adjl posted...
I'm struggling to wrap my head around this one. I would think that moving toward the Sun's gravity well would take less energy than moving away from it, unless it's more a question of how much you have to deviate from earth's orbit (in which case I guess it takes more effort to start moving perpendicular to the orbit than to just deviate outward by a few degrees).
The part that most people don't get is that you can't just aim at the Sun, light your rockets and crash into it. This is because the Earth (and your rocket) are moving at an incredible speed in orbit around the Sun, almost 29.8 km/s. To hit the Sun, you have to slow down, so you would need to reduce your speed by 29.8 km/s.
On the other hand, the velocity required to escape the Sun from the Earth's distance is 42.1 km/s. Since the Earth (and your rocket) is already moving 29.8 km/s, you only need to go 12.3 km/s faster.
That's why it's taken over 6 years and 7 Venus flybys for the Parker Solar Probe to reach 6.1 km from the Sun (about 1 AU total travel distance), while Voyager 2 reached Jupiter (about 4 AU) in less than 2 years using just rockets and Saturn (about 8 AU) in 3, and New Horizons has traveled over 60 AU in 19 years with just a single gravitational boost from Jupiter.