Construction

There were not a lot of very challenging steps to the assembly of the MIRV. The instructions do clearly show you how to assemble it.  I suppose the most challenging steps for me was the gluing, sanding and finishing of twelve fins - a lot more than your average 3 or 4 fin rocket.  What did make the construction easier was that the fins were attached with the styrofoam in place which acted as a built-in fin alignment jig so there was no difficulty in aligning any of the twelve fins.

Some of the fins required assembly from two seperate pieces butt-jointed together. I don't know why, maybe the differing grain direction makes them stronger/stiffer, but otherwise they were small enough to have easily been made from a single piece of balsa.

There are challenges to this kit construction though, which I think is the result of compensating for a design that still needs some refinement in my opinion. I recommend doing a few things that are not covered in the basic kit. Most importantly, if I were to build another one, I would increase the length of the wood dowel used as a launch rail for the upper stages, and move the upper stage's launch lugs as far forward as possible, so that it will better hold the three nose cones together when they are on the booster.  Of course, that would mean the upper stages pop off the rod rather quickly after ignition, but the booster stage already gets these rockets up to speed for the fins to be effective so I think they would continue to safely travel upwards anyways. Pretty much every other multi-stage rocket works fine without a launch rail on the booster.

You could use longer or split lugs to solve that problem, but if one stage does not ignite then they will interfere with the others and you may have a flying mess on your hands. Perhaps three independent thinner rods would have worked better - but that would of course be heavier and more complex.

The upper stages are constructed from a BT-5 tube and shaped with an outer wrap of styrofoam to make a flattened-diamond cross section when fit together.  The three diamond sections fit together to make a larger hexagon when all three stages are assembled for flight. The foam, pretty beat-up from shipping, needed some filler and sanding to make a smooth surface again. I hoped that layers of primer and paint would provide somewhat of a harder shell, but that was not the case and the finished product is still very easily dinged and punctured.

I did almost have a construction mishap though. When gluing the booster's motor tube into the plastic manifold, I hesitated just a bit and the glue caught before I could seat the tube all the way in. I pushed as hard as I could but could not make the last 3/16".  I was worried about upper-stage ignition reliability but it turned out I had no problem with the small gap ...yet.

One major thing I learned from experience: Sand and fillercoat the fins BEFORE gluing them into the rocket with the foam. The foam is very delicate and with all that sanding you are bound to scrape and ding the styrofoam somewhere. Just remember to sand away the balsa fillercoat where you will apply glue.  I would recommend paper laminating the fin surfaces for better smoothness and a bit more strength.

Another step in the assembly involves gluing two plastic pieces together to form the manifold. This critical piece is used to duct the flame from the lower to the upper stages. When you stage that way ("gap staging"), you must allow for the existing cool air in the manifold to escape to allow the flaming pressure from the booster motor to travel to the upper nozzles, so a small vent is needed near the upper stage to let the cool air out of the way. This small vent - nearly invisible - is molded into the plastic pieces at the joint. When gluing them together, Estes warns you to not use too much glue and so I did not (I suspect to prevent over-glue from blocking the tiny vent holes).  Of course that was the first broken glue joint on the first flight, so I say use A LOT of glue, just make sure that the tiny vent holes are clear.  It appears to be some kind of thermoset plastic, so maybe normal plastic cement does not work well here (it's actually made to chemically melt and weld styrene plastic). You might want to try either CA or epoxy glue, so let me know if that works better, I have a feeling I will be gluing it again!

You will notice the rather unique sharp triangle/diamond shapes of the three nosecones. Each nose cone is assembled from two pieces to form a single nose cone. These pieces are relatively heavy and probably allow for a balanced model. The three diamond shapes fit together to form a hexagonal nosecone.  Unfortunately, as individual nose cones there are a lot of sharp corners. When these nose cones snap back from the Estes-short shock cord after ejection, they are perfectly shaped to make a nasty ding in the delicate styrofoam bodies, and as expected I now have little dings.  You may want to experiment with longer shock cords, or long Kevlar cords instead of the normal rubber.

Mounting the shock cords using Estes normal paper-fold method was also very difficult as my fingers are too small to fit down into the BT-5 tube past the shoulder length of the nose cones. Instead, I glued in small Kevlar loops in there, with the ends of the Kevlar frayed to make for a much wider gluing surface.  I have done this with at least three or four other models now, and none of them have broken/seperated in repeated flights. The loop allows me to change out the shock cord rubber when necessary.