Critical Milestone in Liquid Oxygen-Liquid Methane Engine

[josh_simonson]

The ISS panels aren't all that heavy, rather they're attached to a truss that's quite heavy (complete with model railroad!). The main solar arrays will weigh a grand total of 8.7mT when completed, (2.2mT each per launch) while they attach to 13mT truss segments. Here's a quote on power output: <br /><br />Even though the Station will spend about one-third of every orbit in Earth's shadow, the electrical power system will continuously provide 78 kilowatts to ISS systems and users. When the ISS is in eclipse, batteries that stored energy from solar arrays during the sunlit portion of the orbit will supply power. http://www.boeing.com/defense-space/space/spacestation/systems/solar_arrays.html<br /><br />At that power level we're down to 8 months to produce the fuel. Roughly the amount of time currently planned between lunar missions. <br /><br /><br /><br />Electrolysis isn't critical for LEO since boiloff would be negligible between launch and LEO docking. But if one wanted to pre-position fuel in distant locations, like LL2 or Mars, the most efficient option is solar electric propulsion, and that means you need lightweight long term storability. LOX, LH2, and Methane are all out. Going solar-electric for fuel and durable goods delivery reduces the mass fraction to the moon from ~60% down to 5-20% - doubling the amount of fuel/gear to LLO from the same weight at LEO.<br /><br />Decomposing NH3 only takes 92.4kJ, and you get 1 more hydrogen atom than you do with water, so getting H2 from NH3 is 4.5 times more energy efficient than getting it from water, assuming you've already got an available source of oxygen. NH3 is used as a coolant for the ISS, carrying heat from the modules to the radiators, so it's handling in space applications is already well understood.

 

[barrykirk]

<blockquote><font class="small">In reply to:</font><hr /><p> Hey, how about if you go collect the steam exhaust from a LOX/ Methane engine and we will separate out H2 from O2 and re-use them ???? Oh darn, now we will NEED a H2/ O2 engine <<kicking myself now>> <br /><br />OH WAIT !!! <<LIGHT BULB ON />>... .... how about if we just use catalysts and do a reverse reaction of the above ???? <br /><br />2H2O + CO2 ----- /> CH4 + 3O2 <br /><br />then we can re-burn methane and oxygen, and do this all day long !!! <br /><br /><br />I have such GREAT ideas... I need to go patent this stuff ... be right back...... <p><hr /></p></p></blockquote><br /><br /><br />If you re-read my post carefully, you will note that I also considered water as a non-starter, due to it's low, actually negative heat of combustion. I did do the research to verify what the heat of combustion of ammonia is.... And it's very low, which is one of the best reasons why it is not used as a rocket propellant.<br /><br />Hey, you forgot about violating the conservation of momentum required to re-collect the spent water and CO2 from the exhaust.... Oh wait that was another thread....<br /><br />With our current level of technology, using water or ammonia as fuel just doesn't work. Water doesn't make much sense as payload either, other than the small amounts used for drinking.<br /><br />If you want to transport water to the moon. Transport Methane or LH2. It can be burned on the moon with O2 extracted from regolith to make your water. Use Methane if you also need carbon. Use Ammonia if you also need Nitrogen. That is assuming we don't find significant sources of carbon, nitrogen, or hydrogen on the moon.<br />

 

[barrykirk]

Hey, I can think of 2 places offhand where water was used in science fiction.<br /><br />In a couple of early Isaac Asimov short stories published in the 1940's he used the idea of heating water to steam and using the steam as a rocket exhaust. I can't remember but I think that he used a nuke as his thermal source. Remember this was 1940's sci-fi.<br /><br />Also, Robert Heinlein used a spacecraft using water as it's reaction mass. I'm using the word reaction in the Newtonian sense, not the chemical sense.<br /><br />But Heinlein employed some sort of sci-fi type of gadget that converted the entire rest mass of the water to energy and shot photons out the back. And he even had enough thrust to generate over a 1 g of thrust even with the fuel tank full. His spacecraft was 95% water mass at launch and with an engine like that was capable of intersteller, although sublight travel.

 

[josh_simonson]

>If you want to transport water to the moon. Transport Methane or LH2.<br /><br />Nobody is suggesting using ammonia as rocket fuel directly, rather it's a convenient means of passively storing hydrogen indefinitely. If you go with cryogenic fuels like LH2 or methane, you have to pay a big premium to deliver it quickly. It's like sending something overnight/airmail rather than ground/book rate.

 

[propforce]

<font color="yellow">Hey, you forgot about violating the conservation of momentum required.... </font><br /><br />That post was in jest. I'd figure so many posters here disregard the law of thermodynamics as well as the conservation of energy, let's see how many can catch a little disregard in the law of conservation of momentum <img src="/images/icons/wink.gif" /><br /><br />One day a co-worker asked me what's the molecular weight of helium, I replied "which one? regular helium or the monoatomic helium?" That really confused him.... <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Well, if you want to store Hydrogen in space for a long time. Ethane contains a higher percentage of hydrogen by mass than ammonia. Yes the boiling point is slightly lower, but it is much higher than methane. 73 Degrees Kelvin higher. And at pressure that boiling point may rise.

 

[barrykirk]

And what is the flight speed of a sparrow....<br /><br />European or North African?

 

[krrr]

I think the water idea makes only sense in connection with a SEP tug system.<br /><br />These have huge solar arrays (~300 kW) which are used to transport cargo (e.g. water) by electric propulsion from LEO to lunar L1 or lunar orbit. Once there, the powerplant is used for electrolysis and liquefying.<br /><br />Of course, it's not easy. You need lightweight, easily deployable and radiation-resistant solar arrays. Also, a lot of Xenon.

 

[jhoblik]

I was first that bring that idea store our hydrogen and oxygen in form of water. It was for mission to mars almost year ago and I am very happy that it is still alive. I would like to advance that concept little more forward. We don't need to liquefied oxygen and hydrogen for our engine. For interplanetary mission we don't need high thrust in manner of second or minutes, we could speed up for long time. <br />It means electrolyzing water and then using by engine. We will skip liquidation unit and the whole process will be easier.<br />It will save weight of tanks 1 ton 1m3(~10ft3), material could be something like rubber bag.<br />Problem with cryogenic if something failed your fuel vaporize in matter of hours. In case if our electrolyze unit failed you will have time, to fix it and you will not loose resources.<br />For long term mission I didn’t see any alternatives. <br />To expected that cryogenic not failed for years is very risk and one failed event could destroy whole mission.<br />Our mission has to be simple as could and have margin to handle hardware failure, it will increase probability of successfully mission.<br />

 

[nacnud]

Where are you going to get the energy from to split water?

 

[propforce]

<font color="yellow">I was first that bring that idea store our hydrogen and oxygen in form of water. It was for mission to mars almost year ago and I am very happy that it is still alive. </font><br /><br />You are at least 5 years too late to claim that credit. DARPA (hey I am an American so it's ALL CAPS !!) has this chart 6 years ago. It was taken out of an unclassified briefing addressing on-orbit satellite refueling concept.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

So now you abandon Carbon for Nitrogen? You still have to have an oxidizer. Water is so much simpler, the fuel and the oxidizer in a simple to handle, extremely safe form. No cryo-anythings file up a big silver balloon and let it freeze, pretty simple storage if you ask me.<br /><br />Why take more Carbon to LEO than you have to, it's pretty heavy and Nitrogen is no light weight either, though a lot more useful in Space. Ecologically it might be the smartest thing to do, put as much Carbon into Space as we can. The first stage kind of defeats the purpose though.<br /><br />I think it is pretty presumtive to assume an available source of Oxygen. Just to find and exploit any presumed water sources on the moon is going to take all the fuel and all the oxidizer from the surface to LEO. Irregardless of what fuel you can propose. <div class="Discussion_UserSignature"> </div>