On 26/03/2012 3:58 AM, jacob navia wrote:
> Le 25/03/12 07:12, Alan Erskine a écrit :
> The expense is completely enormous. And the usefulness is not much more
> than what an automatic system can accomplish for a small fraction of
> that cost.
You can say the same thing for all spaceflight. The real cost is _not_
going there. Yes, it will be expensive, but have a look at what the
newstarts/upstarts are achieving with space access; give them a simple
order: "Get six people to Mars and return them safely to Earth in the
shortest time and with the least amount of equipment" and they will do
absolute miracles compared to the 'old-timers' like NASA.
>
> Not until we have invested in space technology for a century we will be
> able to go there.
>
> Maybe in 2060, but not before.
As for supplies, it's quite easy to take a cargo module to Mars with the
crew. Once there, the waste matterials (faeces, cans, bottles, paper
etc) can be left behind. Propellant for the return voyage can be made
on Mars - see Zubrin's plan (Mars Direct) for that. On the way to Mars,
the CM could be used to provide some radiation shielding by having it
face towards the Sun for most of the time. And if they're going to be
there for a year (or more), then they can grow fresh food for the return
journey; something similar is done at the Australian Antarctic bases -
based in modified 40ft freight containers. Some supplies would be
needed for emergencies (maybe a leak in the greenhouse or something),
but these supplies are small and only needed until the leak can be fixed
and food production can resume. Human waste can be used, via a
composting system or TDP (Thermal Depolymerisation Process) to provide
whatever nutrients are not present in Martian soil. Nutrients could
also be taken with the crew and would mainly consist of what are called
'micronutrients' that are used in _very_ small amounts. The main
nutrient for plants is carbon dioxide; what a wonderful process plants
use to get rid of their waste - they enable us to breath; that's just a
small bonus of such a system.
Yes, the water recycling system on ISS failed after a couple of months,
but that is where ISS can be really useful for human occupation of
space; we now know which parts of that system are most likely to fail.
Afterall, the actual structure of the U.S. modules has never been used
for people before and they are working quite well.
As for the amount of propellant needed, don't just go by escape velocity
comparisons between Earth and Mars - remember that to get from Earth
Orbit to the Moon, the Saturn V used just 5% of its total propellant
supply at launch. The propellant needed to get from Mars orbit back to
Earth is considerably less than that needed for the entire trip from the
Martian surface. If necessary, that can also be made on Mars, but it
could be sent into Martian orbit ahead of the crew, say using UDMH and
N2O4 which are storable for many months/years. That means the crew
vehicle can be scaled back somewhat.
As for artificial gravity, I agree that it may be needed for such a
voyage, but people don't need 1G for comfort or good health; one-sixth G
is easier to achieve and 'live' with. A system of ion thrusters could
be used to slowly increase spin to 0.38G before arrival at Mars and then
the same thrusters could be used to slowly increase G levels for the
return to Earth.
I remember seeing video of Skylab crew members 'jogging' around the
inside of the OWS; the same exercise could be used to reduce the effects
of zero-G. This would eliminate the need for artificial gravity for
most of the journey altogether. That brings Bigalow's space station
modules into use (large internal diameter with minimal weight/mass).
And you don't need a long module, just a wide one.
As for radiation on Mars, why not use a system similar to that proposed
for the Moon - bury habitation modules under a layer of Martian soil?.
Easy enough to do considering the lack of rocks in some areas. A small
mini-loader could be used. This also provides a more permanent location
for people when the second crew arrive.
Going to Mars and returning safely isn't all that difficult and it isn't
all that expensive; even when compared to Apollo. My own Moon return
idea could be expanded to get people to Mars as well as people to the
Moon. Getting to Mars is more difficult than getting to the Moon, but
no that much more.
It takes about 10% more energy to escape Earth gravity compared to
getting to the Moon. Once on the way, more supplies are needed, but
only a small amount more air/atmospheric gases. As for escape
propellant, it depends on the outward journey time and also
decelleration at the end of the trip (arrival at Mars).
After all this typing, my fingers are sore; I need a break for a while. ;-)