Now you take the rocket in low earth orbit, and slow it down while firing the rocket at an angle to retain its altitude. You drop a big, many miles long bungee cord down with something on the end of the cord that can maneuver and hook up to the payload. Then you accelerate the rocket back to orbital speed or even back to the moon, while reeling in the payload.
Not possible. Rockets are not helicopters. Can't "slow it down while firing the rocket at an angle to retain its altitude."This is just nonsense
Yes of course it takes the same energy to accelerate the payload into orbit, but you don't have to burn 95% of your propellant to get the rocket off the Earth if you start from the Moon.As I said, the Space Bungee rocket would not be in free fall orbit. It could be travelling any speed you want. You don't have to hook up at 7 km per second. You could be going 50 miles an hour if you want.
Since we now know there is subsurface water all over the Moon, not just fossil water in shaded craters at the poles, water is not a scarce item.
You might even get the government to give the company a small tax credit for supplying you with the methane.
Quote from: bradjensen3 on 08/09/2017 05:59 amNow you take the rocket in low earth orbit, and slow it down while firing the rocket at an angle to retain its altitude. You drop a big, many miles long bungee cord down with something on the end of the cord that can maneuver and hook up to the payload. Then you accelerate the rocket back to orbital speed or even back to the moon, while reeling in the payload. Not possible. Rockets are not helicopters. Can't "slow it down while firing the rocket at an angle to retain its altitude."This is just nonsense
Let's see how gently and patiently we can debunk it, though
There is nothing dodgy about heating water and using it as reaction mass.Yes of course it takes the same energy to accelerate the payload into orbit, but you don't have to burn 95% of your propellant to get the rocket off the Earth if you start from the Moon.As I said, the Space Bungee rocket would not be in free fall orbit. It could be travelling any speed you want. You don't have to hook up at 7 km per second. You could be going 50 miles an hour if you want. I'm not talking about shooting a rocket to the Moon, filling up with reaction mass, then doing the space bungee thing. The Space Bungee rocket would start from the Moon, and return to the Moon for reaction mass refills. If those guys are right about the millions of microcomets impacting the Earth, it might be possible to refill from then. But the safe bet is to use water from the Moon.For that matter, if the payload had a nuclear rocket engine, you could use the Space Bungee rocket as a tanker and deliver a water reaction mass to the payload. Since we now know there is subsurface water all over the Moon, not just fossil water in shaded craters at the poles, water is not a scarce item.
There is nothing dodgy about heating water and using it as reaction mass.
Trying to stay in "orbit" going 50 mph would run you out of propellant very quickly. You'd need way more propellant than just launching normally from Earth.
Quote from: meberbs on 08/09/2017 08:37 pmTrying to stay in "orbit" going 50 mph would run you out of propellant very quickly. You'd need way more propellant than just launching normally from Earth.I am not suggesting that the rocket hover, or go 50 miles an hour for any period of time, if at all. My point is that the rocket doesn't need to be in free fall. The interaction between the Space Bungee rocket and the payload doesn't have to be at 7 km/second. Once again, the underlying notion is to raise a payload using a balloon into the upper atmosphere. Then use a rocket coming form the Moon into low Earth orbit to basically swoop in and grab the payload, and accelerate it into orbit using fuel from the Moon.
I am sorry I got off into side discussions with people who think rockets can't hover and can only go one speed.
It seems to me that there are two factors that lead to expense in putting a payload in orbit. The first is atmospheric drag, and the second is gravity.
The amount of work it takes to accelerate that mass is the same, but it is much cheaper to do that work using a rocket fuelled on the Moon, than using rocket fuel hauled from the Earth's surface.
Thanks for the suggestion to look at the skyhook stuff. Sounds like a fantasy to me.
Well I guess that explains all the Harrier crashes...
Of course a rocket can hover. It isn't what you would normally do.
If you think it is nonsense that a rocket can hover, we aren't speaking from the same physical framework.
Once again, the underlying notion is to raise a payload using a balloon into the upper atmosphere. Then use a rocket coming form the Moon into low Earth orbit to basically swoop in and grab the payload, and accelerate it into orbit using fuel from the Moon.
A harrier is not rocket and does not hover above 5000ft
A rocket basically can not hover at orbital altitudes
That is correct. You don't understand the basic physical framework and orbital mechanism There is no stopping in space without massive thrust and propellant quantities many times our capabilities.
Now we move from the Moon's surface to low earth orbit. For efficiency sake we have a smaller stage, a skimmer, that decelerates in the upper atmosphere, hooks the payload and accelerates it back to orbital speed. The skimmer then connects back to the Moon rocket, perhaps to repeat its process several times. It does not matter if the total work done is more than the work done by blasting the payload off the Earth's surface into orbit, because the fuel is far cheaper, the rocket is reusable, and the effort of getting the rocket and reaction mass into orbit from the Moon is a tiny fraction of what it would be from the Earth's surface.With abundant water on the Moon, the economics of space travel will change.
Which is basically impossible. 1. Just starting from the point of grabbing the payload, the rocket is going close to the size of existing rockets to push the spacecraft and payload back "towards" the moon. The altitude saves only a few percent propellant. 2. Conversely, the propellant to slow down the spacecraft propulsively* to grab the payload is also going to be near the same amount it took to get to the moon. 3. So now but since the spacecraft which is on a (large) return rocket slowed down to pickup the payload, the rocket that is doing #2 has to be much more massive.* ignoring any aerobraking
Doesn't matter about water on the moon, the link up wont work
Okay the skimmer aerorbrakes down to near nothing speed and pops up its own hydrogen balloon. It drifts lowly and peacefully over to the payload. A big robot arm takes the payload and puts it inside the pod bay. HAL then accelerates from zilch to 7 km per second into orbit. (I don't really think it is necessary to do it this way but the point is I do think something can be engineered.)
I don't care so much how much propellent it saves. I just want to get the payload to where I can accelerate it with propellant from the Moon, not the Earth. In many cases the payload will be going to leo or geosynchronous orbit. At least at first.
there is not as much "abundant" water on the moon as you think and it doesn't matter, it doesn't work. There is no way of taking a rocket from the moon and picking up a payload within the earth's atmosphere. It doesn't matter if the propellant is free.
Let's concede for a moment that I'm an ignorant loon. You think it is physically impossible to send a rocket from the Moon and retrieve a payload in the earth's atmosphere?
I have no intention to 'stop in space' whatever that might mean. I appreciate everyone explaining that I can't do what I never intended to do.
It does not matter if the total work done is more than the work done by blasting the payload off the Earth's surface into orbit, because the fuel is far cheaper,
the rocket is reusable,
and the effort of getting the rocket and reaction mass into orbit from the Moon is a tiny fraction of what it would be from the Earth's surface.
...1. I don't care so much how much propellent it saves. I just want to get the payload to where I can accelerate it with propellant from the Moon, not the Earth. In many cases the payload will be going to leo or geosynchronous orbit. At least at first....
So let's say the bungee cord version is on hold. Instead we have a rocket on the Moon. It is nuclear powered. No I don't think nuclear power is magic and has unlimited energy. It uses water for reaction mass.Now we move from the Moon's surface to low earth orbit. For efficiency sake we have a smaller stage, a skimmer, that decelerates in the upper atmosphere, hooks the payload and accelerates it back to orbital speed. The skimmer then connects back to the Moon rocket, perhaps to repeat its process several times. It does not matter if the total work done is more than the work done by blasting the payload off the Earth's surface into orbit, because the fuel is far cheaper, the rocket is reusable, and the effort of getting the rocket and reaction mass into orbit from the Moon is a tiny fraction of what it would be from the Earth's surface.With abundant water on the Moon, the economics of space travel will change.
Which is a classic reverse bomber approach. If you have stupid amounts of fuel you can pick up small popup payloads occasionally. But the scenarios where you can even have a reverse bomber begin to approach contrived; you need an extensive propellant production infrastructure in orbit and/or on the moon which implies a significant space presence, which if have such a thing, means you aren't picking up small payloads rarely in a functioning business economy or a massive national program.
So the story starts sliding towards things like picking up payloads from uncommon/unscheduled/unfixed places, or it's a fiction about terrestrial apocalypse lunar survivors picking up something/somebody from an earth with zero space infrastructure. Otherwise the rational economic choice for a major space transportation system is a high throughput infrastructure system such as momentum exchange tethers which can reduce the unit cost.
Blowing through several hundred tons of precious lunar water...
(rather than MX tethers using lunar surface slingshot chucked sandbags) to pick up one guy is an egregious and vulgar display of kinetic energy, which is why a reverse bomber tickles my redneck rocket engineer funny bone but not much else. There's a pull quote from the book "The Cassini Division" that applies well here, "That is the most shocking waste of delta-vee I have ever seen".
bring water from the moon in Space Zeppelins
Quote from: bradjensen3 on 08/10/2017 12:04 ambring water from the moon in Space ZeppelinsYour ideas are intriguing to me and I wish to subscribe to your newsletter.
Quote from: bradjensen3 on 08/10/2017 12:19 amLet's concede for a moment that I'm an ignorant loon. You think it is physically impossible to send a rocket from the Moon and retrieve a payload in the earth's atmosphere? It is.https://forum.nasaspaceflight.com/index.php?topic=42119.msg1635027#msg1635027https://forum.nasaspaceflight.com/index.php?topic=41207.0Need means of propulsion other than chemical or NTR.And it is silly to bring "abundant" lunar water (even if it was free) deep into the earth's gravity well and atmosphere. There is water already available. There is no advantage.
No I am not proposing anything that violates physical laws or includes magical engineering.
Now everyone who assume that water is scarce on the Moon is probably wrong.
Of course, my whole argument and proposal is based on the idea that water is not precious and scarce on the Moon. I think I have mentioned that several times. Your -as far as I can tell- unjustified assertion that water is scare on the Moon negates everything I am saying. While you might be with the majority in thinking that there is hardly in water on the Moon, that does not make it so. Until the Clementine returns, people thought there was virtually no water on the Moon. Based on the two bodies we have actually set foot on, the Earth and the Moon, and the one that we have observed most closely and deeply, Ceres, water seems to be everywhere. (The Mars probes so far are pretty much robot dune buggies.) If it were me, I would be looking for a planetary process that generates water. The notion that most or all of the water on the ground came from the sky is hard to defend I would think.
...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...
My proposal is water heated by a small nuclear reactor.
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.
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.'
Part of the problem with this discussion from my point of view is that you aren't accepting my central premise for the point of this discussion, that water is plentiful on the Moon. I understand this is not currently an Established Fact, but I think the possibility that it soon will be is enough to start thinking about what to do with it.
Recent water on/in the Moon article https://phys.org/news/2017-07-scientists-spy-evidence-moon-interior.htmlNo, I wasn't thinking of extracting hydrogen and oxygen from bauxite on the moon. Not That There's Anything Wrong With That.