Don't go quoting Zubrin at me! I
know The Case for Mars, believe me. Besides, a more realistic ISP for a CH4/LOX rocket is 350s, not 380s; look at the Astronautix list of LOX/LCH4 engines, nearly all of them have ISPs of about 350s, and high ISPs are usually more complex to achieve--complexity is not exactly what you want for a Mars launch system. You get a much bigger benefit from not having to cart around a Sabatier and RWGS reactor plus the liquid hydrogen than you lose from the 80s shortage in ISP (especially since you can exploit aerobraking more heavily on the return trip and it's a lot easier to launch from Mars than Earth). No CO/LOX engine has been developed
mainly because CO/LOX performs poorly, isn't storable, and CO is very toxic; flame temperature problems are solvable, but the others are killer since you can get better performing propellants which are either not toxic (kerolox, hydrolox) or are fully storable (hypergolics). On Mars, however, since there aren't any convenient refineries or hydrogen-liquefaction plants lying around, the fact that you can produce your fuels from the atmosphere alone is much more useful.
You also might want to read
this report from NASA about electrolyzing carbon dioxide (hint: it's easier than Zubrin says, due to technology development since the early '90s, and you'll probably want to do it anyways to help close life-support loops). It's not like electrolysis is that poorly understood compared to the Sabatier reaction, either.
Taken a proper look. I stand partially corrected. Suppose I should have stated my previous post as being Own Opinion.
I checked Astronautix.com, which shows LOX/LCH4 Engine Vacumn Isp's of between 322s for the RD-184 to 379s for the RD-167 - with 350s being the average. 380s Isp is certainly achievable, via optimum oxidiser/fuel ratio plus closed-cycle combustion - so long as it can handle the pressures and temperatures exerted on it.
I also know a bit about Reverse Water Gas Shift (RWGS) Reactors, they literally have thousands of hours of service life already, in submarines, and
are very heavy - an intentional design feature so they can double up as ballast. They can be made lighter. And at the time of writing for
The Case for Mars, was the best system available. It's been fifteen years since however, so I consider the information provided to be dated.
NB: While the above does have solid fact in it. It's best to treat it as opinion.
Now for a few questions:
1) While on Mars, you will want a lot of mobility, how do you plan on achieving that? IMO, a habitable ground rover would work best, but needs a solid, reliable power source. I see three ways: a LOX/LCH4 combustion engine using Martian CO2 as the buffer gas; a CO/O2 combustion engine, again using CO2 buffer gas from the Martian Atmosphere; or a Solar+Lithium Ion Battery Electric ground rover.
2) Do you intend to put a number of communication satellites in orbit around Mars and the Mars Orbital Plane for round-the-clock Earth-Mars Communications? I would.
3) Would you use NTR for the outbound leg and possibly the return trip?
Actually, the third question raises a good point IMO. With a reliable Nuclear/CO2 engine, the whole CO/O2 vs LOX/LCH4 debate becomes moot. Furthermore, it provides the ERV with two distinct advantages over the LOX/LCH4 ERV Zubrin advocates.
1: Needing only the Martian Atmosphere at the propellant, if, for some insane reason the Hab and ERVs land literally at opposite sides of the planet, you can just hop the ERV over and fill the tanks again. This isn't possible with LOX/LCH4.
2: You can use the ERV for truly global exploration on the very first mission. Essentially doubling it up as a ballistic (Nuclear rocket using Indeginous Martian Fuels) NIMF.
Those two points say everything IMO. Your thoughts?