Brief:
This is the new Semroc A10-0T booster unit for the Centurion, Vega, and Goliath rockets. It is meant for existing, single stage rockets using the ST-16 (old Centuri style) body tubes. It will be interesting to stage a 13mm booster to a 18mm sustainer. I've never used a lower powered booster (A10) with a higher powered sustainer (B6 or C6, a A8 is also listed as a sustainer engine).

Construction:
The booster kit consists of:

• 1 Body Tube ST-825
• 1 Engine Tube ST-520E
• 1 Ring Coupler HTC-16S
• 1 Ring Set CR-EM-516
• 1 Engine Hook EH-18
• 1 Shroud Sheet IEM-516B

All parts are pretty much standard except for the centering rings. The laser cuts are tight and clean. The centering rings for the ST-5 series engine tube have eight elliptical holes cut into them. I would assume this is for venting while staging. Read through the directions before building. With two shrouds and four centering rings, take it slow and follow directions.

I reinforced all the tube ends with Super Glue.

STEP 3: I sanded the tube coupler's ends flat and square with a sanding block. I wanted to (slightly) increase the gluing surface.

STEP 5: The small centering rings (with the eight holes) fit too loosely on the 5 series engine tube. I build up the inside edge of the ring with some "rings" of white glue. The instructions suggest using CA to glue them in place. The instructions suggest: "Make sure to keep glue out of the holes". You would have to use a Teflon tube out the front of your CA bottle to control the flow. The holes are very close to the body tube/ring joint.

I was reluctant to apply a thin film of CA around the ring edges before punching out the holes. I was afraid the glue would get into the holes. I punched out the holes, then applied glue to the edges of the rings.

The instructions say "A thin film of CA around all the ring edges harden them and keep them from de-layering. After I easily punched out the holes, I noticed outside layer of the ring was starting to peel. The CA layer held down the lifting layer.

STEP 6: Says to slide the engine mount inside the body tube until the end with the hook is even with the body tube. The hook will over hang slightly. It just didn't read well. I know they meant that the engine tube should be even with the outside (larger diameter) tube. The hook overhangs more than slightly, it overhangs by 1/4".

STEP 8: Normally I hate paper shrouds. Hate paper shrouds! The shroud material was glossy on one side and matte on the other.

I wanted the printed lines on the inside, so the glossy surface ended up on the outside. For once, these paper shrouds glued together without any problems. I pre-curled them over a thick Sharpie pen barrel. One thin coat of white glue was enough for the glue tab to hold well.

The paper used for the shroud went together smoothly, with no bumps or bends. But when glued together, the seams were opposite. One upper-smaller shroud overlaid to the right, the lower shroud tab laid to the left. There wasn't any other way to correct this unless I would make one shroud with the gloss surface out, the other with the matte paper side out. Not really a big deal. But, (on one shroud pattern) Semroc may want to switch the side the tab sits on.

Both shrouds fit well. I had to widen the mouth of the larger shroud slightly to fit over the ST-8 main tube. It's not a fault of the shroud pattern, paper shrouds always seem to need a little adjustment.

Finishing:
Even without paint, the finished look is great! On my Centurion the booster extends 1 1/4" beyond the trailing edges of the fins, but it still looks cool. And structurally it feels strong.

With the gloss paper surface on the outside, I really don't have to paint it. But the exposed browned edge of the upper centering ring will need a touch up.

I enjoyed the build. It's nice when the shrouds cooperate.

Construction Rating: 4 out of 5

Flight:
With the engines installed and the booster unit in place, the engines ends are separated by about 3/8". I tested the fit with a A10-0T in the Booster 16 and a C6-5 in my Centurion.

Summary:
PROS: A fun build and the shrouds cooperated for once!

CONS: When built, the shroud tabs face opposite sides. One goes to the right, the other to the left.

Overall Rating: 4 out of 5