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SPACESOCIETY
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Engineering of the International Space Station Explained
Overwiew
The international space station was launched in 1998 and since the year 2000 crew members are on board. It is ooperated in low earth orbit at an altitude of 400 km. One reason for this is that at this height, the aerodynamic drag is so high that debry cant stay in this orbit for long times and therefore there is a lower chance of the ISS getting hit by debry. The downside of this is of course that more station keeping is needed from the proulsion system on board. The ISS makes about 16 orbits a day . Involved in the development and sustainment of the ISS are five space agencies: The NASA, ESA, Japans JAXA, Canadas CSA and russias roscosmos. From these five agencies the operation of the ISS is secured through 2030.
Here is an overview of the ISS, to which we will get later in detail. Overall the ISS is 109 meters in length and 73 meters in witdth, with mass of 419 tons and cam carry 7 crew members.
Docking Ports
Let us first get us to how the ooperation of the iss can be sustained in orbit. The cargo supply from earth to the iss can be delivered under others from spacex cargo dragon and in the future from the dream chaser space plane. The Crew Transport can be done by crew dragon, the soyuz rocket and with boeing starliner in the future. All in All eight spaceships can be connected over docking ports at once.
The Docking system was developed by all ISS space agencies together in 2010. The Docking ports have an internal diamter of 0.8 meter for crew and cargo transfer, connections for power , data command, air and communication are also available.
The docking procedure is cut into two phase, the first phase is soft capture where 6 servo actuated legs remove any relative motion between space craft and station. In the second phase, hard capture, 12 pairs of mechanical hooks connect to the capsule to fixate it.
Electrical system
The electircal system plays a big role in the overall design of the ISS. The operation voltage of the ISS is 120V or 28 Volts. An advantage of the higher voltage is that smaller conductors can be used, this saves mass and space on board.
50 Percent of the energy generatey by the solar panels of the iss is stored in lithium Ion batteries, this needed to cover for the 35 min eclipse time without sun in each orbit. The batteries are installed outside of spacestation at the truss structure, through this more habitable volume is avaible inside the station, but also the replacement and maintenance of the batteries is way more difficult.
The ISS has different clusters of solar panels to produce power. There are 4 Pairs of main panels which are capable of tracking the sun, for the optimal sun light angle. Each array has an area of 375 square meters and produces 80-120 kw power with an Voltage of 180V.
Another cluster is the russian array, these are way smaller and produce only 5 kw of power with 28 volts, but they can also be rotated.
The last cluster is the Roll out array panel formation. They are lightweight and flexible, overall they are 30 percent lighter, have only one fourth the volume of the main panel arrays and have the same performance.
Thermal Subsystem
Another Important Subsystem is the Thermal control system of the ISS. Overall there are 10 radiators implemented to extraxt up to 70 kw of heat from the space station per orbit. The Heat is produced by the impiging sunlight, the electrical power subsystem, scientific experiments and the crew on board.
For better radiation properties the Radiators are using ammonia liquid which is toxic, to prevent crew contact with the liquid the necessary components are located outside the iss. There are two external independent ammonia coolant loops running through the radiators. Inside of the ISS are running two water cooling cycles one low temperature and one with medium temperature. To connect the Exteranl and internal coolant loops 5 heat exchangers are used.
The main cluster constists out 2 assemblies with 3 times 8 radiators, with an area of 23,3 meters times 3,4 meters. The secondary cluster constist out of 4 Assemblies with 7 radiators, with an area of 13,6x3,4 meters. All radiators have deploy and retract mechanism.
Science modules
Of course the iss is primarily in orbit to conduct resaerch and science experiments. And for this reason the other subsystems are needed. There are 4 science modules: Destiny, the unites stated resaerch modul, Columbus the european science module, The japanese experiment modul and the russian Multi purpose laboratory module. In each of the science modules there there standardized experiment express racks. These have standardized mechanical interaces for sciences payloads, can be theraml controlled, have standardized power and data interfaces and can be supplied with nitrogen or vacuumed. All in all ther 33 racks with each having 10 payload positions, therefore 330 science experiments can be installed on the ISS
Additionaly there are external payload facilites. These are fully exposed to the space enviroment, here space materials can be tested or as an example cosmic rays can be detected.
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