Solving for Aphelion of a Comet: What am I Doing Wrong?

[Logarythmic]

It is given that the perihelion for a certain comet is r_{per} = 0,2301 AU and the eccentricity is e = 0,999846.
My mission is to find the aphelion.
I know that this is given by

r_{aph} = a(1+e)

And I have used that

a = \frac{r_{per} + r_{aph}}{2}

This gives me

r_{aph} = \frac{r_{per}(1 + e)}{1-e}

and then I get that r_{aph} = 2988 AU. This all seems very simple so what am I doing wrong?

The correct answer should be r_{aph} = 4698 AU

 

[Logarythmic]

Ok, I got it. Small variations in e and r_{per} will give a big difference in the aphelion. ;)