Steel

Thanks! Rocket nozzles aren't quite that simple unfortunately. Generally you can get most of the potential thrust from a short nozzle with a well designed bell contour, however increasing the length can also improve your thrust slightly. The size of this increase is dependent on how good the nozzle is, so generally you'll see a larger effect for simple nozzle (i.e conical) than for more complex ones. However, the biggest thing that changes with nozzle length is ISP, since a longer nozzle has a larger exit area, thus a larger throat-to-exit area ratio and thus a faster exhaust velocity. Mass flow rate is fixed for any given combination of chamber pressure, throat area and outside pressure, so the nozzle has no effect. Basically, it scales with exhaust velocity, which is related to thrust and ISP. It also differs depending on the design of the nozzle, but that's another story.

You'll have to define your variables to stop everyone guessing. I'm assuming mass flow rate, thrust and something to do with pressure?

Without a magnetosphere it would be blasted away pretty quickly, though since it's likely that it never really had one then it's very difficult to say. Technically, the moon still has a very tenuous atmosphere, so I guess it also depends on where you draw the line.

Ok, I was wrong on that one then. The average velocity would be below escape, but a significant proportion of the high velocity tail of the energy distribution would still be above it. There's also the non-thermal mechanisms such as the solar wind to contend with too.

As @Green Baron mentioned, the average molecular velocity would be way higher than escape velocity, so it would go pretty rapidly (though how the atmosphere would get there in the first place is an interesting question)

As long as by "quantum-mechanical" you mean "relativistic", then yeah I agree

If it's a completely different mission architecture and not just an update of the original, I'd start a new thread anyway to avoid confusion

Stresses are the main concern, but since the nozzle extension alone for the M1DVac is about the same size as an entire M1D system- and has an exit area about 7 times larger - drag and aerodynamic effects are also a big concern. (see image below for reference) Shortening it doesn't really work too well, you'll lose so much ISP that you'll end up having to carry a lot more fuel. Obviously the worst case is if you get rid of the whole extension, which adds around 40 s of ISP, so you'd need to carry around 15% more fuel to compensate. This subsequently means the first stage won't push the second stage as far or fast, which in turn means you have to carry even more fuel e.t.c.

Isn't this argument a bit cyclical? For this to be worthwhile, the recovery spacecraft and it's launcher must be fully reusable (otherwise you need a recovery spacecraft to recover the second stage of the recovery spacecraftcraft and so on forever). Surely though, if we have the capability to create a fully reusable recovery craft, then you could just made slight changes to it and turn it into a fully recoverable launcher and then eliminate the need for a recovery craft in the first place?

It's pretty good, since all imperial units are now defined as an exact number of metric units

1) Hard to say, since these are alien bodies (and thus could/will work completely differently to our bodies). If they are very close to humans then they're stuffed (for want of a better phrase), since we currently have no way of re-animating frozen human bodies unless they have been incredibly carefully looked after with life-support. If they're nothing like humans then ther'es no way to answer the question, since we've never seen any advanced beings that are not like humans. 2) There's no biological limit that we're aware of. The sort of life you're talking about here is so unlike anything we've ever encountered that we simply have no data to answer that question I'm afraid.

Have you done the calculations to get the throat area, chamber volume e.t.c to roughly the correct size?

There's absolutely no guarantee that it will ever be cheaper (and equally no guarantee that it won't be cheaper). There's no way to predict it because nothing like this has ever been done before.

If you plan to use air (probably not the best plan, since its only 21% oxygen) you'd need a compressor set up to actually get the required flow rate into the chamber. Gaseous oxygen is not too hard to get hold of, and would serve the purposes of a rocket engine far better. Also, there are existing examples of people who have done DIY GOX rockets to help you along. Also, if you haven't seen this thread, I'd highly recommend checking it out, it's pretty extensive on calculations and such.

Unfortunately there aren't any nice analytical equations for those things. You end up with differential equations, which you (or a computer) would have to integrate at small intervals along your ascent trajectory in order to get the answer. I'm assuming you're talking about the rocket equation? In that case there are two masses, the full mass (including any additional stages) and the empty mass (i.e the mass without propellant)

Unless the amount of gas is large enough that it can effectively transmit sound to you, then no. No. Depending on the amount of potentially explosive stuff onboard it may reduce into to very small pieces, but most stuff that boosters are made of do not combust, so there is no way that they can burn up completely. Most boosters will break up into small pieces.

You are implying that ATC and air transport companies are involved in widespread bribery and corruption, so I'd be slightly careful

There aren't many "parts" to the rocket equation, it is very simple as far as rocket science goes and you can derive it directly from conservation of momentum. Unless we have the laws of physics completely wrong, it should be pretty correct!

I don't blame you. After all, Einstein wasn't particularity satisfied with quantum mechanics! It's unintuitive, complicated and difficult to explain; even with a physics degree I've barely scratched the surface. No problem, I enjoy talking about his stuff with people. Also, by trying to answer your questions, you've helped me clear up some things in my own head that I didn't completely get before, so thanks!

It doesn't. The point i'm trying to make is that in quantum systems, the particles don't behave as individual particles, the system acts as a whole. The whole system has a possible set of outcomes based on its current set up, external forces e.t.c, and each outcome has a certain probability of occurring. When you leave the system alone and come back to observe it, it will be in one of these outcomes. There are no interactions between members of the system in the same way as you get in classical systems. The PEP essentially means that in these systems, it will never be possible (i.e the probability of it occurring is exactly zero) for there to be a system outcome where two fermions are in the same quantum state.

Believe me, I wish this were simpler! Essentially, the second electron cannot occupy that filled state because the wavefunction of the system (basically a bit of maths that determines the probabilities of each possible outcome of the system, given its current conditions) literally does not allow another electron to exist there. You may have heard that quantum systems behave probabilistically, well the PEP basically means that there is zero chance (that is exactly zero, not negligible, not incomprehensibly small, literally zero) that the second electron will be found in that same state, it can only ever be found in another state. The particles are not interacting to tell each other anything, its just that the system as a whole has a zero chance (a statistical impossibility if you will) that you will see the second electron in that state.

It's not sidestepping the issue, I'm just trying to explain it to you without lying (a la popular science) about what is actually happening (or at least what we think is happening). What you're saying about this effect being caused by interactions of particles with other particles is what is wrong with your statement. In a quantum system, you do not have distinct particle interactions. The system behaves as a whole, with the outcome of events determined by the state of each particle within it. It's a subtle difference, and one that is near impossible to get across to someone who hasn't studied the maths behind quantum mechanics which determines how the whole thing behaves. The long and the short of it is that degeneracy pressure is not caused by a "force" due to interactions between the particles, its is caused by the intrinsic behavior of the degenerate system as a whole. Maybe think of a white dwarf or neutron star not as a collection of electrons or neutrons, instead try to see it a one huge quantum blob. This "blob" has intrinsic behaviors that are totally different to that of a collection of normal matter and largely unrelated to the classical behavior of the stuff its made up of.

It only appears to be a force from a layman perspective, it is not actually a force. In objects with densities as high as in white dwarves, the collection of matter that makes up the object basically ceases to behave as a group of distinct particles in continuum and becomes one large quantum system, which we call degenerate matter. In a quantum system particles may only have certain energies corresponding to certain quantum states. One property of fermions in a quantum system is that they cannot share these quantum states, thus to add another fermion into the same volume, it must occupy a different state with a higher energy. This means that compressing degenerate matter requires energy, and this behavior manifests as degeneracy pressure that opposes gravity, but isn't a force. This is one of those things that makes you suddenly realise just how weird quantum mechanics is, when a quantum system can resist gravity without an opposing force.

There is reasonably good evidence that it exists in some form [1], if we assume that GR is somewhere close to full description of gravity. Otherwise GR is wrong (or at least incomplete) and we have very little understanding of how gravity truely works. Assuming one of the current theories of it is correct, no one has ever seen it and no one ever will. This is because, by it's definition, it does not interact with light and so cannot be seen or detected using electromagnetic radiation. [1] https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence (I know it's wikipedia, but it's good enough for the purposes of this discussion)

The force that keeps us from falling into the centre of the Earth is just the mutual electromagnetic repulsion of the electrons in the atoms, not the PEP. The PEP only kicks in for super dense objects like white dwarves. The PEP itself is not a force and nor does it act like one, it's just the slightly hand-wavy popular-science analogies that make us think it is a force. The PEP is actually a fundamental behavior of fermions in quantum systems. This thread explains quite well.