New perspective on the CEV methane engine requirement

[gunsandrockets]

NASA's removal of the requirement for the CEV to use a methane propellent rocket engine generated much anguish in the pro-space exploration community, but maybe it wasn't such a bad decision after all.<br /><br />Aside from whatever merits methane rockets have for the purely lunar mission, they are valued for missions to Mars which employ ISRU to resupply the rocket on the Martian surface. But what if a different propellent could be made even more easily than methane?<br /><br />I found an interesting article about a process for methanol production on Mars. Supposedly, from the same amount of hydrogen feedstock, twice as much methanol/oxygen can be produced compared to methane/oxygen, and produced for half the electrical power. Here's the link...<br /><br />http://www.pioneerastro.com/Projects/index.html<br /><br />...and here's an excerpt...<br /><br />"The Methanol Mars In-Situ Propellant Production (MMISPP) is a method for producing both storable fuel and oxygen on the surface of Mars with 95% of the required raw material derived from the Martian atmosphere. In the MMISPP system, a reverse water gas shift reactor is run in series with a catalytic methanol reactor to combine a small quantity of imported hydrogen with Martian atmospheric CO2 to produce methanol and water, with the latter product subsequently being electrolyzed to produce oxygen and return hydrogen feedstock to the system. The methanol/oxygen bipropellant so produced can be used as either rocket propellant or to feed electrochemical fuel cells to drive rovers or other ground vehicles. The performance of methanol as a rocket fuel is attractive, and its density is high, making vehicle design easier. In the system employed, approximately 20 kg of methanol/oxygen bipropellant are produced for every kilogram of hydrogen imported to Mars, an attractively high leverage ratio. The primary advantage of the MMISPP system however, is its low

 

[gunsandrockets]

From the "Lunar Sooner" plan<br /><br />http://www.spaceref.com/news/viewsr.html?pid=19768<br /><br />Excerpt...<br /><br />ESAS baseline was to use LOx/Methane propulsion.<br /><br />* Initial studies indicated a performance advantage coupled with an ISRU strategy for Mars.<br />* Common development for CEV, lunar ascent stage and Mars ascent/descent propulsion.<br /><br />* Significant risk, cost, schedule and technical driver. Reliability growth through multiple applications.<br /><br />* Mars mission ISRU strategy is very conceptual today<br /><br />* Don't want to over constrain the Mars architecture while increasing cost and risk to initial CEV deployment<br /><br /><br />* After further analysis, it was determined that LOx/Methane has little if any benefit to the lunar architecture. <br />* CEV and lunar ascent stage will not utilize LOx/Methane propulsion. Other state-of-the-art alternatives, including storable and non-toxic options will be evaluated. Still achieves reliability growth through multiple applications.<br /><br />

 

[danwoodard]

Main advantages of methane/lox were higher Isp and no toxics. Will the CEV now use hypergols?

 

[mikejz]

Well you have to remember that Apollo orbited retrograde to allow fo the free-return option. If Methane is used, the lack of experience with the fuel might result in a similar option. If hypers are used, Nasa might feel them proven enough to use prograde orbits.

 

[henryhallam]

What is the advantage in using a prograde lunar orbit?

 

[mikejz]

I must be mistaken then, sorry.

 

[mikejz]

I was under the impression that it came at a significant delta-V penity.

 

[danwoodard]

Hypergolics are cheap to develop because refrigeration and ignitors are not needed, but _substantially_ increase operating cost because of all the complex handling procedures and (particularly with manned vehicles) contingency preparations. Storable nontoxics (i.e. nitrous-oxide/propane) have the lowest operating cost but take about a 15% hit in Isp. Cryogenics have a higher Isp, and methane is highest of the hydrocarbon fuels (perhaps 330 vs 288 for hypergol) Cryogenics have, so far as I know, never been used in long duration missions (i.e. 6 months storage of the CEV at the ISS) and would probably require active cooling or a really well insulated (and heavy) tank. But even this would pay for itself over the long term by increased performance and saving the cost of handling hypergolics. Biting the bullet and developing the new technology now would make space more accessible... assuming we are in the business of developing new technology. Just my opinion.

 

[mikejz]

It would be worth adding that long term storage of cyro fuels would have a clear spin off toward unmanned missions, esp for a Europa orbiter/lander mission.