Supplies

Any manned mission to mars will require provisions to sustain its mechanical systems, crew, and crew activities.

Life support systems, for example, require relatively steady streams of material resources in order to sustain a suitable environment for the crew.

Supplies for Life Support

The most basic supplies for life support are those necessary to maintain the life and health of the crew. Over the course of any given day, people must have oxygen, water, and food in sufficient quantity and quality, or they will eventually perish from the deficiency. Other materials, such as medications, cleaning supplies, scrubber cartridges, etc. must also be provided over the course of the mission to keep the life support system functioning and to prevent illness and/or death. Human beings require these materials on a daily, weekly, or monthly basis, and the life support system and cabin stores are responsible for providing them.

The following is an example of material usage rates for a given open loop life support system:

Human Consumption
	Usage (kg/cycle)	Use Cycle (days)	% Recycled
Oxygen	1.1	1	0%
Water	4.4	1	16%
Food	1.1	1	0%
Nitrogen	0.5	1	0%
Lithium Hydroxide	1.1	1	0%
Toiletries	0.02	1	0%
Detergents	0.1	30	0%
Medications	0.2	180	0%

The figures listed above are anticipated averages over time for a single crewman, and should not be considered exact for determining instantaneous rates of consumption. They were prepared using assumptions about crew activity level and cabin environment that may not apply to a given mission as a whole, either. These figures also include assumptions about the type of life support system used, and are not equally applicable to systems of varying efficiency. However, in principle a table of this type can be prepared for the average performance of any given life support system, and used to estimate its long term useage of supplies.

The formula for projecting total use of a material supply for an entire mission is:

Net Consumption = Crew Size x Mission Length x Useage x ( 100 - % Recycling ) / 100 / Use Cycle

which will yield a rough estimate for the supplies consumed, assuming the recycled portion is of negligible mass compared to the total (an assumption that breaks down for some supplies in closed loop life support systems for which replenishment is never required).

This method of estimating consumption can be applied to other supplies used by the crew. Clothing use, for example, can be estimated in this fashion.

Clothing
	Unit Mass (kg)	Use Cycle (days)	% Recycled
Jackets	0.36	180	0%
Coveralls	0.75	6	95%
Shoes	0.50	360	0%
Belts	0.18	360	0%
Trousers	0.35	6	95%
Shirts	0.12	3	95%
Socks	0.02	2	95%
Underwear (Men's)	0.08	2	95%
Underwear (Women's)	0.11	2	95%
Thermal Underwear	0.20	3	95%
Towels	0.25	14	95%
Washcloths	0.03	7	95%

Again, the table given includes assumptions about the type of supplies used and the conditions under which they are used. The recycling rates given include the assumption that much of the clothing used will be washed, but this is not justifiable for shorter missions. Most of the figures given are weighted averages that do not reflect the properties of individual articles of clothing or the exact pattern of their use. For example, it can be extreme to wear a single shirt for three days straight under improper conditions; however, with judicious use of undergarments and drying to protect the fabric against sweat and other body soil, it can be perfectly comfortable to wear the same shirt at three different times during the mission without washing. Washing a garment generally requires several times its mass in solvents, and it is desirable to put it off as long as possible, or dispense with it altogether if the mission is of short enough duration. Also, simple cabin temperature control can extend useage cycles for some articles of clothing, such as jackets.

Similar tables can be prepared for other supplies used by the crew at a consistent rate or that have a limited useful lifetime.