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Spacecraft Basics

What's in a satellite?

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Space Environment Basics Introduction to Radiation

Control Systems

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Structures

Spacecraft Structures Basics

Power

Spacecraft Power Basics Batteries

Software

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Thermal

Spacecraft Thermal Basics

System Engineering

System Engineering Basics Requirement Basics Design & Construction Standards Overview

Communication

Spacecraft Communication Basics

Propulsion

Introduction to Propulsion

Spacecraft Power Basics

Key Points

  • Power systems are the power sources (like solar panels), power storage (like lithium-ion batteries), and power distribution (like cables). Those three things can get surprisingly complex and everyone loves a good power engineer.

  • Solar panels and batteries continue to get better all the time. There’s always new vendors and technology to consider. Even still, there are approaches that have been used for years that you don’t have to reinvent and that allows you to help multiple programs in a short amount of time once you know what you’re doing.

  • Most power systems engineers come from electrical engineering backgrounds. A bachelor’s degree is great for most people, with a handful of people getting Masters degrees so they can do research. There are few PhDs who do this type of work on a spacecraft.

Introduction

Power systems are more than just solar panels and batteries. You’ve got to think about different power levels, cables, safety, backup solutions, and more. This can be a fun field since you tend to work multiple programs at a time and get to influence many missions.

 

A Bit More Detail

As mentioned above, the three main categories of power systems are energy input, energy storage, and energy distribution. 

Energy Collection

solar panels

Energy input is almost always solar panels, but nuclear thermal power is used sometimes and there’s growing interest in using more of it. 

When you use solar panels, you have to size them for the average amount of daylight. Almost all satellites see the sun for around 50% to 70% of their orbit and darkness for the other part when they go into the shadow of the Earth. So if you need 100 W of power all the time, you’ve got to size your solar panels for more like 200 W. You also need to take into account that solar panels lose their efficiency over time, so you’ve got to design for things getting worse. And then there are pointing issues, damage, and more to consider. This means that your simple 100 W design really needs to be more like 250 W or more.

 

Energy Storage

batteries

Energy storage can be challenging because, unless astronauts are there, you can’t change the batteries. If you think about how bad your cellphone batteries get after a few years, it can be similar in space. Like the solar panels, you have to assume a certain performance at the end of the battery’s life and design backwards.

For a long time, the batteries have been nickel-metal hydride or some nickel variation. This is because it’s (relatively) safe and people understand it well. Lately, though, lithium-ion and other lithium varieties have been showing up on more spacecraft. They take more engineering to make sure they don’t explode, but their performance gains have been considered worth it.

You might also hear the terms “Primary Battery” and “Secondary Battery”. A primary battery is one that cannot be recharged. You buy it fully charged, put it in your spacecraft, and use it for the first part of your mission, usually before your solar panels have been deployed. Once it’s dead, it’s dead forever. Secondary batteries can be recharged. They’re more expensive than primary batteries and you need a battery control system. 

 

Energy Distribution

power distribution

There are three sub-categories here: Voltage conversion, cabling, and ripple management.

Solar panels give you voltage higher than you want to use. The ISS panels, for example, give you over 150V before any conversion. Some space batteries can accept voltage that high and some do better with voltage closer to 24V. And most hardware wants around 28V or less. So the power engineer needs to convert high voltage down in several steps.

Because there are different voltages, there are different cable diameters to use. They also need to make sure everything is grounded and that they’re not accidentally creating fields or antennas that would hurt the spacecraft. For big systems, you may have parallel paths so that if one fails, the spacecraft can keep working. Figuring out how to do that and when (or if) you want to connect them to each other in what is called “Cross-strapping” can take some deep thinking.

Rippling is variations in the power profile going to your sensors and other systems. For a big motor, it’s okay for the voltage and current to vary by 5%. For a detector on a camera, though, the requirements can call for fractions of a percent variation. The power engineer is responsible for understanding where and how to provide clean power to things that need it.



Curated Videos

  1. https://www.youtube.com/watch?v=E3vcHiWQ_Ms
    There is outstanding information in this video. Its production quality is not high, but look past all that and you’ll learn more in one hour than you could from many other sources.

  2. https://www.youtube.com/watch?v=wkVwWtRUqq4
    Some spacecraft use plutonium decay to power spacecraft. The Simply Space channel covers this with great animations.

  3. https://www.youtube.com/watch?v=Zpl03HZ5r_w
    This is part of a livecast overview of space power today and into the future. It’s got great overview information and can help you design a solution from just a handful of requirements. You’ll also learn about why people really want to get nuclear options into space.

  4. https://www.youtube.com/watch?v=flbIrOa3wyI
    This is a lecture format with PowerPoint slides. The presenter talks about the systems you need and also how they work. It’s a good option for a medium-depth dive.



Curated Links

  1. https://www.nasa.gov/smallsat-institute/sst-soa/power
    NASA has a collection of small satellite articles including this one on power. Check out this one and the others too.

  2. https://solarsystem.nasa.gov/basics/chapter11-3/
    NASA has another overview page here. This one is a little more high level than the first one and would be good for people just learning.

  3. https://rtcl.eecs.umich.edu/rtclweb/assets/publications/2013/main_satellite.pdf
    The authors cover some of the details around solar panels and batteries and discuss how to design around them. For instance, they talk about the effect of temperature on solar panel efficiency and the non-linear discharge rate of batteries.

  4. https://www.aerospacelectures.com/Power%20System%20Design%20for%20Earth-Orbiting%20Satellites.pdf
    This is a series of PowerPoint slides that gives an overview of power systems and a few equations to help solve first-order sizing. Side note: Dr. Guven and the aerospacelectures website has many of the same goals like this one. If we’re missing content, you might find what you’re looking for there.

  5. https://iopscience.iop.org/article/10.1088/1755-1315/149/1/012059/pdf
    The paper gives a detailed look at the power system designed for the Surya satellite. It’s a good resource for the practical implementation of a power system.