Happy Moon Day!

[Az]

It doesn't mean that it has to, of course. But from what I can see from overseas ( might not be a correct vision ) - they usually do.

the Apollo program yes - US defense spending - no. My basic point was that if I was a citizen of the US, I'd prefer the country's tax dollars spent on an enormous, too-costly, space exploration scheme, rather than pouring hundreds of millions of dollars, many of them into building **** like the F-22, and others, especially, since the needs of the US wrt the military conflicts they are fighting aren't fullfilled by those. ( Of course, war in Chinahahahahaha)

[Drake Tungsten]

F-22

F-35

[KrazyHorse]

the Apollo program yes - US defense spending - no

NASA is a defence agency?

???

[DanS]

But there are is probably a ~ 1.5 order of magnitude reduction in chemical Earth-LEO launch prices that is low hanging fruit.

Dude, there's almost that much with a 60% improvement in exhaust velocity on a relatively slow flight to a nearby planet. If you want to talk about Mars in 4 weeks or the Belt in under a year then the payoff to exhaust velocity is much, much higher (it goes up literally exponentially with delta-v)

I've thought about this some... If you were to have the 60% improvement in exhaust velocity, would that require a one-year flight to Mars? Would you need a nuke reactor?

For the 4 weeks to Mars (AFAIK, probably more like 6 weeks with VASIMR), that would require a nuke reactor. There's some novel engineering needed to step around the pitfalls. We already have some backlash with just launching the RTGs. Admittedly, we haven't really thought creatively about the launch of nuke materials. F.e., I've never seen a launch escape system proposed for a probe containing nuke materials.

In any event, with a 6-week travel time, could you get in more than one one-way trip per annum per spaceship?

[DanS]

the Apollo program yes - US defense spending - no

NASA is a defence agency?

???

Well, let's be clear. Before von Braun was building Apollo rockets to launch men to the moon, he was building V2s to launch munitions onto London and Redstones to launch strategic munitions onto Moscow.

Post-Sputnik, Americans had a complex about Russian military technology. I wonder if those fears hadn't been sublimated with Apollo, we would have spent an even fantastically greater amount via von Braun on other useless military technology.

[KrazyHorse]

If you were to have the 60% improvement in exhaust velocity, would that require a one-year flight to Mars?

I have no idea what this means.

Exhaust velocity is a measure of spaceship mas times delta v per propellant mass

The problem is merely that high-throughput rate (high propellant mass per second) tech is chemical, and that has low exhaust vel and vice versa. Chem rockets give you very little delta v, but they give it to you all at once. An equivalent propellant mass ion driven ship gives you loads of delta v, but spread over way, way too long a time. With chem rockets you fire and forget. With ion thrust you boost all the way. If we can increase the rate at which ion thrusters burn through their fuel EVEN IF it costs us some of our total delta v gain then we still come out ahead. Or we can figure out a way to get higher exhaust vel chem stuff, even if it is impossible to burn through it as quickly as regular chem does. You only need the REALLY fast chem burns when you're lifting from a dead start deep in a gravity well. Once you're in orbit you can take more time. Burn for a week, it doesn't matter. The real insight is simply that total delta v only increases logarithmically with fuel load, but linearly with exhaust velocity.

[KrazyHorse]

Dan, re NASA and defence: I know the history. The point was that by Apollo Congress was appropriating for civilian space stuff as a separate item from military stuff. It wasn't all coming from the same defence budget, which appears to be what Az was claiming.

[KrazyHorse]

Dan, re NASA and defence: I know the history. The point was that by Apollo Congress was appropriating for civilian space stuff as a separate item from military stuff. It wasn't all coming from the same defence budget, which appears to be what Az was claiming.

[DanS]

I have no idea what this means.

I thought you had a particular technology and flight plan in mind for the 60% increase to some place like Mars.

If we can increase the rate at which ion thrusters burn through their fuel EVEN IF it costs us some of our total delta v gain then we still come out ahead. Or we can figure out a way to get higher exhaust vel chem stuff, even if it is impossible to burn through it as quickly as regular chem does.

I'm not disputing the math. Rather, I'm making a practical trade looking at proven technologies -- well, at least the good stuff in the lab like VASIMR is included as proven. Chemical propulsion is a known beast. It's relatively simple and clean compared to propulsion with a nuke reactor. As best we can tell, chemical propellants are reasonably plentiful at most significant way-points. If we can transport propellants out of Earth's gravity well with reusable rockets (resulting in a ~ 1.5 order of magnitude reduction in launch prices from Earth to LEO), chemical propulsion should be reasonably inexpensive and sufficient as main thrust for conquering the inner solar system.

(Admittedly, the asteroid belt is an interesting case. That's pretty damn far.)

That's not to say that electrical propulsion will lack uses in the inner solar system, in applications where nuke reactors aren't needed. And I would be perfectly happy seeing a viable reactor that minimizes the inherent negative points. But realistically at this point, nuke reactors on any transport are a strictly regulatory government-only affair -- not suited to use by the private sector.

[DanS]

By the way, I am interested in higher ISP chemical propulsion that doesn't use all the nasty chemicals. Almost no basic experiments have been done on chemical propulsion since the 1950s. And those experiments were focused mainly on getting us out of Earth's gravity well.

There might be something there. But for purposes of our discussion here, that's an unknown.