Author Topic: Earth to Orbit with a Space Bungee  (Read 5736 times)

Offline bradjensen3

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Earth to Orbit with a Space Bungee
« on: 08/09/2017 05:59 AM »
Earth to Orbit with a Space Bungee- Yes, I'm serious.

The recent discovery that the Moon has vast quantities of water leads to a different method of taking payloads into orbit.

Imagine if you will a rocket that has a small nuclear reactor for its energy source, and vast quantities of water for reaction mass. This rocket starts from the Moon, and returns to low earth orbit.

Meanwhile you take your payload and haul it up to about 100,000 feet with a hydrogen balloon. On top of the payload there is a big handle like an easter basket. Or something much more sophisticated than that.

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.

You don't have to lift the reaction mass from the Earth's surface.

You could burn some of the hydrogen to pressurize the remainder and reuse the balloon and hydrogen.

You could move a lot of mass into orbit quickly and cheaply this way.

Obviously I don't mean to use an actual elastic bungee cord, but you would use something that functions in a similar way.

Since the rocket remains in space, it operates efficiently and reduces drag losses to almost nothing.

Think about being able to put hundreds or thousands of people in orbit at once. Think of being able to stock a Moon colony and keep it supplied.

This is as close as we can get to a Space Elevator with current technology. We could start with inanimate payloads to make the engineering easier, and work our way up to moving people.

You could also park your rocket in a higher orbit and swing a much longer bungee as a pendulum thru the upper atmosphere  to pick up the payload.

The basic concept is to use water reaction mass obtained on the moon or elsewhere in space to do the work of accelerating payloads into orbit.
« Last Edit: 08/09/2017 06:05 AM by bradjensen3 »

Offline Flying Beaver

Re: Earth to Orbit with a Space Bungee
« Reply #1 on: 08/09/2017 06:44 AM »
Besides all the other issues associated with plans likes these (massive heating, shock, weight of a self supporting cable over a 50-100km+ distance, and (slightly) dodgy method of propelling the lunar spacecraft) the energy required to accelerate the total system of the ballon payload, propellent and engines up to 7~km/s is still the exact same as it would be for say a high altitude air launched rocket (why need stop by the moon?). The force from the tether/payload/winch is still countered by the engines, so the payload is literally dragged up to orbital velocity by the lunar spacecraft on some sci-fi strength cable (on some equally massive winch (which would start, to save obliterating the payload from acceleration, by unspooling at a rate 7 km of cable, per second).

edit: i'm tired and didn't have too much time to write this. Other will be able to debunk more in-depth with lack of current cable tech.
« Last Edit: 08/09/2017 06:52 AM by Flying Beaver »
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Offline Asteroza

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Re: Earth to Orbit with a Space Bungee
« Reply #2 on: 08/09/2017 09:16 AM »
Compared to a HASTOL or LEO rotovator paired with a popup rocket, this seems kinda hard to do. Search previous threads about reverse bomber/unbomber designs to get a feel for these kinds of designs, and the tradeoffs and assumptions regarding discrete vehicles servicing occasional payloads versus higher throughput "fixed" transport infrastructures like HASTOL. A lot of the assumptions don't line up well for reverse bombers.

A momentum exchange tether as infrastructure, using electrodynamic propulsion (effectively zero fuel), or waste rock mass delivered via mass driver from the moon (raw momentum exchange downwards), to recover momentum lost picking up payloads from earth, is much more efficient and stable but presupposes a large cargo stream to support that infrastructure. Note the rock mass can be used for shielding and concrete in orbit as well so it is not a true "waste" export from the moon. HASTOL can also be the first of many tethers in a "Lunar Railroad" network of momentum exchange tethers.

See Tran Cislunar Railroad

Water is a precious resource, I wouldn't want to blow it on earth local milkrun infrastructure where possible.

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #3 on: 08/09/2017 03:31 PM »
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.


Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #4 on: 08/09/2017 08:00 PM »
Most hydrogen gas is made from methane.

Methane itself is a lifting gas, although not as good as hydrogen or helium.

However, about 3% of all methane is flared at the wellhead because it is in a place where there is no pipeline or gathering system for it.

You could drive your payload to that well head and lift it into the upper atmosphere for very few dollars since they can't sell the gas to anyone else.

You might even get the government to give the company a small tax credit for supplying you with the methane.

Offline Nomadd

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Re: Earth to Orbit with a Space Bungee
« Reply #5 on: 08/09/2017 08:09 PM »
 Is that you Dmitry?

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #6 on: 08/09/2017 08:15 PM »

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

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #7 on: 08/09/2017 08:35 PM »

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

Well I guess that explains all the Harrier crashes...

Of course a rocket can hover. It isn't what you would normally do.

There are certainly multiple ways to engage the payload.

If you think it is nonsense that a rocket can hover, we aren't speaking from the same physical framework.
« Last Edit: 08/09/2017 08:49 PM by bradjensen3 »

Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #8 on: 08/09/2017 08:37 PM »
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.

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.

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.
Where do you get that from? Last I checked any water outside the poles is very low concentration, and possibly they were detecting hydroxyl salts, not water.

You might even get the government to give the company a small tax credit for supplying you with the methane.
Why would there be a tax credit for this? Remember methane is a powerful greenhouse gas, so burning it is generally better than releasing it.

Offline Lar

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Re: Earth to Orbit with a Space Bungee
« Reply #9 on: 08/09/2017 08:37 PM »

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

Agreed, as written it's not workable at all. Let's see how gently and patiently we can debunk it, though... and perhaps all learn something? If not, back to dead threads (it was there once already) it goes. (feel free to just ignore the thread if you can't be bothered)
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Offline whitelancer64

Re: Earth to Orbit with a Space Bungee
« Reply #10 on: 08/09/2017 08:42 PM »
The basic idea here is an old idea (unsurprisingly, there are only very rarely new ideas in space travel...)

https://en.wikipedia.org/wiki/Skyhook_(structure)

If you had a rocket that could "hover" relative to a stationary position on Earth for an indefinite period of time while remaining at an Earth-orbital altitude, you wouldn't need to bother with the complexity of a skyhook. That thing would have more than enough fuel capacity to be able to land on Earth and blast off back to the Moon without refueling.
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Offline Lar

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Re: Earth to Orbit with a Space Bungee
« Reply #11 on: 08/09/2017 08:45 PM »
Bradjensen: take a look at the post by Asteroza, and read the link they are pointing to. Also look up HASTOL and Rotavator, and the links others gave... and pay attention to the mass balances that have to be taken into account. Conservation of momentum can't be evaded.

Also when replying, it's good to quote posts (like this)

Let's see how gently and patiently we can debunk it, though

... the web interface posting mechanism gives you lots of tools, explore them. Helping your readers helps you too.
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Offline Ictogan

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Re: Earth to Orbit with a Space Bungee
« Reply #12 on: 08/09/2017 09:19 PM »
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.
You may not have to burn off any propellant to get the rocket off from the earth orbit, but you'll have to have more delta-V to get from the moon to LEO and back. And then you need the delta-V to tug something out of earth's atmosphere to LEO in addition to that...

Online hop

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Re: Earth to Orbit with a Space Bungee
« Reply #13 on: 08/09/2017 09:35 PM »
There is nothing dodgy about heating water and using it as reaction mass.
Water can certainly be used as reaction mass, but it's generally a low performance option. You seem to be assuming that a nuclear reactor provides essentially unlimited performance, but this is not the case. Nuclear thermal only provides moderate improvement over chemical rockets in the best case, and water is not the optimal propellant.

If you want to convince anyone that your proposal is viable, you need to define the required performance of the rocket and show that credible designs are capable of achieving it. What is the required delta v? What are the assumed ISP, thrust and mass fraction, and how do they compare with real systems that have been built or designed?

If you haven't done this with actual numbers, then you have no basis to believe that your concept is viable.

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #14 on: 08/09/2017 09:49 PM »

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.

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.

The basic idea here is to do the work of taking a payload into orbit using reaction mass not lifted off the Earth.

I agree that the amount of water on the Moon is not certain at this point. However recent news articles suggest it is relatively abundant.  I get much of my science news from phys.org.

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.

You reduce the drag by raising the payload into the upper atmosphere with a balloon.

The expense of gravity is basically the expense of accelerating the mass of the payload to orbital speed.

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.

By 'rocket fuelled on the Moon' I mean a rocket using water from the Moon as its reaction mass.

Thanks for the suggestion to look at the skyhook stuff. Sounds like a fantasy to me.



Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #15 on: 08/09/2017 10:15 PM »

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.

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.
See hop's post above for the list of things that you need to calculate to show that this is a viable concept.

I am sorry I got off into side discussions with people who think rockets can't hover and can only go one speed.
You missed the point of Jim's post, which was a more blunt way of saying what I did, what you described is not practical.

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.
Neither of those is the primary factor, most of the energy of a rocket launch goes into getting orbital velocity more than fighting the atmosphere or gravity. Your "slow down then speed back up" concept just makes this worse, and the balloon portion does not help with the primary issue.

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.
Again, work out the numbers. I can't see this helping if you don't keep the spacecraft carrying the fuel moving at orbital velocity, but this causes problems with the capture.

Thanks for the suggestion to look at the skyhook stuff. Sounds like a fantasy to me.
They at least have used real numbers, so while skyhook seems impractical to me, your concept is more of a fantasy than the skyhook concept.

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #16 on: 08/09/2017 10:53 PM »

Well I guess that explains all the Harrier crashes...


A harrier is not rocket and does not hover above 5000ft


Of course a rocket can hover. It isn't what you would normally do.
 

A rocket basically can not hover at orbital altitudes


If you think it is nonsense that a rocket can hover, we aren't speaking from the same physical framework.

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.


Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #17 on: 08/09/2017 11:10 PM »

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.


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

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #18 on: 08/09/2017 11:45 PM »

Well I guess that explains all the Harrier crashes...

A harrier is not rocket and does not hover above 5000ft

And bananas are not papyas. A jet powered mechanism can hover. A rocket-powered mechanism can also hover.  The thing I am proposing is not designed to hover.


Of course a rocket can hover. It isn't what you would normally do.
 

A rocket basically can not hover at orbital altitudes

not for long, anyways.


If you think it is nonsense that a rocket can hover, we aren't speaking from the same physical framework.
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.

.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.

I understand the orbital mechanism well enough to realize that free fall orbit and hovering are not the only two choices for locomotion.

[/quote]

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.



Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #19 on: 08/09/2017 11:58 PM »

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.

 Doesnt matter about water on the moon, the link up wont work

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #20 on: 08/10/2017 12:04 AM »


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

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.

2. Let's not ignore aerobraking, at least for the skimmer.

3. One would hope one rocket trip from the moon would do multiple or many bungee lifts before returning to the Moon. We don't care how big the rocket is on the Moon.

For that matter, why not a space station in orbit, bring water from the moon in Space Zeppelins, fuel up the skimmer and retrieve the payload.

Over and over again.

Don't think  'amount of propellant' or 'size of spacecraft'. Think 'dollars spent'.


Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #21 on: 08/10/2017 12:11 AM »

 Doesn't matter about water on the moon, the link up wont work

"Other than that, Mrs. Lincoln, how did you like the play?"

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.)




Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #22 on: 08/10/2017 12:13 AM »

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.)

No, that can't be engineered with chemical or NTR engines.  Chemical rockets don't have the ISP and NTR doesn't have the thrust to make it work. The mass of the water still has to be brought deep into the earth's gravity well


 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.


That will only work with payloads already in orbit. 

But there isn't as much "abundant" water as you think
« Last Edit: 08/10/2017 12:19 AM by Jim »

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #23 on: 08/10/2017 12:19 AM »

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 was just beginning to think you were warming up to the concept.

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #24 on: 08/10/2017 12:21 AM »

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?


It is.

https://forum.nasaspaceflight.com/index.php?topic=42119.msg1635027#msg1635027
https://forum.nasaspaceflight.com/index.php?topic=41207.0

Need 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.
« Last Edit: 08/10/2017 02:41 PM by Jim »

Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #25 on: 08/10/2017 12:22 AM »
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.
That is basically what you said when you used the only number you have mentioned so far: 50 mph. Even if just temporary this would lead to absurd fuel usage.

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,
Exactly how would the fuel be cheaper?

the rocket is reusable,
Ever here of SpaceX and Blue Origin? Fully reusable rockets will exist well before mining water on the moon will.

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.
Not true, even ignoring the deceleration to meat up with the payload (assuming it is all aerobraking by some magic). 2.74 km/s delta V to get from moon to LEO, and the gravity and atmospheric drag only account for about 1.3-1.8 km/s on a typical launch. It is more efficient to just launch it from Earth to that point, and a whole lot less complex. (Not to mention you still would be dealing with some of that air and gravity drag)

https://en.wikipedia.org/wiki/Delta-v_budget#Earth.E2.80.93Moon_space.E2.80.94high_thrust

Offline stefan r

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Re: Earth to Orbit with a Space Bungee
« Reply #26 on: 08/10/2017 03:43 AM »
...
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.
...

There is a good idea in there.   Read the link suggested by Asteroza: http://hopsblog-hop.blogspot.com/2016/08/tran-cislunar-railroad.html

A company in Seattle is already making your "bungee cords".  http://www.tethers.com/papers/JPC00MMOSTT.pdf

You do not need "propellant" from the moon.  If your "bungee code" is good enough for this project you can use it as a "sling shot".  If you shoot a rock with a sling shot you pick up the equal and opposite momentum.  If you had a sling shot material that could fling stuff at 7km/s then the mood rocks give you more deltaV than rocket fuel.  Currently manufactured "bungee cords" cannot get quite that much velocity. 

Offline Asteroza

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Re: Earth to Orbit with a Space Bungee
« Reply #27 on: 08/10/2017 04:21 AM »

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".
« Last Edit: 08/10/2017 04:27 AM by Asteroza »

Offline savuporo

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Re: Earth to Orbit with a Space Bungee
« Reply #28 on: 08/10/2017 04:31 AM »
MX tethers are looney, but fun to think about anyway

http://spacetethers.com/
Orion - the first and only manned not-too-deep-space craft

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #29 on: 08/10/2017 08:03 PM »

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.



This is why I am talking about using water from the moon. Mining water and using it directly in a heat engine would be the simplest way of using reaction mass from the Moon (except for microwave-sintered moondust in a magnetic railgun launched with a rotary slingshot - the rock rocket).


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.


i'm going to make separate post on why momentum exchange servers won't ever be built.


Blowing through several hundred tons of precious lunar water...


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.

(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".



All economically useful work is done in a wasteful fashion.
« Last Edit: 08/10/2017 08:38 PM by bradjensen3 »

Offline HailColumbia

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Re: Earth to Orbit with a Space Bungee
« Reply #30 on: 08/10/2017 08:30 PM »
bring water from the moon in Space Zeppelins

Your ideas are intriguing to me and I wish to subscribe to your newsletter.
-Steve

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #31 on: 08/10/2017 08:35 PM »
Why momentum systems will never be built.

Several of you have helpfully sent me links to skyhooks and beanstalks and other momentum and tether systems.

I've been reading these proposals for decades.

Here is my understanding of why such momentum systems will never be built.

1. At this point in time, the engineering involved requires materials technology that doesn't presently exist. Of course, with nanotechnology research, graohene and boron nitrid discoveries, this might change at some point.  I'm not holding my breath.

2. The consequences of any structural failure of the lower part of a skyhook or beanstalk would involve large scale human disasters.   The risk is far too great for any reward that is contemplated.

3. Skyhooks would involve hundreds of billions of dollars in costs once we have the materials. A beanstalk would cost trillions. Nobody is going to spend that much money on an untried system that also has problem 2.

4. Everything must go from low earth orbit. Every satellite will have to be at a geosynchronous point or beyond, because lower satellites and even space junk will eventually faceplant into the skyhook or beanstalk structure.

5. The certainty of new technology developments means the system could easily be obsolete before it ever gets completed.

Some of you have also mentioned the 'reusable rocket' revolution. While these chemical rockets can be reused in part, generally after a lot of cleanup and new parts replacement, they are at the wrong end of a very deep gravity and atmospheric-drag well.

Yes, if my assumption of cheap plentiful water on the Moon is wrong, then my proposed system will not work. I agree with everyone who thinks that.

No I am not proposing anything that violates physical laws or includes magical engineering.

You are right, I stopped studying math after calculus and I put my slide rule in a drawer in 1974.

I understand that is is fair to challenge my assumption of cheap and plentiful water on the Moon.

Everyone who assumed there was no water on the Moon is almost certainly wrong. Now everyone who assume that water is scarce on the Moon is probably wrong. We will know within a few years, don't you think?

Meanwhile, looking ahead at possibilities, I think it is interesting to say how would you lift payloads from the Earths surface using reaction mass from the Moon.

Also I think I misspoke in adopting someone else's 'Moon based propellant' term. Sorry. By propellent
i assume you mean chemically combining rocket fuel, which I am not talking about at all. My proposal is water heated by a small nuclear reactor. Reprocessing the water into chemical fuels would be a huge waste of time and money, except perhaps for some hydrogen peroxide with a tungsten catalyst for attitude thrusters.


Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #32 on: 08/10/2017 08:40 PM »
bring water from the moon in Space Zeppelins

Your ideas are intriguing to me and I wish to subscribe to your newsletter.

This made me smile, thanks. For some of my other crazy ideas about space exploration, see ceresprime.com
« Last Edit: 08/10/2017 08:45 PM by bradjensen3 »

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #33 on: 08/10/2017 08:44 PM »

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?


It is.

https://forum.nasaspaceflight.com/index.php?topic=42119.msg1635027#msg1635027
https://forum.nasaspaceflight.com/index.php?topic=41207.0

Need 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.

I will check out your links and get back to you.

Meanwhile, of course it makes a difference if you light up a nuclear rocket on the Earth's surface - not physically, but politically. Unless you can figure out how to launch a rocket based on hysteria, it will never get off the ground.


Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #34 on: 08/10/2017 09:26 PM »

No I am not proposing anything that violates physical laws or includes magical engineering.


yes, you are.  Anything that requires docking or mating at altitudes less than 80 miles or speeds above Mach 1 require magical engineering.

And there is no benefit bringing lunar water any lower than that also.
« Last Edit: 08/10/2017 09:29 PM by Jim »

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #35 on: 08/10/2017 09:28 PM »
Now everyone who assume that water is scarce on the Moon is probably wrong.

no, that is wrong.   water is still scarce on the Moon

Offline Stan-1967

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Re: Earth to Orbit with a Space Bungee
« Reply #36 on: 08/10/2017 10:59 PM »
Now everyone who assume that water is scarce on the Moon is probably wrong.

I think you have the burden of proving your definition of "scarce" carries the same meaning that others commonly accept it to be.   As you pointed out, if you are wrong on this point, your proposal fails.

I sense a vast disconnect with that usage, which drives you to scheme ways of using lunar water in highly wasteful ways that do in fact rely on magical engineering, as well as a magical love of your overall idea.   Do you think that if it (water) comes from the moon, it must be therefore be cheap and wonderful?   Maybe it will be neither if used how you propose.

From what I gather reading all your posts, you think there must be some internal process inside the moon making water in great quantities & it will also be readily accessible once we find it.   It is true that hydrated minerals deep within the interior of the moon may hold vast amounts of water, but that water is inaccessible as far as any current technology could hope to make use of it in a way that moves the moon-water "scarcity" needle off of redline empty.  Pointing to Ceres or Mars is meaningless, as each body has it's unique history, properties & orbit that determine composition.

So what then is the standard for plentiful moon water?  Plentiful enough for the inhabitants of a science outpost to drink, grow a few space potatoes, maybe enough to fuel a few space vehicles continuing onto to destination outside earth orbit?   I think good arguments can be made that the moon has plentiful water to meet those simple needs.

What you are proposing is far beyond that.   "Plentiful" in your scheme requires the following:
1.  Enough to fill up a space zeppelin.  ( i.e 200,000 tons of H2O if it was close in size to the Hindenburg)
2.  Impart 2.7 kps velocity to that 200,000 tons of H2O & spacecraft mass to get it down into LEO
3.  Drop a "Skimmer" ship out of orbit and drop another 7kps or so of velocity using aerobraking & rockets
4.  Do #4 accurate enough to rendezvous with a payload somewhere in the atmosphere ( where exactly?)
5.  Then accelerate your skimmer ship another 7kps into LEO back to the space zeppelin floating up in LEO.

You said you know some math, stopped short of doing calculus.  That is fine.  Show the following using the rocket equation ( just an algebraic function):

A.  How much plentiful moon water will be burned in step 1 & 2 ( you will need to commit to a realistic rocket ISP & ship mass to avoid magical engineering assumptions)
B.  What is the mass of the skimmer ship & how much water will be needed for step 3,4, & 5

There is also a problem with your assumption of cheap lunar water vs. earth water.  If you have the lunar infrastructure to mine water in quantities to make it plentiful enough to do what you propose, the $/kg of payload launched from earth to enable that lunar infrastructure will also make earth a much cheaper point of origin for bulk material.

 

Offline Asteroza

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Re: Earth to Orbit with a Space Bungee
« Reply #37 on: 08/11/2017 12:05 AM »

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 doesn't matter if the moon had a pond or an ocean. The water is too useful for the general space economy as a hydrogen source (for deep space propulsion and industrial/ECLSS use) to be used for earth local milkrun propulsion that can be reasonably substituted with other propulsion methodologies (momentum exchange using bulk downmass offset, electrodynamic propulsion via the earth's magnetic field, hell just using a PROFAC style rig to scoop nitrogen from earth atmosphere) that don't consume preferred resources.

I'd note that Hop's cislunar railroad 3 MX tether setup is feasible using current materials technology today, and these are comparatively lightweight structures that present no serious ground hazards (compared to a full space elevator, which even with a cut accident has been described as a string floating down from the sky because most of it is that light). There are crossing orbit/debris clearance issues that while non-trivial, are still very feasibly dealt with (we need to clean up trash anyways, and we can force tether harmonics and maneuver the tether around collision points). A "zero" stage for the railroad being a HASTOL-like rotovator to do the actual initial pickup is also feasible materials-wise today, but the fast rendezvous to capture the popup payload is still a little hairy (but no more so than a classic reverse bomber if doing the grab in vacuum just above the karman line).

I think it was J-goff who wrote about lunar propellant tankers that use their own cargo to rise out of the moon's gravity well. You lose a sick percentage just lifting from the moon alone (only deliver 11% of propellant mass to LEO with chemical propulsion and that's with staging the lunar lift rocket and transfer orbit rockets, I think only 40% or so with an NTR and staging?), so using a single NTR reverse bomber from the lunar surface uses painful amounts of propellant. Even staging a LEO reverse bomber from a generic NTR cislunar shuttle tanker that launched from the lunar surface is painful, and a LEO reverse bomber operating from a LEO propellant depot supplied from the moon still uses painful amounts of propellant though less.


Offline stefan r

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Re: Earth to Orbit with a Space Bungee
« Reply #38 on: 08/11/2017 02:50 AM »
...It is nuclear powered...

Of 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. 

Online hop

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Re: Earth to Orbit with a Space Bungee
« Reply #39 on: 08/11/2017 03:08 AM »
My proposal is water heated by a small nuclear reactor.
What are the ISP and thrust to weight ratio of this system? What does your proposed system require? If you don't have a specific numbers, then how can you claim:
Quote
No I am not proposing anything that violates physical laws or includes magical engineering.

In reality, getting decent performance out of nuclear thermal is hard in the best of times. Using a sub-optimal propellant will only make it harder, potentially requiring "magical engineering" to match the performance of chemical rockets. Describing your system as "a small reactor that heats water" suggests you aren't familiar with how specialized and high-strung systems like NERVA had to be to get ~850 ISP, or the struggles the designers of those systems went through to make it survive a full duration burn.

Offline Asteroza

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Re: Earth to Orbit with a Space Bungee
« Reply #40 on: 08/11/2017 03:32 AM »
...It is nuclear powered...

Of 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.

Oxygen propellant through an NTR?

Do you WANT oxidation? Because that's how you get oxidation...

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #41 on: 08/11/2017 05:38 AM »
You said you know some math, stopped short of doing calculus. 

Actually I said I stopped studying math after doing calculus, unless you consider statistics for psychology and multiple regression for ecnometrics more math.

All of that was in the late 1960s and early 1970s so I am a bit rusty.

My calculus was college prep in high school, and while I derived a lot of personal satisfaction from it, it was not integral to my further success.

I remember Newton stole it from Leibniz , but then Newton was accused of stealing lots of things.

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #42 on: 08/11/2017 06:11 AM »
From what I am now reading about Nerva (tested with specific impulse of 850 seconds) and later NTRs, they are so poisonous you could never use them in or near the Earth's atmosphere.

There's almost no carbon on the Moon, so you would have to use liquid H2 and LOX, which doesn't provide nearly as much thrust. Also it's a lot harder to fuel up. 

It has been suggested that I learn all the formulas for orbital changes etc, so I will spend some time doing that, which sounds like a lot of fun.

I assume if someone actually had web site for calculating all these things, all of my helpful listeners would be rushing to point them out to me.

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.

I'm sure you all can all do the math in your head while blowing your nose, but it is going to take me a bit longer.

There are people planning to build balloons that can transition to space now.  Still early planning stages I believe.

Offline Asteroza

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Re: Earth to Orbit with a Space Bungee
« Reply #43 on: 08/11/2017 09:03 AM »
JP Aerospace , their Ascender LTO, and their Orbital Ascender are very different beasts. Orbital Ascender takes about a week to get to orbital speeds and altitude after launching from a floating station located at 140K feet.

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #44 on: 08/11/2017 10:51 AM »

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?


Not think but know it is not possible.   It borders on crazy.

You were the one who said they understood orbital mechanics but the used the terms:  hover, 50mph,  and then slammed us for not understanding.
« Last Edit: 08/11/2017 11:00 AM by Jim »

Offline Stan-1967

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Re: Earth to Orbit with a Space Bungee
« Reply #45 on: 08/11/2017 04:12 PM »

It seems to me that you are pulling one of my tentacles but I don't know for sure which one.


==> BradJensen3,

It takes some high heat to make the toughest steel! 

Don't be discouraged if you feel some sharp elbows in response to your ideas.   You jumped into the fire pretty quick with your first comments & ideas being the start of this thread topic.  Don't be discouraged, people here generally offer criticisms in very tactful & constructive ways.  Rules of this board are to be excellent to each other.

This is a great place to come to learn, and also to contribute if you want to do that.  Welcome to NSF & I hope to see you commenting elsewhere.

Online hop

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Re: Earth to Orbit with a Space Bungee
« Reply #46 on: 08/11/2017 04:27 PM »
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?
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.



Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #47 on: 08/11/2017 07:43 PM »
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?
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.

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?

And yes, I said a rocket can go at any speed, even down to 50 miles and hour, but that doesn't mean I want to do that. I was just reacting to the seeming assertion that the pickup vehicle could only go at free fall orbit speed.

Hey and for that matter, the payload could accelerate before pickup.

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.

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?

Of course I would not want to bring the entire rocket into the atmosphere, that after all was why I started by talking about bungees.

Hey maybe it would be fun to have the Bungee mothership in orbit around the Earth AND Moon, drop a skimmer as it approaches near Earth, which then aerobrakes into the upper atmosphere down below Mach 1, snatches the payload, accelerates back to above orbital speed, and joins the Mothership on the next orbit a couple of days later. 

Then you would just need to expend enough fuel to run the skimmer and maybe adjust the momentum of the mothership and skimmer a bit on each orbit.

Send some more fuel up as you pass the Moon every couple of orbits.

Super Virtual Bungee Cislunar Conveyor Belt!

Why bother with the mothership? Because human beings work better in groups on a stable platform. And this would be much better preparation for human interplanetary exploration than sitting with your ass in the air on the ISS.

Not that there's anything wrong with that.

You could also launch H2O from the moon and make liquid H2 and O2 on the mothership while it is zipping along in its weeklong orbit. Well about 4 to 5 days, right? I remember it took 2.something days to basically coast to the Moon back in Apollo days.

Hey you could use this setup even without the balloons and the skimmer.

I think the first one should be called "Bozo' for 'beautiful orbiter zipping overhead.'

So pi in the sky momentum based systems make sense to you, but this doesn't. Wow.

No I don't know why 'people who work with this stuff' would dismiss it out of hand.

There is a lot for me to learn in hearing 'you can't because.' Some of your objections I agree with. Others I do not, because in part we are not working from the same assumptions. You assume there isn't much water on the Moon because that's what you have been told. I am assuming, for the sake of this proposal, that lunar water is plentiful, not just enough to grow a few potatoes.

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.

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.

« Last Edit: 08/11/2017 08:12 PM by bradjensen3 »

Offline Stan-1967

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Re: Earth to Orbit with a Space Bungee
« Reply #48 on: 08/11/2017 08:27 PM »

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.


Well I guess if we are to approach this from a philosophy perspective, the thread should be moved to the section for "Spaceflight Entertainment & Hobbies/Disney's Star Wars Theme Park" section.

Since you Kant define your problem in terms an engineer can respond to, I'll leave a few helpful "Kant" quotes:

"It is beyond a doubt that all our knowledge begins with experience."

"Thoughts without content are empty, intuitions without concepts are blind."



Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #49 on: 08/11/2017 08:51 PM »
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.
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.

Online hop

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Re: Earth to Orbit with a Space Bungee
« Reply #50 on: 08/11/2017 08:57 PM »
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?
I was describing what would be required for the concept presented in http://forum.nasaspaceflight.com/index.php?topic=43538.msg1711276#msg1711276

You've thrown out so many variations of the concept, I picked one that had obvious, insurmountable problems that didn't require a bunch of calculations to demonstrate.

Quote
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?
Because that's not how orbits work. Once you get below orbital velocity, you aren't in orbit any more. You can get down to LEO velocity in multiple passes (provided you're OK with multiple passes through the Van Allen belts), but after that you are all-in for the equivalent of Shuttle, Soyuz etc. Only going to a few thousand km/h instead of zero really doesn't help much, the peak heating is in the earlier parts of re-entry.

Quote
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.
Propellant is by far the cheapest part of most existing rockets, so yeah, probably not. A re-usable tug going between LEO and higher orbits using lunar propellant would likely be a much more practical use of theoretical free Lunar fuel.

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #51 on: 08/11/2017 10:02 PM »


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.

No, Not that at all.  The lunar module flew to the exact same stable orbit that the command module was in and then docked.   After the crew transfer, the lunar module was undocked ( With it and the command module still in a stable orbit) and thrusters fired to cause it to impact the moon. The command module stayed in the stable orbit for awhile (hours and then later missions, days) before firing to go back to earth.

Online Req

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Re: Earth to Orbit with a Space Bungee
« Reply #52 on: 08/11/2017 10:46 PM »
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.
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.

This belongs in the Q&A section, but it seems like a quick mspaint may help.  Things only orbit because they are going so fast that they never hit the ground.  Imagine throwing rocks at various speeds, from slow(red line) to green(fast enough to reach orbit.)  You don't just fly up there and then you're floating around in space, you will fall if you slow down.

This makes a few things clear:

1)  Most of the energy is spent gaining that velocity(throwing the rock.)
2)  It takes a lot of energy to counteract that velocity.
3)  There's a lot of energy saying that you are going this direction at this speed.  It takes a lot of energy to fight it in any other way(plane/inclination changes and etc.)
« Last Edit: 08/11/2017 10:59 PM by Req »

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #53 on: 08/14/2017 06:07 PM »
I'm not sure why I seem like such a dunce to you guys. Of course I know how a free fall orbit works. Basically the object in orbit is moving away from the earth at the same speed it is falling towards the earth as a component of its angular velocity.

Unless it runs into something (including a bit of atmosphere in low earth orbit) it will continue to do so forever.

Typical low earth orbit is about 90 minutes. Geosynchronous orbit is about 24 hourswhich is why the satellite seems to stay in the same place.

The period of the orbit is basically set by the force of gravity at the distance from the center of the mass that is being orbited, along with the total distance travelled in the orbit, which is roughly 6.28 * the radius of the orbit.. At Earth sea level is 9.8 meters per second per second. The higher you go the longer the orbit takes, until at the distance of the moon which is somewhat less than a quarter million miles, it takes almost 28 days.

The moon is not in a stable orbit. It is gradually leaving the Earth's orbit because it is being accelerated thru gravitational interaction with the Earth's oceans in the form of tides. The Earth's rotation is also slowing for the same reason. Basically the Earth rotation is slowing and the energy is being used to accelerate the Moon.

In the 1960s we learned this stuff in elementary school thru jr. high.

Someone said if you shed delta V thru aerobraking you end up inside the atmosphere and then you are basically doomed to reentry.

So you shed MOST of your delta V thru aerobraking and the last bit while outside the atmosphere using your cheap rocket fuel.

Of course my final desire has nothing to do with Earth orbits or the Moon. I really want to do this with Ceres, escape velocity .51 km/second,  Vast quantities of water available. Lots of other resources including carbon.

Think about re-engineering space exploration so it is not dependent on general public enthusiasm and politicians' promises.

That's where I am trying to go with this. 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.

« Last Edit: 08/14/2017 06:14 PM by bradjensen3 »

Offline stefan r

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Re: Earth to Orbit with a Space Bungee
« Reply #54 on: 08/14/2017 06:52 PM »
... 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.

Use your asteroid materials to manufacture solar panels (or mirrors aimed at generator).   Beam energy to earth.  Use electricity to split water.  Use a reusable H2/LOx rocket to launch to space (can also use H2 for methane production).  This is sustainable and all energy originated from space.  But I would never call it a "space bungee". 

If an idea requires lots of infrastructure in space it will not get very far on this forum.  There are lots of options once(if) humans transition into space.  But there first needs to be a way to launch that initial infra-structure. 

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #55 on: 08/14/2017 07:10 PM »
PS Thank you Jim for all your helpful posts. Also Stan and others.

I know you mean the best for me, and I appreciate it.

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.

The other part is that I don't know the formulas for orbital dynamics or the method of applying them. I promise to learn those soon. A nice engineer across the street who owes me some time, and I'll ask him to help me learn.  We trade time and resources from time to time. I believe he thinks I am a bit crazy too, but he is extremely polite about it.  With him, I discuss my ideas about nuclear synthetic oil.

I am not a nuts and bolts engineer, but I am a software engineer for the last 40+ years and I do understand that things have to work in a practical fashion.

It is not enough for things to work mechanically, they must also function economically, and behind all economics is politics.

It has been almost 50 years since a man first walked on the Moon. That man is now dead. The reason space exploration proceeds at such a snail's pace is because it is an expensive luxury, not a self-supporting economic activity.

I think we can change this in the next two or three decades.

So how would you guys get things off the Earth, using non-Earth-based resources?

Offline whitelancer64

Re: Earth to Orbit with a Space Bungee
« Reply #56 on: 08/14/2017 07:17 PM »
Even if water was plentiful on the Moon, to the point that it could be used freely, and for things like propulsion, it wouldn't be a good use of it to fly nearly all the way back to Earth, reduce velocity a great deal, drop a tether, and pick up a payload from high in the atmosphere, and accelerate again to go back to the Moon.

There are a whole bunch of complex technical issues in there that could probably be solved, but ultimately it would be both much simpler, and a better use of (and would use less) fuel to land on Earth, then launch back to the Moon.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline Jim

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Re: Earth to Orbit with a Space Bungee
« Reply #57 on: 08/14/2017 07:55 PM »

So 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.

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #58 on: 08/14/2017 08:52 PM »

So 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.

"Under current constraints and circumstances."

I thought this part of the forum was for advanced topics.

I'm a disaster recovery guy in real life.

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.'

Maybe you do mean it is impossible to make a water based rocket that can lift from the Moon, reach lunar escape velocity, partially aerobrake in the Earths atmosphere, send a skimmer into the atmosphere to retrieve a payload hanging from a balloon or launched ballistically from a balloon (or maybe an Airbus!) and accelerate it to orbit.



Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #59 on: 08/14/2017 09:51 PM »
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.'
Close, but replace "current conditions" with "any conceivable conditions."

Offline stefan r

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Re: Earth to Orbit with a Space Bungee
« Reply #60 on: 08/14/2017 09:59 PM »

So 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.

It can make a lot of sense.  An orbital ring has been described and there are several versions. 

Momentum exchange tethers also have detailed description.  They are not likely to reach into the atmosphere.  Velocity at the end of the tether will be much higher than surface velocity.  But they could haul material out of Earth's gravity well.  Tethers can take momentum by deorbiting junk satellites or deorbiting mass from asteroids or the moon.  Rockets attached to tethers can burn lunar oxygen. 

A space station burning or accelerating lunar oxygen is also using outside resources to rise higher in the gravity well. 


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.

It might help if you distinguished between "water" and "hydrogen containing minerals".  Pottery makes call the clay "bone dry" before they put it in the kiln.  Then they heat it slowly to boil off the water.  Then they raise the temperature to remove chemically bound water from the surface of particles in the clay. 

Bauxite or gibbsite (Al(OH)3) is a mineral.  I would say that batch of bauxite can be dry and "not have any water in it".  If you process bauxite into aluminum metal there must be some oxygen and hydrogen atoms around. 

Suppose we had a chunk of pure gibbsite larger than Texas conveniently located at the moons equatorial surface.  A lunar colony will still have better uses for hydrogen then sending it into Earth's atmosphere.  Extracting hydrogen from gibbsite is painful.  The hydrogen would be needed in lunar greenhouses and could be used to launch away from Earth. 

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #61 on: 08/14/2017 10:35 PM »
Recent water on/in the Moon article https://phys.org/news/2017-07-scientists-spy-evidence-moon-interior.html

No, I wasn't thinking of extracting hydrogen and oxygen from bauxite on the moon.
Not That There's Anything Wrong With That.

« Last Edit: 08/14/2017 10:37 PM by bradjensen3 »

Offline meberbs

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Re: Earth to Orbit with a Space Bungee
« Reply #62 on: 08/14/2017 10:46 PM »
Recent water on/in the Moon article https://phys.org/news/2017-07-scientists-spy-evidence-moon-interior.html

No, I wasn't thinking of extracting hydrogen and oxygen from bauxite on the moon.
Not That There's Anything Wrong With That.
The adjectives in that article may have caused you to miss the number. In the parts that have water, what they found is 0.05 % by weight or 1 part in 2000. This means processing 2 tons of regolith to get 1 liter of water. This basically translates to your "plentiful cheap water" assumption being something that will never happen.

Of course most of the recent objections to your idea have moved past this and just pretended that there is an ocean on the moon to point out why the rest of your concept still will not make sense.

Offline bradjensen3

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Re: Earth to Orbit with a Space Bungee
« Reply #63 on: 08/14/2017 10:57 PM »
If we need more water on the Moon, why not bring it from Ceres?

Ceres has a lot of water, and it is probably available thru ice volcanoes.

Ceres has 1/30th Earth gravity and an escape velocity of .51 km/second.

Use water from the Moon with a NTR engine giving specific impulse of 420 to head for Ceres.

Use automated rockets with hydrogen peroxide engines with spcific impulse of 140 to send giant water balloons back to the Moon. Aim for a crater with high walls all around just entering the 14 day lunar night. Grab up some significant percentage of the water as it cools down.

Or aim near the poles and let the moon 'distill' the water intos its ice caches.


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