For all that effort to reduce oxidiser mass by using atmospheric oxygen, it's still 80% propellant by mass. Saturn V was 85%.
Still impressive if they can make it work, since of course Saturn V wasn't reusable.
We need a better way to get to space
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Re: We need a better way to get to space
#52For all that effort to reduce oxidiser mass by using atmospheric oxygen, it's still 80% propellant by mass. Saturn V was 85%. Still impressive if they can make it work, since of course Saturn V wasn't reusable.
So, with Saturn-5 only 15% was dry mass - and with Skylon 20%? That's 33% increase. Moreover, Saturn-5 was staged - and Skylon is single-stage, and have single stage to orbit with 20% dry mass looks somewhat like a miracle.
Re: We need a better way to get to space
#53I 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 muc…
Is it not possible to dampen phonons before they will break the thread? You probably don't need to have vary long monomolecular threads, you can have many shorter ones weaved in a thicker rope.
Re: We need a better way to get to space
#54I 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 used to think space elevators are practically impossible because of interactions with lower flying space objects. Now I'm less sure; perhaps we can have a technology of active avoidance.
Other problems - like an extremely capable cable material, ways to climb up and down etc - are getting gradually solved over last years, so I'm cautiously more optimistic than before.
Re: We need a better way to get to space
#55Earlier quoted context omitted.
> 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 geos…
No, it wouldn't. As you extend the not inconsiderable mass of the cable towards the earth, your centre of gravity will move inward with it. Assuming your ship massed nothing compared to the cable, then the centre of gravity will be at the midpoint of the cable.
For the space elevator to work, the centre of gravity must be precisely in geostationary orbit (otherwise the entire elevator will drift relative to the ground).
You could achieve this by having a massy ship, and then carefully moving the ship outwards as you unreel the cable. But it's easier to have two cables. It also solves some other engineering problems, such as reaction effects as you control the speed at which the cable unreels.
Re: We need a better way to get to space
#56I'm no rocket scientist but I could imagine rockets having a place in regular space travel. Lets assume that we can harness solar power efficiently and safely store the extra energy in hydrogen and oxygen gas. Then let's say that we could construct sturdy and modular components that can be disassembled and re-assembled at some kind of orbital station, so that the boosters that take people into orbit for whatever reas…
Sea Dragon [1] is slightly similar to that.
Fuel is a small part of the cost of a rocket, most of the cost is in the engines and structures. Cheap production of hydrogen or oxygen is unlikely to make things much cheaper.
Also, any mass left over at engine cut-off requires a large quantity of fuel at lift-off and possibly necessitating a larger more expensive rocket. This would make re-purposing of boosters in orbit less likely.
Re: We need a better way to get to space
#57Earlier quoted context omitted.
Light-gas guns may be a good contender while railguns are sorted out. https://en.wikipedia.org/wiki/Light-gas_gun
Surprisingly, I actually did a fair bit of research into this field. Both rail guns and light gas guns cap out at around 6km/s, and you really want 8km/s (more actually, for hypersonic drag loss) for this to be economical. Otherwise you need to launch a large enough rocket to make up the 2km/s difference, and you stuck solving the rocket equation again. Except you've subjected your rocket to 1000g, and the odds of it…
Still, g-hardening may not be a showstopper. Artillery shells routinely have electronics in them nowadays. It doesn't have to be reusable, but needing only 2km/s from outside the atmosphere basically.
Edit: have you looked at these people's work? https://en.wikipedia.org/wiki/Quicklaunch
Re: We need a better way to get to space
#58Earlier quoted context omitted.
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 muc…
Is it not possible to dampen phonons before they will break the thread? You probably don't need to have vary long monomolecular threads, you can have many shorter ones weaved in a thicker rope.
Good question. I am not an expert in this in any way. I'd think that you have to have dampners in the lattice of the crystal. The only way that works is to dope the lattice with either another 4 valence element, like silicon, or to dope the carbon itself with something. The only think I can think of is to modify the isotopes to be VERY heavy which is obviously therefore radioactive and would need to be replaced a lot. If you used silicon dope then you'd reduce the interatomic strength and therefore make the rope possibly too weak to be used.
I thought that the whole point of carbon nanotubes was that they are the only thing with the 'pull strength' (forgetting the term here) that could withstand the tension. If you weaved them, then you would rely on the Van Der Waal forces to keep the tubes together which is much weaker. Also you have to contend with the phonon interactions, anything tangential to that 'plane' has no effect on the strength, you have to be a part of the lattice to effect things.
Then again, I don't do research in this area.
Re: We need a better way to get to space
#59Earlier quoted context omitted.
Surprisingly, I actually did a fair bit of research into this field. Both rail guns and light gas guns cap out at around 6km/s, and you really want 8km/s (more actually, for hypersonic drag loss) for this to be economical. Otherwise you need to launch a large enough rocket to make up the 2km/s difference, and you stuck solving the rocket equation again. Except you've subjected your rocket to 1000g, and the odds of it…
Still, g-hardening may not be a showstopper. Artillery shells routinely have electronics in them nowadays. It doesn't have to be reusable, but needing only 2km/s from outside the atmosphere basically. Edit: have you looked at these people's work? https://en.wikipedia.org/wiki/Quicklaunch
Yep, very true. My notes, if you find them inspiring:
https://docs.google.com/document/d/1tD8H8B4Umfmqf-8uOH2zoR72...
I think the oil derrick idea was a bit crazy (why make the problem harder than it has to be?), but the concept is sound provided that the rockets are fairly inexpensive.
I think the idea of launching to an arbitrary orbit appeals to engineers, but economically it would be more efficient to launch to a common orbit, and use cheap fuel to change orbits later if necessary. Of course, in-space refueling is only in the concept stage (but getting solved!).
To get above 6km/s, the only way I know of would be to use induction tracks (see Lawrence Livermore patent in doc). The original problem with the EM methods was getting high power switches to work repeatably. They used to cost a fortune, and last only for 10s of cycles. However this problem was solved by a completely different industry in the last couple of years (connecting wind power to the grid), and now you can get them cheap on Alibaba.
The major difficulty, actually, would be: 1) Sound pollution (not many places have high mountains, easy industrial access, and no local population). 2) Hypersonic drag (which is quadratic with velocity at that reynolds number). This is half as hard at 6km/s than 8km/s.
Re: We need a better way to get to space
#60www.et3.com gradually leading up to the top of everest, jettisoning the capsule (6,500 km/h (4,000 mph)) to break out of the atmosphere. I have not done the math, physics, etc on this, but it's an interesting idea worth exploring. But that said, do we really belong in space when we cannot care for our own? Wouldn't that be akin to giving sugar to ants? only multiplying suffering and cruelty exponentially in space? Pe…
Interesting, let's say it should be our first priority, how does that translate into action?
Please remember that mobilizing large amounts of people towards a goal is hard problem, specially when the goal involves copious amounts of research and experiment.