Quote from: bradjensen3 on 08/09/2017 11:45 pm...It is nuclear powered...Quote from: Asteroza on 08/11/2017 12:05 amQuote from: bradjensen3 on 08/10/2017 08:03 pmOf course, my whole argument and proposal is based on the idea that water is not precious and scarce on the Moon...... The water is too useful for the general space economy as a hydrogen source Why use the hydrogen? Oxygen is a gas and it expands when heated. The ISP would be lower but there is more than 1022kg of oxygen.
...It is nuclear powered...
Quote from: bradjensen3 on 08/10/2017 08:03 pmOf course, my whole argument and proposal is based on the idea that water is not precious and scarce on the Moon...... The water is too useful for the general space economy as a hydrogen source
Of course, my whole argument and proposal is based on the idea that water is not precious and scarce on the Moon...
You said you know some math, stopped short of doing calculus.
So you guys still don't think someone could launch a rocket from the Moon and pick up a payload in the upper atmosphere of the Earth?
It seems to me that you are pulling one of my tentacles but I don't know for sure which one.
Quote from: bradjensen3 on 08/11/2017 06:11 amSo you guys still don't think someone could launch a rocket from the Moon and pick up a payload in the upper atmosphere of the Earth? No, not even close with current technology, and if you had the technology to do it, you wouldn't need to because RLVs from Earth would be easy.What you are suggesting requires that you send a full sized orbital LV (think of something like Falcon 9, Atlas 5, Soyuz...) from the moon, fully fueled and bring it to stop in the upper atmosphere.If you want to do it without dropping stages every mission, it needs to be an SSTO, which is something we've never built.You have suggested aerobraking, but coming from the moon, that means you need heat shielding equivalent to the Apollo vehicles. Even from LEO, you need shielding equivalent to the Shuttle. But your vehicle still needs a mass ratio on a par with things like Falcon 9 (or much better, if it's single stage), which have no heat shield.If you decide to brake propulsively instead, your braking rocket needs performance equivalent to putting that fully fueled LV into orbit.There are a whole lot of other problems, but hopefully that gives you an idea why people like Jim who actually work on this stuff dismiss it out of hand.
Oh yeah, I know. I'm surrounded by engineers but I should learn to be one myself. I Kant expect you guys to all become philosophy majors overnight.
From what I have read, something like 95% of the rocket fuel used on an Earth based rocket is spent getting the payload to the point where it can be accelerated to orbital speeds. To me that says rocket fuel in orbit is worth 20 times as much as rocket fuel on the Earth's surface. Therefore unless it costs 20 times as much to make rocket fuel on the Moon and deliver it to Earth orbit, the idea has merit.And that's only the cost of the fuel.
If I don't need a rocket nearly that big to get to the Moon from Earth orbit, why would I need one that big to get back, particularly when I can use aerobraking to slow it down when I get to Earth orbit.Why would you ever want to bring something to a stop in the atmosphere? I made the comment that you don't have to capture the payload at 7 km/second, and now we are talking about coming to a stop in the atmosphere?
If I am not planning to do a re-entry of the entire rocket, why do I have to do heavy duty aerobraking all at once? Can't I do something simpler by aerobraking on multiple orbits?
You are telling me that even if the Moon was full of free rocketfuel, it still wouldn't be worthwhile to lift stuff out of the Earth's atmosphere with it.
Although I am now wondering if that is what the Apollo lunar lander did with the command module since the lunar lander then impacted back on the Moon's surface. When it reached the command module it must have reduced its speed temporarily, which was regained when the command module ditched the lunar lander and then accelerated back to orbital and eventual lunar escape velocity.I don't remember Walter Cronkite explaining it in that much detail at the time.
Quote from: bradjensen3 on 08/11/2017 07:43 pmFrom what I have read, something like 95% of the rocket fuel used on an Earth based rocket is spent getting the payload to the point where it can be accelerated to orbital speeds. To me that says rocket fuel in orbit is worth 20 times as much as rocket fuel on the Earth's surface. Therefore unless it costs 20 times as much to make rocket fuel on the Moon and deliver it to Earth orbit, the idea has merit.And that's only the cost of the fuel.No, you got your facts backwards, the 95% is mostly spent accelerating it to orbital speeds, not getting it to the point where it can be accelerated.The 20x price only applies to refueling in LEO using lunar sourced propellants, which is not a new idea.Your concept involves either slowing down, which doesn't save fuel, or a high speed rendezvous, which you have proposed no practical method of. And yes, there are in between options if you want the worst features of both concepts.
... Is it most efficient way to get stuff of the ground? Almost certainly not. Is it the most sustainable way to do it? I think so.
So how would you guys get things off the Earth, using non-Earth-based resources?
Quote from: bradjensen3 on 08/14/2017 07:10 pmSo how would you guys get things off the Earth, using non-Earth-based resources? You don't. You use Earth-based resources to get things off the Earth. Bringing non-Earth-based resources into the Earth's gravity well to get out of the gravity well makes no sense.
So far I hear people telling me 'it's impossible' when I think what they mean is 'it's not economically sensible in current conditions.'