> "Gravitational assists can help, but they can also help you get other places."

Without gravitational assists, you need ~30km/s to drop into the sun, and far less to go other places. With gravitational assists both can be easier, but going to the sun will still be one of the harder places to go.

That aside, if you are going to loop it around Venus, why not just hit Venus? I'm sure Venus wouldn't mind.

Yes, I did read that. But what I didn't understand is why you were disregarding what seems to be a key part of interplanetary travel. The point that johngalt and I are making is that "falling" isn't the only way to get there.

Now, the real point seems to be that the Sun's gravity doesn't help you get there — in fact it works against you! You must rely on very precise calculations and instrumentation to target yourself there. So why not dive straight into another planet instead of using it for a gravity assist. That I can understand.

Gravity assists are helpful but they're not all-powerful. There's a hard constraint: your orbit is deflected more as you make your point of closest approach lower, but you can't make it too low without hitting the atmosphere. (Unless you actually want to crash into Venus instead of the sun; in which case, knock yourself out, but the moon is closer.)

Math time: a Hohmann transfer orbit from Earth to Venus will have 2.7km/sec of excess velocity when it reaches Venus. That means your orbit has a 44000km semi-major axis. With a closest approach of 6100km, that gives you a minimum eccentricity of 1.137; if I'm doing my trigonometry right, the most orbital speed you could lose in a single flyby is 4.2km/sec, or about 11% of your speed relative to the sun.

(See http://en.wikipedia.org/wiki/Hohmann_transfer_orbit and http://en.wikipedia.org/wiki/Hyperbolic_trajectory for details.)

You could do better with multiple carefully-orchestrated flybys, but the point is it's not as simple as just heading for the nearest planet and letting it fling you wherever you want to go.

> Why remove it when you can just deflect the rocket by the gravity of Venus and redirect the rocket directly towards the sun?

The fundamental thing you are missing is that to point the rocket directly at the sun required removing all of the orbital velocity. If you were to just point a rocket directly at the sun ignoring its relative motion and burn you would never actually hit the sun. You would just burn forever and never make any progress.