A Brief Look into Spacecraft Control


A rendering of NASA Orion Spacecraft. ESA.


In honour of securing a spot on the ESA Online Ladybird Guide to Spacecraft Operations course, I thought I would compile a bit of general information on how to guide a spacecraft. This is the type of stuff I will be learning more about when the course starts in September! I hope you find this as interesting as I do.


When thinking of jobs in the space sector, many people think of the more visible jobs, such as astronauts, physicists, and engineers. However, there is a lot more going on behind the scenes than you know.


Perhaps you've tuned into a rocket launch before, such as when Starlink satellites were being launched. Now, you just think of the satellites as being in orbit around the Earth, it's just up there. That's where you are mistaken.

The EU in space graphic from the European Commission.


A lot of work goes into spacecraft control, where operators ensure that satellites are healthy, obtain the correct data, and figure out how to make satellites work if problems arise. Basically, spacecraft operators are the people who know exactly how the spacecraft works, in case any problems arise.


There are a few specific sub-systems of a spacecraft that must be tailored to each mission depending on the goals of the spacecraft. However, the ultimate goal of the guidance, control systems is to create the smoothest journey possible for the spacecraft. When creating -and controlling- these systems, even the smallest margin of movement have a large influence on results. Let's have a quick look into some of the critical sub-systems of a typical spacecraft:


Attitude, Determination and Control Subsystem (ADCS)


Courtesy of ECE3SAT


This is a crucial element for any spacecraft, since it provides pointing accuracy and payload stability. They are what detect the attitude (the orientation) of the spacecraft, and can vary it if need be. It employs sensors and actuators, while using control law and on ground simulations to control the spacecraft, and verify its performance.


Power


This one varies depending on where the spacecraft is going, what it is doing, and how long it will be there. Generally, power will come from at least one of the following power sources: the Sun, batteries, or unstable atoms.


Spacecraft control team. Courtesy of ESA.


Solar powered spacecraft use solar panels which convert the Sun's energy into useful electricity, but becomes less efficient the further away from the sun they are. They are also limited by a planet's weather and seasons, which is why scientists developed power sources using batteries and atoms. NASA's Mars Exploration Rovers, Spirit and Opportunity, both use solar power.


When missions only have to last a short time, batteries are very useful. They only work for a short amount of time, but are very tough, and thus suitable for actions such as landing a spacecraft on a planet.


Radioisotopes are another method of powering a spacecraft, as their systems can produce power for a long time, even in harsh environments. When atoms are unstable, they break apart, and release energy in the form of heat. The difference between the heat and the cold temperature of space can be used to make electricity.


On Board Data Handling (OBDH)


The OBDH stores and carries data between a spacecraft's electronics units and the ground segment, with help from the TT&C subsystem. With the advancements in computers that have become common on spacecraft, the OBDH functions include processing commands sent from TT&C, ensuring processing capability is correct for the mission, and downlinking telemetry to the ground.


Telemetry, Telecommunication & Control (TT&C)


This system is on the ground, and ensures that the spacecraft is functioning correctly. It essentially provides a link between the satellite and the ground. If you've ever seen a movie with those giant satellite dishes, that's where the TT&C is hosted. This is the system that orders the satellite to adjust its orbit, perform system backups, and more. Think of it kind of like a housekeeper making sure that everything is on track.



Thermal and On Board Software (OBS)

On board software. Courtesy of University CubeSat team.


This is the system where all satellite subsystems are controlled, where the thermal unit controls the temperature of payloads, equipment and satellites to protect the flight hardware and ensure the spacecraft operates at high performance. After all, when in orbit around Earth, the temperature can range from well below freezing when in the shadow of Earth, to temperatures that soar above boiling temperature.


Due to sensors inside the control system, the motion and environment of the spacecraft can be monitored from the ground to ensure that the on board software is functioning correctly.


Orbit Control System (OCS)


Soyuz Attitude Control System. Courtesy of Sven Grahn.


Remember that spacecraft are always orbiting something. Whether that is the Earth, or other celestial bodies, it is important to design the spacecraft so it remains efficient and effective. Then, it needs to be closely monitored to ensure that everything is going to plan.


When it comes to navigating a spacecraft, there are a few main aspects that include:

  1. Designing a trajectory (planned flight path) of the spacecraft, which is in the area of mission design

  2. If the spacecraft goes off track, flight path control brings the wayward craft back to its reference trajectory

  3. Keeping track of the real life spacecraft position through orbital determination when the mission is underway

Some of the primary terms to know for guidance, navigation, and control systems include:

  • Sensors, which determine where the spacecraft is pointed, how fast it is turning, and how it changes speed

  • Control devices, which act as the brain of the operation, which changes the pointing direction, the rate of turning, and the spacecraft's speed

If you are interested in learning more about spacecraft operations and control, then check out an ESA article here and the video below. Space Careers UK also has a great profile of the job, as well as the available paths to become an operator.



I hope you learned something new today!


What are your favourite "hidden" jobs to learn about?


Chrissy


References: NASA, ESA

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Mechanical Engineering student. Future space engineer. Writer. Runner. Passionate about getting more women into STEM.

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