Interesting paper on all this:A CHEMICAL APPROACH TO CARBON DIOXIDE UTILIZATION ON MARS
As regards the thread title CO/O2 looks like a very usable system for work *on* Mars and acceptable performance for ascent *from* Mars.But slightly off topic does it also make a viable fuel for return *from* Mars?{snip}
LH2/LO2 is the obvious propellant for the EDS but would it be a serious hit in tank size and payload to go with a return propellant *solely* mfg on Mars?
Also, here's an interesting proposal from Zubrin, et al, of a mixed methane/CO/O2 propellant Martian ISRU rocket system, which benefits from the added density of CO but retains most of the Isp of methane while also making the production equipment easier and smaller and more productive for a certain energy input, and Methane/CO/O2 all are storable at the same temperature, making common-bulkheads easier:http://www.techbriefs.com/component/content/article/3365http://hdl.handle.net/2060/20080047195Mars Rocket Propulsion System (published November, 2008)Sounds like a total win, except you still have to have more development of rockets using such a propellant combination (EDIT: And, you still will likely need to bring hydrogen from Earth).
You mean for return to Earth? I think LOX/LH2 is far from obvious for that, with hypergolics being the clear favourite, followed by LOX / methane produced from Martian carbon dioxide with hydrogen / water brought from Earth.
Quote from: Robotbeat on 05/10/2010 07:04 pmAlso, here's an interesting proposal from Zubrin, et al, of a mixed methane/CO/O2 propellant Martian ISRU rocket system, which benefits from the added density of CO but retains most of the Isp of methane while also making the production equipment easier and smaller and more productive for a certain energy input, and Methane/CO/O2 all are storable at the same temperature, making common-bulkheads easier:http://www.techbriefs.com/component/content/article/3365http://hdl.handle.net/2060/20080047195Mars Rocket Propulsion System (published November, 2008)Sounds like a total win, except you still have to have more development of rockets using such a propellant combination (EDIT: And, you still will likely need to bring hydrogen from Earth).It sounds complicated and less reliable. Don't think you can mix liquid CO and liquid methane. If not, then you need 3 tanks for pressure fed system, or 3 pumps for gas generator cycle. on top of that, where do you generate methane? on mars? you need to bring hydrogen, equitment to make methane, and extra set of tool to make CO. How about, producing biogas(methane) while your astronauts are on the way to mars, at the same time you have a robot producing CO on mars surface. In stead of mixing methane and CO, the lander use methane for descent, and the same lander same engine same tank use CO to ascent.
carbon monoxide boils at −191.5 °C, methane melts at -182 °C. When you have liquid CO, does methane supposed to be ice?
I still don't see how "Zubrin proposal" is interesting. If you make CO and O2 on mars surface, you don't need to bring any raw material, as long as your solar panel and equitment whatever work, it keeps making propellant. On the other hand, you want extra methane, you need to bring hydrogen, that's logistic problem, worst case you need to launch from earth all the way to mars.Is it really worth that extra performance? you know 290s isp is not so bad, F-1 only has 263s. I was thinking you can use robot craft to bring extra CO+O2 fuel up to mars orbit for return flight propellant back to earth, that Zubrin proposal just bust my dream.
The Martian atmosphere has 3 % nitrogen. How feasible is it to extract this and produce nitrogen tetroxide (NTO)? Might be much easier to handle than LOX on Mars, since it does not need to be kept cool for 2+ years and could easily be stored as a liquid or even as a solid.I don't know if NTO can be used as an oxidizer for CO or CH4, but if you bring hydrogen with you, you could produce hydrazine. NTO+Aerozine-50 (1.93 O/F ratio) is storable, well known as a rocket fuel and just 5 % hydrogen by weight.EDIT: Corrected numbers
Necrobumping this thread, but...I recently saw a presentation by Geoffrey Landis, and he said that the optimal exhaust velocity from an energy standpoint is equal to about 2/3rds of your mission delta-v (exhaust velocity equal to current velocity is actually the most efficient as it leaves the exhaust with exactly zero kinetic energy relative to the rest frame, but requires you to adjust your exhaust velocity continuously, and also requires ridiculously big tanks at the beginning). The very minimum effective delta-v (ignoring gravity drag, but including gravitational energy and ignoring aerodynamics and including the benefit from Mars' rotation) is 3.4km/s. Let's say we get really good thrust/weight ratio and low drag, then perhaps the real-world delta-v could be about 4km/s.2/3rds of 4km/s is 2.7km/s. That is doable by CO/O2. Thus from an energy perspective, CO/O2 may actually be more efficient from an energy perspective than other propellant combos (unless you "cut" them down by adding CO2 or something to the propellant), plus is ubiquitous on Mars and very dense. It's almost like Mars is telling us to use CO/O2......if only CO/O2 weren't so dangerous to test on Earth. Still, we use hydrazine which is pretty fantastically horrible, so I don't think CO/O2 would be impossible.
It would be amusing if flying to Mars, landing, cracking CO2 into CO and LOX, then launching, flying back to LEO, and refueling an Earth LEO propellant depot proved cheaper than refueling a propellant depot from Earth.