Earth is our prison - How to escape it?

[Egg]Egg · Postby **[Egg]Egg** » Mon Mar 13, 2017 5:37 am

We are in a prison on Earth. The universe taunts us by showing places we can't ever visit even with going at the speed of light.
If we want a long-term future, we need to escape, but how? What's keeping us here in the first place? Turns out we owe the universe a debt that is 4.5 billion years old.
Everything in the universe with mass; attracts everything with mass. We call this Gravity, the weakest force we know of which is why birds can fly. The closer you are to a giant piece of mass, say for example the Sun, the stronger the attraction is or the more you're pulled.
This traps us on Earth. We are in Earth's gravity well.
To explain it: Being in a gravity well/prison means you owe gravity energy. In our universe things do not like to change their speed or direction. To convince them to move, you need to expand energy. Take it for example. Your mouse is stationary. You move it by expanding energy, to get it where you want.
Billions of years ago, there was a gas cloud containing trillions and trillions of dust particles. The gravitational pull caught them together until they made a new planet, and with the new planet came a gravity well. The deeper you are, the more energy you owe gravity. If you don't find a way to get enough, you can't leave, no matter what you do. Because your octillions of atoms were once part of the dust that the universe expanded on to get to this place. Okay, how do you do that?
How to escape the gravity prison
To get into space, we need to go through a complicated process of exchanging energy.
For this, we build a Negative Potential Energy Repaying Machine, known by their more boring name "rockets" (I hope I can build one to pack my family so they don't get murdered by millions each year)
Rockets work by using some of the most energetic chemical reactions humans know about to explode fuel in a controlled way. This converts chemical energy to kinetic energy. The exhaust of the reaction is directed outwards, which pushes the rocket out of Earth. By expanding a lot of energy, we are increasing our gravitational potential energy. Complicated way of saying that we're paying back our energy debt to Gravity. Sounds simple? No it is not. It's a lot trickier than it sounds.
When you burn fuel to get into orbit, you're actually losing energy by heat, exhaust and atmospheric drag so you actually need much more. It's not as simple as piling a huge amount of radioactive, really explosive, dangerous fuel close to your payload and detonate it. You need a controlled burn which is very complicated and makes your rocket very heavy, which means it has more mass, which means you need more energy, which means you need more fuel to lift up your rocket, which means you need more rocket to carry that fuel, which means you need more rocket to carry that new fuel and so on. At the end of this madness, you need 100x the weight of your payload to be able to launch. Ariane 6 (a European rocket) will weigh 800 tons and should be able to launch 10 tonnes into geostationary transfer orbit, or 20 tonnes into Medium Earth Orbit.
But a rocket can only produce so much thrust, so there's a maximum weight after which it just won't take off. As said, too much weight = won't lift off. So you cannot just build bigger and bigger fuel tanks, life doesn't work like that. This is the tyranny of the rocket equation and means space flight will never become easy. But wait - Getting to space is not good enough and you are actually still inside the gravity prison at the edge of space, so you'll crash back to Earth. Staying in space is much harder than getting there. To be in a stable position, so it can stay for a while, a rocket has to reach low Earth orbit. To do this, you need a LOT of kinetic energy which means going extremely fast. At an altitude of 100 kilometres, this means going at 8 km/s, 28,000 km/h which is fast enough to travel Earth in 90 minutes. Here's a trick; instead of going straight up we can go sideways. Earth is a sphere. So going sideways fast enough (even though you're falling towards Earth) the ground will curve away beneath you. So as long as you're above the atmosphere (100 km above) you'll be able to stay there in orbit. This is what the ISS does, falling around earth, expending energy from time to time to stay fast enough. There is no air in space to slow objects down, so the ISS is continuously going at this speed.
So, back to the rocket stuff.
To be as effective as possible, rockets aren't built into one giant piece, but contain other smaller rockets. If we look at orbits in scale, the low Earth orbit is laughably close to Earth. To deploy , let's say satellites on leave for other planets, requires another round of energy debt repayment. Getting into orbit is the most difficult part of space light to us right now. For example, to get to Mars, half the fuel is required to go to orbit, the other half to return. We use multistage rockets. We don't need empty fuel tanks, so we just drop them. Rockets today shed their boosters and main stage as they ascend with each successive stage being it's fully contained rocket, complete with it's own engine and fuel. Take it like a supermassive Russian doll. This is why getting to space is hard.
Sounds complicated? Don't worry, it's just rocket science.
Next Topic will be round 2 of Black Hole talk