The balloon cut-down mechanism is actually a little eccentric to the norm. It's a "Square Toroid" with a thickness of maybe 4-6mm. This ring has 8 strands of kevlar that connect at equal distances to each other on the ring, then connected to one main line to the balloon. This is therefore called the "Balloon Tension Rejection Ring". A fitting where the capsule houses the parachute will also be the connection point of the BTRR with the Inner Diameter being close(0.6mm) to the Outer Diameter of the housing, it fits over, and connects to spring loaded latches. The latches are restricted from movement due to a servo controlled push-rod, that would retract from the space and allowing those latches to retract inward. The design complication with this is that ALL forces are transferred through these latches. So engineering them to work correctly and keep the balloon where it needs to be is a tad important. Any tension on the balloon line would be terminated, and the capsule would fall back to Earth.
The parachute system is closely tied in here as well: A drogue chute will be on top of the parachute housing, and when that BTRR jettisons, the drogue should would essentially be pull up from turbulence, and provide:
1. Dynamic stability of the capsule while keeping expected speeds.
2. Main chute deployment.
There will be a hatch on top of the parachute housing that would be connected to the drogue chute. A to-be-designed-mechanism would allow the drogue chute to pull the hatch, then the parachute out. The q (dynamic pressure) on a 12" parachute going ~120 MPH would be enough to pull the main out for sure. So no worries there.
All of the functions of the flight would be controlled from a Trackuino with temperature, barometric pressure, and GPS sensor readings. A safety mechanism would be greatly needed, but I think it would become
too cumbersome. So working out everything here first would be a prerequisite. A skydiver said he could test our capsule at around 10,000' AGL once it's ready, so we can see if everything goes well for the big one.
Hope that helps.
HALONSC Project Manager
HALONSC Lead Aerodynamicist