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OTHER ITA SITES:
Satellite Launches and Operations
A satellite is built in such a way that it is as light as possible. This way it can carry more fuel with it, which increases its life in orbit. The total weight is determined by the rocket(s) that carry the satellite into space. The rocket is able to bring a certain amount of weight into orbit and this is something the manufacturer of the satellite has to take into account when designing a new satellite.
In order to bring a satellite into space it needs to first enter a low earth orbit (LEO). To get into LEO the rocket needs to reach an altitude of at least 200 km (120 miles) and a speed of no less than 29.000 km per hour (18.000 miles per hour). This is the most difficult and expensive part of the launch of a satellite. There is an enormous amount of energy needed to reach LEO.
Generally 2 rocket stages are needed to bring a satellite into LEO. The first rocket stage brings the rocket up into the thinner air at higher altitudes and speeds the rocket up enough to have the second stage bring the rest into LEO. Depending on the mission a third rocket stage is used to bring the satellite into higher orbits, for instance a geostationary orbit.
Operations in Space
Once they are in space satellites need to be completely self-sustained, since they can not receive power from earth. They also need to be able to survive the launch, which is not a soft ride. Once in space the satellite needs to generate its own power, being able to orient it self, dissipate heat, deal with cosmic radiation and protect it self from micro meteors.
Electricity is the main form of energy for all equipment on board and for orientation. Fuel is on board for moving the position or changing the orbit. In case of a geostationary orbit, the satellite needs to be kept inside a imaginary box so that it always stays in the same place as seen from earth. In case of other satellites, fuel can be used to change the orbit, or maintain an orbit. A satellite in low earth orbit for instance still receives a tiny bit of friction from the atmosphere which causes it to slow down and eventually fall back to earth. A slight boast every now and then to speed the satellite up ensures that it stays in orbit.
Electricity comes from solar panels with a battery back for when the solar panels do not receive sunlight and for when the solar panels aren’t deployed yet.
Orientation of the satellite is extremely difficult. In case of a geostationary satellite it is like aiming a light beam on a dartboard that has been placed 300 feet away, while at the same time going around the dartboard in 24 hours. When you do that, you have a reference, the ground. A satellite doesn’t have this fixed reference and needs to create this reference by it self.
A satellite creates its own reference through the use of spinning wheels. A spinning wheel has the property that the axis maintains it position due to the centrifugal force as it spins. - This effect can also be seen in a spinning top. It maintains its upright position when it spins. - Slowing the wheels down or speeding them up a bit is also used to change the orientation of the satellite, hence ensuring that the antennas always point in the direction of the covered area on the earth.
Space is cold; its temperature is almost absolute zero. But objects in space can be hot, especially when close to a hot celestial body like the sun. Our very existence depends on the energy the sun gives us. The same goes for satellites; their main source of energy is the sun. A satellite heats up because it is exposed to sunlight. Also the electronic equipment inside the satellite generates heat.
On earth there are 3 ways to dissipate heat from a body. Through convection heat energy can be given to the passing air which then transports the heat away. Through conduction, which means the heat is transferred to another body. Another possibility is through radiation.
A satellite has no other option than to use radiation to dissipate heat as there are no other bodies around and no air to cool them. It radiates the heat energy through louvered panels, meaning that they do not face the sun so that they don’t collect heat, but just radiate the heat in the direction of black space, which is very cold.
Cosmic Radiation and Micro meteor Protection
The earth is protected by its atmosphere from most cosmic radiation and small meteors. In space a satellite needs to have its own protection. Shielding of all electronic equipment is necessary, especially computer circuits which are so small that very low levels of radiation can already do damage. A satellite collides with very small meteors which damage solar panels and other equipment that is exposed to space.
Even though small meteors do not disable a satellite, it does have an impact on its life span. Solar panels will gradually produce less power because more and more solar sells will be disabled over time.
Another effect that radiation has is that materials can become brittle. This effect can also be seen in plastics that have been exposed to sunlight for a long time.
Over all a satellite has a hard time living in space. Even though Space seems to be just an empty whole of nothing, it actually is a very unfriendly environment full of invisible damaging radiation and tiny particles (meteors) that are dangerous because of their high speeds.
By Gary Davis
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