More on building the Princess Cecile

July 16, 2012

Those of you who have followed my ramblings as I slowly work on a (mostly) scratchbuilt model of the starship Princess Cecile from David Drake’s Lt. Leary science fiction book series – here’s your next little bit:

The thruster quads I was trying to cast in resin turned out to be a challenge. I tried several different molds, trying to make one as a one-piece casting with the mold in two halves, and as two separate halves poured, sanded flat, and glued together.

In both cases I had problems with air bubbles or voids. Splitting it vertically in two helped a bit, but that still required getting the halves exactly flat and so they would line up when I glued them together. I learned a lot about the behavior of resin and moulding rubber, though!

The more time I spent with these parts, the more I was convinced the quads were just too big. They would scale out to 10 to 12 feet across, nozzle to nozzle. Granted, a warship has to maneuver quickly and so they would need to be larger, most likely, than on a commercial spaceship.

The trend today is that such thrusters would be mainly contained inside the hull of a spacecraft, I guess, if there is such a trend. The thrusters on the SpaceX Dragon vehicle only show the openings of the rocket nozzles.

A test firing of the Draco thruster for the SpaceX Dragon

You can see the thruster openings on the SpaceX Dragon – the four ovals below and to the left of the hatch.

No doubt about it, the Dragon is a well-designed little ship. But she’s not a fighter, and (hopefully) she will never have to take battle damage. The ships of the RCN routinely are repaired during battle by the riggers, who wear armored spacesuits because there’s stuff flying around out there. Drake usually refers to the riggers as needing to repair the rigging and sails so the ship can re-enter the Matrix. The design of the RCN ships was predicated on making them as similar to sailing vessels as possible for narrative purposes, I think.

One other point is that the RCN ships are built on steel hulls and are an interesting combination of high tech and low tech. In one of the books a ship is radically rebuilt on the ground on a mostly uninhabited planet. Just like the sailing ships of Aubrey or Hornblower, sometimes the crew finds it must effect major repairs without the benefit of a shipyard.

So…external thruster quads just sounded like a good idea to me. Here is the Apollo command and service module combo, showing the thruster quads:

See the thruster quads?

Closeup of the Apollo Service Module thruster quad

So…I still wanted them on the exterior of the hull, so they could be repaired or replaced without quite as much danger of explosion. It didn’t make sense to me to have them located inside the hull placing a bunch of small (relatively)  rocket engines where they could be dangerous to the crew, with openings through the hull for the exhaust.

So I made a couple of sort-of tetrahedrons about 3/8 of an inch on a side out of balsa foam. It’s a little too porous, but once I cast some I could sand the sides smooth. I also made a few small rocket engine bells based on the FP von Braun ferry rocket engines. I glued one set together. Here it is, next to the old master:

Test version of the new quad.

The whole thing is less than  3/4 of an inch across. That still makes it about 12 scale feet across, but I think they will look more in-scale and they are about as small as I can make them. I may try making one with the “shoulder” on the engine bells removed. That would make it smaller, but it would also make it far more delicate – the nozzle throat is about 1/16 of an inch!

I’ve not drilled out the engine bells. I should have done that first, with a pin vise. I’ll have to do that on the next set before I attach them.

I think these will give the ship a bit of a “retro” look, which is what I’m going for, anyway. I don’t see the ship as a beautiful, streamlined aerodynamic vehicle – in fact, Drake notes than when entering the atmosphere too fast it is far too easy to tear the rigging right off the hull. This is a ship that does not enter an atmosphere ballistically. It is under power at all times.

So, slow going. One other thought it to somehow create even smaller engine bells that would look more like the Apollo bells. I just don’t know how I would hold them on!


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