[tophat9000]

So the space craft are moving slower then expect out from the solar system then what they would expect from gravity alone …in effect the have a very slight drag "head wind"…

Well space is not a pure vacuum ..it is full of gas and debris

And the solar system gravity would be pulling all that gas and debris INWARDS to the solar system…

In effect creating a very slight gas and debris “head wind” the outgoing spacecraft would be flying in to

So you cannot calculate the drag of solar system gravity alone on anything outbound... you would have to account for gas and debris being drawn in to the solar system causing a gas and debris “head wind” …

And the amount of gas and debris in that “head wind” is an unknown variable

[Tellurian]

I wonder when Pioneer 10 reaches heliopause, or if the astrophysicists can even say.