Phoenix Booster FRR

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Design

The forward retention ring serves 2 main purposes:

• It retains the forward closure from sliding past the end of the motor casing.

• It couples the motor casing to the mission package tube.

In order to accomplish this, certain design considerations were made.

The forward closure presses upward on the FRR. The force it applies is equal to the chamber pressure times the ID of the motor casing. The FRR must be able to withstand the load of the peak pressure (given by the Propulsion Sub-team) with a safety factor of 2.

Working with Propulsion, we decided that the FRR will have 2 row of 12 ¼-20 holes that interface with the motor casing. This was based on calculations that Prop did for the motor casing.

Using FEA, I decided that this cross section worked under the following conditions:

• 8,836 lb from the forward closure

• 3 ft-lb preload on the bolts (this puts 960 lb tension in the bolt)

• FRR made of 6061 T6 Aluminum

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This design has straight walls, unlike the sustainer FRR. This is because having 2 rows of bolts would make this quite difficult to manufacture. Instead the wall thickness was decreased until the safety factor was a little above 2. The safety factor is 2.35

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For the forward part of the FRR, which is designed to interface with the mission package tube, the design was much simpler. This is because the weight of the airframe rests on the FRR shoulder. The main job of the forward-most screws are to restrict rotation about the central axis of the rocket and bending about the other axes. The surface that the screws attach to is extra long to prevent this kind of bending.

These screws also hold the mission package tube on during the descent back to the ground, but there are no major forces associated with this. 4 10-32 screws were used for this.

Manufacturing

TBD - waiting to return to campus

The plan is to use one of the semi-CNC lathes in The Deep as well as a radial indexer.

Testing

Static Fire?

Requirements:

Retain motor (pressure reqs)

Attach MP tube to motor case (depending on MP tube structure)