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Old 03-09-2008, 05:41 PM   #1
Perigee
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Default The Practical Eagle

Brian Johnson's design of the Eagle is a beautiful thing, but not really viable from a practical point of view; the VTOL thrusters on the undercarriage wouldn't be up to the task, especially in full gravity, and I'll be darned if I can figure out where they stow any fuel supply at all.

I'm fiddling with a writing project with aspects not dissimilar to some concepts in the 1999 universe, and I'm trying to work out some logistics. Logically, a trip offworld from Earth would start at an L1 station, which would allow transfer to specialty vehicles built for specific offworld destinations - not unlike the transport method suggested in 2001.

The problem is that it also seems logical that, for reasons of parts and maintenance across a fleet, an adaptable workhorse vehicle makes sense. It would also aid greatly in some sticking points of the story when specialty launch preparation might not be available and under full G and colony intercourse is required, requiring independent VTOL capabilities.

Full spectrum use of such a vehicle would have to range from personnel transport to colony resupply; possibly modular construction would allow for vehicle sizing and re-purposing.

Assume the shipyards were part of a moon base better than four times the size of Alpha, serving mainly as foundry, mining, repair and construction with the needed engineering know-how to create and repurpose - Lockheed Martin, in a one-stop shop.

You guys are the Eagle Transport forum; it's your rabbit to ponder those beasts. What are your thoughts on a more practical, flexible version of a VTOL space transporter?
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Old 03-09-2008, 06:32 PM   #2
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Default Space Elevator

Perigee,
I agree that in 'real' term the eagle would not cut it on a full earth gravity take -off if you take current engines. However, given the refuelling rig seen in some episodes, and a possible change from chemical to nuclear rocket engines, it may be possible.

The system I think is more likely would be the "Space elevator". A cable anchored at the highest land point on the equator, spanning up to a change station half way to the L1 (Lagrange 1) point this could then allow transfer of cargo and personnel to a chemical or nuclear powered transport to any of the 3 Lagrange stations, where the starship going to their particular destination would be 'berthed'.

Traditionally starships have not needed things such as aerodynamics as they are not required to travel in an atmosphere, and this would still hold true of your "Mothership". However, and as you are specifically asking about an Eagle type "Workhorse" This MUST include some form of ability to land on a minimum of Earth gravity planets, possibly higher, and take off again to return to the mothership. Therefore with the dictates of form following function, the primary consideration has to be a large or extremely efficient engine. Unless you have a hugely overpowered engine, some form of wings and control surfaces will also be necessary. The problem with this is you would have to know the make-up of the target atmosphere.
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Old 03-09-2008, 06:46 PM   #3
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For example, if you used a nuclear engine to turn water into steam the steam can be used to generate thrust by causing it to build pressure and then releasing it through a small enough hole. The smaller the hole the greater the thrust for a given pressure. In Earth's atmosphere this is no problem. The water returns to the atmosphere and helps replace the water on board the craft. There would still be a net loss of water, and this could be replenished by the mining of either Jupiter's rings or the Asteroid belt.

However, in an atmosphere such as that of Mars, any moisture released from your craft could react with the constituents of the atmosphere and form compounds such as Hydrochloric acid. This would obviously have detrimental consequences for your craft.
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Old 03-09-2008, 07:07 PM   #4
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The smaller the hole the greater the thrust for a given pressure.
And physics takes another punch to the ribs.

By that criteria, the highest thrust would come from a hypodermic syringe. I think you're confusing the velocity at which the gases would be exiting the engine v the area over which the thrust was acting.

It's more basic than that. The fuel only contains so much energy to do so much work. A slow burn via a small engine can provide a small amount of thrust for a long period or you can burn the lot quickly in a big engine. In space, this would make little difference since the same amount of energy is moving the same amount of mass. Only the rate of excelleration will be different but on Earth, the amount of thrust generated must overcome the gravity pulling the rocket back to the ground if the vehicle is to rise.
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Old 03-09-2008, 07:35 PM   #5
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Yes, it was rather a bad analogy I admit, but in that message what I was trying to say (Badly) is that we currently do not know the damage we could cause in atmospheres of different composition. If we are to prove ourselves as a responsible species worthy of space travel, we need to consider the effect of our actions on a galactic scale. Can you imageine how put out we would have been if E.T. had come here and not been able to phone home because he had set our atmosphere alight and killed most of the population?

Also, I was not talking of burning a fuel in the sense of chemical rockets. Steam under pressure has incredible force, some steam pipes used in steam curing of rubber have been known in the past to rupture with a force that could take flesh from bones and cut the bones themselves. If this force could be harnessed to replace a chemical rocket thrust, then you could make it into space. However, due to the fact that, unlike chemical rockets, you need to restrict the flow to the highest degree, the force of the steam itself would cut your nozzle to ribbons and reduce your actual thrust to levels below escape velocity before you got higher than the cruising altitude of a modern jet..

Conventional chemical rockets work in our atmosphere because of the composition of our atmosphere. Yes, the combination of Hydrogen combustion in the presence of Oxygen produces thrust. But in an atmosphere that is more Oxygen heavy than ours ( approximately 18% IIRC) could lead to a larger combustion than intended as atmospheric Hydrogen burns.

Our chemical rockets would work and produce thrust in a pure Hydrogen atmosphere, because of the in-built supply of Oxygen , and would not ignite the entire planet's atmosphere due to the limiting effect of oxygen availability.
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Old 03-09-2008, 09:54 PM   #6
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Let's back up a bit. If you take a rocket and fill it with a single gas that remains a liquid while under pressure (or extremely cold temperature), you can simply open the aperture. The pressure inside the can drops and more liquid turns to gas continuing to feed the flow of gas through the aperture. Think airbrush propellent can.

If you can increase the rate of expansion of the gas, you can generate more thrust.

The easiest way to do this is to add a second liquid gas that reacts with the first when mixed. If the combination generates heat, that will increase the rate of expansion. In the case of the Saturn V, the initial stages were powered by a mixture of hydrogen, which would provide the energy, which was liberated by the chemical reaction of combustion with the oxygen carried as the oxidiser. The igniting of the mixture heated the gases so that they expanded much more rapidly than if they had merely both been mixed and allowed to 'squirt out'. Combustion is a self sustaining chemical reaction all the time there is a fuel to burn and an oxidiser to allow the reaction to continue but it needs a kick start.

However other chemicals mixed together will react violently with each other also causing their combined expansion to greatly increase. The Lunar Module engines used a mixture of hydrazine and unsymmetrical dimethylhydrazine which goes under the more mouth friendly name of Aerozine. It's still used today with dinitrogen tetroxide as the oxidiser (yes, I had to look that bit up). The advantage of using these chemicals in space bourne ships is that the reaction occurs as soon as the two chemicals come together so you're guaranteed the engine will work providing the valves controlling them open. There won't necessarily be a flame as combustion in the sense we know it is not occuring. They are still reacting however.

Nuclear engines don't need such reactive substances. In theory they can use almost any liquid which will flash into a gas when heated because nuclear engines basically superheat anything that goes through them causing the same rapid expansion of the resultant gas. That means that water, if found on the moon for example, would not only provide oxygen to breathe and hydrogen as a fuel when seperated, but also be a liquid fuel material in it's own right. You could refuel a Moon landing craft with water for the return trip to Earth. Essentially steam power although instead of a coal fire being used to heat it, a nuclear reactor is used.
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Old 03-09-2008, 10:36 PM   #7
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which is essentially what I was saying, but with added science.

If you take that nuclear engine, use it to heat water to steam, use the steam as your thrust generator, the only thing coming out of your exhaust is water vapour. On earth, this would be considered an environmentally friendly method of getting things into space.

Do this on the martian soils and your water vapour turns to Hydrochloric acid, and you damage the martian environment. Who is to say that the exhaust from what we consider standard rocket motors - from whatever fuel they use - will not be harmfull to the environment of some alien planet?



I also believe that the Bergman shield is in fact not a gravity shield, but an inertial adjustment field. (And why not, both are as physically impossible!)
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Old 03-09-2008, 10:41 PM   #8
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Originally Posted by Weaponsmith View Post
I also believe that the Bergman shield is in fact not a gravity shield, but an inertial adjustment field. (And why not, both are as physically impossible!)
We're straying dangerously close into the Scottish Series territory here!
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Old 04-09-2008, 02:31 AM   #9
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Ok - just so we can get the idea down, here we go -

Our recent slide back into a cool-war made me wonder what would happen if, some 300 years in the future, we experienced an apocalyptic event on earth. Our L1, Moonbases, and planetary colonies would essentially be left without central control and resources on earth would have to be scavanged for what they were worth; essentially, Earth becomes another hostile environment. In addition, one might assume that the Other Side had their own installations. Would the war escalate, and what would it take to close ranks? These disparate bases have been around long enough to have already achieved their own identities - almost countries to themselves, except up until this point corporate control and Earth's ability to regulate trade kept them in alliance.

I'm working up the framework of a multi-part series of novels investigating the idea. Obviously, specialty bases - let's say Venus, as an extreme example - would have to have unique structure and transport... which would cause all sorts of havok, since it impedes contact. But those flights would have been channeled through L1 anyway, so the craft needed to navigate different worlds remain undamaged.

L1 and the moonbase would be most closely aligned, simply due to proximity to earth; most of the government regulatory agencies, space program and corporate front end administrators would have offices there. Traffic would be steady between these points - Earth, Moon and L1 - probably using a space plane to L1, and shuttles to the lunar surface. I'm not sure, post apocolypse, there would be remaining areas to use and service them. That's where the transport problem comes in.

Obviously, under these circumstances, an elevator probably would be out of commission; we're going to need to be able to get to earth and back on our own steam, since, at that point, space, and not earth, is our base of operations.

Over the course of the day, I've been toying with a "Spider" - multiple thrusters arrayed out from the payload body with engine size and number adaptable to the task at hand. Could be I may have to go all Star Trek doubletalk on the actual fuel and engine specs. But it would allow for a 4-armed, low weight hopper for personnel and a full heavy-16 for cargo.

Since I am anticipating Martian colonies, our group would have already developed vehicles for transporting offworld under .4 G... unless I want to screw everyone's life up, and have them reliant on those elevators. Which might be fun.

Last edited by Perigee; 04-09-2008 at 02:46 AM.
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Old 04-09-2008, 03:31 AM   #10
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Sounds a lot ike "Babylon 5" without the aliens as bad guys. I don't mean to rain on your parade but it would take quite a hook to set it apart from quite a few Sci Fi novels, films, and TV shows.
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Old 04-09-2008, 08:37 AM   #11
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Would it not be easier just using anti-gravity forcefields to lift Eagles without all these chemical propellant thingies?
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Old 04-09-2008, 09:33 AM   #12
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Actually the strings worked pretty well... I don't know what the hassle is.
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Old 04-09-2008, 10:03 AM   #13
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Originally Posted by Tony42 View Post
Actually the strings worked pretty well... I don't know what the hassle is.
Excellent.
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Old 04-09-2008, 12:08 PM   #14
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Originally Posted by Tony42 View Post
Actually the strings worked pretty well... I don't know what the hassle is.
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Old 04-09-2008, 07:37 PM   #15
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"With the titanic rumble of the subwoofers, Carter felt himself slammed against the pilots chair as the craft struggled against gravity. Scanning the readouts on the panel before him, he snapped, "We've got a failure of string integrity on thruster four! We need an effects crew out there - now!

But it was too late - with a wrenching sound, the craft lurched suddenly downwards, shearing the remaining strings, plummeting, spinning down to the unyielding surface of the set floor below.

"Alan! Alan!!"
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Old 04-09-2008, 08:02 PM   #16
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Nah, it wasn't an unyielding floor, it was a sofa!

Paisley, probably. Good job Ford Prefect and Arthur dent got off 10 minutes before!
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Old 10-09-2008, 08:03 AM   #17
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Quote:
Originally Posted by Perigee View Post
Brian Johnson's design of the Eagle is a beautiful thing, but not really viable from a practical point of view; the VTOL thrusters on the undercarriage wouldn't be up to the task, especially in full gravity, and I'll be darned if I can figure out where they stow any fuel supply at all.

The pipes/struts/crosspieces, that are the frame of the Eagle. Imagine them hollow, and full of fuel.
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Old 10-09-2008, 12:43 PM   #18
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The pipes/struts/crosspieces, that are the frame of the Eagle. Imagine them hollow, and full of fuel.
But wouldn't you then need a whole shed load of pumps and stuff?
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Old 14-09-2008, 11:57 PM   #19
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I will assume that, if the technology to build the Eagle is in place, than the pumps and valves needed to make it work would also exist and have been fully vetted before the first one was even tested. As the designers progressed from prototype to final production model, the most efficient configuration for the whole system would be worked out.
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Old 15-09-2008, 11:43 AM   #20
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Quote:
Originally Posted by Perigee View Post
we're going to need to be able to get to earth and back on our own steam,
Oooh, what a lovely idea; steam-powered space craft.


Pssssssshtcoffpsssshhtcoffffpsssshhtcoffffpsssshht coffffpsssshhtcoffff...

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