> It could also be used in tight gravity assist flybys to accelerate probes to incredible velocities, maybe making interstellar probes a lot more practical.
Would 1-5 earth masses really provide enough of a yeet to appreciably affect the speed of a probe? Jupiter is about 300+ earth masses and we're not flinging probes out to stars using him.
You can get a lot closer to the center of mass of the black hole, which should drastically increase acceleration since it falls off with distance squared.
FWIW I’ve read several explanations of why this works, including some confidently claiming that one or more of the others was wrong, and a couple of which kinda made sense as I was reading them, but not a one of them has made a lick of sense to me after I thought about it for a while. Despite all the attempts at understanding it, I still couldn’t tell you why it works (aside from “this math says it does” which is a shit answer)
[edit] the other thing you can do, even at the same time is:
But the specific effect in question seemed to be the Oberth Effect, given the mention of throwing off mass.
Gravity assist just relies on the body in question being really heavy and in (orbital, say) motion in some fashion that’s useful to you. Kinda “pulls” you along. You steal a negligible amount of energy from a huge body, which translates into some decent speed for your very-light spacecraft.
OK so I was totally confused by the Oberth effect and how it could possibly be and so did some research.
Now I have no idea why or how kinetic energy has a quadratic relationship with velocity, but it does. Something something work something something square of velocity, who knows. If someone could explain that to me like I'm 5 I would totally appreciate it.
But if we just take that as a given then we can develop an intuitive understanding of the Oberth Effect pretty easily if we remember that velocity is only relevant to a reference frame. So when you burn at periapsis (at top speed aka when youre closest to our black hole) your energy relative to the black hole is increased a lot more because for a given unit of fuel you add the same amount of velocity, and doubling your velocity is more than doubling your energy. That energy is what carries you up and away from the black hole and towards your apoapsis (or the stars)
It makes sense if we just pretend to understand why it is that somehow magically KE is proportional to the square of its velocity IDK
I can't ELI5 (don't like such things anyway) but if you know calculus, the v^2 follows directly out of trying to integrate momentum (or quantity of motion, a fun phrasing) with respect to velocity. Momentum is mv, units are kilogram * meter/second. Integrate with dv, you get 1/2 mv^2, units are kilogram * meter^2/second^2. (Double-check, take the derivative of that with respect to v, and you get mv.) This 1/2 thing times otherthing^2 relationship actually shows up all over the place in math and physics, it's quite beautiful, and incidentally another reason to prefer using tau=2pi instead of pi...
Imagine a car is moving at a speed of 10 m/s. The driver hits the brakes. How much distance does it need to stop?
The main idea is that brakes have a constant force, and the change in speed is always constant. Let's say they reduce the speed in 1 m/s each second.
The first second the car travels 10 m and the new speed is 9 m/s.
The second second the car travels 9 m and the new speed is 8 m/s.
The third second the car travels 8 m and the new speed is 7 m/s.
...
The ninth second the car travels 2 m and the new speed is 1 m/s.
The tenth second the car travels 1 m and the new speed is 0 m/s.
So the total distance until it stops is 10+9+8+7+6+5+4+3+2+1. If you make a pile of bloks and you put first 10, then 9 over them, then 8 over them, .... you get a nice triange. The base is 10 and the heigh is 10, so the total number of blocks is 10*10/2. [1] [2]
So the car needs 10*10/2 m to stop. You can repeat the calculation with other initial speeds, and the result is V*V/2.
I'm not sure if it's intuitive, but the energy is proportional to the distance to stop.
Another posibility is to throw a toy car verticaly, and calculate how hight it goes. It's the same calculation. The maximal height is V*V/2. I think it's easier to imagine that energy is proportional to maximal height.
[1] If you actually count them, the result is 55 insted of 50, more details in https://en.wikipedia.org/wiki/Gauss_sum , but 10*10/2 is a good aproximation.
[2] If you split the time in half seconds and use smaller and smaller blocks, and then use calculus, you get 10*10/2.
Would 1-5 earth masses really provide enough of a yeet to appreciably affect the speed of a probe? Jupiter is about 300+ earth masses and we're not flinging probes out to stars using him.