I presume it's a bit simplified, but ...

What if we launch a rocket, the same speed but opposite direction of the orbit of our planet around the sun.

Will that rocket fall into the sun?

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    $\begingroup$ Do you mean a speed of 30 km/s in the opposite direction, or a speed of 0? $\endgroup$ – Hobbes Jun 27 '16 at 16:47

In a simplified sense, yes.

Relative to the sun, the Earth moves at approximately 30 km/s. So if we could launch a rocket in the opposite direction of Earth's rotation at 30 km/s, it would have a velocity of 0 relative to the Sun, and would be accelerated directly towards it by gravity from the Sun ("falling towards it").

This assumes that a rocket could be accelerated to 30 km/s before leaving Earth's orbit however. See this answer to a previous question if you want to see the upper speed limits on systems that we can launch. The fastest system we've launched has been New Horizons at 16.26 km/s.

  • $\begingroup$ Thanks. And I wasn't really looking for a practical way, just the principle of it. $\endgroup$ – Emmanuel Delay Jun 24 '16 at 6:52
  • $\begingroup$ The principle is: Your rocket is de-orbiting the sun and free from any forces but the sun gravity it ill fall on it $\endgroup$ – jean Jun 24 '16 at 20:18
  • $\begingroup$ Note through smart trajectory and gravity assists, you could send a rocket into a (very elongated) solar retrograde orbit. It would first involve launching it somewhere near Pluto's orbit, possibly a help from Jupiter in turning more towards retrograde, then performing a burn to accelerate in the solar-retrograde direction (and possibly catching some gravity assists to increase that speed). The fundamental question here though is WHAT FOR? $\endgroup$ – SF. Jun 27 '16 at 16:13

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