346 Actuator Selection :  The key selection criteria to fulfill best the system goals are:   • Aiming at a cost -efficient  solution, the actuators are modified commercial of the shelf (COTS)  products.   • The system should be usable in a broad range of launcher sizes and separation conditions . Pneumatic  actuators give the advantage to tailor its performance by the adaptable  energy  storage via the  pressure. T his allow s a mission customized, optimal rotation initiation.  For this , the very same qualified  actuator is compatible for a wide range of applications.   • To lower the shock coming from the separation process, the work to s eparate the PLFs  is aimed to be  applied with low force over a long stroke  which leads to a very smooth transformation to the needed  kinetic energy for the required movement .  Gas springs provide a force over the full (adaptable) stroke, where the force reduction over stroke is  depending on  the (adaptable) gas volume ratio from contracted to extended configuration. This brings  also a remarkable advantage in comparison to commercial  steel springs where a long stroke  providing  continuous  high forces  leads to an increase in total length and with this a need for increase d spring   diameter or additional suspension structure due to potential instability.   • The gas spring stores the energy  for the movement  within  the actuator itself . This has  an advantage  over other pneumatic actuators in terms  of energy per weight  ratio because  no additional gas storage  tank is needed.   • A high qualified pressure capability of the actuator leads to a relative high energy per weight  ratio  that  can be achieved.   • Gas springs of this type are normally used in airplanes and trucks . Consequently,  they have high   heritage  in demanding environment resistance and s olidity against vibration.   • The preload ( pressurization) can be done in the very last moment before flight in the contracted  configuration. All installation  work can be done safely without internal forces.  

Given the goal for a scalable system and usage of the actuator on different launchers, together with the  dependence of actuators location and launchers geometr y to the required actuators force and stroke, the  gas springs showed during the design development the advantage of being very flexible in application.  

Design Description:   In Figure 3 the actuator is shown as a schematic with explanations for the individual parts . 

Figure 3. COTS Gas Spring Actuator  Schem atic 

The COTS actuator is composed with the following parts:   1. Cylinder  contains the pressurized gas (N2)  and guides the piston movement.   2. Piston rod is the moving part of the actuator  and defines the stroke.  Its diameter defines the active  area the pressure acts on for the force.  It is covered by a very strong protection against corrosion.   3. Connecting parts  are adapted to meet the INTERFACE  to the fairing . They are designed to sustain  the vibration during launch, to transfer the force during rotation and enable the actuator to stay   completely  on the fairing after separation.   4. Piston bearing is the small part inside the cylinder that guides the rod and contains a jet , enabling  the use of the full cylinder cavity as pressurized volume and allows the control of the movement  velocity .  5. Guiding piece that seals the pressure volume and guides , together with the piston adapter,  the  movable piston rod. 1 2 34 5