What Are The Systems in a Spacecraft?

by Carson
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OSIRIS-REx spacecraft

A spacecraft is a sophisticated machine that carries many systems and instruments to sustain itself and conduct scientific investigations. Let’s find out about the components in a spacecraft.

The Power Subsystem

For a spacecraft to operate properly, it must first get a power supply. There are two main types of power supply for space probes, namely solar panels and RTGs (Radioisotope Thermoelectric Generator).

Solar panels are usually used in missions that explore the inner Solar System because these space probes tend to get more sunlight. They consist of photovoltaic solar cells, meaning that they convert light into electricity. The cells use semiconductors like silicon sprinkled by elements with one less or one more outer electron than the semiconductor (such as phosphorus and boron) to create electric fields after photons strike the cell.

RTGs are used for recent Mars rovers or spacecraft exploring the outer Solar System since there may not be enough sunlight for the solar panels to power the entire spacecraft in these locations. RTGs use the radioactive decay of plutonium-238, which is unstable, to generate heat, which then creates electricity using another component of the RTG.

The Communication Subsystem

If a spacecraft cannot communicate with Earth, what’s the point in investing billions of dollars in launching it? To ensure that data flows in both directions, we need a transmitter and a receiver. A spacecraft usually have at least two antennas, which are the low-gain and the high-gain antenna.

The signal strength of the low-gain antenna (LGA) is lower, but its signals can be heard in almost all directions. Meanwhile, the high-gain antenna (HGA) can transmit data at higher speeds but only sends signals in a narrow range. Therefore, the HGA must accurately point toward Earth when transmitting signals to ensure that it can be received.

The LGA is mainly used for short-range communications, such as talking to Earth at several astronomical units away. However, if the distance is increased to tens of astronomical units from Earth, the spacecraft must use the high-gain antenna, which is the dish-shaped object on one side of the spacecraft.

Attitude Control and Trajectory Correction Subsystems

Even if the spacecraft’s trajectory is calculated thoroughly and the launch is executed perfectly, there might still be some mistakes in the spacecraft’s orbit, potentially causing it to miss the target. Moreover, the HGA needs to steer for it to point toward Earth for communication, and the solar panels need to be steered to make the cells face the Sun if the spacecraft relies on solar energy.

Therefore, a spacecraft must correct its path using thrusters, which use rocket engines to propel the space probe in a specific direction. Furthermore, the spacecraft’s orientation must be obtained by gyroscopes and stellar reference units for the spacecraft to steer toward the correct direction.

Science Instruments

Your space mission won’t be complete without science instruments, which are the components that collect data to facilitate scientific studies. The science instruments in a space probe might include:

  • Imagers
  • Spectrometers
  • Magnetometers
  • Radio Science Instruments
  • and more…

Imagers use lenses and/or mirrors to reflect and/or refract incoming light to focus it into a single point. After that, the resulting image will be collected as digital information for algorithms to analyze and transmit the photo. Spectrometers detect light waves from the target and analyze what wavelengths are absent from the spectrum to figure out the composition of the target. Magnetometers measure magnetic fields using the Hall effect, where magnetic fields can deflect electrical currents. Radio science can helps us learn about miscellaneous properties of the target by observing how the radio waves are modified when they reach the target.

Life Support Systems

Space is a place where people need life support systems for them to survive. If these systems are removed, the astronauts will die quickly.

These systems should include air supply, water supply, food supply, space toilets, and interfaces to control the spacecraft in case human intervention is needed. Sanitization systems are necessary to ensure the resources are clean and free of harmful and toxic chemicals. The spacecraft should also reuse materials as much as possible to reduce the number of resupply missions.

For instance, the Advanced Closed Loop System maintains a stable supply of air for astronauts. Firstly, the air that the astronauts exhale will be directly reused after the carbon dioxide in the air has been filtered. How do we deal with the carbon dioxide and the oxygen? It will not be stored and accumulated inside the spacecraft! Therefore, additional devices are installed that turn carbon dioxide into water and methane. The water supply will be split into oxygen and hydrogen using the Oxygen Generation Assembly, creating a source of hydrogen for methane to be made and supplying oxygen to the air in the spacecraft.

An illustration of the Advanced Closed Loop System in the ISS
Information Source: ESA10
Image created using Canva

Data Handling Subsystems

No spacecraft is complete without a computer. If nothing can control the behavior of different hardware millions of miles away, the space probe will become useless.

The data handling subsystem should include a main computer with storage devices, RAM, a processor, an interface to control other hardware, and everything else that a modern computer has.

Moreover, it must have the ability to read messages from Earth and turn them into instructions, and convert the data that needs to be sent into actual radio waves that antennas on Earth can receive.

Furthermore, it must also carry algorithms that help analyze the data collected from the instruments, decide when to take measurements or photos, and create reports for the spacecraft to send useful information back to Earth.

Conclusion

In this article, we’ve talked about the systems that are required in a spacecraft (life support systems are only necessary for crewed spacecraft). This includes the power subsystem, the communication subsystem, attitude control and trajectory correction systems, data handling systems, science instruments, and life support systems. If we’ve missed anything important, please contact us in the comments below to improve the article. Moreover, you can learn more about this topic by visiting the webpages in the references below.

References and Credits

  1. (n.d.). Basics of Space Flight. Retrieved October 3, 2021, from https://solarsystem.nasa.gov/basics/chapter11-1/
  2. (n.d.). Basics of Space Flight. Retrieved October 3, 2021, from https://solarsystem.nasa.gov/basics/chapter11-2/
  3. (n.d.). Basics of Space Flight. Retrieved October 3, 2021, from https://solarsystem.nasa.gov/basics/chapter11-4/
  4. (n.d.). Anatomy of a spacecraft. Retrieved October 3 2021, from https://www.esa.int/Science_Exploration/Space_Science/Anatomy_of_a_spacecraft
  5. (n.d.). Spacecraft Systems. Retrieved October 3, 2021, from http://www.braeunig.us/space/systems.htm
  6. Michael Dhar. (2017, December 6). How do solar panels work? Retrieved October 4, 2021, from https://www.livescience.com/41995-how-do-solar-panels-work.html
  7. Jessika Toothman, Scott Aldous. (n.d.). How Solar Cells Work. Retrieved October 4, 2021, from https://science.howstuffworks.com/environmental/energy/solar-cell.htm
  8. (n.d.). Spacecraft and Science Instruments. Retrieved October 5, 2021, from http://phoenix.lpl.arizona.edu/science05.php
  9. Chris Woodford. (2020, August 13). How Hall effect sensors work – Explain that Stuff. Retrieved October 5, 2021, from https://www.explainthatstuff.com/hall-effect-sensors.html
  10. (n.d.). Advanced Closed Loop System. Retrieved October 5, 2021, from https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Research/Advanced_Closed_Loop_System
  11. (n.d.). Venus Express orbiter instruments. Retrieved October 5, 2021, from https://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Orbiter_instruments

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