On Aug/13/2018 at 4:44 PM, Niklas Holsti wrote :
On 18-08-13 21:03 , JF Mezei wrote:
On 2018-08-13 02:47, Niklas Holsti wrote:

And it took a hulking big launcher, plus AIUI an extra final rocket
stage, to give this small probe enough delta-v for that.

My question pertains to what direction this delta-v is being applied.
Straight to the sun to cause elliptical orbit?


or retrogade to slow the proble's speed around the sun so it drops orbit?

The Parker orbit diagrams shown in eg. Wikipedia all have an aphelion at
the Earth's orbit, not farther from the Sun. This suggests that the
launch delta-v is fully or mainly retrograde, orthogonal to the
probe-Sun line, resulting in an elliptical orbit with an aphelion at the
launch distance (Earth orbit). Later, gravity assists from Venus seem to
reduce the aphelion distance somewhat (as well as reducing the
periohelion, as intended).

The delta-v was as you said parallel to Earth's orbit in the retrograde
direction but you can't deduct that from the aphelion because there is a
Venus gravity assist manoeuvre on the first orbit.


Alain Fournier