It is common knowledge that iron will rust. Because iron is exposed to air, about 21% of the air is oxygen, and oxygen will react chemically with iron to produce red iron oxide, or what we commonly call rust. If there is moisture in the air, iron will rust faster; and to keep iron from rusting, you have to find ways to keep it from coming into contact with oxygen - such as applying a layer of rust-proof paint.
A friend asked: the space station in space flight, where there is neither oxygen nor water, if we put the iron outside the space station, is it never rust?
The correct answer is: iron still rusts, and rusts quickly.
Unlike the Chinese space station astronauts, when the ISS astronauts exit the capsule, they have to push a hatch cover outward. This time you will see some dark stains around the edge of this hatch, in contrast to the white cover cloth.
If we zoom in on the image and look closely at these dark stains, we will see that it is actually rust.
This hatch of the ISS Joint Airlock Module is primarily used to protect the astronauts' exit hatch from micrometeorites and other tiny space debris impacts. It has no sealing performance, only a few magnets installed in the periphery, usually magnets sucked out of the hatch iron ring, astronauts out of the cabin first open the internal sealing hatch cover, and then this protective cover to the outside a push on it.
Most of the space station shell is made of aluminum, aluminum is very light and better corrosion resistance. Since the joint airlock module exit hatch is considered to use a magnetic cover, a stainless steel ring was installed at this location - it is this stainless steel ring that rusted in space and was recorded by the hatch cover.
You may ask, isn't there a vacuum in space? There is no air, why even stainless steel will still rust?
Both the International Space Station and the Chinese Tiangong Space Station fly in space at an altitude of about 400 km above the ground, and many times we call this space and think of it as a vacuum, a place where there is no air. In fact, there is still a lot of air around the space station.
Those who have studied geography should remember that the Earth's atmosphere is stratified: from the ground to a height of 12 km is the troposphere, then up is the stratosphere, mesosphere, thermosphere, and the outermost is the exosphere. The height of the thermosphere is in the range of 80 km to about 700 km, and the space station and most satellites are in this altitude range.
Although we call the 100 km altitude from the ground "atmospheric boundary" (Carmen line), out of this boundary into space, in fact, this "space" also has air, and there is a lot of air.
Under normal circumstances, the International Space Station in orbit, every month to "fall" 2 km, because the station is affected by air resistance at all times. In order to maintain the orbital altitude, the International Space Station needs to turn on the engine from time to time to "lift the orbit", which consumes 7.5 tons of fuel per year, costing $210 million (about 1.5 billion yuan)!
The European Space Agency has calculated that there are about 3.8 × 10^(-12) kilograms of air per cubic centimeter in space at a distance of 400 kilometers from the ground, which is roughly equivalent to millions of atoms in the space of a small finger, about 90 percent of which are oxygen atoms.
The ancients used to say "high places are not cold", but the atmosphere at an altitude of 400 km is called "thermosphere" by scientists, why is this?
The Earth's atmosphere blocks most of the harmful solar radiation and high-energy cosmic rays, but in the atmosphere above 80 km, where the air is thin, intense ultraviolet radiation heats air particles to 2500°C and photolyzes molecules into atoms.
Around the space station, there are more than a million oxygen atoms per cubic centimeter, and because the station travels at 7.6 kilometers per second, the oxygen atoms hit the surface of the station at the same rate.
Unlike ordinary oxygen, atomic oxygen is more reactive and will oxidize the metals it encounters, including bare stainless steel.
The oxidation reaction between atomic oxygen and spacecraft materials in space is called "space corrosion", and early spacecraft were plagued by space corrosion, with high-precision bearings often jammed. Later scientists in the moving parts surface coated with a thin layer of gold, and lubricated, gold will not be oxidized, so that the following iron is protected.
Aluminum is also susceptible to oxidation, but aluminum oxidation forms a hard aluminum oxide film on the surface, so the problem is not very serious. We rarely see plastic on the surface of spacecraft, an important reason is that it is sensitive to atomic oxygen and ionizing radiation and needs special coatings to protect it, so despite its light weight and cheap price, plastic is generally not used.
Summary.
The outer surface of the space station rarely uses iron components, because steel is prone to rust in space. Affected by solar radiation, the Earth's outer atmosphere has a large amount of atomic oxygen, atomic oxygen is active, it is easy to corrode the metal, so the spacecraft surface corrosion prevention is an important task.
#International Space Station
