Interplanetary Mission Consumable Mass Balance

Transit Consumable Budget

Mission duration 270 d

Closed-loop recycling efficiency 93%

Crew size 4

Onboard reserve margin 60 d

Cumulative unrecycled mass at arrival

–

Resupply threshold reached

–

Reserve margin remaining at arrival

–

How it works

Water (3.6 kg/person/day) and oxygen (0.84 kg/person/day) pass through the closed-loop ECLSS: condensate, urine and CO₂ are reclaimed at the recycling efficiency you set. Food (0.62 kg/person/day, dry mass) is not recycled on a chemical/regenerative loop — it is carried in full for every day of transit.

net_daily = crew·[(water+O2)·(1−eff) + food]
cumulative(t) = net_daily · t
reserve = crew·(water+O2+food)·margin_days
resupply_day = reserve / net_daily

Mission duration — total one-way transit days. The unrecycled shortfall accumulates linearly with time, so a long Mars transit turns a small per-day gap into a large total deficit.
Recycling efficiency — the fraction of water and oxygen reclaimed each day. Moving from 99% to 93% multiplies the daily makeup mass roughly sevenfold — a small stated shortfall, but it compounds every single day of the transit.
Crew size — scales every term linearly; more crew means the same efficiency gap burns through the reserve margin faster.
Reserve margin — the contingency consumable mass carried at launch, expressed as days of full (unrecycled) consumption. Once cumulative unrecycled mass exceeds it, the mission has no more slack — a resupply or abort becomes unavoidable.

Real-world relevance: this is why ISS resupply cycles (weeks away) tolerate lower recycling efficiency than a Mars transit will need — with no resupply possible for months, ECLSS designers must close the loop far tighter, because the same 5–7% water-recovery shortfall that is a rounding error in low Earth orbit becomes a multi-tonne deficit by the time a crew reaches Mars.

Cumulative unrecycled mass Reserve margin capacity Deficit zone