On 18-08-14 01:00 , Alain Fournier wrote:
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.

Yes, but that Venus fly-by seems to have only a small effect on the
orbit, judging from the diagrams, and even the initial part of the orbit
seems to be almost tangential to Earth's orbit rather than crossing it.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .