The parachute deployment system used in the BAHAR project was made with the goals of light weight and reliable operation in mind. Light weight is achieved by using an almost all fiberglass construction method. The system has undergone many tests consisting of deploying the parachute from the ground with no failures. This system is flexible in that it will work with a heavier nose cone or a lighter nose cone with no modifications needed. We have tested it successfully with a 2.2kg cylinder in the nose cone (CATS payload) with no problems. The true test will be the actual flights which introduce a lot more variables! :)

Description of Operation:
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The deployment system has an electrical connector for the rocket computer to ignite a charge of black powder. When this charge goes off a floating bulkhead pushes up against a fixed ring on the inside of the nosecone. This force pushes the nosecone off a sleeve attaching it to the rocket. As the nosecone is travelling away from the rocket a cord between the floating bulkhead and the main rocket body unwinds. Once this cord unwinds fully, the floating bulkhead is pulled away from the ring in the nosecone. The floating bulkhead is attached to the parachute which is in the nose cone and as the nosecone continues to travel away from the rocket the parchute is pulled out. The floating bulkhead is also attached to the nosecone. Here is a simplified drawing of the system:

Overview of system:

Overview of the parachute deployment system

Outside view of system:

The nose cone slides down over the rocket body until it hits the bottom
of the sleeve and at the same time the floating bulkhead is
squeezed between the explosion chamber and a fixed ring in the nosecone.
It is a very tight fit and in our tests some smoke leaks past the floating bulkhead
into the nosecone but no heat damage has occured to the parachute.
When the powder charge goes off and until the cord between the rocket body
and the floating bulkhead is fully unwound, the bulkhead is squeezed
tightly against the ring in the nosecone so not much of the blackpowder smoke
can leak into the nosecone. We have also used electricians tape around the
perimeter of the floating bulkhead. This increases compression
(like a piston ring kinda :)

Spectra cord:

Here is a closeup of some of the high strength cord we use to attach the floating bulkhead
to the lower half of the rocket, the nosecone and the parachute.
We wrap this cord in electricians tape to protect it
from the heat and flame of the parachute deployment charge.
The cord has a woven sheath with very fine white filament spectra cord inside.
I was told that spectra has the same tensile strength as kevlar but with better bending properties.
We obtained this cord from a local sailmaker.

Various Pictures of the Parachute Deployment System:
Female threads at the bottom of the parachute deployment system (top of electronics bay).
Male threads to attach to the top of the electronics bay.
Closeup of the hardware on the explosive chamber, including the male threads.
Side view of the explosive chamber.
Top view of the explosive chamber.
Closeup view of the floating bulkhead.
the floating bulkhead on the explosive chamber.
The explosive chamber held above the electronics bay.
The explosive chamber attached to the electronics bay.
Here is a closeup of the blackpowder charge in its heatshrink tubing package.
The blackpowder charge ready to go.

Detailed Drawings of the Parachute Deployment System with Measurements:
Drawing of the bottom half of the parachute deployment system.
Drawing of the explosive chamber.
System overview drawing.

Concerns with the current design:

1. at high altitude deployment, the low air pressure may decrease the efficiency of the black powder.
We may use more black powder to correct this or cold-gas deployment (CO2 canister) or a pressurized rocket casing.
We may also fill the explosion chamber up with something to displace the air and act
as an insulator so that being in a vacuum and being at sea level would have the same effect.

2. the round cord can be frayed or cut easier than a tubular or flat cord on the rocket body if a high speed deployment occurs.

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