Bill Phil

Clone Wars is back for another season! The show was cancelled with two seasons left unmade. I don't about you guys, but this is really exciting to me. What are your thoughts?

None have ridden on flourine rockets either.

Well, some were crazy enough to think of nukes for propulsion... or at least got on board with the idea.

I don't think cost was the real issue. Governments have been the major funding source for rockets for decades. A higher propellant cost wouldn't be too much of an issue. The government can afford it. It likely was the handling issues and the costs and risks associated with them. And of course the risk of having large amounts of the stuff in a rocket. Heck, having large amounts of lox and lh2 were problem enough as it was. You can get more than 540 seconds of specific impulse with flourine and lithium with some hydrogen. If it has a high enough thrust to weight, this can allow SSTOs to carry significant payloads. But it's way too hard and dangerous to handle.

Trying to understand what others are thinking or how they would react is important. It's not an easy thing to do, though.

I honestly don't think chemical rockets will allow us to build up the necessary in-space infrastructure anytime soon. Even with BFR and the like. I think it may happen using chemical rockets next century. But they're just not capable enough. Bases on Mars? Maybe. Interplanetary civilization, as in colonies? Doubtful. Not to say I wouldn't like some really cool stuff to happen.

It may or may not. But in any case, Hermes is explicitly nuclear electric. At least in the book...

If I recall, Mir was supposed to have Soyuz derived modules, and not FGB modules. These would need propulsion to rendezvous and dock... Still not that accurate. A reactor, as part of a nuclear electric system, would.

You're not wrong... But not wholly right. If we know the youngest is a boy, we can only be in cases 2 and 4, still 1/2 probability. But the child we know the gender of can be either the oldest or the youngest. If we are asking how likely the second child is the same gender as the first, it's 1/2. If we're asking how likely is the oldest child the same gender as the younger, it's also 1/2. If we're asking how likely the two children are the same gender, knowing that one child is a specific gender, then it's 1/3. Are we asking the likelihood of both children being the same gender while knowing the gender of one child, or are we asking the likelihood of one child having a certain gender? It's up to interpretation.

Once in Berlin always in Berlin... The city that consumes ALL...

According to Mendel, the odds of two children in a row being sons is 1/4. It's slightly different, due to the slightly higher probability of having a son. However... we know that one child is male. We don't know if this one was the second or first child. Since the two events should be independent, 1/2, or around that. Like successive coin flips, knowing previous outcomes doesn't change future outcomes. Depending on how we find out that one child is a boy. Could be 1/3 as well, since one of the four possible pairs is ruled out, the pair with two girls. Oh, ambiguity!

This gives me an idea... What if we had a kind of fantasy world, that was realistic. We could have a whole "Lord of the Rings" style thing happen, and then a big reveal that the world is actually a generation ship on a thousand year journey to... say... Trappist-1 (why not?). Probably not a new idea, but then again, what is?

It really is a small world after all...

I'm more excited about Apollo 8's 50th later this year. Launch date coincides with my Birthday. What's cool is next year we get three lunar mission 50th anniversaries, two of which are landings. It's also kind of sad, though...

TTGL is great fun and way less dark. But I wouldn't call it a space mecha anime. Much of the action is on Earth without any spaceflight. Don't get me wrong, it's awesome. But... In UC Gundam, the majority of humans live in space. Not even on Mars or the Moon, but in rotating space stations. The technology is far more realistic, although the propulsion tech is pretty much impossible... like in most sci-fi.

With less mass you generally get less of an increase in velocity, assuming energy is the same. One fourth as much mass and you only get twice as much velocity. This means you get half the momentum in the exhaust, but you get more change in momentum per unit of propellant.

You appear to be unaware of Gundam.

The momentum isn't really the same, given the same energy. Solve for momentum in the kinetic energy equation. A higher velocity reduces momentum - as it is in the denominator beneath energy - and the lower mass being used for thrust reduces momentum as well, this also means that thrust, the change in momentum over time, would be less. Momentum is still conserved in the whole system though. Assuming the energy output is equal, then, at least for thermal engines, the exhaust momentum will be higher in the lower isp engine. One way of looking at it, although it may not be totally correct, is that the rocket gains more momentum, per unit of used propellant, when using the high isp engine as compared to the low isp engine. Less momentum in the exhaust means more momentum in the rocket, but also a lower thrust. Thrust is change in momentum over time, mv is momentum, the mass flow provides the m, exhaust velocity is v, and the mass flow also provides the time.

Lighter molecules have a higher average velocity for a given temperature. So there's that. For non thermal engines - like a mass driver - it doesn't really matter... Exhaust velocity is a measure of efficiency in one regard, that being how much of your rocket needs to be propellant/reaction mass. Exhaust velocity is equivalent to specific impulse (when used as impulse - change in momentum - per unit mass, which is dimensionally equivalent to velocity), and specific impulse (velocity) tells us how much change in momentum we get out of 1 kg of propellant. Thus, a higher specific impulse means less mass needed for a given change in momentum, meaning a smaller mass ratio. That's how it measures efficiency. Planes get an advantage, they measure change in momentum using the air taken in by the engine, but only measure the used reaction mass as the fuel carried on board, and not the air. They get to use air as part of their reaction mass. Saturn V used hydrolox on second stage.

@Scotius Helium-3 on the Moon isn't really worth it. You have to process billions of tonnes of lunar regolith to get a few tonnes of He-3, and there's not much reason to believe that He-3 will even be used, considering its rarity. More on-topic: There's water ice in shaded regions, but it may be better to extract oxygen from the regolith (it makes up almost half of it by mass), using chemical processes. Then bring in some hydrogen from Earth or another source. Hydrogen makes up a very small portion of water, by mass.

I was referring to the infrastructure they propose. Seems very Von Braun to me. There's not much evidence backing up the need for that size, even at 1g. It's just commonly accepted. Coriolis effects would be weirder on smaller structures... We'd need to study it more in depth, to find out the comfort issues. I do think that a pair of bolas would be a good intermediate system. Only real problem would be getting people to the rotating modules in a comfortable way.

@kerbiloid As long as all the First Ones leave afterwards, I'm fine with that.

Sounds like the book Inherit the Stars.

In real life? Either on the ground, and then launched in one piece, or launched in separate pieces. Mir used docking ports, while the ISS uses the Common Berthing Mechanism and docking ports. Berthing is generally more complex.

Well, yeah, I guess. Really it's cool cause you can go to other moons of the primary with dinky chemical rockets.