Barry Gershenfeld wrote:

> >- If in a circular orbit and you fire an essentially instantaneous
> >retrograde burn (rockets fire forward along the orbital path), you will
>  ...
> >    - now be at the Apogee (highest point) of an elliptical orbit
> >    - lower the Perigee (lowest point) even more, which will now be exactly
> >on the other side of the planet.
>  ...
> >If you fire a Posigrade (rockets fire behind you along the path of your
> >orbit) burn at Perigee you can "circularise" your orbit (Alice's Hohman
> >transfer orbit.)

As an aside, a Hohman transfer orbit minimises delta v and fuel burn, but not
travel time.

> Problem.
> My retrograde firing lowered the other side of the orbit, creating
> a perigee.  Now I want to lower the apogee to make the new smaller
> orbit circular.

At this point, you are at perigee and traveling too fast for a circular orbit
because of the speed gained while descending in the gravity well.  So while at
perigee, you fire retrograde to slow down to the speed for a circular orbit at
the perigee altitude.

>  So I go around to perigee and fire again.
> Posigrade?
> Drops the Apogee?  Not in my simple mind. (Here we go again...)

Try firing retrograde on the other side of the planet while at perigee for the
transfer orbit..

Jim

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