In article om,
says...

On 2016-11-25 19:32, William Mook wrote:

Propelled by Methane and LOX - that's different than the crew systems being powered by methane. The amount of methane consumed during launch, and boost into Mars transfer trajectory is vastly larger than the amount of methane produced from life support processes.

Launch and escape from earth are not a concern as launch is done with
fuel from ground over many launches to bring fuel up. And escape from
Earth would happen well before the passenger waste would have generated
significant amoumt of methane.

However, the methane generated during the 90 or more days to mars would
help *reduce* amount of fuel needed to get into Mars orbit and then
de-orbit.

If human waste produces methane, does it make sense to use energy to
recycle methane to something else when you can use it almost directly
for engines ?

Gnat's farts. In the big scheme of things, you're not going to want to
use methane produced from human waste for propulsion. We're talking
mass fractions here. What fraction of the overall spacecraft mass is
the methane produced? Maybe you'd use it for maneuvering thrusters,
maybe. But "propulsion" is laughable.

Jeff
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