Using waste for propulsion ?

On Dec/1/2016 at 2:15 AM, Fred J. McCall wrote :
Alain Fournier wrote:

On Nov/30/2016 at 6:31 AM, Fred J. McCall wrote :
Alain Fournier wrote:

On Nov/29/2016 at 9:47 AM, Fred J. McCall wrote :
Alain Fournier wrote:

Le Nov/28/2016 à 9:53 PM, Fred J. McCall a écrit :
Alain Fournier wrote:

On Nov/27/2016 at 10:26 PM, Fred J. McCall wrote :
Alain Fournier wrote:

On Nov/27/2016 at 1:17 AM, Fred J. McCall wrote :
JF Mezei wrote:


100pax over 3-4 months will consume large amounts of food. That is a lot
of mass that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste. Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


I know it's hard for you, but think about it. Most of the mass of
food (and feces) is water. You're going to get the water back for
recycling on the back side of the process. That means each person
will generate 1-2 ounces of solid waste per day once the water has
been recovered (and you'll get 3-6 ounces of water out of the same
waste stream). Let's use the larger number as more 'favorable' to
your case; 100 people (not sure what 'pax' are when they're up and
dressed) will generate around 12.5 pounds of solid waste per day. That
waste is a mix of dead bacteria, indigestible food elements like
cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and
even then most of it isn't going to 'convert'. Recovering the water
is more valuable, since you can make things like breathing air out of
that stuff. So you're going to accumulate a little over half a ton of
such cruft during the course of the trip.

It's not one or the other. You can very well recover the methane and the
water and grow food. Plants don't need the methane from human waste to
grow. So after extracting methane, the waste isn't any less fertile than
it was before extraction.


What 'methane' is there to recover? To get methane from ****e, you
have to process the ****e, removing carbohydrates. That makes it less
fertile because you've removed all the carbon and hydrogen.


Plants don't need carbon in soil, removing carbohydrates is not a
problem. Plants get their carbon from CO2 in the air.


Try growing plants in soil with no carbon in it and see how that works
for you (it mostly will work very poorly, if at all).

Do you have a site to support that claim.
https://en.wikipedia.org/wiki/Plant_nutrition#Carbon
Doesn't seem to agree with you.


While carbon isn't used directly by plants, it seems to be very
important in enabling soil chemistry that is essential to plant
growth.

http://www.unep.org/yearbook/2012/pd..._2012_CH_2.pdf

Maybe I missed something in there. But here is what I saw.
1) Soil organic matter is important because it slows down water run off
which is important not only because plants need the water but also
because this reduces erosion and loss of soil and nutrients.
2) The large amounts of carbon in soil world wide is important because
if all that carbon was released in the atmosphere that would exacerbate
global warming.
3) The biota, mainly bacteria, in the soil decomposes soil organic
matter, releasing the carbon into the atmosphere, which leaves behind
important nutrients.

Point 1) There shouldn't be any large sudden rain fall in the spaceship
carrying colonist to Mars. So this is irrelevant here.
Point 2) I think we will both agree that spacecraft greenhouse warming
is a non-issue.
Point 3) Basically says that to provide nutrients to plants, the carbon
must be removed.


The proof is in the pudding. Go grow some plants of various types in
sand with no carbon content. Fertilize at will, but nothing with
carbon as a component. Let us know how that goes.


The hard part of that would not be growing the plants. It would be
extracting all carbon from manure. Of course that means that on a
spaceship they also wouldn't be able to extract all the carbon in a
bio-digester, only most of it. Therefore your pudding isn't germane to
the current discussion. But if you do succeed in extracting all the
carbon from manure without extracting other nutrients and add it to
sand, there shouldn't be much of a problem to grow plants in there.

Also, how can you possibly imagine that Martian colonists would bring
sand as the base for their soil?


I'm sorry. I was deafened by the screeching from you dragging the
goalposts like that.


You are hearing sounds that don't exist. I haven't dragged any goalpost.


Alain Fournier