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Japan starts space elevator experiments

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Re: Japan starts space elevator experiments

#241

Post by jstarfish »

p1mrx wrote: post #54
Keyframe wrote: post #38

Earlier quoted context omitted.

And how exactly do you plan to 'knock out' people safely for eight days, or even just a few? Heck, even for just a few hours without medical equipment and personnel?

The medical technology for human stasis doesn't seem particularly unattainable, when compared against building a carbon nanotube tether into orbit. Some mammals are able to hibernate for months.

General anesthesia kills 1 in 100,000 patients, and that's with medical personnel standing by in actual hospitals, much less a skeleton crew of people strapped to a spacebound elevator.

We don't understand ourselves or our bodies anywhere near as well as we can understand or advance materials science. My money is on new cables before reliable stasis.

Re: Japan starts space elevator experiments

#243

Post by adrianN »

Keyframe wrote: post #233
adrianN wrote: post #224

Earlier quoted context omitted.

No, we don't even know if warp drives are allowed by the laws of physics. We have a pretty good idea how to do hibernation: Saturate the tissue with some cryoprotectant and freeze it very quickly. The problem is that we don't have a cryoprotectant that is sufficiently non-toxic and we can't freeze anything as big as a human quickly enough.

Of course we know. Bend space and don't travel faster than light. We JUST need exotic matter of sufficient energy density to carry around.

Yeah and since nobody knows whether the exotic matter needed actually exists, we don't know whether bending spacetime in the required way is physically possible.

On the other hand, we can successfully freeze and thaw bunny kidneys.

Re: Japan starts space elevator experiments

#244

Post by usrusr »

tartuffe78 wrote: post #134
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?

The station at the end is in orbit, so it's the difference between trying to climb a ladder to the Moon, and trying to jump to the Moon.

At the risk of being too pedantic, a rocket is much more like farting yourself to the moon than like jumping. The benefits of ladders remain.

Re: Japan starts space elevator experiments

#245

Post by chriswarbo »

mojomark wrote: post #209
sigmaprimus wrote: post #162

I'm a bit confused the ISS is only 408km from the earth's surface so why would it take 8 days at 200kph? Unless they are including the speed of orbit in which case the earth is already rotating at 1600 kph. What am I missing here?

They said the tetger would be 36,000 km. 36,000/200kph = 180 hrs... 180hrs/24hrs/day = 7.5 days. Why the tether needs to be 36,000km long wasn't mentioned.

In terms of angular speed (e.g. revolutions per minute), lower orbits are faster, higher orbits are slower (think of a Mercury year versus a Neptune year).

The ISS circles the Earth every 92 minutes. If we dropped a cable from the ISS (or another satellite at the same height), the anchoring point (e.g. something like a floating oil platform) would also have to circle the Earth roughly every 92 minutes. That's not feasible.

Satellites at 36,000km circle the Earth every 24 hours, which is the same speed that the Earth rotates. If the satellite is orbiting around the equator, going the same direction as the Earth's rotation, then we would not have to move the anchor (the Earth's rotation would do it for us)

Re: Japan starts space elevator experiments

#246

Post by joering2 »

jaggederest wrote: post #102
zepearl wrote: post #91

Earlier quoted context omitted.

Yes, but probably only in general (meaning only from a theoretical point of view without considering external forces)? E.g. as soon as the cable has headwind (in the opposite way of the planet's rotation) the cable would slack off, the thing in orbit would slow down & lower its altitude (how much? Would it anyway have to always skim the upper atmosphere?) => then as soon as the cable gets tailwind the opposite would…

For practical purposes the atmosphere ends at 500km altitude. The cable is going to have to be 36,000 kilometers long. Atmospheric effects are pretty much rounding error at that point - imagine trying to swing a 10 foot long pole by blowing on the first inch.

Just fantisizing here, but helium baloons go over 50km up; can this elevator cable be vertically supported by solar-powered helium-filled heat packs alongs its way, with horizontal stabilization of large fans blowing in oposite direction (lower atmosphere) and tiny rocket boosts in above-atmosphere region similar to how sattelites correct their orbits?

Just fantasizing here..

Re: Japan starts space elevator experiments

#247

Post by chriswarbo »

I really like the space fountain concept: it's utterly ridiculous, but completely feasible. It also doesn't need to be as big as a space elevator to be useful (a partial space elevator wouldn't work); space fountains can be as big or small as desired, and applications like radio towers have been mentioned.

It would be nice to see even a metre long demo, which I imagine might be possible as something like a student project (4 coil guns exchanging ball bearings).

Re: Japan starts space elevator experiments

#248

Post by jimmcslim »

timonoko wrote: post #237

The Giant Space Wheel (of Seveneves) is so much more attractive than space elevator. That is a large mass on geostationary orbit having smaller pods rotating at the end of ropes. Those pods can be lowered to atmosphere and synchronized with earth rotation. Elevator pod comes down and can stay down maybe couple of hours and then jerked back to heavens. All energy comes from the sun - collected at the center station. S…

Also known as a skyhook.[1]

[1] https://en.m.wikipedia.org/wiki/Skyhook_(structure)

Re: Japan starts space elevator experiments

#249

Post by misja111 »

blahedo wrote: post #29

> "...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…

Comparing to a typical submarine, it's three times as much space per person. Submarines typically have 30 square feet pp, 18m x 17.2m for 30 people is 93 square feet.

Re: Japan starts space elevator experiments

#250

Post by jimmcslim »

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.

Given a major plot arc in the trilogy was...

(SPOILER!!!)

... the destruction of the space elevator by a terrorist organisation and the consequent destruction on the surface of Mars as the cable, released from its counterweight, wrapped itself around the planet... I’m not sure it’s a great example :-)

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