Table of Contents

Basic Parts of the Spacesuit

The spacesuit plus its built-in life support system is also known as an EMU. Some people might first think of the animal, but EMU is actually short for Extravehicular Mobility Unit. Why the big name?

When an astronaut performs a spacewalk, he’s performing an extravehicular activity. This refers to any activity that’s taking place outside of the protection of a spacecraft. The word mobility refers to the ability to move. The suit is a unit—one big item that’s made up a lot of smaller items. So, the EMU or spacesuit is really its own little spacecraft that lets an astronaut move around in space.

The EMU is made up of 18 parts and 14 layers. In fact, the suit weighs a total of 114 kg or 250 lbs when worn on Earth, but weighs nothing in space! However, it still retains its mass in space. (That’s because mass is measure of how much matter is in an object while weight is the effect of gravity on a mass.)

The suit is heavy because the developers had to ensure that all of the astronaut’s basic necessities were available in the suit. Not only did they think of their protection and a life-support system, but they also thought of other scenarios such as hunger, thirst, and having to go to the bathroom!

Here’s a closer look at the 18 parts:

1. Primary Life-Support System (PLSS)

   The PLSS is a backpack that’s necessary for providing oxygen, removing carbon dioxide, and hooking up power, voice communication devices, and equipment that can transmit the astronaut’s medical information back to Mission Control. The pack can work for an average of seven hours. During that time it is monitored by a built-in computerized warning system to alert the astronaut of any problems within the unit.

2. Displays and Control Module (DCM)

   This is an irregularly shaped box of switches, valves, and digital displays that gets mounted on the chest. It controls the primary life support system and the secondary oxygen pack.

   Along the top are switches for power, communications mode selection, caution and warning. There is also a switch that controls the water that is fed to the Liquid Cooling-and-Ventilation Garment. A digital display is used to monitor the various suit circuits.

   At the top left of this module is an emergency relief valve. If the primary life support system were to ever malfunction, the astronaut would still have access to the secondary oxygen pack. To activate this secondary oxygen pack, all the astronaut would have to do is open a purge valve by squeezing a set of pinchers. This valve releases air pressure on the chest plate—this is the same valve that is used at the end of EVA to depressurize the suit.

   Also on the left, a step down from the purge valve, is the mechanical-suit pressure gauge.

   Along the right-hand side of the module, are two switches: the ventilation-fan switch and the push-to-talk switch. The ventilation-fan switch can activate and deactivate a fan which circulates air through the helmet and other parts of the suit. The push-to-talk switch is similar to one you would find on a CB radio. If the astronaut wants to talk, he has to push the button to be heard, and if wants to receive voice messages, he has to release the button.

   On the front of the panel are other controls for volume, temperature, and suit pressure.

3. EMU Electrical Harness (EEH)

   You can think of this as a connector to both the communications system and the medical instruments that’s used to transmit information about an astronaut’s heart rate. This is worn inside the suit.

4. Secondary Oxygen Pack (SOP)

   The SOP was created as a back-up measure to ensure the safety of the astronauts. It is a detachable unit that connects to the bottom of the primary life-support system (PLSS). The pack features two mini tanks that supply a total 30-minutes worth of oxygen—enough time to get the astronaut to the Shuttle’s airlock.

   The SOP operates in what scientists call an "open loop". Unlike the PLSS, the SOP doesn’t rely on a system that measures or monitors how the oxygen is being used and it does not conserve or recycle oxygen. Instead, the oxygen travels from the PLSS to the rest of the suit, but the contaminated oxygen gets dumped into space.

   This back-up supply can be activated manually with a valve or automatically when the oxygen pressure in the suit drops below 23.79 kilopascals.

5. Service and Cooling Umbilical (SCU)

   While you were in your mother’s womb, you were connected to her via the umbilical cord. That umbilical cord transported nutrients from her body to yours, and removed wastes from your body.

   This Service and Cooling Umbilical (SCU) does a similar job. It connects the Shuttle’s airlock support system to the suit to support the astronaut before an EVA and to provide an in-orbit recharge for the Primary Life Support System. It contains lines for power, communications, oxygen, water recharge and water drainage. Its ultimate job is to conserve and preserve anything that the life-support system might need during the EVA.

6. Battery

   This pack powers up the EMU during an EVA. It can be recharged in orbit.

7. Contaminant Control Cartridge (CCC)

   This cartridge is used to remove carbon dioxide and any contaminants from the rest of the suit. It was built as part of the PLSS to purify oxygen for recirculation.

8. Hard Upper Torso (HUT)
   
   
   

   The HUT is not only used to protect the upper body but it’s also used for mounting or securing the other parts of the suit. The arms, the helmet, the in-suit drink bag, the Primary Life Support System, the Displays and Control Module, the EMU Electrical Harness and the mini-workstation tool carrier, can lock onto the HUT. The HUT joins with the lower torso with a metal body-seal closure.

   The HUT is built to be a tough, protective layer. It’s constructed with fiberglass and is covered by fabrics that guard against micrometeoroids.

9. Lower Torso
   

   This is made up of the pants, boots, and lower half of the closure at the waist. It also has D-rings for a safety tether and a waist bearing. The waist bearing lets the astronauts twist from side to side when their feet are locked into foot restraints while working in space.

10. Arms (left and right)

    The arms have a shoulder joint, elbow joint, and upper arm bearings that allow the astronauts to bend, lean, and twist. The arms also have glove-attaching closures. There’s also a small wrist mirror to help the astronauts view parts of the suit that they can’t see.

    If you looked at the left arm, you’d find a spiral-bound checklist of procedures.

11. EVA Gloves (left and right)

    If you look at the bottom of an EVA glove, you’ll see that it has a ring. This ring is used to snap onto the sleeve of the upper torso. It also contains a wrist bearing that is used to help the astronaut rotate his hand.

    

    On the opposite end of the glove are rubber finger caps. The scientists chose silicone rubber to so the astronauts could have some sense of touch when working with equipment and tools.

    Along the gloves are loops. Tethers connected to small tools can be latched onto the loops to prevent the items from floating off into space.

    The astronauts also like to wear thin fabric comfort gloves with wristlets--band of materials worn for warmth--within their EVA gloves.

12. Helmet

    The helmet is a clear plastic pressure bubble that allows the crew member to see in the dark. It is fitted with a neck disconnect ring and ventilation distribution pad. A valve was built in to remove carbon dioxide and to act as a backup purge valve to use with the secondary oxygen pack.

    There is also an Extravehicular Visor Assembly that attaches to the helmet. It has a gold visor to allow the astronaut to work in the presence of the Sun.

13. Liquid Cooling-and-Ventilation Garment (LCVG)

    Imagine wearing long thermal underwear that have plastic tubing running throughout it! These tubes are used to carry cool liquids all over the body to maintain a comfortable temperature during an EVA. There are also gas ventilation ducts and many water and gas connectors that are connected to the primary life support system via the HUT. The garment is one piece with a zippered-front and weighs less than 15 kilograms when it’s dry.

14. Urine Collectors

    So, what happens when you have to go to the bathroom and you’re wearing a bulky spacesuit? When you gotta go, you gotta go! The space suit developers created urine collectors just in case the astronauts need a quick bathroom break!

    You can think of urine collectors as materials that absorb or collect urine during the spacewalk. Male spacewalkers wear a pouch called the Urine Collection Device while female spacewalkers wear absorptive multi-layered shorts called Disposable Absorption and Containment Trunks. Both can hold almost one whole litre of fluid.

15. Extravehicular Visor Assembly

    This attachment goes over the helmet. The metallic-gold-covered visor is used to filter out the harmful effects of the Sun’s rays and is equipped with adjustable blinders. Astronauts can also attach four "head lamps" and a postage-stamp-sized colour TV camera to this piece if necessary.

    The four "head lamps" are handy because the spacewalker will spend every other 45 minutes of every second hour in darkness.

16. In-Suit Drink Bag (IDB)

    This water-filled bag is nestled into the HUT. It has a straw-like tube that reaches up into the helmet so that the astronauts can have a drink when they get thirsty. It contains a little more than two and a half cups of water.

17. Communications Carrier Assembly (CCA)
    
    
    Click to enlarge

    This fabric cap—also known as a "Snoopy Cap"—is outfitted with built-in earphones and a microphone for use with the EMU radio. Communication between the astronaut and Mission Control are necessary at all times.

18. Airlock Adapter Plate (AAP)

    The HUT is kept on the wall so that an astronaut can squeeze up into it once the space suit pants are on. This plate is used in the airlock to hold the HUT in place as the astronaut gets dressed.