Introduction to satellite subsystems

                                                                       Interior of a model satellite.

After the previous introduction to recent satellite history we will see the different elements of a space mission, which are:

  • Space segment
  • Application
  • Orbit
  • Launch
  • Ground segment
  • Operations
  • Communications

We are going to analyse the fundamentals of space missions and the subsystems which are necessary for the correct development of the spacecraft.

The first of the subsystems and the most crucial, as it is the motivation for the mission, is the payload. It can be rather scientific, to study physical elements of space; astronomical, to observe space objects; Earth Observation, to watch Earth; and telecommunications, for the transmission of information.

Payload subsystem.

The next subsystem is structures, whose missions is to support and secure all the equipment, since the assembly on Earth, during the testing, transportation, orbit and launch. Being the latter one the most critical time, as the satellite is highly stresses to g-forces when accelerating and getting into orbit. To have a better understanding of a launcher distribution and structure the following website can be visited to know the components, stages and materials of a rocket:

And in the next video you can see such launcher in action.

Launch of Ariane 5 from French Guiana.

Despite being Ariane 5 a good solution for setting satellites in orbit, it is possible to put smaller satellites in orbit with more efficient and cheaper solutions that require less resources. Such as cubesat deployments, like the dispenser that can be found on the International Space Station (ISS) of the following image.

ISS Nanorack ejecting two cubesat into orbit.

Multiple smaller satellites can also be launched with the same rocket, by allocating them in a central structure and following a synchronized system for deployment once in orbit. This way the cost per kilogram of launch is reduced.

Soyuz envelope with four satellites to be launched simultaneously.

Then it is the electrical power subsystem, its mission is to generate, adjust, store and energy to the payload and subsystems.

Electrical power subsystem.

There must be multiple sources in case one stops working, for example in an eclipse or a malfunction. For that reason, there should be batteries to store the energy during the  dark periods, to avoid the satellite from shutting down.

When the satellite is in the shadow it must continue operating.

For producing such energy multiple sources can be used, like solar photovoltaic, the most common one; radio-isotope reactor, where the decay of material produces heat; nuclear reactor, where nuclear fission produces heat; and finally fuel cells, where chemical energy is converted into electricity.

To compare with the power of some spacecraft we will compare it with some home appliances, like a portable computer, that would need around 45 Watts, or a dishwasher, which has a power of 1,500 Watts. One satellite could produce up to 5,900 Watts from solar panels and the ISS is able to produce 100,000 Watts to satisfy its power requirements.

Objects and the power they require.

Closely related to the electric subsystems is the mechanical subsystem, that is able to deploy bigger surfaces than the satellite area with solar panels, so the energy input can be greater. Thus, it is key that the mechanical subsystem work in order for the rest of the satellite to have enough energy.

Unrolling of a flexible solar panel.

In the next figure it can be appreciated the evolution of efficiency of electric batteries, decreasing the amount of weight necessary for the same performance, allowing that weight to be used for more payload, more sensors and less necessary fuel for putting it in orbit.

Best research-cell efficiencies, NREL.

We hope you enjoyed learning about satellite subsystems, we will continue learning about satellite subsystems in the next article.

Jesús Lucero Ezquerro

Jesús Lucero Ezquerro

Collaborator in Earth Observation - B. Eng. Aerospace Engineering at T.U. Madrid - MSc. in Astronautics & Space Engineering at Cranfield University.
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