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Japan starts space elevator experiments

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Re: Japan starts space elevator experiments

#201

Post by yters »

dang wrote: post #192
yters wrote: post #186

Earlier quoted context omitted.

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.

Well, I appreciate you civilly correcting me, which you seem to have a good history of doing, so I apologize for my tone.

Re: Japan starts space elevator experiments

#202

Post by a1369209993 »

jjeaff wrote: post #178
a1369209993 wrote: post #65

Earlier quoted context omitted.

You'd need to accelerate at 68 G's[0] (foreward for the first four minutes, backward for the last four). Not neccesarily unsurvivable, but your passengers (and most cargo) are likely to be unpleasantly pastelike. We should probably treat it more like commercial air travel than compressive-structure elevator rides. 0: 200kph*8day/8min/2min => 67.981081 gravity

I don't think 68 Gs is survivable at all. At least not for more than a fraction of a second. 46 Gs for a few seconds is the most a human has survived that we know of. 10 Gs for 1 minute is lethal.

> unpleasantly pastelike.

I don't think you'd get actual paste, but yes, 8-minute space elevator rides aren't looking very physically possible.

Re: Japan starts space elevator experiments

#204

Post by djsumdog »

DEADBEEFC0FFEE wrote: post #168
ObsoleteNerd wrote: post #164

Earlier quoted context omitted.

99% of the comments about this story online think that they're talking about making one NOW. They don't think they can do it now. They're starting initial research into a few isolated systems required to do it one day in the future when materials science and all the other aspects catch up. It will take decades of R&D, but someone might as well start on the bits we can do now, like a system for climbing the tether (wh…

Fair enough. We have to start somewhere. Perhaps a tether climbing rig will be be useful in future megacity skyscrapers.

The base tether point would need to be far away from anything! In the book Red Mars by Kim Stanley Robinson, one is placed in Trinidad and Tobago.

The most dangerous part would be slowly dropping the cable; lower it to the point where it could be pulled into a magnetic clamp -- without destroying everything in its path.

Re: Japan starts space elevator experiments

#205

Post by bencompanion »

sigmaprimus wrote: post #166
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?

My bad, missed the explanation below, go synchronization requires a much further distance than the iss. So I guess they will also have to make a new station or shuttle system to get to the iss.

Getting from GEO back down to LEO would require pretty serious energy to reduce your altitude. You could possibly get off the elevator early, but you would need to then get up to orbital speed for whatever altitude you're at, which would be non-trivial for LEO.

The ISS will almost certainly be decommissioned by 2030 anyway, and we're not going to have a space elevator by then. There'll still be other stuff in LEO that we want to get to though.

Re: Japan starts space elevator experiments

#206

Post by a_silly_name »

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…

8 days of uncomfortably close quarters on ascent may be a good way to psychologically prepare folks for a perhaps slightly-less cramped orbital experience.

Re: Japan starts space elevator experiments

#207

Post by Aeolun »

Bahamut wrote: post #127
theothermkn wrote: post #117

Earlier quoted context omitted.

The center of mass of the cable-counterweight system orbits at geosynchronous height. Also, the gradient of gravity will Stabilize the attitude in the desired orientation. None of this should be construed as an endorsement of space elevators, though. They will never happen on Earth as it exists now. Over and above the material science, you have to clean out LEO of all satellites before you even start construction. It…

The satellite issue is why I don't think a space elevator as currently conceived will ever make it.

If you have a cable capable of holding a space station and counterweight, no satellite is going to stop it.

Re: Japan starts space elevator experiments

#208

Post by mrep »

imh wrote: post #149
drdeca wrote: post #142

Earlier quoted context omitted.

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,…

Isn't the rocket equation just a momentum equation? Does it escape that? If we brought something up, would we not pull the satellite it's attached to down, requiring more momentum from somewhere?

No, the elevator has counterweights at both ends which each pull on the tether more than the object being moved due to gravity and centripetal force. The object on earth pulls more though which keeps it tethered. The elevator that is moving than exerts extra force to propel itself up but not more than what would drag the top counterweight down, thus, the rope still stays fully extended.

Think of it like holding a rope tight between your arms and putting a robot that moves on it but ends up not exerting enough force to cause it to slack. Your arms (earth/space teather and the in space counterweight) and the object being moved would keep the same overall motion between all 3 objects (your body would just turn).

The space elevator is similar except earth is way more massive than the object being moved so nothing really changes. Also, due to gravity, you have to expend extra energy to move from the bigger object (earth) to a smaller object (space elevator counterweight), aka, the minimum energy cost of moving things out of gravity wells.

Re: Japan starts space elevator experiments

#209

Post by mojomark »

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.

Re: Japan starts space elevator experiments

#210

Post by [deleted] »

cstross wrote: post #118

This isn't the first such experiment (with tethers in space) but previous ones (such as the Shuttle tether experiments from 1996 onwards: https://www-istp.gsfc.nasa.gov/Education/wtether.html ) discovered some unanticipated and terminal problems ... and as they flew aboard a time-limited Shuttle mission there wasn't really any scope for attempting repairs/fixes on orbit. Also, it's arguably obvious with 20/20 hindsig…

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