Because 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 highly-eccentric yet stable 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.
(Edit to add: I may have explained this poorly. Basically, if you don’t change your orbital speed at all, any movement you make toward or away from the host body means you just end up in an orbit of the same average distance, but in a more eccentric [elliptical] shape.)
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.
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.
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.
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.
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.
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.
What does engulfing the earth mean to you? The mass of the sun expanded to a body 1 au would not be very dense. My money says the earth would continue to orbit “inside the sun” for quite a while, but the orbit would degrade more quickly.
But yes, I argue get them out of the earths gravity well and let Newton handle the rest, no reason to propel them in any direction, eventually they’ll get to the sun.
If the sun became a red giant tomorrow, and Earth found itself inside the outer layers of solar atmosphere, then drag would start slowing it down. In less than 70,000 years, it would fall close enough to the center to be torn apart by tidal forces like one of Saturn’s moons (assuming it hasn’t already been vaporized).
If we’ve already waited 5 billion years to have our revenge, whats another 70k? The lowest amount of Delta V we can spend on this project is zero.
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 (aerobraking!) within the Sun will slow whatever is left of you enough to sap your orbital energy
Because the Earth is really cookin’, and
anythinganyone 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 highly-eccentric yet stable 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.
(Edit to add: I may have explained this poorly. Basically, if you don’t change your orbital speed at all, any movement you make toward or away from the host body means you just end up in an orbit of the same average distance, but in a more eccentric [elliptical] shape.)
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.
Why would you need to entirely cancel the earths orbital velocity, surely you just need to cancel a tiny bit of orbital velocity?
Edit: https://space.stackexchange.com/questions/43913/do-you-need-0-km-s-velocity-to-crash-into-the-sun
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 a great explanation, thanks! 🙏
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.
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.
What does engulfing the earth mean to you? The mass of the sun expanded to a body 1 au would not be very dense. My money says the earth would continue to orbit “inside the sun” for quite a while, but the orbit would degrade more quickly.
But yes, I argue get them out of the earths gravity well and let Newton handle the rest, no reason to propel them in any direction, eventually they’ll get to the sun.
If the sun became a red giant tomorrow, and Earth found itself inside the outer layers of solar atmosphere, then drag would start slowing it down. In less than 70,000 years, it would fall close enough to the center to be torn apart by tidal forces like one of Saturn’s moons (assuming it hasn’t already been vaporized).
If we’ve already waited 5 billion years to have our revenge, whats another 70k? The lowest amount of Delta V we can spend on this project is zero.
No that’s not really the case, the earth will be destroyed.
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 (aerobraking!) within the Sun will slow whatever is left of you enough to sap your orbital energy