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Table of Contents
Working Inside a Spacesuit
Entering and Exiting the Airlock
The airlock is a cylindrical transition chamber between the inside and the outside of an orbiter (or space station). The pressure in the airlock is variable and can, on request, correspond to the pressure that exists inside or outside. Without an airlock, opening the hatch (exterior door) of a spacecraft would, in a matter of seconds, empty it of its atmosphere, and everything that is not anchored would be drawn into the void of space. In the case of the space station, the airlock connects the middle deck of the cabin to the cargo bay in which payload is transported. The cargo bay is not pressurized and both of its large doors, on the back of the orbiter, open directly into space.
Astronauts who have completed the preliminary pure oxygen-breathing phase and who have put on their maximum absorption garment go through the airlock, where they finish putting on their suit. Once the helmet and gloves have been donned and sealed, the pressure inside the suit is increased slightly above the pressure in the airlock (at this stage, the pressure inside the airlock is still the same as in the cabin, i.e. approximately 101 kPa). This difference in pressure makes it possible to identify potential leaks in the suit. If no leaks are detected, the suit is automatically depressurized to its operational pressure, i.e. 29.6 kPa. The inside latch of the airlock is closed and, at this point, the airlock is entirely depressurized.
Before the outside latch is opened, in order to avoid accidentally drifting away, astronauts connect their suit to the inside of the airlock using a safety strap. If two astronauts are getting ready to exit, the first to exit connects his strap to the airlock while the other connects his tether to the first one’s suit. The outside latch is then opened. The astronaut bends forward toward the opening and attaches a second strap to a tether mounted outside.
The first astronaut in line to exit also connects his coworker’s strap to the external tether. Once this operation has been completed and each astronaut’s suit has been attached solidly to the external portion of the spacecraft, the straps connecting them to the inside of the airlock are detached. The astronauts can then start their extravehicular activities.
Resistance to movement
The absence of atmosphere outside the suit should, in theory, facilitate the astronauts’ movements. Unlike on Earth, astronauts do not have to overcome the resistance of the ambient air while moving one of their body parts. However, the presence of atmosphere inside the suit partially offsets this advantage. Despite the relatively low pressure that is maintained voluntarily in the suit, it nevertheless remains slightly stiff, which restricts movements.
Since the suit is not one with the astronaut, and the astronaut basically “floats” inside it, each movement causes gas displacements that make subsequent movement more difficult. In addition, as we will see in the next section, work in space remains difficult due to, among others, the absence of friction and the reductionof gravitational forces.
Gravity
Although the microgravity environment enables astronauts to support the weight of their suits, it makes it difficult or even impossible to engage in the same movements we make on Earth. To understand this, we must refer to a basic law of physics as stated by Newton, called The Third Law of Motion or Law of Interaction. According to this law, whenever one body exerts a force upon a second body, the second body exerts an equal and opposite force upon the first body. This law is also illustrated by the common expression: for every action, there is an equal and opposite reaction.
In concrete terms, for our astronaut, this means that when exerting force on an object in space, the object will be projected in the direction the force is applied. The added challenge though is that the astronaut will also be projected, but in the opposite direction. When trying to tighten a bolt on a large object, the astronaut is likely to begin spinning around the bolt, in the opposite direction of the force being applyed!
But why is it that on Earth, we can accomplish these same actions without any problems? To answer this question, we must call upon Newton once again and understand the First Law of Motion or Law of Inertia (inspired by Galileo). According to this law, every body continues its state of motion or rest in the absence of an external force. In practice, inertia is considered as being the ability of heavy objects to resist movements imposed on them. The more massive an object, the greater its inertia.
On Earth, the gravitational force that keeps our feet solidly anchored to the ground, also makes it more difficult to lift objects. In fact, the law of inertia will dictate that the more massive the object, the more difficult it will be to lift.
When you lift heavy weights above your head, what happens? According to Newton’s Third Law, the weights oppose the upward force exerted by your legs, which in turn is also opposed by the upward force of the planet. This force is very real and, in theory, should make the Earth move slightly downward. But, given the First Law, our planet’s inertia is so significant that the force of resistance to motion that it opposes causes it not to move.
In space, astronauts do not have a planet under their feet, anchoring them and thereby helping them make the simplest movements. There are, however, massive objects they can use to increase their inertia and that of the suit: an orbiter, a space station or even a robotic arm, like Canadarm2. To carry out their extravehicular activities, the astronaut’s feet must almost always be anchored firmly in stirrups.
Movements and Working with the Canadarm
The objective of the Canadian robotic arm called Canadarm, also called the remote manipulator system, is to assist astronauts when handling and positioning significant loads such as satellites or sections of the International Space Station (ISS) during its construction. There are two versions of the robotic arm: Canadarm, which is mounted inside the cargo bay of space shuttles, and its new big brother, Canadarm2, which is installed permanently on the ISS platform. Canadarm has six degrees of freedom, that is, six joints enabling it to move almost like a human arm. As for Canadarm2, it has seven joints, which gives it even more flexibility than a human arm.
Since it is difficult for astronauts to translate from one point to another in space, the robotic arm is sometimes used to transport them.
