Heiwa has a point. If someone says they will do a fly by around the sun for a gravity assist, you know it's full of shit. As you know Earth is constantly moving sideways relative to the sun at about 30km/s. To get to the sun you have to cancel this sideways motion. It is much easier to get a space craft out of the solar system than it is to the sun because you only need to worry about the escape velocity of the Earth which is 11km/s. Just wait for the right time (when Earth is in a good position relative to your target in the solar system) and go. If the probe has to go around the sun first it must use orders of magnitude more fuel and energy to pull it off. Waste of time, money and resources.
He does not have a point.
Thats because he has zero idea what he is talking about.
https://en.wikipedia.org/wiki/Hayabusa2[/size]
It is not going anywhere close to the sun.
It is using the earth for a gravity assist to get into a higher orbit to match the asteroids velocity and position.
You can use gravity assist to gain or lose orbital velocity depending on how you approach the gravity well.
Hayabusa needed the additional velocity to get the the Ryugu. It was launched with a much smaller rocket than curiosity rover, and needs about the same orbital apogee (actually greater).
It is not time constrained, so they can add more mass to get to a faster orbit with a smaller rocket, all thanks to earths gravity assist.
But you are correct. If you want to get to the sun you need to cancel out our sideways (orbital) velocity, which is why it is very hard to get to the sun or even Mercury. But not impossible. If you have the time, you can send a space craft nearly anywhere with enough gravity assists.
Or you know, anti matter :p