Author Topic: Earth to Orbit with a Space Bungee  (Read 3322 times)

Online 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'.


Online 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 »

Online 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. 

Online 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

Online 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

Online 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.


Online 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 »

Online 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.

 

Online 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. 

Offline 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.

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