Raukk

Thank you, I heave read that. Sadly the cost of those systems was not disclosed in the article.

The idea was never intended for backbone networking, but for "Last Mile," given the low cost of a LCD screen it may be possible to get decent bandwidth (100+Mb/s) for less than $1000 per mile, which I think is several times cheaper than Fiber-optic. Also, my question was, "is it possible", not "is it practical".

The original idea that spurred this question is the idea of free-space optical communication and that "a picture is worth 1,000 words." In theory I could shine a laser through a beam-expander and then an LCD display (or DLP) to a receiving station some distance away that would take the image an turn it into data. If no data was lost in transmission (not realistic) my cellphone's screen could transmit 300+ MB/s (2560x1440, 30hz, 24bit color depth). I know that example is simplistic and flawed but you get my point.

The longest range I've heard for a projector is 300m (on one that costs as much as my car) and I was thinking ranges of 1-2 mile(s) as very long distances. If I wanted to project an image on the moon I think the laser would melt the LCD. Lol, now I want to project my face on the moon.

That was what I thought! Could you then in theory make a projector that would go very long distances?

I apologize if this question is dumb. I understand that LCDs work by polarized light and by the ability to change that polarization of light passing through the Liquid crystals, and the light is normally provided by a back light. If that back light was removed and replaced by a laser would the laser light pass through the LCD the same as normal light and if it does; once it exited the LCD would the laser light still be a laser (ie. not expanding)? As a rough example, could an image be projected at a distance by a laser traveling through an LCD screen? Thanks for any input, my optics knowledge is a bit rusty.

The Traditional guns would be great for point defense and knife fight range given the reduced weight you mentioned, but the much higher velocity of a rail-gun would win out for long ranges, even at 100km you would need crazy high speed to get to the target in under 10 seconds, and 100km is short range for space. Rail-guns and lasers have the same downside, tons of mass to support the huge power budget and radiate the heat, which makes the cost for damage ratio high. I'd personally prefer Missile volleys, the enemy knows that a few have nukes and the rest are traditional, but intercepting all of them would be hard, also shrapnel could damage or disable point defenses. The downside is the long flight time required to reach the target.

I apologize that I have not read this whole thread; I’m probably saying what many others have already said. First, having wars in space is a very bad idea. Using current(ish) tech: There are a lot of possible situations for the battle, like being in orbit around a planet, or near an asteroid/L-Point, or in deep space. All of which have different tactics and technologies. Ultimately it all boils down to the tradeoff of main traits Speed/Armor/Weapons. Chose one major and one minor, ex. Missile is Fast with ok Damage but Battleships are Armor with some Weapons. In Orbit, a war would require mainly battleships because of the Kessler syndrome that would result from many battles. A battleship would have heavy armor (to ignore the debris) and ok guns but no speed, and it would probably also house fighters/drones/missiles. Any small craft without a dock would eventually be worn down and destroyed by all the debris in orbit after the initial battle or 2. A fixed point of interest like an L-Point or asteroid would likely have defense stations or battleships on the defending side but not on the attacker side. Because this would be like a siege the attackers would focus on high attack ships with decent maneuverability. The attacker would stay at long range and bombard the defenders that can’t abandon their base/resources. In deep space it could really be any variety of craft but would likely lean towards the speed and firepower spectrum. Using hit and run tactics against heavy slow targets would be a good way to wear down the enemy. The equipment used by the ships would be mostly determined by what the other faction is using and what is available. Heat: in space heat must be radiated away, if not, then you melt. Radiators that get rid of lots of heat are large, unarmored, vital parts of your ship. If you have to little radiators then you can’t do much without melting, but if you have a lot of radiators then you have lots of weak spots. Weapons/Armor: Very heavy, thick armor would be very expensive for us to launch into space and increase fuel costs of flight and therefore impractical. Lasers are great for space because of the speed of light, but could be blocked by good armor, create tons of heat, and take tons of power, as well as being massive. With these points Lasers are sniping weapons for use at huge distances or for use as point defense. Mass drivers/rail guns fire high velocity shells that can do tons of damage, but even at high speeds they must be very well aimed and will take a long time to hit their target, giving a good chance to dodge. Missiles are much slower and easily shot down but can redirect midflight to follow targets, missiles would likely explode into shrapnel well before the target is reached or carry a nuke. Armor and countermeasures can be designed for all the weapon types proposed, a very fine mist over a large area could refract lasers to negate or reduce their attack, missiles can be intercepted, and debris can be blocked with spaced armor (like the ISS uses). Rail guns would require very good armor to block but very little to dodge (in 100 km scale battles, even at 5km/s it gives 20 seconds to move). Fighters/Drones: with the cost of keeping someone alive in space I don’t expect that manned fighters will be used ever. Point defense drones are most likely with the possibility of interceptors or bombers. Ground Attack: Nuking is the most effective, Lasers loose power to the atmosphere, missiles are large and expensive for their damage, bombs specifically designed for this would work ok, and rail guns are good for precise targets. Actually invading from orbit is laughable given the troop/material/supplies needed to be delivered to the surface you’d be better to just bomb them into the stone-age and then set yourselves up as their gods. I would expect that most battles would either be over very quickly (minutes) or end in a draw. There is the chance for a real slug fest but it’s unlikely given the physics of orbits and the distances involved. No matter how this goes, I feel that everyone loses.

@KerikBalm: That is what I was thinking by the end of it, but I'm guessing that the physical constraints of the combustion chamber to deal with the 4x temperature would be to great to overcome (or would make LH2 more viable). Edit: If my initial (and probably wrong) calculation is right then the Al2O3 would need to be at 5.6 times the temperature of the H2O leaving the engine. That means that you are dealing with 10,000-20,000 degrees C for the engine, I don't think we have any material that can deal with that. As was mentioned with the SRBs, it's a much different reaction that carries a lot more mass per unit energy but gives a lot more (and lighter) resultant compounds which would mean a lower operating temperature. After this very informative thread I have come to the conclusion that in theory an aluminum rocket would be as effective or more than LH2, but in reality constructing such a rocket is not possible/economical, especially when LH2/LOX is so common and well understood.

I assume the reason they use ammonium perchlorate rather than a more Oxygen dense Oxidizer is for the multitude of molecules that this reaction creates? Wouldn't that mean a higher pressure at a lower temperature, I assume Al + O2 would just melt the rocket? When compared to my earlier calculations this reaction has a much worse MJ/Kg so it must have some other benefit. If anyone knows the official reason that they use that combination then I'd be curious to hear it.

I was assuming that if Iron was needed (Ferrous metals are useful) it would be easier to mostly refine the Iron oxide with excess aluminum for the refinery, then to purify the dirty Iron, being that iron melts at a lower temperature than is needed to refine it, I assume that would be easier to achieve. I understand the thought, but I assume this is for a theoretical mars base. Because you need food to eat then you should just get your Ox from plants, Mars One has been getting flack because it would have too much Ox, not too little. If it was on the moon then there would be other problems but I think getting it from Metal is about the most energy intensive way to get Ox.

Yep, that's what I get for over simplification.

I'm not sure why this is a quote of my comment, I was asking for the source of his ISP numbers, not how much of it exists on the moon. I'd point out that we are swimming in Aluminum too. "Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal in the Earth's crust."

Thank you, that's quite interesting. I'll have to look around that site more, I really wish they would show their math/source. I'm going from the simplified idea that if you pump 15 Mega-Joules into 1 Kg of material regardless of it's density it would still exit at the same speed E= 1/2 M V^2. I'm probably not taking into account the Ideal Gas law PV=NRT, where 1KG of H2O would have more moles than 1Kg Al2O3 and then the higher pressure would make a higher exit velocity.

Interesting, might I inquire where you got both those numbers from?

I'm curious of the intent behind this question. If you are thinking industry on Mars then I'd ignore getting any oxygen out. If you are thinking of getting breathable air, then plain Co2 (or maybe water) is your best source. As for how much energy is used, I think the Wiki page for different metals or oxides would have that, I believe that Aluminum is around 50 Mega Joules per Kg. If I was going to Mars I'd want to bring a method of refining Aluminum, someone already mentioned you can make thermite and reduce iron with aluminum, and thereby getting 2 refined metals for the price of one.

Aluminum as rocket fuel? This discussion is purely theory, and for fun. Please point out any errors: math/logic/etc. Note: numbers are from Wikipedia unless otherwise stated. At first glance Aluminum seems like a terrible Rocket fuel, but after I ran some numbers it appears that it could compete with LH2. I’m aware of other projects using Aluminum, like AlIce: http://en.wikipedia.org/wiki/ALICE_(propellant) But I just want to talk about theoretical ideas with this thread. Initially the Energy Density of LH2 of 141.86 MJ/Kg versus Aluminums 31 MJ/Kg seems like an obvious winner except that for a rocket the Oxidizer must also be carried on board and should also be included into that equation. For every 2 atoms of H we need one atom of O; 2*H + O = H2O : 2*1 + 16 = ~18 molecular weight, so for each Kg of LH2 we need 8Kg of LOX. 141.86 / 9 = 15.762 MJ/Kg when the LOX is included in the weight. Interestingly Aluminum being reduced to AL2O3 smaller Oxygen requirement; 2*AL + 3O = Al2O3 : 2*27 + 3*16 = ~102 molecular weight, so for each Kg of aluminum only .889 Kg of LOX is needed. Which means 31/1.88 = 16.41MJ/kg is the energy density per Kg of fuel + LOX, which is higher than LH2. Looking at these numbers I assume that I made a mistake somewhere in the math or science somewhere. The other Thing I find interesting is that Aluminum is almost 40 times denser than LH2, so that when you consider an equal amount of energy, say 10,000 MJ (about 1 cubic Meter of LH2). LH2 would take 70.85 Kg and 566.8Kg of LOX, LOX is 1141 Kg/cubic meters, so 566/1141 = ~.5. The total LH2+LOX fuel has a volume of 1.5 cubic meters. Aluminum needs 323 Kg to create that amount of energy, at 2700 Kg/cubic meter that is a volume of 0.12 cubic meters; it also requires 287Kg of LOX, giving an additional .251 cubic meters for a total of .371 cubic meters. Which gives us a ratio of 1.5 to .371 gives us a total of 4 times as much volume in fuel for LH2 as for Aluminum. I am sure there are huge technical hurdles to making Aluminum a Rocket Fuel, but if it has the same energy density as LH2 but ¼ the volume I would expect it to be under more significant development. My current conclusion is that I have missed something or done some math incorrectly or else we would see more research into making rockets powered by Aluminum. What are your thoughts on this? If my logic and Math is correct, what do you think are the technical hurdles that would make Aluminum non-viable?

While I'm unsure of the energy budget or the resources required; it would be possible to use Electrolysis to split water into Hydrogen and Oxygen and collect them in separate containers before feeding the Hydrogen into a fuel cell supplied with O2 from the green house, the excess oxygen from the Electrolysis could be stored or vented. I assume the fuel cell power and H2O products would be recycled back into the closed system. I have no idea if this would be a better or worse solution than the other ones stated in this thread.

Thanks for all the informative responses, I am trying to ignore R&D costs since those are spread between an undetermined number of launches. I understand that the Falcon 9 is kept as a trade secret, are there any Rockets which have been disclosed more fully, like the Saturn V? (Since the space shuttle is not a traditional rocket it may not be as good for a comparison)

HAHAHAHAAA.... oh wait, that was serious huh? Hum, I guess that explains why they are trying for re-usability so bad. Personally I'd look at reductions to the cost of the hardware even if it increased the fuel amount (though that can cause more hardware I guess).

Looking at Wikipedia; they quote the cost per launch of the Falcon 9 at around $60 million and quote the weight at 1,115,200 pounds. If this cost is just for the rocket then it’s about $50 per Lb, which seems like a lot given that most of the weight is fuel (which is much cheaper). So my question is, does anyone have the cost breakdown of a real Rocket, ie. How much of the cost is fuel, structure, legal, development, etc.? Thanks, Raukk