Primary life support system

A primary (or portable or personal) life support system (or subsystem) (PLSS), is a device connected to an astronaut or cosmonaut's spacesuit, which allows extra-vehicular activity with maximum freedom, independent of a spacecraft's life support system.

When used in a microgravity environment, a separate propulsion system is generally needed for safety and control, since there is no physical connection to a spacecraft.

The portable life support system used in the Apollo lunar landing missions used lithium hydroxide to remove the carbon dioxide from the breathing air, and circulated water in an open loop through a liquid-cooled garment, expelling the water into space, where it turned to ice crystals.

Some of the water was also used to remove excess heat from the astronaut's breathing air, and collected for dumping into the spacecraft's wastewater tank after an EVA.

The OPS maintained suit pressure and removed carbon dioxide, heat and water vapor through a continuous, one-way air flow vented to space.

It was tested at the Houston Flight Center by James P. Lucas, working for Hamilton Standard, and by various astronauts in neutral buoyancy tanks at Dallas.

It was tested in space for the first time by Rusty Schweickart in a stand-up EVA in Earth orbit on Apollo 9.

Oxygen (O2), carbon dioxide (CO2) and water vapor are drawn from the extremities of the suit by the liquid cooling and ventilation garment or LCVG, which sends the gas to the PLSS.