It's been quite a while since I posted about the structural core design. Previously I described how I had to create a detailed CAD model to help engineer the core so the center of gravity was sufficiently low - important to ensure aerodynamic stability. I've made quite a few adjustments since then to accommodate packaging needs of various components and a few other small issues.
So here's an updated CAD model with the core in the "as-built" condition, conveniently exploded so I can give you a guided tour.
The HAPP core structure
Most important are the decks. Previously I had four. Now there are only three. Let's check them out from bottom to top. First there's the Propulsion Deck, which holds the carbon fiber air tanks and regulators. Next is the Electronics Deck. The flight computers sit on top of this deck, but the 12 RCS valves attach to the underside - this helped to lower the CG significantly. Finally we have the ELS Deck, which includes the cradles for the parachute mortar tubes (not pictured) and the three aerodynamic strakes.
I've also show how the various structural components attach to the main strut. All three decks have carbon fiber L-brackets underneath, which are bonded in place with specialty epoxy. The ELS strakes are bonded into place using small carbon fiber brackets cut from hexagonal tube sections.
Lastly I've shown the balloon tether up at the apex and the parachute tether arms just on top of the ELS Deck.
Put 'em all together and you get something like this:
HAPP core extracted from aeroshell after flight tests