In the first episode of the Foundation series on Apple TV, we see a terrorist try to destroy the space elevator used by the Galactic Empire. This seems like a great chance to talk about the physics of space elevators and to consider what would happen if one exploded. (Hint: It wouldn't be good.)
People like to put stuff beyond the Earth's atmosphere: It allows us to have weather satellites, a space station, GPS satellites, and even the James Webb Space Telescope. But right now, our only option for getting stuff into space is to strap it to a controlled chemical explosion that we usually call "a rocket."
Don't get me wrong, rockets are cool, but they are also expensive and inefficient. Let's consider what it takes to get a 1-kilogram object into low Earth orbit (LEO). This is around 400 kilometers above the surface of the Earth, about where the International Space Station is. In order to get this object into orbit, you need to accomplish two things. First, you need to lift it up 400 kilometers. But if you only increased the object’s altitude, it wouldn't be in space for long. It would just fall back to Earth. So, second, in order to keep this thing in LEO, it has to move—really fast.
Just a quick refresher on energy: It turns out that the amount of energy we put into a system (we call it work) is equal to the change in energy in that system. We can mathematically model different types of energy. Kinetic energy is the energy an object has due to its velocity. So if you increase an object’s velocity, it will increase in kinetic energy. Gravitational potential energy depends on the distance between the object and the Earth. This means that increasing an object’s altitude increases the gravitational potential energy.
So let's say you want to use a rocket to increase the object’s gravitational potential energy (to raise it to the right altitude) and also increase its kinetic energy (to get it up to speed). Getting into orbit is more about speed than height. Only 11 percent of the energy would be in the gravitational potential energy. The rest would be kinetic.
The total energy to get just that 1-kilogram object into orbit would be about 33 million joules. For comparison, if you pick up a textbook from the floor and put it on a table, that takes about 10 joules. It would take a lot more energy to get into orbit.
But the problem is actually even more difficult than that. With chemical rockets, they don't just need energy to get that 1-kilogram object into orbit—the rockets also need to carry their fuel for the journey to LEO. Until they burn this fuel, it's essentially just extra mass for the payload, which means they need to launch with even more fuel. For many real-life rockets, up to 85 percent of the total mass can just be fuel. That's super inefficient.