: Japan starts space elevator experiments

#197

Post by perl4ever »

ridgeguy wrote: post #177
perl4ever wrote: post #75

Earlier quoted context omitted.

TIL forwards acceleration is called "eyeballs in" and backwards is called "eyeballs out". It looks like 6 Gs is about as much as is feasible for an extended period of time.

Brief search didn't get me anything about longest ride on a centrifuge, which I guess would be the only way to test G-tolerance over extended periods. Where 'extended periods' means > an hour. Any pointers to 6 Gs as being tolerable, for how long? Tnx.

Don't know, I was quoting a figure for 10 minutes. 6 gs for 10 minutes will get you to 35 km/s, which I believe exceeds any rocket launches so far.

Re: Japan starts space elevator experiments

#198

Post by mac01021 »

djsumdog wrote: post #195
ghaff wrote: post #30

For those looking for a popular culture examination of space elevators--albeit from a number of decades back--check out Arthur C. Clarke's The Fountains of Paradise. It also deals with some of the engineering issues, though again it's quite old.

Also the Mars Trilogy (Red Mars, Green Mars, Blue Mars) by Kim Stanley Robinson. Honestly that's my favorite Sci-Fi novel series of all time. Just give Red Mars a try and I prosome you won't be able to put it down.

Gave it to my father after reading it. He thought it was too slow and didn't have enough of a narrative arc, and he opted not to finish reading.

I loved the trilogy, though.

Re: Japan starts space elevator experiments

#199

Post by mvilim »

jessaustin wrote: post #196
mvilim wrote: post #170

Earlier quoted context omitted.

There are two types of energy at play here: the gravitational potential energy and the kinetic energy of the orbiting object (necessary to maintain an orbit). As you climb the cable, the force of gravity pulling you back to earth decreases, and the centrifugal force pulling you away from earth increases. The difference between these two is the force you need to provide to climb the cable. I believe you are correct fo…

Geosynchronous orbit is 42 km from the center of the earth while the ISS orbits 7k km from the center of the earth. s/center/surface/g ...although I'm not sure that's right either. The point is that anything 42 km from the center is still very much inside the earth.

Sorry, dropped a k on that 42. Should be 42k km. Though there are clearly no calculations here, using the distance from the center of the earth is standard for gravitational calculation. It makes more sense to say that the ISS is 7000km/42000km=1/6th of the distance to a geosynchronous orbit than to say it's 400km/35000km=1/90th.

Re: Japan starts space elevator experiments

#200

Post by larkeith »

ridgeguy wrote: post #179

I'm curious about space elevator phenomena related to lateral ∆V. At Earth's equator (zero altitude - i.e., on the ground), an object moves spinward at about 0.46 km/sec. In geosynchronous orbit, an object has to move at about 3.07 km/sec. A space elevator car ascending from stationary on the equator to a terminal at geo altitude would require a tangential (lateral) ∆V of 2.61 km/sec. This is in addition to the energ…

(In case you were unaware, this is the Coriolis force)
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