Satellites often stay operational for years, in an environment where it would be enormously difficult and expensive to pop by and change the batteries. That raises an obvious question: where do satellites get their energy from?
What do satellites use power for?
A satellite in orbit doesn’t generally need power in order to keep orbiting, with occasional exceptions that we’ll look at later on.
Satellites mainly use their power supplies to maintain their electronic systems. This enables them to carry out the tasks they were designed for: photography, for example. It also allows them to transmit to or receive transmissions from Earth.
Because power isn’t necessarily essential to keep a satellite orbiting, it’s possible for a satellite to run out of power but remain in orbit. This is a problem, as it means the satellite is no longer performing a useful function, can’t be controlled from the ground and may obstruct other satellites.
If you’re interested in how satellite operators dispose of satellites before they run out of power, take a look at our article ‘What happens to old satellites?’
There’s one clear source of energy for satellites to draw on: the sun. Because satellites orbit above the clouds, they don’t experience the drop in energy production that Earth-based solar panels face during overcast days.
Solar energy began to be used very early in the history of artificial satellites. The first solar-powered satellite was Vanguard 1, the fourth artificial satellite to go into orbit around Earth (and the oldest manmade object still orbiting), which was launched by the US on 17 March 1958 and has now been in space for over sixty years.
Although clouds aren’t a concern for satellite solar panels, satellites don’t always have access to solar energy. At times, the Earth will be between the satellite and the sun; in other words, from the satellite’s perspective, the sun will be eclipsed. Because of this, it’s necessary to have a source of power that can be used in darkness.
This power is provided by rechargeable batteries. These batteries are charged by solar energy when the sun is visible. When the sun is eclipsed by the Earth, the charged batteries can still power the satellite, and they will be able to recharge when the satellite’s orbit brings it back into sunlight. These batteries don’t last forever – eventually, they’ll wear out to the point where they can’t hold a charge – but they can keep a satellite in operation for years.
Solar energy can help satellites carry out their day-to-day tasks and communications. If the satellite needs to be moved, though, it requires fuel.
In the normal course of orbit, a satellite doesn’t need to burn fuel; it’s kept moving by gravity and the lack of friction in space. However, satellites are generally launched with some fuel, which can be used to operate thrusters in a variety of situations. For example, fuel is useful for:
- Moving the satellite into the intended orbit.
- Reboosting a low Earth orbit (LEO) satellite by increasing its altitude and speed, ensuring that it stays in orbit for longer. LEO satellites tend to experience small amounts of atmospheric drag, causing their orbit to decay over time, and will fall out of orbit without occasional reboosting.
- Avoiding collisions with other satellites or space debris. Satellite operators need to stay aware of potential collisions and take action if the risk becomes too high. The ESA infographic ‘The Cost of Avoiding Collisions’ explains that, on average, each of ESA’s Earth satellites needs to be moved twice per year to avoid a potential collision.
- Disposing of a satellite by slowing it down at the end of its life, causing it to fall into the atmosphere.
- Disposing of a satellite by raising it into an orbit beyond all currently active satellites: a ‘graveyard orbit’.
The fuel that satellites use in the present day is generally hydrazine-based. Because hydrazine is toxic and must be handled in full-body protective gear, the space industry is conducting research into safer fuels to work with.
We’ve already seen substantial changes in how satellites are powered. The first artificial satellite, Sputnik 1, had no solar panels and was powered entirely by batteries, which ran out three weeks after its 1957 launch. In the future, we’re likely to see more improvements, from safer fuel to longer-lasting rechargeable batteries.
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