Hab Consumable Masses in Mars Direct

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This is the page for estimating the masses of consumables in Mars Direct as part of the Tsiolkovsky Compendium Project. On page 92 of his book The Case For Mars, Zubrin estimates them to be as follows:

  • Consumables: 7.0 Tonnes consisting of (TCFM page 92):
    • Oxygen: 160 kg total (1 kg/man*day at 80% reuse)
    • Dry Food: 1600 kg total (.5 kg/man*day at 0% reuse)
    • Whole Food: 3200 kg total (1 kg/man*day at 0% reuse)
    • Potable Water: 0 kg total [?] (4 kg/man*day at 80% reuse)
    • Wash Water: 2080 kg total (26 kg/man*day at 90% reuse)


Consumption Rate

On the space shuttle, Oxygen is used at a rate of .8 kg per person*day [3]. Zubrin's 1 kg per day seems reasonable, especially considering that astronauts will be using this Oxygen at a high rate. This reference [1] suggests that under a high metabolic load, such as that will probably exist for astronauts doing work on Mars, .96 kg per day is more reasonable. 1 kg per day is a good starting point considering margin necessities and losses.

Reuse Rate

Based on technologies pioneered on the ISS, 90-95% closure for oxygen seems reasonable [citation needed]. Assuming the lower number, that is 0.1 kg per day of oxygen. Over 600 days with 4 people, that is 240 kg. With 95% closure, that is 120 kg of oxygen. An intermediate value falls at 180 kg, right near Zubrin's 160 kg.

Total Mass for 600 day Mission

Based on the above, a figure of 180 kg of Oxygen is a reasonable estimate.

Dry Food

Consumption Rate

On the ISS, each crewmember needs 1.77 kg per day of dried food [2].

Reuse rate

Zubrin assumes a 0% reuse rate for food. This basically assumes no regeneration of food, and since food is basically not regenerated on any system, there is no reason this should change unless significant farming is to be implemented. In the opinion of the writer (Jumpboy11j), farming would be experimental as opposed to a staple in the mission, and for this reason it is unwise to count on farming to provide a significant part of the food allowance.

Total Mass for 600 day Mission

1.77 kilograms per day over 600 days is a total of 1,062 kg per person over the course of the mission. With the standard 4 person Mars Direct crew, that is a total mass of 4,248 kg of food. Zubrin uses the much lower estimate of just 1,000 kg total based off .5 kg per day. However Zubrin also includes whole (non-dehydrated) food in his launch manifest, which presumably makes up the difference (see the discussion of whole food below).

Based on the minimum possible energy content for totally dry food of 4 calories per gram, and a daily calorie intake of 2,500 calories, which is on the high side if the crew is mixed-gender [1], each crewmember will need .625 kg/day of food. Since the food will also contain significant amounts of fats and proteins which have a higher specific energy, .5 kg/person per day for totally dehydrated food is theoretically possible. However, 1.77 kg per person*day is more realistic given that is what is used in real life.

Whole Food

Consumption Rate

Reference [2] does not mention whole food, so presumably none is consumed on the ISS. However resupply missions do bring whole food with them to boost morale, so presumably we should be able to find some numbers.

Reuse Rate

Not relevant (see discussion of dry food).

Total Mass for 600 day Mission

One ISS crew member consumes in one day 1.77 kg of dry food (with 0.8 kg of water to hydrate it), and 1.62 kg of drinking water. One Mars Direct crew member consumes in one day 0.5 kg dried food, 1.0 kg of whole food, and 4.0 kg of drinking water.

If the same water/dried food mass ratios are used for Mars Direct as for the ISS, then 0.3 kg water is required to hydrate the dried food [0.5 kg MD dried food * (0.8 kg ISS water / 1.77 kg ISS dried food), conservatively rounding up to significant figures]. This totals to 1.8 kg [0.3 kg water + 0.5 kg dried food + 1.0 kg whole food] of whole food per crew member per day. As an ISS crew member consumes 2.6 kg of whole food per day (1.77 kg dried food + 0.8 kg water], Mars Direct's 1.8 kg is suspiciously low (67% of ISS consumption levels).

For a conservative estimate, ISS levels of food consumption should be assumed (which includes only dry food). The Case for Mars presents good arguments for the inclusion of whole food, however, so further research should be done find accurate assessments of whole food requirements and consumptions rates on real space missions.

Potable Water