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Author Topic: Alien propulsion won't work IRL  (Read 14183 times)

Offline morse

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Alien propulsion won't work IRL
« on: May 29, 2012, 07:36:24 pm »
Since you want to be a "hard sci-fi", you should change your alien propulsion ideas.
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It uses direct matter-antimatter annihilation to generate thrust by injecting protons and antiprotons into the reaction chamber, then channeling this explosive force out the back of the engine.
Well, sorry, but this just won't work this way. The linear momentum preservation law tells us, that in order to move forward, we need to throw something backward, easy as that. Suppose the antimatter itself is this "something". 1000 points of AM is 10 grams, while a full tank is ~50 points, means, 0.5 grams + 0.5 grams of matter = 1.0 gram. Assume the engine efficiency is 100%, and this gram goes out at the speed of light. The mass of the ship is... well let's say 30 tons (the mass of MiG-29). 3*10^9 / 30*1000*1000 = 100 m/s. The full tank provides one-time acceleration to the speed of 100 m/s in the absence of friction. Happy journey!
In the air, this engine can still work as a ramjet (http://en.wikipedia.org/wiki/Ramjet), although ramjet is working only on high speeds, and you have to think of some other propulsion system to give the ship initial acceleration.
But anyway, in space - you're out of luck.

Offline ShipIt

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Re: Alien propulsion won't work IRL
« Reply #1 on: May 29, 2012, 08:04:33 pm »
So we cannot use the idea of the Alien AM-Engines in 'Flight Simulator 19 Gold'?  :-\

Offline Nutter

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Re: Alien propulsion won't work IRL
« Reply #2 on: May 29, 2012, 09:13:22 pm »
How about having antimatter reactors and plasma drives?

The annoying thing about this is that it's bloody hard to find a propulsion method that properly illustrates their technological advantage without resorting to some sort of agrav or something of the sort.

Seriously, glorofied rockets and FTL just doesn't sound right, does it?

Of course, if they do manage to strap a propulsion system we tend to keep for sattelites and deep space craft on an atmopsheric craft...well, the hills would start looking like a nice place to be.
« Last Edit: May 29, 2012, 09:15:11 pm by Nutter »

Offline Crystan

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Re: Alien propulsion won't work IRL
« Reply #3 on: May 29, 2012, 09:29:24 pm »
So we cannot use the idea of the Alien AM-Engines in 'Flight Simulator 19 Gold'?  :-\
Rofl

Offline morse

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Re: Alien propulsion won't work IRL
« Reply #4 on: May 29, 2012, 10:00:10 pm »
The annoying thing about this is that it's bloody hard to find a propulsion method that properly illustrates their technological advantage without resorting to some sort of agrav or something of the sort.
Oh, it actually is very simple. Try this: "we do not understand the underlying physics completely. whatever it is, it lies well beyond every modern theory"
And yes, I understand the difference between sci-fi and boring reality, but even sci-fi must be self-consistent and go in accordance with the current science. So if you want to provide an explanation on some tech, let it be correct. If you can't - just provide nothing, like you do with antimatter.

About FTL I also have a complain. In "alien origins" you say "FTL violates relativity", which is, of course, true, but what you actually meant was "the way the ship pops in violates relativity", which is not exactly true, as we do not know how the ship pops in.
The theory of relativity is too well-established to just say "this ship violates it" and pretend that you are still a "hard sci-fi". But the thing is, that no theory can be "the theory of everything", every theory has it's scope, and you just need to go outside this scope, and limitations of this theory won't apply anymore. Modern human science doesn't go outside relativity theory, alien's - obviously does.

Long story short: when you need to describe something beyond modern physics, do not try to apply modern theories to that, because in that case you'll be bound to the restrictions of that theories. Just say "we do not have theoretical basis for what we see".

Offline TrashMan

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Re: Alien propulsion won't work IRL
« Reply #5 on: May 29, 2012, 10:05:58 pm »
Good point.

and why is anti-grav bad? Isn't UFO:AI supposed to be a fan.based spiritual sucessor to X-Com? X.com had anti-grav in several shapes and sizes. It even had a enemy that floated on a mini anit-grav engine.

Offline Crystan

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Re: Alien propulsion won't work IRL
« Reply #6 on: May 30, 2012, 12:24:28 am »
Good point.

and why is anti-grav bad? Isn't UFO:AI supposed to be a fan.based spiritual sucessor to X-Com? X.com had anti-grav in several shapes and sizes. It even had a enemy that floated on a mini anit-grav engine.

Did i miss something? Probably missread antimatter with anti-grav?

Offline Sarin

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Re: Alien propulsion won't work IRL
« Reply #7 on: May 30, 2012, 02:07:46 am »
The annoying thing about this is that it's bloody hard to find a propulsion method that properly illustrates their technological advantage without resorting to some sort of agrav or something of the sort.

This is where it began.

IMO the biggest problem with AM engines is the fact that UFOpaedia overstates energy gained from M/AM anhillation. Easiest solution-change the units. Instead of 1 unit AM=0.01 g, let's do 1 unit=1g. Only thing nescessary is to overwrie a few words in UFOpaedia about AM, alien engines and AM storage building.

Offline Kildor

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Re: Alien propulsion won't work IRL
« Reply #8 on: May 30, 2012, 03:47:23 am »
May be because ufoai is not x-com at all?
X-com also has ellirium, cydonia and flying suits, which we do not have.

> Did i miss something? Probably missread antimatter with anti-grav?
Trashman have had another model, but it cant be included to the game without anti-gravitation. Well, I prefer game without anti-gravitation and model. But he always can make a mod or even fork.

Btw, we need some models, why do you not want to make they?

Offline morse

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Re: Alien propulsion won't work IRL
« Reply #9 on: May 30, 2012, 10:48:59 am »
>we do not want agrav

Well, sorry to disappoint you guys, but with this
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In the simplest terms, it's a gravity sensor, scanning for minute changes in a background gravitational field. Everything travelling through a gravity field disturbs the field to some degree based on its size, mass and composition.
in "alien detection" you already gave the aliens the ability to play with gravitational field so advanced, that simple agrav looks child's play.

Offline Crystan

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Re: Alien propulsion won't work IRL
« Reply #10 on: May 30, 2012, 12:15:43 pm »
> Did i miss something? Probably missread antimatter with anti-grav?
Trashman have had another model, but it cant be included to the game without anti-gravitation. Well, I prefer game without anti-gravitation and model. But he always can make a mod or even fork.
Well yes i know but he came up with that in this thread from nowhere ;)

As far as i can tell - its actually ridiculous to discuss science things in a scifi game which is about a alien invasion in 70 years in the future - as long as it sounds reasonable iam fine with it. But thats just my personal opinion. :D
« Last Edit: May 30, 2012, 12:18:51 pm by Crystan »

Offline TrashMan

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Re: Alien propulsion won't work IRL
« Reply #11 on: May 30, 2012, 02:06:50 pm »
May be because ufoai is not x-com at all?
X-com also has ellirium, cydonia and flying suits, which we do not have.

IIRC, flying suits are in the TO DO list.

Also, if you want ot make the setting even mroe believalbe, set the date a bit lower. 70 years in the future, adn yet it doesnt' look like it and doesn't feel like it.

2030 or 2040 work FAR better than 2084, given the look and deisgn and "feel".

Offline Kildor

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Re: Alien propulsion won't work IRL
« Reply #12 on: May 30, 2012, 03:36:31 pm »
If I remember right, the flying suits are jetpacks-jumpsuits, not real flying suites.

And yes, I totally agree with you about misplaced year of the game, currently it is not 2084 at all.

Offline Jon_dArc

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Re: Alien propulsion won't work IRL
« Reply #13 on: May 30, 2012, 03:46:52 pm »
Well, sorry to disappoint you guys, but with thisin "alien detection" you already gave the aliens the ability to play with gravitational field so advanced, that simple agrav looks child's play.
They were given the ability to observe gravitational fields to that level—I'm not seeing anything that implies that they're able to manipulate them other than the old-fashioned "move masses around" approach.

~J

Offline Starbug

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Re: Alien propulsion won't work IRL
« Reply #14 on: May 30, 2012, 03:48:20 pm »
*WARNING BIG POST AHEAD*

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In the simplest terms, it's a gravity sensor, scanning for minute changes in a background gravitational field. Everything travelling through a gravity field disturbs the field to some degree based on its size, mass and composition.

Well, sorry to disappoint you guys, but with thisin "alien detection" you already gave the aliens the ability to play with gravitational field so advanced, that simple agrav looks child's play.

Nooo you mis-read that. The alien detection does not 'Play' with the gravitational field at all, it detects changes in the background field, caused by other objects passing through it. Its purely Passive. Remember, all objects with mass have their own gravity, just that its too tiny for *us* to detect on anything other than a planet, (or a mountain, if you've got more sensitive equipment. Think GRACE. Its been  in orbit since 2002)

With regards to how the aliens do it, think of the gravitational lensing effect that stars have on the space around them but on a much, much MUCH tinier scale. They are detecting how much the mass of an object (say, a fighter jet) is bending the space around it, due to its (tiny) gravitational field.
(I THINK, obviously I don't know how the aliens do it, its not said exactly in the game. But I'm fine with that. It explains enough to be believable on current science, but doesn't make up a bunch of sci-fi explanation for how stuff works. And it can't anyway, since the point of view its from, we don't have the same theoretical know-how as the aliens do)

Since you want to be a "hard sci-fi", you should change your alien propulsion ideas. Well, sorry, but this just won't work this way. The linear momentum preservation law tells us, that in order to move forward, we need to throw something backward, easy as that.
Yes, Newton's 3rd law, 'The action and reaction forces between two bodies are equal, opposite'.
Chemical engines work by throwing out lots of mass (all that Hydrogen + Oxygen) at a high velocity (thats what all the combustion is for), giving lots of momentum (Mass x Velocity). The space shuttle, for instance, throws out lots of fuel with lots of momentum out the back, and it goes forward.

However, Newton's 3rd law ALSO applies to EXPLOSIONS. Thats how a gun works.
When you fire a gun, a bullet comes out one end, and the barrel recoils in the other. But the barrel and the bullet are not pushing on each other!! There's an explosion inbetween, which pushes on both. The barrel contains the explosion, so most of the force goes into pushing the bullet forwards and the barrel back. If the barrel wasn't strong enough, it would also explode outward, but that's not too fun.

The antimatter engine, as described in the UFOpedia, is effectively using the explosive force to push the rocket along. Not the craziest idea we've had. (see 0.23 - 1.18). (It doesn't use little bomblets like this, but the principle is the same.)

Suppose the antimatter itself is this "something". 1000 points of AM is 10 grams, while a full tank is ~50 points, means, 0.5 grams + 0.5 grams of matter = 1.0 gram. Assume the engine efficiency is 100%, and this gram goes out at the speed of light.
While your numbers are lovely, what you're doing is effectively how an Ion engine works, i.e firing a constant stream of low mass particles (ions in this case) out the back of a spacecraft at near-the speed of light. A different way of getting lots of momentum. Good for space, but not for getting off the planet :P.

In the air, this engine can still work as a ramjet (http://en.wikipedia.org/wiki/Ramjet), although ramjet is working only on high speeds, and you have to think of some other propulsion system to give the ship initial acceleration.
But anyway, in space - you're out of luck.
NO  >:(. Anti-matter Annihilation DOES NOT EQUAL combustion!! Combustion requires Oxygen (space rockets work cos we take our own liquid oxygen with us).
Anti-matter Annihilation changes Matter into Energy direct. E=mc2. (Cliché I know, but yes, you can actually use that equation here!). Mass, x Speed of light squared = Shitloads of energy. The mass actually isn't there anymore... its been converted to energy. Mass is in effect a different form of energy. Conservation laws of Mass and Energy are not broken.
Both can result in explosions, yes, but Combustion requires oxygen.

How about having antimatter reactors and plasma drives?

The annoying thing about this is that it's bloody hard to find a propulsion method that properly illustrates their technological advantage without resorting to some sort of agrav or something of the sort.

Seriously, glorofied rockets and FTL just doesn't sound right, does it?
That sounds like a good idea to me. Using the explosive force of anti-matter as the propulsion did strike me as *glorified rocket engine* as well, it didn't quite sit right.
Also if you are using the antimatter as the propellent, how off-earth would you use it to go FTL?? Antimatter reactor and plasma drives seems to make more sense to me. (With FTL as some separate system, that does whatever it does using the power from the reactor)

Since the aliens can get plasma weapons working in our atmosphere fine, plasma engines sound plausible. The engines as they are look like they could be plasma engines or whatever. Antimatter reactor could definitely get lots of power out of them. No need to say how they work, just that for the aliens, they do.
« Last Edit: May 30, 2012, 04:01:05 pm by Starbug »