Release Device Performance
Separation mechanisms must be able to:
- Preserve their structural integrity under loads on ground and in flight
- On command, when commanded physically separate the structural segments
- Impart the necessary work between the separating bodies
- Not produce any forces, motions, stresses, or debris lessening the stability or structural integrity of the continuing body
- Protect the payload (i.e. payload fairing separation)
- Not impair the mission
Release Device Analysis
When considering stage separation mechanisms dynamic analysis of both the release mechanism design and the bodies to be separated is vital. The analysis is used to predict the nominal performance of the considered mechanisms and an estimation of any tip-off errors from standard tolerances on the design parameters.
For missions where there are no complex aerodynamic forces acting on the bodies to be separated, determining the worst combination of values and then confirming a satisfactory separation under these conditions provides for the design of release mechanisms with intrinsically high reliability. More complicated computer simulations of the separation are performed when the mission includes humans or complex forces, where weight is critical or the mission requirements are extremely stringent. Each force, moment, component and situation are reviewed in extreme detail with six-degrees of freedom. Analysis will also include Monte Carlo Methods and statistical studies, partial derivatives. These separation-dynamics studies include examination of both separations occurring in earth’s atmosphere (which are more complex) and those occurring in space. In the end, reliability is the goal in site no matter what depth of analysis is used. In depth studies on flight separation mechanisms by NASA and the military provide additional insights into depth of testing and analyses done on stage separation.
Some of the effects stage separations will encounter include
- Attitude-control-system forces and torques
- Sequencing of events
- Nozzle-flow separation
- Fuel sloshing
- Mass and inertia properties of the two bodies
- Extreme high heat & humidity
- High structural loads
- Aerodynamic wake
- Inter-stage aerodynamic pressure
- Atmospheric pressure
Common stage separation mechanisms and pyrotechnic fasteners on rockets and launch vehicles we produce include:
Confined linear explosives such as our flexible confined detonating cord offers all the advantages of a quick, clean release with none of the contamination associated with many line-cutting release devices.
Linear Shaped Charge – a metal sheath with the explosive energy follows the line or shape of the sheath cutting the structure in it’s path. This will produce extremely high shock and very high fragmentation.
Mild Detonating Cord is a metal clad detonating line threaded into a position on the separating body. There will be high shock and high fragmentation, but the fragmentation can be contained.
Fragmenting Explosive Bolts or Nuts – this is a notched bolt or nut with an internal explosives charge, producing high shock and high fragmentation.
Non-fragmenting Explosive Nut – a two-step release, the sealed explosive mechanism frees the bolt when initiated and is followed by piston impact ejecting the bolt. This device provides low shock and and no fragmentation or contamination.
Impact-Failure Bolt – another type of explosive bolt, this bolt drives a piston and the impact causes tension or shear failure in the necked-down section. There is no fragmentation or contamination and this device has very low shock.
Pin Pullers – a pin holds a bolt stud or connecting link in place, when gas pressure is induced by an initiator a pin is pulled releasing the connection. There is low shock and little to no fragmentation or contamination with this type of separation device.
Pin Pushers – a pin holds a bolt stud or connecting link in place, when gas pressure is induced by an initiator a pin is pushed releasing the connection. Similar to the Pin Puller above, there is low shock and little to no fragmentation or contamination.