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Couldn't you theoretically escape a planet's gravity without going into orbit? I mean, gravity weakens by the square of distance, so it wouldn't be long before
by ythn 8y ago
Couldn't you theoretically escape a planet's gravity without going into orbit? I mean, gravity weakens by the square of distance, so it wouldn't be long before Earth didn't have much influence on you
- aphextron 8y agoNo, you would just be in a different kind of orbit. You would be in Earth orbit until reaching escape velocity, at which point you would be in Solar orbit.
- alistproducer2 8y agoso are you saying that even though I could escape Earth's gravity going at sub-orbital velocities that I would still need to be going fast enough to avoid being pulled into the sun?
- aphextron 8y agoDisclaimer: the entirety of my orbital mechanics knowledge derives from Kerbal Space Program. I cant recommend it enough if you're really interested in building an intuitive understanding for this stuff. But no, it's not that you would be pulled into the sun. You would simply be in a solar orbit just like the earth, unless you continued accelerating and reached solar escape velocity (~600km/s). You can think of gravity like successively larger "wells" which you must escape from if you want to go anywhere. You can't just point a spaceship at a planet and go there.
- kuschku 8y ago> You can't just point a spaceship at a planet and go there. Disclaimer: You can, you just need so much power it’s like flying with a helicopter from your bedroom to the kitchen, absolutely wasteful.
- a_t48 8y agoThe main question at that point becomes: how can you carry that much fuel?
- Florin_Andrei 8y agoDepends on how efficient the engine is. If you're riding a nuclear rocket, you don't need that much fuel.
- kuschku 8y agoTheoretically? Fusion reactor + ion drive. Throw enough power at those and you can accelerate for a long time.
- isostatic 8y agoOne thing you learn from KSP is it requires less energy to fly into to alpha centauri than fly into the sun.
- mannykannot 8y agoGetting the Parker Solar Probe down to the sun will take 7 flybys of Venus to use its gravity to slow down, over 6 1/2 years. http://parkersolarprobe.jhuapl.edu/The-Mission/index.php http://parkersolarprobe.jhuapl.edu/The-Mission/index.php 'Journey to the Sun.'
- pdonis 8y ago> solar escape velocity (~600km/s) That's for escaping from the surface of the Sun. At Earth's distance from the Sun, the velocity needed to escape from the Sun's gravity is only 42 km/s.
- garmaine 8y agoYou can’t escape Earth’s gravity going at sub-orbital velocities. Earth escape velocity is higher than any orbital velocity.
- marcosdumay 8y agoYou don't escape Earth's gravity at sub-orbital velocities. Escape velocity is always larger than orbit velocity. What the GP said is that if when you reach Earth's escape velocity, there is still a long way to go until you have Sun's escape velocity (so you are on a solar orbit), and after you reach that, there is a huge distance until Milk-Way's escape velocity, and an even huger way until you escape the Local Group.
- pdonis 8y ago> even though I could escape Earth's gravity going at sub-orbital velocities That's not what he said. Escape velocity is higher than orbital velocity (as ythn pointed out upthread). And escape velocity from Earth is still slower than Earth's orbital velocity around the Sun, which in turn is lower than escape velocity from the Sun's gravity at Earth's distance from the Sun.
- kabdib 8y agoSure, just reach escape velocity (well, in the right direction). It's higher than orbital velocity, obviously. To escape the solar system you'll need a bit more velocity on top of that. We do this all the time with probes to other parts of the solar system. Manned missions (Apollo) used a small number of earth orbits before doing the burn to get to the moon primarily to ensure that systems checked out before making the bigger step.
- isostatic 8y agoEscape velocity will work in any direction (assuming no wind resistance) Unless you hit the ground, or a mountain, or a plane, or the moon, etc.
- kabdib 8y agoHitting the ground was exactly what I was trying to get across. Otherwise, discounting pesky atmospheric drag, your vector doesn't matter.
- alistproducer2 8y agoThis is what I was getting at. The article mentions escaping a planet's gravity, not orbiting it.
- neaanopri 8y agoThe amount of fuel (delta-v specifically) to reach orbit from a given altitude is always less than the amount of fuel needed to escape the planet's gravity.