Steel

If I had to put money on it, skylon will fly 5-10 years after they demonstrate the engine actually performs as planned, assuming they get funding to develop the whole vehicle themselves and some huge Aerospace firm doesn't just buy the rights to the engine. Bear in mind all they have now is a pre-cooler I think 2020 might be a tad on the optimistic side

Because you keep saying that Pluto is "basically a planet again" with no evidence to support it.

Looks good, a quick look at the concept list suggests this would be great for anyone with a reasonable maths background (i.e knows their way around basic calculus and algebra) who want to learn the basics of orbital mechanics along with some other stuff.

Exactly my argument, you cannot regulate borders effectively without military force.

What's your source on that?

Let's not talk about "future crewed versions" of a design that is not even finalised for an unmanned prototype. And that's overlooking the fact that the engines haven't even been fully designed, built or tested and probably won't be for some time.

Yeah if you're interested you can read about the Black Arrow rocket, which was a British rocket with engines burning high test peroxide (i.e hihgly concentrated peroxide) and RP-1.

So let's begin, Pluto is definitely not "basically a planet again", it's a dwarf planet and will stay that way unless the rules are amended again. Secondly, Planet X is not 100% confirmed yet, it has never been observed and the evidence for it is not enough to call it a discovery yet. Thirdly, as mentioned above, it can very easily orbit the Sun, because that is how orbital mechanics work. Fourthly, since it's never been observed we don't know anything about it's composition except some guesses based on data and existing theory. Finally, we did not know about it because there was nothing to indicate anything was there until very recently. Uranus is the furthest out any planet had been found by deliberate direct observation. Neptune was only discovered because it's gravitational influence allowed us to know where to point a telescope to see it. Also, before new horizons, one of the most detailed pictures of Pluto we had was this. Then bear in mind that planet X is several times further away from us than Pluto and you get some idea of why no-one knew it was there.

Peroxide is nowhere near as bad as you make it sound, if stored correctly its pretty harmless. There are companies on the internet that will sell qualified buyers 80-90% "Propellant Grade Peroxide" in jerry cans loaded onto pallets. Also hydrazine is not used as a rocket fuel due to its propensity to detonate when just sat around. It may be toxic but it does not just explode at random intervals (especially when correctly stored), otherwise you would never even think about using it as a storable propellant in a missile (as it was all through the cold war).

Yes you can make it arbitrarily low, but not zero unless the velocity is zero. The point is that any object that moves (i.e has a non-zero velocity) through the atmosphere will always have work done on it by the atmosphere to slow it down. Under no circumstances is this energy stored in the system with the capability to be put back into the object later. The buoyancy of an object is unrelated to it's air resistance in this case. Also an object falling will have work done on it by the atmosphere, again you're confusing the issue by talking about rising and falling, which is a conservative system due to it being governed by gravity. If you take a space elevator and put it sideways (so that gravity is taken out of the equation) there is no way to move anything from one end to the other without losing energy from the system to drag.

Not true, work would be done by the atmosphere on the way down and on the way back up again by the atmosphere, which would require input of power to overcome. The net work done by gravity, however, would be zero. I'm aware of thought experiments as well as the use and value of simplifying assumptions. However in this case we are looking at an effect caused by an object interacting with the atmosphere, with the catch that this object has been hypothetically modified to not interact with the atmosphere in any physical way, so what does this show?

I'm fairly sure something interacting with the atmosphere via only conservative forces would break a fair bit of physics. I.e if you move an object to the ground and back up to where it started there would be no net work done on it by the atmosphere.

But that is just a false claim to history. Why would they be the best of humanity if they are from a nation hell-bent on claiming land on another planet with the intent to exclude others? Also historically explorers claiming new lands represent the worst of humanity, usually bringing disease and destroying cultures that have been around for years

But that is now when there is nothing at stake. If there is the possibility of claiming land then they go from friendly astronauts to explorers, who tend to have a fairly intense animosity towards their rivals

That's a shame, it has some great underlying themes despite some (at times) fairly poor writing. It also debates a little the merits and flaws of terraforming.

Why do these threads exist? There is no point discussing how something outside the laws of physics interacts with the laws of physics, because it doesn't make any sense. If you have a "completely frictionless projectile" how is it interacting with the air molecules to cause ram heating?

Also on a side note, if you have't already you should read Red Mars by Kim Stanley Robinson. Has some really interesting ideas about Mars colonisation, the role of transnational corporations and the idea of a treaty governing the settlement and exploitation of resources and whether it would be upheld at all.

But to be honest, the only reason borders exist on Earth is due to armed conflicts. How do you determine who's been where and who owns what? Do rovers count or just astronauts? And what is the incentive to cooperate once you've expanded?

OK, so what's to stop China (just an example, could be any nation) landing the first man on mars, claiming it as part of the People's Republic of China and claiming that any attempt to land on it will be trespassing/ a border violation/ an invasion?

Nice idea, although I feel that although the re-usable first stage has some heat-shielding, it would be no-where near enough to survive a full re-entry. Also, the issue with cross-feed is that it's never been successfully demonstrated, and even the F9H will not have cross-feed in it's first iterations, so the capability is a few years (at least) away.

You are right the the forces are larger at take off, but it's the direction of the forces that's the issue. Any rocket stage is strong in one direction (regardless of whether it's a booster or a core stage) which is vertically. As soon as you introduce lateral loads they are considerably weaker, to the point where landing on its side could cause catastrophic issues if not strengthened appropriately.

Just realised there's a little over-complication in my answer. Instead of using the equations for rmin and rmax you can just do as @Padishar said and use a = (Pe + Ap) / 2 to get the apoapsis. You only need the rmin and rmax equations if you want a number for the eccentricity.

Using vis-viva you can work out the semi-major axis of the orbit. Assuming r is the periapsis, you can rearrange the equation rmin = a(1-e) for e. you can then use rmax = a(1+e) to get apoapsis and vis-viva again for velocity. *This is an over-compicated solution, see my next post*

Yeah, you've misunderstood the question, which is: why is there not a bigger difference in the situation described?

That's how I understand it. How much of a difference does "pretty much the same" encompass?