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We need a better way to get to space

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Re: We need a better way to get to space

#41

Post by david-given »

rthomas6 wrote: post #21
nickff wrote: post #8

Earlier quoted context omitted.

Reaching orbit is mostly an issue of velocity, not altitude. This is why balloons can get very high, above of almost all earth's atmosphere, while being far from orbit. Rockets spend most of their ascent traveling nearly horizontal to the ground (they only go straight up at the beginning to get out of the densest part of the atmosphere).

What about geostationary orbit wrt balloons? Do the balloons slow down horizontally a lot during the ascent? If not, what if we floated a rocket up most of the way and let the rocket do the rest?

You've just described a ballocket. You launch a rocket from a very high altitude balloon.

You gain nothing from the height, because you still need to spend ~10km/s getting up to orbital velocity, but you don't have to push your way through the thick lower atmosphere any more. Rockets don't work very well in atmosphere, so you do get fuel savings due to more efficient engines.

I don't know if this has ever been tried for real.

Re: We need a better way to get to space

#42

Post by blisterpeanuts »

It's a slick looking video, but what about reentry? It's not that hard to get a ship up there (the X-15 was flying to the edge of space 50 years ago), and launching like a jet plane obviously has many advantages over rockets, but when it comes back down it's going to hit the atmosphere at a pretty high velocity, unless it's carrying enough fuel to gradually lower itself back into airspace where the jets can kick in. The craft in the video does not appear to have VTOL capability.

But, if they can solve such problems, great. I'm thinking that eventually we'll have some kind of electrical or hybrid mass driver (catapult) system for getting non-human cargo into low orbit[1], much cheaper (and quieter) and obviously could accomplish many launches a day for one-way missions.

You could get a large space station or interplanetary craft up there rather affordably using this approach. Specialized reentry vehicles as well. Launch the parts cheaply, robots assemble the parts in orbit, then launch the humans expensively.

1. https://en.wikipedia.org/wiki/Mass_driver

Re: We need a better way to get to space

#43

Post by imglorp »

jcfrei wrote: post #25
drewg123 wrote: post #22

I was hoping the article would talk about space elevators, and not space planes. I'm eagerly awaiting materials science and geo-politics to mature enough to allow the construction of space elevators. https://en.wikipedia.org/wiki/Space_elevator

I don't really see the benefits of space elevators, to be honest. At an altitude of 100km the gravity is still virtually the same. And you still need a huge amount of fuel in order to put your rocket/plane into orbit. Unless you build an elevator with a height of 42'164km (geostationary orbit) - but that seems unrealistic to me.

There's a very real possibility that a conductive cable would generate tons of power which could be used by the climber plus surplus on the ground.

Re: We need a better way to get to space

#45

Post by dTal »

david-given wrote: post #39
gjulianm wrote: post #34

Earlier quoted context omitted.

I think the problem with space elevators are not as much with the materials but with the logistics of deploying that. How do you get the cable up there? You can't just shoot up a rocket with a cable attached and expect the cable to stay upright: it would fall down unless you give it horizontal speed. But if you do that, you'd probably end up orbiting the Earth and tying it up with the cable. The other option would be…

> You can't just shoot up a rocket with a cable attached and expect the cable to stay upright... Well, actually... Package your cable up, launch it, move to geosynchronous orbit. Start deploying your cable. Once it gets long enough, say a few kilometres long, tides hold it rigidly pointing towards Earth. You solve the counterweight problem by also extending a cable outwards from your launch vehicle, so keeping the ce…

>You solve the counterweight problem by also extending a cable outwards from your launch vehicle, so keeping the centre of gravity still

I don't follow. If you didn't do this, wouldn't your centre of gravity still remain still? Just start at geostationary and make sure you have enough mass to act as a counterweight already on-ship (doesn't have to be in the shape of a cable). The center of gravity will remain in geostationary, the cable will reach the ground, and the ship/counterweight will end up at just the right height to balance it.

Re: We need a better way to get to space

#46

Post by Balgair »

drewg123 wrote: post #22

I was hoping the article would talk about space elevators, and not space planes. I'm eagerly awaiting materials science and geo-politics to mature enough to allow the construction of space elevators. https://en.wikipedia.org/wiki/Space_elevator

FYI for all the readers here: Carbon nanotubes won't work, the phonon effects (lattice interactions) in that very large crystal usually add up to break them after a few cm. Think of it like like a very narrow and very long tube half filled with water. There are vibrations along the length of it, some big and some small in amplitude. When those random waves in the water tube interact, they can add up, sometimes so much so that they break the tube. I know that is now totally correct, but that's the gist.

http://www.ruf.rice.edu/~rau/phys600/p273.pdf

Many more here:

https://scholar.google.com/scholar?q=carbon+nanotubes+phonon...

Re: We need a better way to get to space

#47

Post by marcosdumay »

baldfat wrote: post #17
aggieben wrote: post #5

Giant railguns. That is all.

Squished human beings, but good for some cargo. Would be cool if we could shoot fuel and metal into space, but the heat would be through the roof through the first layer of atmosphere.

Well, thew bigger the railgun, the less it squishes the humans.

You'll also need some rockets to get into orbit. But I always wondered how much of the rocket one could replace with a rail.

Re: We need a better way to get to space

#48

Post by T-A »

david-given wrote: post #41
rthomas6 wrote: post #21

Earlier quoted context omitted.

What about geostationary orbit wrt balloons? Do the balloons slow down horizontally a lot during the ascent? If not, what if we floated a rocket up most of the way and let the rocket do the rest?

You've just described a ballocket. You launch a rocket from a very high altitude balloon. You gain nothing from the height, because you still need to spend ~10km/s getting up to orbital velocity, but you don't have to push your way through the thick lower atmosphere any more. Rockets don't work very well in atmosphere, so you do get fuel savings due to more efficient engines. I don't know if this has ever been tried…

Rockoon? https://en.wikipedia.org/wiki/Rockoon I particularly like the steampunk vibe of https://en.wikipedia.org/wiki/JP_Aerospace#Airship_to_Orbit_...

Re: We need a better way to get to space

#49

Post by gjulianm »

david-given wrote: post #39
gjulianm wrote: post #34

Earlier quoted context omitted.

I think the problem with space elevators are not as much with the materials but with the logistics of deploying that. How do you get the cable up there? You can't just shoot up a rocket with a cable attached and expect the cable to stay upright: it would fall down unless you give it horizontal speed. But if you do that, you'd probably end up orbiting the Earth and tying it up with the cable. The other option would be…

> You can't just shoot up a rocket with a cable attached and expect the cable to stay upright... Well, actually... Package your cable up, launch it, move to geosynchronous orbit. Start deploying your cable. Once it gets long enough, say a few kilometres long, tides hold it rigidly pointing towards Earth. You solve the counterweight problem by also extending a cable outwards from your launch vehicle, so keeping the ce…

The first issue would be touchy, I think. You'd have to find a way to deploy gradually the cable, or else each end would gain really high speeds that could break the cable when it stops deploying.

Regarding the second part... If the cable is severed, the lower part goes down and the upper part goews away as it does not have an anchor on Earth anymore (I think). Either way, you lose the cable. If it's a bit higher, maybe it doesn't burn up completely (for example, in Spain we've recently found space junk landing almost unharmed in a field [1]). And if it's several kilometres long (just a few hundreds) it could cause considerable damage.

1: http://elpais.com/elpais/2015/11/05/inenglish/1446724352_762...

Re: We need a better way to get to space

#50

Post by david-given »

T-A wrote: post #48
david-given wrote: post #41

Earlier quoted context omitted.

You've just described a ballocket. You launch a rocket from a very high altitude balloon. You gain nothing from the height, because you still need to spend ~10km/s getting up to orbital velocity, but you don't have to push your way through the thick lower atmosphere any more. Rockets don't work very well in atmosphere, so you do get fuel savings due to more efficient engines. I don't know if this has ever been tried…

Rockoon? https://en.wikipedia.org/wiki/Rockoon I particularly like the steampunk vibe of https://en.wikipedia.org/wiki/JP_Aerospace#Airship_to_Orbit_...

Er. * cough * Yes, rockoon, not ballocket.

In my defence I (a) am coming down with a horrible cold, and (b) read The Register...

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