Don't want to rain on your parade, but you might want to pick up Michael Kube-McDowall's "Trigon Disunity" novels. The gravity-well ships in those books are virtually identical to yours, both in general layout and function. There's even the same Pushme-pullyou" reference to Dr Doolittle.
Not to belittle what you're doing. The overall concept is cool, and well executed. It's just that you've stumbled on an idea that's been done before, which you may want to look into for copyright reasons, particularly if you intend for your story to be more than "fanfic".
I have read those books actually, and they were the inspiration for my setting. My version will be different in some aspects and the same in others. Just as many books use versions of hyperspace, warp drive, jump drive, wormholes, etc; I don't think it will be a problem.
The good thing about a copyright is it protects the copying of portions and/or all of the text. (somebody correct me if I am grossly off base here) Taking a single idea from the book is not against copyright . (though carefully re-worded copies of the original story could also be trouble)
My setting is actually closer to Piper's Terro-human future history. I just decided I liked this form of drive system better, so I transplanted it.
Besides, you know the old saying "Good artists copy, Great artists steal"