Why is that - wouldn’t you be working against solar gravity? Like you don’t have to get them there quickly, just launch them in some orbit that will decay and be taken in?
I remember watching a video about that. The gist is that you have to leave earth orbit or something idk.
Why would an orbit decay without something to slow the spacecraft down like an atmosphere? The problem is that any object we launch from earth has a lot of orbital velocity, which makes it almost impossible to hit the sun directly, you would have to use a lot of complex gravity assists from the inner planets to take away enough momentum. Using gravity assists to accelerate outwards is much easier
Why do you need to hit the exact center of the sun to have the desired results? Get it within the orbit of Mercury and I’ll be happy enough.
That’s what the premise of this post was. It’s a common saying to “shoot something into the sun”, which sounds easy at first but is actually quite hard to do. That’s the joke
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.
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
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.
That’s assuming all cows are a point on a frictionless 2 dimensional plane.
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you don’t need to hit the sun dead center to be incinerated.
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the sun is huge
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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.
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.
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
That’s the thing - in space, orbits don’t decay. Orbital decay only happens if there’s dust or atmosphere that you bump into along your orbit to slow you down. But in interplanetary space, there’s no dust or atmosphere, and certainly not enough to decay your orbit fast enough to achieve results (otherwise, the Earth would have already decayed and melted in the Sun)
You need to spend fuel to lower your orbit to hit the Sun, and you need to spend fuel to raise your orbit to escape the solar system. It turns out to be really freaking difficult to hit the sun because it simply requires so much fuel to lower your orbit enough to hit the Sun.
You are making 2 opposing assumptions there, 1) there is nothing to bump into in outer space, the earth picks up 43 tons of new mass every day.
- the earths orbit would decay, the earth is absolutely massive compared to the amount of mass gained, and also off gasses a significant amount of mass every day.
If orbits don’t decay, why do even high orbit satellites need to make elevation corrections?
If you put a small body into outer space it would absolutely be (slowly) effected by the miasma of particles out there.
And let’s not forget we don’t have a time table for reaching the sun, and we aren’t aiming for the middle of the sun to see results. And as you approach the sun you will bump into more and more particles as they too are being drawn around the sun.
It’s an easy talking point from the Internet and high school text books, it is disregarding of many actualities of our universe. It would be true if the sun were an infinitely small point on a 2 dimensional plane with a perfect lack of friction.
And while for instantaneous results it would be easier to get something out of the sun’s gravity well rather than hit the exact middle of the sun, practically, if you have time, and you don’t actually need it to hit dead center of the sun, it’s much cheaper and easier to incinerate something proximal to the sun than it is too send it out of the solar system.
Also let’s not forget gravity sling shots work in both directions.
To escape a body of mass you need to have enogh velocity (kinetic energy) to overcome the gravitational pull of that body. You can imagine it like a ball sitting in a bowl. With little velocity it will just roll back and forth but if it’s fast enough it can roll out of the bowl and escape it’s influence.
That critical speed is called “escape velocity” and it depends on mass and distance from a body. The escape velocity of earth (from the surface) is about 11.2 km/s and the sun’s escape velocity (from earth orbit) is about 42.1 km/s. Earth orbits around the sun at about 29.8 km/s. If you launch in the direction of Earth’s orbit, you will orbit the sun already at about 41 km/s, so you “only” need 1.1 km/s more to escape the sun, too.
If you tried to reach the sun, you could launch in the opposite direction leaving you orbiting the sun at about 18.6 km/s. Since there is almost nothing in space you won’t slow down from friction and the orbit won’t decay. Instead you’d have to accelerate opposite the direction you’re traveling. Now, calculating exactly how much you’d need to decelerate isn’t trivial since you don’t want a stable orbit but an elliptical orbit that just touches the sun at the closest point (perihel). I don’t know how much deceleration that takes, but it’s propable that it’s easier than accelerating by 1.1 km/s to escape the sun.
