Release the panels within a tight package
The spring-loaded solar panels needed a compact mechanism that could hold them stowed and release on command. I owned the mechanism development, comparing push and pin-pull concepts while balancing available force, mass, volume, and integration with the spacecraft.
The key question came before detailed CAD: how much force would the actuator need to withdraw the loaded pin?
Size the actuator from the load path
Spring torque loads the two pin contacts. With only 7 mm between their moment arms, a modest spring moment produces substantial contact force—and friction that the actuator must overcome.
Two torsion springs load the stowed panel.
d₁ = 118.5 mm; d₂ = 111.5 mm. Equal contact magnitudes assumed.
Using an estimated static-friction coefficient of 0.30. This is a sizing estimate, not a measured friction load.
The estimate ruled against relying on a 5 oz-force solenoid (about 1.39 N). It also gave me a force target for sourcing a pneumatic actuator that fit the available envelope.
Compare force with packaging
| Candidate | Why consider it? | Decision |
|---|---|---|
| Small pull solenoid | Low mass and volume; 0.25 in stroke, 5 oz-force rating. | Below the estimated friction load; prototype could not overcome the system load. |
| IMI Bimba 00725 | Compact pneumatic pin-pull; the analysis deck records >30 N at 100 psi. | Successful actuation supported choosing this path and finalizing the brackets. |
The rated pneumatic force is pressure-dependent. The test notes separately list a 0.5–1.0 lbf return-spring force; that is not the cylinder’s pressure-driven output force. The available record does not state the operating pressure for every test.
Use prototypes to narrow the options
Hinge / swing-door concepts
Bench tests on July 31 overcame latch friction. These concepts were not tested with the actual panel assembly; vibration retention and temperature behavior remained concerns.
Gear and lock
Bench tests confirmed lock operation and gear meshing. Combined tubing and the actual panel assembly were not tested. Increasing complexity favored a simpler pin-pull approach.
Small solenoid
The August 12 test could not overcome the system load, consistent with the first-principles force estimate.
Pneumatic pin-pull
The August 21 test demonstrated actuation. A follow-up with the propulsion system also supported release, although alignment play prevented a clean spring-open motion in that setup.
I made targeted prototype modifications to answer specific questions without rebuilding the entire assembly. Those checks helped narrow the options before committing to the next design iteration.
A decision supported by analysis and testing
The hand calculation established a force target. Prototype tests ruled out the small solenoid and demonstrated actuation with the pneumatic option, supporting the decision to pursue that approach.
The evidence demonstrates mechanism development and functional testing. It does not establish flight qualification or completed vibration and thermal qualification.