The Advanced Life Support System is a marvel of genetic engineering. Microbes with short life spans have been created that ingest CO2 and excrete oxygen. This system removes the need for bulky oxygen tanks and CO2 scrubber assemblies, giving the ship more room for valuable cargo. A ship without an ALSS must dock at a star base after a period of one month per size class above small (1 month for small, 2 months for medium, 3 months for large, 4 months for huge, 5 months for capital, 6 months for dreadnought, 7 months for station). An ALSS increases these times to 6 months per Size Class (6 months for small to 3.5 years for a Station).
A ship or station with an ALSS, and 1 Arboretum per 2 Size Classes (3 for a Station or Dreadnought, 2 for Capital or Huge and so on) never needs to resupply. A Fighter without an ALSS is extremely vulnerable without a carrier, needing to resupply every 24 hours. With an ALSS a pilot can last 2 weeks.
Note that an ALSS without the proper number of Arboretums on a space station is pointless since space stations can only use their acceleration to turn and cannot dock at a star base.