Life support recyclers: scrubber maintenance intervals
The interval on the plate assumes nominal crew. Almost no ship runs nominal crew, and the correction is not linear.
Every atmosphere recycler has a scrubber cartridge interval stamped on the plate. That number assumes nominal crew, nominal activity and nominal atmosphere composition. If your ship matches all three, you may stop reading.
Crew count is not linear
The intuition is that twenty crew on a forty-crew system means double the interval. It does not, for two reasons.
First, the cartridge has a shelf life independent of load. A cartridge at half load does not last twice as long; it lasts about 1.6 times as long before the sorbent degrades on its own.
Second, and less obvious: low crew counts often mean higher per-crew activity. A skeleton crew on a long transit is doing more EVA, more maintenance and more physical work per person than a full complement. The LSR-6 measures actual CO₂ load rather than counting heads, which sidesteps this entirely — but if your recycler counts heads, apply the correction manually.
| Crew (of 40 nominal) | Naive interval | Real interval |
|---|---|---|
| 40 | 1.0× | 1.0× |
| 30 | 1.33× | 1.2× |
| 20 | 2.0× | 1.6× |
| 10 | 4.0× | 1.9× |
Below about a quarter load the sorbent shelf life dominates completely and the interval stops extending at all.
Surge crew is worse than it looks
A recycler rated for 40 nominal and 56 surge will handle 56 crew. What the surge rating does not tell you is that cartridge consumption at surge is not 1.4× nominal — it is closer to 1.7×, because the system runs the scrubbing stage harder and hotter, and heat degrades sorbent.
Plan surge operations with cartridge stock at 1.7×, not 1.4×. Running out of scrubber cartridges with 56 people aboard is a scenario with no good improvisation.
Hot-swap changes the maintenance culture
When cartridge replacement requires taking the loop down, crews batch it — they wait until several bays need service and do them together during a scheduled window. Batching means some bays run well past their interval.
With hot-swappable bays there is no reason to batch. Replace each bay when that bay is due. This sounds like a small operational detail and it is the single largest factor in real-world recycler reliability that we have measured.
The number to actually watch
Not cartridge age. Not cycles. Watch days of remaining endurance at current crew count, and watch it as a trend. A recycler whose endurance figure is falling faster than the calendar is telling you a bay is degrading early — usually contamination, occasionally a seal.
Percentages hide this. Days do not. If your system only reports percentage, compute the days yourself and write them somewhere the watch officer sees them.