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".