So after a fun launch there's the not-so-fun damage assessment and repairs. And the fun challenge of figuring out how to improve parts for the next launch.
The 9-cluster motor mounts have an obvious weak point: they are snaping at the end of the BT-20 motor tube where the 3D-printed part has holes to reduce mass. The magnet rings that hold the landing legs in place are also taking a beating.
The 3D printed parts are easily replaced and I can remove the holes to make them stronger.
The the loss of the 18" BT-20 tube is really annoying.
Recall that the entire booster motor assembly looks like this:
It runs the entire length of the booster so that the magnetic upper booster attachment to the core rocket can release when the entire motor assembly ejects out the back of the booster during
rear ejection recovery.
An obvious improvement would be to swap the upper and lower sections of the BT-20 motor tube so that the shorter section is in the location prone to damage. But I intend to delete the entire 18" BT-20 motor tube by redesigning how the upper booster attachment mechanism works.
Currently a pair of magnets at the upper booster and lower booster attachment secure the booster to the core using the motor assembly.
Shown here with the booster body removed.
The booster ejection charge causes the entire motor assembly with its magnetic sheer pins to slide downward; replacing the attracting magnets in the upper and lower booster mounts with a repulsive magnets that push the booster away from the core.
Shown here with the booster nose cone in place for reference.
The booster motor then needs to
completely eject from the booster to deploy the recovery chutes. Any sideways force on the BT-20 tube as it ejects from he booster body
damages the BT-20 tube.
Here an otherwise successful launch has a booster assembly with a failed BT-20 tube.
My solution is to create a magnetic booster attachment that uses the pressure of the booster motor ejection charge to push the booster attachment magnetic sheer pin
upward instead of using a BT-20 tube to pull it
downward.
This means creating a part that moves up and down inside the booster nose cone, like a piston in an automobile engine.
Here the new booster magnetic sheer pin is shown in orange inside the booster nose cone.
The new mount would use a centering ring to support two magnets: the first attracting magnetic sheer pin would hold the booster to the core.
A 2nd new part (in blue above) will hold the booster attachment part in place and includes a guide to prevent it from rotating inside the booster nose cone.
The pressure from the ejection charge will move the booster magnetic mount upward; replacing the attracting magnet with a repulsive magnet.
Air pressure inside the booster nose cone will escape through the holes hidden behind the grid fins.
The completed assembly looks like this:
Viewed from the side: attracting magnetic sheer pin in place.
Viewed from the bottom with the booster attachment in the lower position.
The pressure from the ejection charge moves the magnetic sheer pin booster mount upward inside the booster nose cone.
The guide that prevents the booster attachment from rotating or falling down inside the booster is friction fitted to allow tuning of the position of the booster attachment magnets.
So this is how I hope to delete the VT-20 motor tube.
The new attachment magnetic mount inside the booster nose cone.
In summary, the new magnetic booster attachment mount:
- Weighs less than the old BT-20 based mechanism
- Reduces the total number of upper booster parts by 1: 4 instead of 5 or 20%
- Eliminates a single point of failure: the booster motor assembly 18"BT-20 tube
- Eliminates the need to align the upper and lower booster magnetic sheer pins to the core.
- Is backward compatible with existing booster nose cones.
- Simplifies installation of the booster motor, because it is so much shorter
- Increased probability of booster rear ejection success, because the motor assembly is so much shorter
- Moves the center of gravity upward by concentrating the parts in the nose cone, rather than along the length of the booster.
I just don't know if it will work...
