Three levels of rockets decreases (one latter firing after the other runs out of fuel) in the Delta 4 Heavy helped considerably as boosting PSP of goal, but it's not enough to repeatedly flew the probe same to the sun.
Three different rocket stages (one firing after the other runs out of fuel) in the Delta 4 Heavy helped considerably with boosting PSP toward that goal, but it's not enough to repeatedly fly the probe close to the sun.