Steel

But that misses the point of what a lot of people have been saying, there is (at least to lot of people) a fairly major difference between a planet and a moon that should be recognised it their names. I think the main issue here boils down to the fact that this naming system is mostly used by two groups who have wildly different needs from a naming system: 1. Planetary Scientists, whose argument goes something like "When you're studying the body itself, there's no fundamental difference between a moon and a planet, so why not call them both planets?" 2. Astronomers/Astrophysicists, whose argument goes something like "Of course they're fundamentally different! Just look at their orbits, one directly orbits the star, the other does not" The issue arises because these two view are fundamentally incompatible. We've had to decide whether to name them based mostly on the characteristics of the body or mostly on the characteristics of it's orbit, but the side that we've come down on won't make everyone happy. (of course current definitions do specify that the body must be gravitationally rounded, but is mostly based on orbital behavior)

As well as every single moon and spherical object in the solar system. To my eyes rather than change the definition of a planet, it would make more sense to change the name "Planetary Scientist" since they freely admit that they don't just study planets

Short answer I'm afraid: no. As @mikegarrison mentioned, unless you're doing brachistochrone trajectories (you're definitely not with an ion drive), any orbital trajectory where the impulse cannot be assumed to be instantaneous needs to be computed numerically.

See @VaPaL 's post above

It is?! Well I completely missed that part!

I think the reason it's not reusable is probably the issues getting something that big to reenter safely/be controllable in atmosphere going the wrong way.

I believe you're right. Interesting and completely off topic (hence in spoiler box) musing below:

Other than, engines, airframe, aerodynamic design, avionics, controls, passenger capacity, range and a few more I haven't though of, no absolutely nothing But seriously, as @Gaarst said above, just because they look similar doesn't actually mean they are the same in any way.

Privately-developed, not privately funded. EDIT: no I'm still wrong. I think most people just misquote "first privately-developed liquid-fuel launch vehicle" as "first privately-developed launch vehicle"

Yes, but those engine were not used at launch, they were glorified (and highly complicated) RCS thrusters. My point was that to launch the shuttle again you have to build a new fuel tank, to launch a F9 again you do not.

You could rewrite it as an energy gradient (you can do whatever you like!) but it would be incorrect. The whole heat of fusion thing is accurate, more energy in doesn't change the temperature above the melting point, thus doesn't change the heat transfer to the next wafer until it melts. Just to throw another major annoyance into the works, have you considered the fact that the heat capacity of materials changes with temperature? EDIT: not that you really need to, a reasonable average will get you close enough

I disagree. The way I (and I would imagine SpaceX) would argue it is as follows: SpaceX 1st stage: launch, land, inspection, refuel, relaunch. One fully self contained stage that can be (in theory) relaunched many times. Space Shuttle: launch, land, inspection, build a brand new external fuel tank, refuel, relaunch. "Stage" is not self contained, requires a new fuel tank to be built for every launch. By that logic you can see why SpaceX are claiming it's the first reusable stage. The shuttle orbiter being reused is a bit like that plan for the Vulcan to reuse the engines of the first stage, and ESA would definitely not claim that just saving the engines was reusing the whole first stage.

No rocket will ever be able to produce those conditions because the rocket would immediately destroy itself (any rocket with a 36000 K exhaust temperature would)

There's literally no rocket (and no mix of chemicals) that could produce those conditions. The wiki won't say because we know next to nothing about Jupiter's core. We think it's probably metallic hydrogen and we've made some guesses from that, but we have no solid evidence.

Regrettably I imagine that there is no magic formula, precisely because there's a lot of factors at play, all changing at different rates due to different things (as it looks like you're discovering). AFAIK the only way you're going to get an answer is numerical simulations (which is what it looks like you're putting together with your first principals stuff). Word of advice on numerical simulations, don;t try to do them on an Excel sheet, you'll just give you and your computer a headache!

So this is one of these threads that never actually goes anywhere because the question basically boils down to "what happens to the laws of physics when we violate the laws of physics to create a situation" and so doesn't really make any sense. Nonetheless: So, because the vacuum is inherently absent of most matter, there is very little thermal conduction (i.e no convection, so only heat transfer is via radiation), so not much would happen to the temperature of the ice. The pressure probably (and that is a huge unknown) wouldn't have too much of an effect either if this is just a small bubble inside a huge ice structure, so you'd essentially just have a vacuum chamber inside the ice. In this case, since you have effectively an infinite heat and pressure reservoir, the ice would melt and shatter due to the pressure. Not entirely sure what you're asking here. Almost certainly no way of knowing, considering my first statement!

But they can't afford a launch, see above:

The other problem you might get with a foam is the fact that it's not totally solid might mean it doesn't form a coherent shock out in front of it and so it just gets obliterated by aerodynamic forces/local heating of very thin bits of metal

Well if you looks a their share price its only a capital raise of about 25 million euros (I also have no idea who that Swiss auditor is, but they're completely insane). They still have nothing more than a concept and the rights to any money made if they ever get their concept to work.

Wow, I don't exactly know why but I'm blown away by those images!

That's fair enough. @Matuchkin The issue really boils down to the fact that as soon as you go into the depths of n-body dynamics it becomes quite ill-defined as to what being in an orbit around something actually means, especially since we don't really know if any given orbit is stable if we look far enough forward into the future.

Ok, maybe I was just a little being pedantic ( ), but your definition about being within the SOI/hill sphere/whatever else you want to call it doesn't work for all types of orbit, there are some in which the orbiting body is not in the SOI for the entirety of it's orbit.

Except the definition of a sphere of influence when it comes to gravitational computations is a sphere in space in which the gravitation force from a body is dominant and so all other gravitational forces can be neglected. It's a bit like saying the small angle approximation exists physically. If you can give me physical example of the universe ignoring the gravitational forces of some bodies then I'll be amazed. As @Gaarst mentioned above, Hill Spheres are things that do exist, and indeed they are not spherical!

Except a sphere or influence is a simplifying assumption to make computations easier, they do not exist physically.

Ok, time for some misconception busting! A Neutron star, much like black holes and other exotic phenomena, do not have any special gravitational effects. A 2 solar mass neutron star will have the same gravitational effects on our solar system as a two solar mass star or a two solar mass black hole (although I'm pretty sure you can't have a black hole with a mass that low), or any other object that has a mass the same as two Suns would. The only difference is when you get closer to a black hole or a neutron star the gravitational gradient is much larger than for a "normal object" because the mass is much more concentrated, so the surface gravity is much higher. However from a distance it acts exactly the same as anything else (at least gravitationally, a neutron star close by would probably sterilise the system with high energy radiation.