On Friday, November 25, 2016 at 7:56:57 PM UTC+13, JF Mezei wrote:
One thing Mr Mook forgot in his analysis:
Musk said his 100 pax ship to mars will be powered by methane.
This is why I wondered if collecting methane from human waste might make
sense, as well as burning/elejcting the rest of the waste. (accelerating
mass bacwards pushes ship forwards).
Even if the amount of methane produced is less than what it needed in
total, it still reduces how much you have to load at start of trip.
Unless the solid waste is needed on mars as fertilizer, you are best off
dumping t before you land since it is pointless to spend fuel to
decelerate and land that mass. And if you're going to eject it, you
might as well do more than mereley throw it is, you should accelerate it
to use it as propulsion.
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.
http://www.space.com/34210-elon-musk...lony-ship.html
A well designed life support system reuses ALL products within the life support system using a modest amount of energy derived from direct solar power to produce
Water (recycled)
Oxygen (recycled)
Carbon black (odor absorber)
Ash (micronutrients used for fertiliser)
from the waste products (including breathing)
As shown, 2.1 kW is suffiicent to fully recycle all the waste from 14 people. So, 100 people requires 15 kW of continuous power. This power can be obtained from concentrating solar photovoltaics which produce about 22 kW per kg of payload at 1 AU and produce about half that at Mars distance.
https://solarthermalmagazine.com/wp-...s_CPV-zoom.jpg
https://web.archive.org/web/20131228...V/Mac_Mook.gif
https://www.google.com/patents/US20050051205
Most large cruise ships have about 4,000 cubic feet of cabin space per passenger (227 cubic meters per couple). So, fifty couples would take 11,350 cubic meters. A sphere 28 meters in diameter (92 ft) houses 100 people at the same densities as large cruise ships. 12 levels across the diameter produces 11 floors - one central floor and 5 pairs of floors.
L x Radius Area
0 0 14.00 615.75
1 2.2 13.83 600.55
2 4.4 13.29 554.93
3 6.6 12.35 478.90
4 8.8 10.89 372.47
5 11 8.66 235.62
**** **** Total 5,716.44
SF SM Cabins
183 17.01 336 - Luxury suite cruise ship
450 41.83 136 - Luxury suite Waldorf Astoria
600 55.77 102 - Luxury suite Waldorf Towers
So, with a luxury cabin with two persons each, you need fifty cabins of that size for 100 passengers. So, half the 'floor space' is taken up by cabins and the rest for 'public space'.
http://www.lpi.usra.edu/lunar/strate...manstoMars.pdf
http://trs-new.jpl.nasa.gov/dspace/b.../1/09-3642.pdf
An array of concentrating photovoltaics have the capacity to generate 500 kW of power at 1 AU- far more than needed to fully recycle 100% of the air and water, and reduce surplus to elemental carbon and micronutrient ash (which is used for fertilisers when on Mars). The mass of a well designed system would be around 25 kg.
For a Mars mission I like the idea of using very high altitude aerobraking to bring the spacecraft onto the surface of Diemos.
http://www.spacefuture.com/archive/t..._company.shtml
And then use water found there and the copious solar power available to create hydrogen and oxygen propellants for supplying rocket belt descents to the Martian surface.
0.87 km/sec is required to take an object from Diemos to Low Mars Orbit.
23,459.0 km - Diemos semi-major axis
3,396.2 km - Mars equatorial radius
5.03 km/sec - Mars escape velocity
3.55 km/sec - Mars Orbital Velocity (low Mars orbit)
1.35 km/sec - Diemos orbital velocity
So, once landed on Diemos, with a spare 200 kW of electrical power - you can break down water ice (if any) into hydrogen and oxygen at a rate of 5.077 litres per hour. Hydrogen is made at a rate of 0.564 kg/hour and oxygen at a rate of 4.513 kg per hour. Using LOX/LH2 hat a O/F ratio of 5.5/1.0 that means that 0.564 kg/hour of hydrogen is combined with 3.103 kg/hour of LOX leaving 1.410 kg/hour of LOX to spare.
Now, to boost from Diemos to Low Mars Orbit requires a delta vee of 0.67 km/sec. After 1.927 hours the person with rocket belt skips into the Martian atmosphere moving at 4.701 km/sec. Aerobraking is used to bring the traveller down to zero speed and zero altitude - using only 0.20 km/sec. Skipping off the atmosphere back into orbit, after slowing to 3.551 km/sec - enters LMO. So, the delta vee to move from Diemos to LMO or the Martian surface itself ranges from 0.67 km/sec to 0.87 km/sec.
On the surface of Mars it takes 3.551 km/sec to enter LMO and another 1.145 km/sec to boost back up to Diemos in 1.927 hours.
Diemos -- Mars 0.67 km/sec - LMO
0.87 km/sec - Mars Surface
Mars -- LMO 3.551 km/sec
LMO -- Diemos 1.145 km/sec
A total delta vee of 5.566 km/sec is sufficient to carry an astronaut to the Martian surface and back to a ship stationed at Diemos. This requires 200 kg of propellant for an 85 kg astronaut in a long duration pressure suit. This includes 30.8 kg of LH2 occuping 439.6 litres of volume and 169.2 kg of LOX occuping 148.4 litres of volume. A total of 200 kg of propellant occupying 588 litres. Four tanks carrying 50 kg each of propellant. Spherical tanks 655 mm in diameter (25.78") with a 414 mm diameter (16.29") LOX tank inside each.
Providing ice is found on Diemos, sufficient propellant is generated to send 6 people to Mars and back via rocket belt every day. Virtually the entire passenger complement every two weeks!