the issue is not counteracting gravity, the issue is decelerating enough to hit the sun
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OpenStars@discuss.online 3 months ago
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?
rockerface@lemm.ee 3 months ago
MF_COOM@hexbear.net 3 months ago
What’s wrong with them striking the sun at full speed?
DefinitelyNotAPhone@hexbear.net 3 months ago
The curvature of spacetime does wild shit to how you would expect physics to work. If you want to fall into a gravity well, you have to slow down or you’ll just slingshot past it.
DragonTypeWyvern@midwest.social 3 months ago
This sounds an awful lot like the the idea that you can never actually catch up to anything because all you can ever do is close the distance by half.
psud@aussie.zone 3 months ago
Picture going for a very tight periapse in a highly elliptical orbit. Now make the periapse lower. Lower still, within the atmosphere or below the surface of the thing you’re trying to hit. If you don’t plan on arriving alive it’s much cheaper to arrive like a meteor
DragonTypeWyvern@midwest.social 3 months ago
This sounds an awful lot like the the idea that you can never actually catch up to anything because all you can ever do is close the distance by half.
cosecantphi@hexbear.net 3 months ago
The reason you need to slow down is because you’re starting on Earth, which means you’re moving fast enough parallel to the sun’s surface that for every foot you fall downwards toward the sun, the sun’s surface curves away by 1 foot. This results in the nearly circular orbit around the sun we exist in.
If you start speeding up, the orbit becomes more elliptical, except your aphelion starts raising away from the sun because now you’re moving fast enough that you’ve moved more than 1 foot sideways in the time you’ve fell 1 foot downwards.
Slowing down has the opposite effect. If you get your speed down to 0, you’ll fall straight down toward the sun as normal with gravity. But you don’t need to go all the way down to 0 velocity to enter the sun, you just need to slow down until your elliptical orbits brushes up against the sun’s surface.
mihor@lemmy.ml 3 months ago
That’s a very good explanation.
psud@aussie.zone 3 months ago
So you have ~30km/s in a near circular orbit. You interact with a gravity well to point your vector at the sun. Sure you’re carrying enough energy to come out of that with a very high aposol, but with the perisol within the Sun that energy will convert to heat
sushibowl@feddit.nl 3 months ago
The problem is, you have so much speed that you keep missing.
Contramuffin@lemmy.world 3 months ago
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.
captainlezbian@lemmy.world 3 months ago
Sir Isaac Newton is the deadliest son of a bitch in space
Donjuanme@lemmy.world 3 months ago
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.
snugglesthefalse@sh.itjust.works 3 months ago
Orbital decay isn’t just friction from particles, you also have imperfections in the orbit and other objects influencing the eccentricity over time. The moon has gravity too for instance.
jballs@sh.itjust.works 3 months ago
Zwiebel@feddit.org 3 months ago
You’re starting with the speed of the earth
OpenStars@discuss.online 3 months ago
Ah… centrifugal force, ofc!:-)
Blaubarschmann@feddit.org 3 months ago
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
Donjuanme@lemmy.world 3 months ago
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.
Blaubarschmann@feddit.org 3 months ago
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
Donjuanme@lemmy.world 3 months ago
My argument is it’s more energy efficient to shoot something towards the sun that will have the same result as hitting the sun than it is to get it out of the solar system.
lugal@lemmy.dbzer0.com 3 months ago
I remember watching a video about that. The gist is that you have to leave earth orbit or something idk.
snugglesthefalse@sh.itjust.works 3 months ago
You leave earth orbit into a solar orbit that is slightly shifted depending on which direction you were facing when you left earth’s orbit
excral@feddit.org 3 months ago
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.
Donjuanme@lemmy.world 3 months ago
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.
Simmy@lemmygrad.ml 3 months ago
Short answer; the earth is orbiting really fast around the sun.
ilinamorato@lemmy.world 3 months ago
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 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.
OpenStars@discuss.online 3 months ago
That’s a great explanation, thanks! 🙏
sushibowl@feddit.nl 3 months ago
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.
skulblaka@sh.itjust.works 3 months ago
I feel like that might be difficult to do without just falling into Jupiter, but I am no rocket scientist.
rovingnothing29@lemmy.world 3 months ago
They would still be destroyed in a hot crucial, so it still works.
Venator@lemmy.nz 3 months ago
Why would you need to entirely cancel the earths orbital velocity, surely you just need to cancel a tiny bit of orbital velocity?
Olgratin_Magmatoe@lemmy.world 3 months ago
Canceling out only a tiny bit puts you on an orbit similar to earth’s. You need to kill basically all of your momentum.
ilinamorato@lemmy.world 3 months ago
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.
Venator@lemmy.nz 3 months ago
But you’d need a higher velocity to orbit closer…
Donjuanme@lemmy.world 3 months ago
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.
sushibowl@feddit.nl 3 months ago
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.
Donjuanme@lemmy.world 3 months ago
Billions of years and billions of times less energy, would you agree?
psud@aussie.zone 3 months ago
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
ilinamorato@lemmy.world 3 months ago
Yeah, gravity assists are a cheat code here, but the delta-V is still being changed—just by stealing velocity from elsewhere.