5 ms·
If you had a ladder stretching all the way into space, you could climb it without needing any rocket propellant
by seibelj 4y ago
If you had a ladder stretching all the way into space, you could climb it without needing any rocket propellant
- kurthr 4y agoOr a sky hook that rotated at the rate of the earths rotation. On the moon it's just about doable with current technology and realistic levels of mass.
- ncmncm 4y agoOr, better, a sky ring. Weighs a bit more, but is an easier target. And the structural stresses work out better.
- BenjiWiebe 4y agoIf you are talking a rigid ring circling the earth, don't forget your attitude jets. Paging Larry Niven...
- ncmncm 4y agoNo, that idea was just dumb. A ring with a diameter matching your skyhook's length might seem to need 22/7 times the mass lofted to orbit, but the stresses on it are much less complicated, so it may be lighter than that. You may imagine one rolling around Earth, dipping to 100 km and flinging off whatever grabs on at up to 10 mi/s. BTW, I calculated that the tensile strength of the material of any rotating ring, whether girdling the sun like Niven's, or just orbiting the regular way like a Halo or Culture "orbital", must be enough to support against its inside surface "gravity" a full radius's length of the material. So, a ring rotating to provide 1G and taking 24hrs to do it (so days are the right length), would have to be about 2M km in radius. It would therefore need to be made out of something that could support a 2M km long constant-thickness cable against 1G, or more than 100x as strong as what you would need for an earthly space elevator. A ring of 100 km radius rotating so that its tangential velocity matches earth orbital velocity less earth's rotation, 7.5 km/s, accelerates anything that latches onto it at 560 m/s^2, or 55 G. One at 1000 km radius would pull 5.2G, a little less strenuous for puny humans; they would need to endure it for a few minutes until flung off. That one would need to be made of stuff that could hold up 5200 km of itself, which might be just within range of what we can make. Methods for dodging satellites are left as an exercise for the reader.
- forgotpwd16 4y ago>On the moon it's just about doable with current technology and realistic levels of mass. Will be interested if you have any studies on it.
- kurthr 4y agoThere are several. Here's one. http://hopsblog-hop.blogspot.com/2016/08/lunar-sky-hook.html http://hopsblog-hop.blogspot.com/2016/08/lunar-sky-hook.html https://hopsblog-hop.blogspot.com/2016/04/liftport-lunar-tether.html https://hopsblog-hop.blogspot.com/2016/04/liftport-lunar-tet... There's also a wikipedia article: https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)
- forgotpwd16 4y agoVery cool articles (and basically the entire blog). Thanks!
- mellavora 4y agoTrue, but you might get hungry or thirsty on the way. I wonder how much water you could carry?
- Sharlin 4y agoConsiderably less than you need to carry in a rocket (separated to constituent atoms to be recombined and pushed out the back)!
- betwixthewires 4y agoAnd you'd expend the same amount of energy climbing it as you would propelling yourself upward with fire.
- breakyerself 4y agoNo because you could run it using electricity transmitted up the ladder. So you wouldn't need to expend energy to carry fuel up the ladder.
- betwixthewires 4y agoI imagine the words "climb the ladder" to mean literally climbing a ladder.
- pfdietz 4y agoUnless the ladder is made of superconductive unobtainium, this will not work (resistive losses kill you). "Real" versions of this scheme would use laser power beaming. Of course, a "real" version of the scheme would also need hefty rockets on the passenger vehicle to keep them from dying if the vehicle fell off the ladder (or if the ladder broke). The rockets are needed to either slow the vehicle before atmospheric entry (so the deceleration is not fatal) or thrust sideways to put the passenger pod into elliptical orbit that just misses the atmosphere. The delta-V needed at the worst case altitude is non-negligible.
- deleted 4y ago[deleted]
- moring 4y agoWould you? A rocket needs to use propellant for the time it stays in the gravity field, i.e. just to "stay still", while clinging to the ladder does not need propellant.
- baq 4y agogoing up is the easy part, high school students can do it. going sideways fast enough to not fall back... that's the hard part.
- Sharlin 4y agoYes; however, going up is not helpful without also going sideways fast enough, and it’s the latter part where almost all of the propellant is spent.
- mburee 4y agoJust need to go a bit further, like, almost 36000km
- MichaelCollins 4y agoWe're all going sideways already, since the earth spins. Climb the ladder up to about 22 thousand miles and you'll be in geostationary orbit. The catch is that nobody can actually build a ladder strong enough. Space elevators from Earth require sci-fi materials.
- andylynch 4y agoAlso when it fails expect the lower end to fall and wreck everything in the area underneath. Which with that length will be a lot! The insurance bill would be … astronomical (see what happened in the Foundation TV show for an example).
- Sharlin 4y agoModern space elevator designs (starting from Brad Edwards’s NIAC study in the early 2000s) propose something much closer to a tether than a tower, maybe some hundreds of tons in total mass and shaped like a gossamer-thin ribbon. The worst-case failure mode of such a design would be rather anticlimactic.
- taneq 4y agoI wonder how much it would help to have jets built in to the elevator which add support using compressed gas or something being pumped through the elevator from the ground? Then it would directly support the structure and also give the option of reacting to outside disturbances.