Comment on Launches
ilinamorato@lemmy.world 3 months agoBecause the Earth is really cookin’, and anything anyone you hurl toward the sun will inherit that orbital velocity as well, meaning that they’ll actually end up going around the sun, instead of into it. And due to the speed it would pick up on its way in, it would basically take up a stable yet highly-eccentric elliptical orbit.
“Well, what if we throw them in the other direction, to make up for it?” That’s called retrograde, and that’s basically exactly what you’d have to do: cancel out the Earth’s entire orbital velocity. Which would take a lot of energy, plus a couple of really exacting gravity assists from planets on the way in.
By contrast, even though the escape velocity from the solar system is no slouch (42 km/s), you get to start with the Earth’s orbital velocity (30 km/s)–meaning you’re already a little under 3/4 of the way there. Plus, if you can make it to Jupiter and Saturn, you can get a significant gravity assist, and they’re much bigger targets for such a maneuver than Mercury or Venus are.
So, yeah, bottom line: you only need a delta-V of about 12 km/s to get out of the solar system, but a delta-V of 30 km/s to get to the sun without going into orbit.
So, yeah, bottom line: you only need a delta-V of about 12 km/s to get out of the solar system, but a delta-V of 30 km/s to get to the sun without going into orbit.
This is true, but the possibility of gravity assists mostly nullifies the difference. If you can get out to Jupiter you can basically choose: either let it sling you out of the system, or let it cancel out all your orbital velocity so you fall into the sun.
I feel like that might be difficult to do without just falling into Jupiter, but I am no rocket scientist.
They would still be destroyed in a hot crucial, so it still works.
Why would you need to entirely cancel the earths orbital velocity, surely you just need to cancel a tiny bit of orbital velocity?
Canceling out only a tiny bit puts you on an orbit similar to earth’s. You need to kill basically all of your momentum.
Good question, but if you cancel out only a little bit of orbital velocity, you just orbit in a little bit closer. Without any appreciable drag acting on you, there’s nothing that will keep your orbit decaying. You’ll just be in a smaller, perhaps slightly more eccentric orbit.
But you’d need a higher velocity to orbit closer…
Yeah, orbital mechanics gets a little bit mind-bendy sometimes. If you’re in a stable circular orbit, accelerating in the direction you’re traveling will actually result in you traveling more slowly because you have moved to a higher orbit, and firing engines to slow down will actually speed you up because you move in closer to the host body and take up a faster orbit.
This is actually a problem spacecraft deal with regularly. If a Dragon capsule is behind the ISS and wants to dock, using its thrusters to accelerate toward the ISS will actually result in it falling further behind. Decelerating will get it closer, though it will then be in a lower orbit. Orbital rendezvous is tough.
That’s assuming all cows are a point on a frictionless 2 dimensional plane.
you don’t need to hit the sun dead center to be incinerated.
the sun is huge
you aren’t in a frictionless environment, your orbit will decay into the sun.
These are all technically correct but fairly inconsequential. Even just to graze the sun you need to lose 90% of your orbital velocity. And although everything orbiting the sun will eventually fall in, the friction is really low. It will take billions of years to lose enough velocity to fall in.
Billions of years and billions of times less energy, would you agree?
If you’re willing to settle for that kind of timeline, you could “launch someone into the sun” by just…leaving them on Earth for five billion years. At that point, the sun will become a red giant and probably expand to engulf the Earth.
You can just change the shape of your orbit (but not your orbital energy) with the help of a sufficient gravity well from solar orbit, so it intersects with the Sun. Drag within the Sun will slow whatever is left of you enough to sap your orbital energy
Yeah, gravity assists are a cheat code here, but the delta-V is still being changed—just by stealing velocity from elsewhere.
OpenStars@discuss.online 3 months ago
That’s a great explanation, thanks! 🙏