I Love Chemically-Fueled, Vertical Take-Off Rockets But Doesn't Humanity Need a More Elegant Way to Get into Space?

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boatgeek

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And yet no Class1 RR has actually taken the plunge and invested in the infrastructure required to make the switch to LNG and show no signs of doing so in the near future.
If the test locomotive(s) you mentioned above pencil out, I have no doubt that the Class 1 railroads will start switching to LNG. There are other issues than the cost of fuel. Cost of engines, cost of training/maintenance/repair, and availability of fuel are obvious questions, as are the interoperability issues that @jqavins mentioned in another thread about brakes. On the other side, there may be grants for switching to LNG, particularly in places that are concerned with smog.

[Edit] I would expect that the test period would be on the order of 5-8 years to see how long-term costs compare. Railroads are conservative* beasts, and the people pushing for LNG will need ironclad proof that they save money to convince management to change.

* In the sense of slow to change, not in the political sense.
 

Funkworks

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I haven't crunched the numbers yet, but I don't think so. 40 000 ft is a big proportion (%) of the Karman line, but a small proportion (%) of low Earth orbit altitudes. I don't mind finding out the numbers but I can't decide if I should do it in feet or meters. Decisions, decisions.
As I was saying, a B-52 or Starship 2 mother ship will bring a load at 15% of the Karman line altitude (edge of space) and 4% of the International space station altitude (typical low Earth orbit).

And here's the altitude data I found (all) and used (bold):
1634159831475.png

So now what's easier: using a jet to bring a rocket/fuel tank at 4% of an orbital altitude? Or just make a fuel tank bigger. Not exactly 4% bigger because it takes more energy when close to the ground, but that's more difficult to calculate.
 
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Jeff Lassahn

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I got the idea somewhere that the reason for making LNG rocket engines is that methane is something you could plausibly synthesize on Mars, while kerosene isn't.
 

Woody's Workshop

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I wonder if a rail gun type launcher might get used in the future to get the rocket started off the pad.
That would certainly reduce the amount of fuel needed.
How many pounds of fuel did the Sat V burn a second on lift off?
Jump start the first 5 seconds and get to 100mph.
I just wish I could be around when the warp bubble will be discovered.
 

Funkworks

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I wonder if a rail gun type launcher might get used in the future to get the rocket started off the pad.
I like rails, but I can't imagine anyone building a rail long enough for people rockets. For people, acceleration has to be kept slow (below 2-5G maybe?), which means a very long rail (that would dwarf skyscrapers). I think bringing people to a decent speed in a rail as short as a skyscraper would hit them as hard as a belly-flop on concrete.
 

brockrwood

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Not quite - it spins end over end to keep it taught. When you catch the bottom - timed so the end spinning down is nearby and near zero relative velocity, it then lifts the payload up and releases it again 180 degrees of spin later. Momentum is exchanged - the average momentum stays the same, so the payload is in orbit and the tether is in a lower orbit. Payload lowering reverses that. Residual losses could be made up by solar electric reboost between cycles.

It takes some of the material advances of a space elevator - but less extreme. Note: I haven't seen recent estimates of how long a momentum exchange tether like this needs to be to keep the Gs survivable.
OH! It's a "Skyhook"! Cool!

 

Woody's Workshop

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I like rails, but I can't imagine anyone building a rail long enough for people rockets. For people, acceleration has to be kept slow (below 2-5G maybe?), which means a very long rail (that would dwarf skyscrapers). I think bringing people to a decent speed in a rail as short as a skyscraper would hit them as hard as a belly-flop on concrete.
It would work well for getting supplies to space and beyond though.
I believe the max G's for humans is 7. But you need the pressure suit that jet fighters ware.
But that is corning G's. Vertical laying on you back may be all together a whole new thing that has to be investigated.
But it seams to me that a human could take more G's on their back than corning.
 

boomtube-mk2

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Arthur C. Clarke used something similar to a "Skyhook" in his novel The Songs of Distant Earth (1986), except in that case the "Hook & Cable" actually lifted payloads off the surface of planets.

In Peter F. Hamilton's Fallen Dragon (2001) a system like the Skyhook was used to fire hypervelocity warheads at invading starships.
 
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kuririn

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I'm not an engineer but all the concepts I've seen involving high speed rail acceleration/rail guns work by imparting a tremendous amount of energy at the start, thus extremely high G forces on the projectile. Numbers that would turn anything organic to jelly.
Keep in mind that the energy/acceleration is only imparted to the projectile/spaceship when it is on the rail. After that it is coasting and being slowed by aerodynamic forces. Don't see how rail can work with only a 7G acceleration.
 

boomtube-mk2

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If only it were possible to electromagnetically accelerate all types of matter not just certain types of metal.
If the EM field effected every atom equally then there would be no G-Forces felt by the payload.
Sadly, only gravity appears to affect matter in this manner and we don't have any control over that as of yet.
 

cerving

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A railgun makes no sense for putting anything into orbit from Earth, because the extremely high G's would be canceled out by the extremely high drag forces due to the initial velocity. It's much better to use a moderate boost so that atmospheric drag at lower altitudes is kept to a manageable level, that's why it's more efficient to have a lower amount of thrust for a longer time. It could work on the Moon, though...
 

kuririn

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A railgun makes no sense for putting anything into orbit from Earth, because the extremely high G's would be canceled out by the extremely high drag forces due to the initial velocity. It's much better to use a moderate boost so that atmospheric drag at lower altitudes is kept to a manageable level, that's why it's more efficient to have a lower amount of thrust for a longer time. It could work on the Moon, though...
I wonder. Same forces and accelerations are in effect for a supergun/artillery shell, and there were proposals to put a projectile into orbit with a supergun a few decades ago.
Project HARP - Wikipedia
Super High Altitude Research Project - Wikipedia
The HARP gun put a projectile briefly into space at an altitude of 179 km.
If the SHARP project had not been cancelled perhaps they could have put one in orbit. Would have been very expensive, But we'll never know.
 

TheAviator

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So here's the deal. Going to orbit is an energy game, not an altitude game. That's why there's such a huge difference between (as pointed out) New Shepard and Falcon 9/Dragon. Both carry roughly the same number of people, but F9 is an order of magnitude bigger. So let's run the complete numbers, shall we?

This is physics class, so we're going to assume that the Earth is a non-rotating, atmosphereless sphere. Not perfect, but it puts a lower bound on how much energy it takes to perform a particular launch. If I were to send an object straight up with the intention of getting exactly to the Karman Line and falling straight back down, I would need roughly 1 kJ of energy per kg of mass to send it on such a ballistic trajectory.

On the other hand, if I were to do a Hohmann transfer from the Earth's surface to a 100 km circular orbit, I would need 31.5 kJ of energy per kg of mass at launch, plus another 0.25 kJ/kg after coasting to apogee. All of this energy comes from the fact that I need to kick the vehicle sideways at nearly 8 km/s (17,900 MPH) at launch to get where I want to go as opposed to only 1.4 km/s straight up to hit the Karman line. And yes, you read that right, you need 32 times the energy to reach orbit that you need to reach space.

There have been proposals to use air breathing (read: jet engine) powered aircraft to get stuff part of the way to space, then use a rocket to finish it. The challenge to this approach is that the key as shown above is not altitude but speed. Such a jet powered first stage would need to reach speeds in excess of Mach 5-10 (roughly 1.4-2.8 km/s at altitude) to be even remotely worth the extra complexity. This is well within the realm of scramjet propulsion, which is in its infancy. Current air launched space launch vehicles (e.g. Pegasus, LauncherOne) get a small performance margin over their ground launched brethren, but the primary advantage is launch site flexibility and relative immunity to weather related delays.

I also wanted to comment about Methane-fueled rockets. Someone pointed out the high cost of refined kerosene as rocket fuel (RP-1/RG-1) because it needs to be very tightly controlled over just using kerosene out of a pump at your local gas station. Unfortunately, this is also true of rocket-grade methane. Early proponents wanted to use LNG straight from the industrial supply and ran into the same problems as did early kerosene rockets. LNG contains, among other things, a not-insignificant amount of ethylene, acetylene, sulfur, and sulfurous compounds. These cause just the same problems for rocket engines as do low-grade kerosenes; i.e. fouling of cooling channels and injectors leading to hot-spots and engine failure. Starship, Vulcan, and New Glenn need/will need to use highly refined Methane and not LNG to avoid these problems. Whether rocket-grade methane will be any cheaper than rocket-grade kerosene remains to be seen. Also, methane does have the disadvantage of being less dense than kerosene, so your stages need to be larger to hold an equivalent mass of fuel, which is what really matters int he rocket equation. See Vulcan stage 1 versus Atlas V stage 1. (Having said that, I am all for methane/LOX engine development for the eventual Mars in-situ fuel generation reasons.)

One last thought: there is a completely green rocket propellant: hydrogen. But that is a whole other logistical can of worms that I'm not going to open.

TL;DR: space is difficult.
 

Charles_McG

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Methane recovered from bio-active landfills? Yes, I know current landfills are ‘sanitary’ and the amount of CH4 they generate isn’t necessarily enough to be worth recovering.
 

cerving

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Methane recovered from bio-active landfills? Yes, I know current landfills are ‘sanitary’ and the amount of CH4 they generate isn’t necessarily enough to be worth recovering.
They used to burn it off... one of the landfills in our area was visible for quite a distance, because of the 40' flame. It's probably easier to do that than to collect it...
 

Charles_McG

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The one by us flares it, too. Too rich to let it drift around where it might collect into a bubble that goes boom - not enough to pay for compression and separation from CO2, water, H2S, and trace crap.
 

brockrwood

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I'm not an engineer but all the concepts I've seen involving high speed rail acceleration/rail guns work by imparting a tremendous amount of energy at the start, thus extremely high G forces on the projectile. Numbers that would turn anything organic to jelly.
Keep in mind that the energy/acceleration is only imparted to the projectile/spaceship when it is on the rail. After that it is coasting and being slowed by aerodynamic forces. Don't see how rail can work with only a 7G acceleration.
Maybe we could separate the cargo from the humans: A high G launch system for inanimate stuff, and then a smaller, human-rated rocket to just get the people into space where they would then rendezvous with the cargo.
 

brockrwood

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As I was saying, a B-52 or Starship 2 mother ship will bring a load at 15% of the Karman line altitude (edge of space) and 4% of the International space station altitude (typical low Earth orbit).

And here's the altitude data I found (all) and used (bold):
View attachment 485506
So now what's easier: using a jet to bring a rocket/fuel tank at 4% of an orbital altitude? Or just make a fuel tank bigger. Not exactly 4% bigger because it takes more energy when close to the ground, but that's more difficult to calculate.
Or we can just use super fancy airships!

 

smstachwick

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Methane recovered from bio-active landfills? Yes, I know current landfills are ‘sanitary’ and the amount of CH4 they generate isn’t necessarily enough to be worth recovering.
Here in San Diego we built the 52 freeway right over such a landifll. Up and down, and up and down, getting air at 65 miles per hour. They've ended up repaving it to smooth it out every few years, the asphalt is 4 ft thick in some places.
 

Pete.D

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True enough. Let me append that as "the only possibly green rocket fuel."
Several nuclear reactor sites are now being upgraded to produce hydrogen from high temperature steam using electrolysis. Nuclear sites are already moderate consumers of hydrogen, but their increased production capacity could be used to provide low cost green hydrogen for fuel-cell powered vehicles and energy storage facilities. Besides rockets, hydrogen can also be burned in turbines and even internal combustion engines.
 

Richard Dierking

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We need to use the Earth's atmosphere and not just fight it. Stratolaunch kind of has the right idea, at least for a start. There's a lot still to do with air-breathing engines and it's much easier to land a launch vehicle by gliding it in. Turnaround would be faster too and vastly increase the locations for launching and return.
Still, another stage would be necessary, but even SpaceX has a expendable stage to obtain orbit.
 

kuririn

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There's something about the noise, smoke and fire of a good old fashioned big chemical propellant rocket launch.
It just feels so, oh, I don't know...........
Cathartic!
😁
 

brockrwood

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There's something about the noise, smoke and fire of a good old fashioned big chemical propellant rocket launch.
It just feels so, oh, I don't know...........
Cathartic!
😁
OK, people. I think we have beaten the "cathartic" thing to death. I will NEVER utter the word again. Unless, you know, I feel cathartic. ;-)
 
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