I think the idea of the Ursa being developed in the time between first contact with the Shivans (or, more likely, since they found out the Lucifer was vulnerable in subspace) is absurd. I think it's much more probable it was an adaptation (the adaptation being specific to killing Lucy) of next generation Terran bombers, the designing of which was already in progress, possibly even already close to being done. Think of it from the designer's point of view.
Hmm, well we only have one shot at this and the fate of our race hangs in the balance. Now that we have these nifty shields, we can strip down the armor and make room for more bombs!
"Project Ursa" was a project dedicated to taking down the Lucifer - however they never stated their means to the end.
I also agree with the "Vasudan engines" explanation of the helios.
Oh and if the Ross 128 deflector array functions anything like a Star Trek then it's for the purpose of moving debris away from space ships and not functioning as a shield. It's basically a tractor beam in reverse to avoid collisions with random junk floating around in space. That is, the Star Trek one. Though I don't know what context the tech room mentions it in, and I'm far too apathetic to look it up.
