Elite on Kickstarter...

[axel000]

Its true to the original but you are right, the chances of anyone ever actually building a station designed like that no matter how far in the future are remote. It doesn't make much sense. The rotational speed in the center hub would create all kinds of difficulty walking around never mind operating a cargo dock and refueling / rearming depot.

[Darkflame]

Pretty sure I read somewhere that as you enter the doc, theres some system that auto-rotates you as the ship does so the outer wall is "down" for the sake of your controls.

I suspect if we are ever seriously building B5-style sized stations, computer-controlled syncing movements would be rather trivial compares to the rest of the problems.

[pogo]

If it's rotating like that, and you want to park on the outside edge, I'm sure it will be not just computer controlled but robot manipulated. Something would grab you and move you into position.

Think of how we do it on Earth, if you want to go to the top of a building. You use a lift. You don't use a rocket. A rocket would be quicker, offer you more autonomy, and could operate anywhere. But a rocket is in comparison orders of magnitude more expensive to run. Because of this it's also far more dangerous and polluting, due to the volume of fuel needed and the speed with which it's expended – explosively basically.

And it's even worse in a space station dock. For one it's a vacuum, so your rocket jets have less to push against and have to work even harder. Also it's enclosed and crowded, so you don't want to be generating large clouds of exhaust gasses.

If we could we'd use something similar to get off Earth, a space elevator. It would be so much cheaper than using rockets that space travel would become routine. Problem is the distance is so great that we've no material (yet) that will stretch that far and not break or collapse under its own weight. But inside a spaceship it's an ideal solution.

[zip accident]

And it's even worse in a space station dock. For one it's a vacuum, so your rocket jets have less to push against and have to work even harder.

This is an utter failure to understand rockets. Rockets work by expelling mass at high velocity, whether they are expelling that into gas or vacuum makes no difference, by the time the matter is that far from the nozzle, it's spent, if there is a difference at all then the rocket would work better in a vacuum.

[Darkflame]

In either case, rockets wouldn't be appropriate in that environment.

Would ion-proposal be enough? You need something pretty gentle/subtle...but maybe not that subtle.

While from an energy standpoint elevator is always best, not sure how well it would work in this scenario. You could lift the ship to the center (that is along the axis of rotation)....but the ship really needs to provide its own "spin" by the time you let go (presumably from thrust given at the ends of its wings).

[Darkflame]

*ion-propulsion

[pogo]

And it's even worse in a space station dock. For one it's a vacuum, so your rocket jets have less to push against and have to work even harder.

This is an utter failure to understand rockets. Rockets work by expelling mass at high velocity, whether they are expelling that into gas or vacuum makes no difference, by the time the matter is that far from the nozzle, it's spent, if there is a difference at all then the rocket would work better in a vacuum.

I've had a look at it and you're right. Atmosphere doesn't help: the output of the rocket's moving too fast, so fast it doesn't bounce off air and push back on the rocket, it simply blasts the air out of the way. The only difference atmosphere makes is it gets in the way of smooth working of the rocket by introducing turbulence which makes it worse.

The other thing I was thinking is that rockets/craft descending in an atmosphere use it, instead of their rockets, to break them and slow their descent. But that only works at speed, whether it's lateral speed used to generate lift (the Space Shuttle's final stages) or going fast enough vertically to push against a heat shield / parachute (in the lower atmosphere). Not in a space station unless it's very big.

Still though this is all unnecessarily complex. Most likely space stations just won't rotate. They may have rotating bits for humans to spend some time in, but they'd be quite small. Once you've got zero gravity many things become easier; not just parking spaceships but building things, packing things, storing things, experiments involving heavy equipment. People coming off spaceships, especially for short times, might not want or be able to cope with normal gravity. Not rotating makes all sorts of things easier: communications, solar power, shields, weapons. Rotating means it has to be structurally much stronger and it has to be proof against things coming lose/being dropped and flying off into infinity.

[pogo]

While from an energy standpoint elevator is always best, not sure how well it would work in this scenario. You could lift the ship to the center (that is along the axis of rotation)....but the ship really needs to provide its own "spin" by the time you let go (presumably from thrust given at the ends of its wings).

The elevator mechanism would be part of the station, so is rotating with it if rotating. Once the ship comes in it's clamped to that which then moves the ship into position. It needs to be physically strong enough, but just enough to hold the craft in place as it can move it pretty slowly. It doesn't require much energy to do this, much less than e.g. rockets. In theory it would require negative energy to move the ship towards the edge, i.e. it could collect energy and store it/use it elsewhere.

(regular elevators do this: as they go down a counterbalancing weight goes up, storing potential energy. This is released, by the weight descending, when the lift goes up, so minimising the amount of power needed to move it)

Another problem. For a massive space ship having it come in and park in the rim of a space station would change its speed of rotation, by about the fraction of its mass of the station. Either the spacecraft or the space station would have to add some extra spin to compensate, on arriving and leaving. Easily done but another extra cost (as you'd have to burn fuel to do it).

[zip accident]

I've had a look at it and you're right. Atmosphere doesn't help: the output of the rocket's moving too fast, so fast it doesn't bounce off air and push back on the rocket, it simply blasts the air out of the way. The only difference atmosphere makes is it gets in the way of smooth working of the rocket by introducing turbulence which makes it worse.

All aero engines work by Newton's law of equal and opposite reactions. A propeller moves an aeroplane forward by moving a lesser mass of air backwards faster, birds wings (in propulsion mode) do the same thing, it's all about reaction, it may look like pushing, but it's actually about reaction and pressure gradients.

[Muttley]

Because the one thing "Elite" needed was for docking to be harder...!

It's actually much easier than in the original.

[Istar]

And it's even worse in a space station dock. For one it's a vacuum, so your rocket jets have less to push against and have to work even harder.

This is an utter failure to understand rockets. Rockets work by expelling mass at high velocity, whether they are expelling that into gas or vacuum makes no difference, by the time the matter is that far from the nozzle, it's spent, if there is a difference at all then the rocket would work better in a vacuum.

I was right in the middle of my own WTF? moment when I read your reply. Personally I would have added something about F=MA, but you got the job done.

[tufty]

This is an utter failure to understand rockets. Rockets work by expelling mass at high velocity, whether they are expelling that into gas or vacuum makes no difference, by the time the matter is that far from the nozzle, it's spent, if there is a difference at all then the rocket would work better in a vacuum.

I'm not sure that's 100% correct. In fact, I'm almost 100% sure you're wrong.

Rockets work, as you correctly point out, by direct application of F=MA; they accelerate a mass (their fuel) by combustion, and are thus propelled by the opposing force. In a vacuum, that's the only relevant force.

The same principle holds for jet engines, although jet engines take their oxidant and a significant amount of their accelerated mass from the surrounding atmosphere. And this is where I feel you may be wrong. Jet engines work not only by direct heating and acceleration of the air flowing though the engine, but also by entrainment of the surrounding atmosphere. Indeed, with the simplest possible jet engine (a valveless pulsejet, which is effectively a specially shaped resonant tube), adding an external passive "ejector" (a simple tube distant from the exhaust which increases entrainment), thrust can be augmented by a factor of nearly 2.5 (see Paxson 2002). The same can be seen in use on modern turbojets, which accelerate by entrainment 3 times or more air than they accelerate directly in the combustion chamber. 3x more mass accelerated by entrainment ~= 3x more force.

Ducted rockets have been shown to produce far more force than the equivalent unducted rocket, although the ducting required is heavy relative to the motor itself. And even an unducted rocket in an atmosphere will entrain a certain amount of the surrounding atmosphere with its jet, thus producing more force than the same motor in a vacuum. So no, a rocket doesn't work better in a vacuum.

[edit]

See also NACA Technical note 431, 1932, figure 3. Note not only that an augmented (with rather unoptimised ejectors) rocket motor produces up to 1.5 time the thrust of the same motor unaugmented, but also that the thrust developed by the unaugmented motor increases with the pressure (and therefore density) of the surrounding atmosphere.

</pedantry>

[pogo]

zip accident's right. I assumed rockets such as those used to lift our space vehicles worked by pushing against air, but they simply don't. They look like it but they're simply going slowly at first, as it takes time to build up speed, especially with fragile human cargo that can't stand many g. It doesn't take long for them to be moving through air at a great speed, making it even less plausible they're pushing against it.

Air's just too tenuous. You push on it it's going to get out of the way. Noisily, i.e. the pressure built up will generate turbulence which will act mostly to disrupt the smooth working of any device.

You can use air to do useful work, but only if it's at much higher effective pressure. If you're moving quickly enough, pressure builds up and you can use it to slow you down. Or you can pressurise it, as inside tyres. But moving at speed or even stationary trying to push on the air around you to make you move would be very ineffective.

[zip accident]

The same principle holds for jet engines, although jet engines take their oxidant and a significant amount of their accelerated mass from the surrounding atmosphere. And this is where I feel you may be wrong. Jet engines work not only by direct heating and acceleration of the air flowing though the engine, but also by entrainment of the surrounding atmosphere. Indeed, with the simplest possible jet engine (a valveless pulsejet, which is effectively a specially shaped resonant tube), adding an external passive "ejector" (a simple tube distant from the exhaust which increases entrainment), thrust can be augmented by a factor of nearly 2.5 (see Paxson 2002). The same can be seen in use on modern turbojets, which accelerate by entrainment 3 times or more air than they accelerate directly in the combustion chamber. 3x more mass accelerated by entrainment ~= 3x more force.

]Ducted rockets have been shown to produce far more force than the equivalent unducted rocket, although the ducting required is heavy relative to the motor itself.

That's a ram-jet I think. I'm not disputing that that only works in the atmosphere.

And even an unducted rocket in an atmosphere will entrain a certain amount of the surrounding atmosphere with its jet, thus producing more force than the same motor in a vacuum. So no, a rocket doesn't work better in a vacuum.

I'm unconvinced at this point that this isn't mistaken, if an unducted rocket produces thrust by moving atmospheric gas in the same direction as the gas stream from the rocket, how is that thrust applied to the rocket motor or the craft carrying it? It seems to me that it may well happen, but it's uncollected and wasted in turbulence behind the rocket, which does nothing for thrust. It would also depend inversely on the speed of the craft, once that reached mach one, there could be nothing, before that maybe pressure? but the pressure in front from motion would balance that I think, maybe except at zero speed?

[edit]

See also NACA Technical note 431, 1932, figure 3. Note not only that an augmented (with rather unoptimised ejectors) rocket motor produces up to 1.5 time the thrust of the same motor unaugmented, but also that the thrust developed by the unaugmented motor increases with the pressure (and therefore density) of the surrounding atmosphere.

I think I'm not seeing most of that page, there seems to be text cut off it at random, for instance the first block of photocopy ends:

... The results show that, although it is possible

I loved jetex motors, it was a sad day when they were effectively banned because the fuses might be useful to terrorists (unless the legislation has been repealled, the fuses are probably still illegal. Strange there's no mention of that these days, it made the radio one news back in the day (which would have been the 1970s).

[tufty]

Ducted rockets have been shown to produce far more force than the equivalent unducted rocket, although the ducting required is heavy relative to the motor itself.

That's a ram-jet I think. I'm not disputing that that only works in the atmosphere.

Nope. A ram jet is just (yet another) type of reaction motor, it's effectively an open-ended version of the combustion chamber of a turbojet.

On the other hand, you might be right. There's definitely additional work to be had from the exhaust jet of a reaction engine, but it may well dissipate uselessly in the absence of a thrust augmentor. In which case there should be no difference (in terms of thrust developed) between an unaugmented rocket operating in atmospheric conditions and the same rocket operating in a vacuum.

Oh, and I found the full NACA archive. Fascinating stuff in there.

Jetex was great, but I thought it was fuel toxicity and, umm, y'know, it being "a fucking rocket motor that could burn your house down" that got them banned, if they were actually banned at all.

If you want dangerous, though, you want an MEW 601. Totally fucking bonkers, they are.