Just Don't Get It

Lol space is so big that even if you try, it’s hard to hit a planet. Also “ksp certified astrophysicist” is a joke, ksp is a video game which teaches you a lot about orbital physics. It’s a common joke in the Spaceflight community that ksp teaches you more about astrophysics than an actual job.

The problem with picking up space trash is that it's spread all over in all sorts of orbit. To pick up said trash, the spacecraft will have to alter its own orbit to intercept trash.

The issue isn't so much the size of the thrusters, but the amount of fuel needed. In space, everything coasts along its current orbit, and to go elsewhere you need to expend propellant to alter your orbit. Either by burning loads of fuel in a short amount of time, or with the thrust spread out over a longer burn time.

And when you're finally ready to head into the sun you need to escape earths gravity well, which takes abbunch.

And to hit the sun you will in effect have to burn enough fuel to cancel out the orbit that you inherited from earth to begin with. I don't have the DeltaV numbers in my head, but the fuel cost is immense.

Think of it as a representation of how much energy is needed for orbits. To get to the moon you need about 1.7 km/s of delta v. To get to sun you need 30 km/s of delta v. To escape our solar system you only need 18 km/s of delta v.

Think of it this way. The earth is moving horizontally to the sun at 29.78 km/s (107,200 km/hr). In order to hit the sun you have to cancel all of that movement otherwise You'll miss the sun and enter a new elliptical orbit.

That's not how orbits work. You can't just point at the sun, accelerate slowly for 10 seconds and then you will arrive in a few hundred years. If you did that, you would still orbit the sun, just in a slightly different orbit than before. To actually reach it or get near enough to it that the junk burns off, you have to expend a lot of energy.

It’s not about speed, but energy. Virtually all satellites are gravitationally bound to Earth. Think of Earth’s gravitational potential as a funnel. The satellites sit somewhere on the walls of the funnel. Now, next to the Earth’s funnel, there’s. much deeper funnel: The Sun’s gravitational potential. But between where the satellites are and the point where the Sun’s potential starts attracting them is still a big "hill" or wall separating the two funnels from each other (the top of that hill is the Lagrange Point L1). So to get a satellite out of Earth’s potential to a point from where it could “fall” towards the Sun still requires a large amount of energy.

To get to the sun you have to decrease your speed. Speed absolutely matters here. If it were possible to round up all the space junk (which it currently isn't) we might as well just set it adrift outside the gravitational influence of Earth

That's just plain not how orbital mechanics works. The difficultly with falling into the sun is that we're starting from a high energy state (orbit) and so in order to fall into the sun we have to scrub all our extra energy to get back to zero.

Think of it in reverse. If you were standing on the sun, it would take an absurd amount of energy to launch into an orbit, and only some of that energy actually goes into lifting your payload. Once your at your orbital height you have to keep adding energy in order to go sideways fast enough to maintain orbit.

It's all the sideways momentum that you have to oppose in order to be able to actually hit the sun.

Edit: Orbital mechanics don't follow your intuition, given that you didn't evolve in an ecosystem where they impact your life. It's actually less energy intensive to climb to a higher orbit first, then scrub your remaining horizonal velocity in order to fall into that sun.

It’s called a gravity assist and can save a lot of fuel at the cost of travel time. (no centrifugal force involved) It also takes a lot of planning effort. It still takes a fair amount of fuel to reach the moon, and to set up more gravity assists. It’s much easier to slow things down just enough that they will fall and burn in the atmosphere.