Table of Contents

The Primary Life Support System

When astronauts leave their spacecraft, they literally carry their lives on their backs. A fibreglass backpack, known as the Primary Life Support System (PLSS), provides them with the "consumables" that they need to survive.

The components include:

• oxygen bottles: provide pure oxygen (rather than air, a mixture of nitrogen and oxygen) for breathing.
• pressurization system: protects against the vacuum of space and keeps body fluids in liquid form.
• water bladders and cooling system: a system for cooling and circulating water through small tubes in the astronaut’s undergarment to regulate body temperature during heavy work.
• contaminant cartridge: a replaceable unit that removes the carbon dioxide the astronaut exhales, as well as odours, particulates and other contaminants from the suit’s atmosphere.
• fan: circulated oxygen and ventilates the suit.
• battery: supplies the electricity used by the suit and the PLSS.
• communications system: transmitters, receivers and an antenna that allow two-way communications and warning alarms between spacewalkers and crew members inside the Shuttle. This system also transmits the spacewalker’s heart-rate data to be monitored by doctors on the ground.
• display and control module: attached to the front of the HUT, this device allows astronauts to control the functions of the PLSS and provides visual and auditory information on the status of the PLSS. For example, it monitors how fast the astronaut is using oxygen and calculates how long the supply will last. It also monitors the pressure and temperature of the cooling water as well as carbon dioxide levels in the suit. It also sounds warning alarms if PLSS systems fail.

If the PLSS fails or runs out of oxygen, a secondary oxygen pack, attached below the PLSS, can supply oxygen and maintain suit pressure for about half an hour. This is enough to allow astronauts to get inside the Shuttle’s airlock in an emergency.

A new safety device, a jet-propelled "life jacket" that attaches to the back of the PLSS, has recently been added, primarily to protect astronauts doing spacewalks from the Space Station. Unlike the Shuttle, the Station can’t chase after an astronaut who accidentally becomes untethered. The new device, known as SAFER, will enable astronauts to fly back to the Station under their own power.

References:

• Shuttle Reference Manual
• Space Station Extravehicular Activity