Looking up at the night sky, you might see something that looks like a star moving swiftly across the cosmos. If it’s not burning up like a meteor, the chances are high that you’re looking at a satellite. As of right now (March 2019), there are nearly 5,000 satellites orbiting our home planet, and engineers are expected to launch 2,000 more by 2030. How do these pieces of aerospace engineering work, and how do they survive the harsh vacuum that surrounds the Earth?
Types of Orbits
There are six different types of orbits that a satellite can take around Earth, depending on its task. Not every satellite needs to circle the planet every day.
Satellites in a geostationary orbit or GEO spin at the same speed as the planet below, allowing it to stay in place above a specific area. Communications satellites are often in these orbits, so your television or mobile device doesn’t have to continually search for a new satellite when the old one passes out of range. Geostationary transfer orbits are slightly lower in the sky. This is where a spacecraft like the Falcon 9 rocket will bring a satellite before releasing it. Once it enters the geostationary transfer orbit, the satellite will fire its onboard rockets and move up to it’s permanent orbit.
Satellites in low Earth orbit or LEO are much closer to the ground — anywhere from 160 km to 1000 km above the planet’s surface. These circle the Earth at high speed, circumnavigating the globe in roughly 90 minutes. Satellites aren’t the only thing in a low Earth orbit though. The International Space Station is also in an LEO.
Medium-low earth orbits are right around 1000 km above the surface of Earth and are usually reserved for telecommunications satellites.
Polar orbits, as their name suggest, mean that the satellite is circling the planet’s poles. Some of these devices are also in sun-synchronous polar orbits, meaning it follows the sunrise and sunset in the polar regions. These orbits are usually between 600 and 800 km above the surface.
The Anatomy of a Satellite
For a complicated piece of machinery, a satellite is made up of relatively few parts. There’s a reason behind this — the fewer moving parts a satellite has, the fewer possible failure points there are since you can’t just walk up to an orbiting satellite and repair it if something breaks.
First, we’ve got the transponders — small transmitters that send signals back to Earth. This enables the team back home to keep track of the satellite’s location in the sky.
Next, we’ve got the station keeping system, a series of small thrusters that help keep the device in its orbit. The satellite can activate these automatically, or they can be controlled manually from the surface.
After that, we’ve got the command and control system — the heart and soul of the satellite. This system can translate and carry out commands sent from the planet’s surface, and handles the day to day operations.
Next comes the antenna system. This is what you’re communicating with if you’re watching satellite TV or tracking your trip on your GPS. The data contained in these signals will vary depending on who it’s being sent to, and why it’s being collected. Satellites are capable of transmitting back everything from location data to radio and television signals, and even pictures and video.
Of course, you can’t have a satellite without a power system. In most cases, satellites have solar panels and a battery bank to keep them running. When it’s facing the sun, the solar panels power the satellite and charge the batteries. When it is away from the sun, on the far side of the planet, it relies on those battery backups to keep working.
Everything is contained in and protected by the satellite housing. This is made up of aluminum plates that protect the inner workings of the satellite from the harsh vacuum of space, and interstellar radiation. Almost all of those 5,000 satellites orbit inside the Earth’s magnetosphere which provides some protection, but it’s not as safe as being down here on the planet’s surface. The housing plates may also have integrated piping to act as a heat sink for the computer components, drawing away heat and allowing it to dissipate into the cold vacuum of space.
Surviving in Space
Satellites experience temperatures as low as -108 C (-162.4 F) in the shadow of the planet and as high as 1376 C (2508.8 F) in direct sunlight. Add that to being in a perpetual vacuum where there is no oxygen or atmosphere to protect them, and we’re left wondering how these delicate computers survive even one orbit.
Satellites have cooling mechanisms for those times when they’re in direct sunlight and heaters for when they’re in the Earth’s shadow. These systems can be active or passive. Active systems provide a precise level of thermal control but require more expensive and heavier components that are prone to failure once they reach outer space.
Passive systems are more reliable and durable, but they don’t provide the same level of temperature control.
What Do We Use Satellites For?
A more accurate question might be ‘what don’t we use satellites for?’ If you’ve ever pulled up Google Maps or Apple Maps on your phone to find your destination, you’ve used GPS satellites. Companies like DirecTV send television shows to their customers by bouncing them off telecommunications satellites. Sirius satellite radio does the same with music.
Satellites take pictures, both for consumer products like Google maps and for military and industrial applications. Communications are relayed across the planet instantaneously. The Iridium satellites — which Space X is currently launching in batches of 10 — will eventually support a global satellite phone network for places that don’t have traditional cell towers.
The Future of Satellite Technology
With nearly 5,000 satellites in orbit around our planet right now, it’s hard to imagine that they could fit any more up there, but scientists and engineers are planning to launch as many as 2,000 more in the next 11 years. The next time you look up and see a satellite streaking across the sky, you’ll have a better idea of what keeps these fantastic pieces of aerospace technology alive in the vacuum of space.