ATMOSPHERIC SYSTEM

	The USS Enterprise environmental system maintains a Class M 
compatible oxygen-nitrogen atmosphere throughout the habitable volume of 
the spacecraft. Two independent primary atmospheric plenum systems 
deliver temperature and humidity controlled environmental gases throughout 
the vehicle. Additionally, a separate reserve system and emergency systems 
provide additional redundancy.

	Atmospheric processing units for the primary system are located 
throughout the spacecraft at the rate of approximately two redundant 
primary units for every 50 mì of habitable shipÕs volume. These devices 
maintain a comfortable, breathable mixture by removing COÛ and other waste 
gases and particulates, then replenishing the OÛ partial pressure. This is 
principally accomplished through the use of photosynthetic bioprocessing. 
The atmospheric processors also maintain temperature and humidity within 
prescribed limits. Once so processed, the breathing mixture is recirculated 
through the plenum network.

	Cruise Mode operational rules specify a ninety-six-hour duty cycle 
for processing modules, although normal time between scheduled 
maintenance is approximately two thousand operating hours. At the end of 
each ninety-six-hour duty cycle, it is normal for the entire atmospheric 
processing load to be automatically switched to the alternate primary 
system. It is, however, possible to individually switch specific system 
elements as needed. Atmospheric plenum flow can be remotely switched at 
utilities junction nodes, so that breathing atmosphere can be rerouted to 
processors at other locations, offering an additional measure of redundancy.

	The reserve system is a third redundant set of atmospheric 
processors, providing up to 50% of nominal system capacity for periods up to 
twenty-four hours, depending on system load. These are intended for use in 
the event of incapacity of major elements of the two primary atmospheric 
systems. The reserve system shares the plenum network of the two primary 
systems, and operates by computerized system analysis, which allows any 
damaged plenum sections or processors to be isolated and removed from 
service.

	Additionally, emergency atmospheric supply systems provide 
breathing mixture to designated shelter areas for up to thirty-six hours in 
crisis situations. These systems draw on independent oxygen and power 
supplies, physically isolated from the primary systems and from each other. 
The emergency systems are not intended to provide shipwide atmospheric 
supply. The emergency atmospheric supply systems provide minimal 
recycling capacity (COÛ scrubbing and OÛ replenishment only), but oxygen 
supply can be significantly extended by drawing on any available supplies 
from the three primary systems, or from any unused contingency supply 
modules.

	In case of major failure of atmospheric supply necessitating use of 
the emergency system, contingency atmospheric supply modules, located at 
most corridor junctions, will maintain a breathable environment for 
approximately thirty minutes, sufficient for the crew to evacuate to shelters. 
Environmental suits would be provided to all personnel required to work in 
areas in which a breathable atmosphere is not maintained. Except in cases 
of large-scale explosive decompression, even a severe atmospheric supply 
failure is expected to permit upward of fifty minutes for evacuation of all 
personnel to designated shelter areas.

	Nominal atmospheric values for Class M compatible conditions (per 
SFRA-standard 102.19) are 26¡C, 45% relative humidity, with pressure 
maintained at 101 kilopascals (760 mmHg). Atmospheric composition is 
maintained at 78% nitrogen, 21% oxygen, 1% trace gases. Approximately ten 
percent of living accommodations can be switched to Class H, K, or L 
environmental conditions without major hardware swapout. An additional 2% 
of living accommodations are equipped for Class N and N(2) conditions. 
Atmospheric processing modules can be replaced at major starbase layover 
to permit vehiclewide adaptation to Class H, K, or L environmental 
conditions.  Æ