347 An important difference of the selected gas spring versus  other pneumatic actuators is that the  full cylinder  is used as pressurized volume. The total amount of energy, the piston force and the force reduction over  the stroke can be adjusted towards the systems requirement by t he ratio between cylinder diameter,  influencing the amount of energy, and piston diameter, influencing the force of the actuator . 

Depending on these parameters, a force reduction from beginning of stroke to end of stroke of less than  15% can be achieved without increasing the total size of the actuator.  

For pressurization a non- flammable, non- explosive and non- toxic gas is  needed. For this the inert  gas  Nitrogen (N 2) is chosen, which meets  all these requirements and is easy to purchase.  

In collaboration with the supplier , the actuator is tailored to the needs of the project. T hese adaptions   include:   • Material adaptions  to meet ECSS  standards2 as coating for the housing and sealing  for bearing  elements.   • Construction of a pressure inlet valve adapter . The actuator is to be pressurized on launch si te,  right before launch, enabling easy and save mounting after PLF closure.   • Pressure sensor adapter in order to surveille the pressure processing.  The sensor is mainly  implemented for this project phase to verify the performance of  the actuator. During the vibration  and life testing the sensor provided  important knowledge about the sealing qualities under external  loads and the pressure behavior when exposed to temperature  gradients and lifetime  tests. As the  sensor is also  already  qualified, the sensor can be used to monitor flight data or be omitted  for  standard implementation during flight to reduce the mass . 

Together with the supplier customization, the interface to the fairing was constructed. They  are constructed   to fulfill the following requirements:   • The interface  has to sustain the internal ly stored energy for the rotation during all phases before  separation   • All vibration loads during launch before separation need to be accommodated by the interface .  • The interface needs  to provide to the actuator the required degree of freedom to allow a smooth  movement without jamming.   • After PLF separation,  the actuator is to be separated from the launcher and gets jettisoned with the  PLF.   • The concept needs to be adaptable to different launcher classes.  

The interface  bracket s, designed to fulfill these requirements , comprise two different adapters for the PLF  and launcher interface. Whereas on the PLF side an eye bearing provides the needed free moving space  but close connection to hold the actuator at the payload shell, a ball  joint on the launcher side prevents  the  actuator from jamming  and releases the actuator after the stroke of the actuator has been reached. In  Figure 4, the actuator with the interface bracket s for the implementation to a PLF is  shown.  

In addition to the analysis of the bracket ’s load sustainability, an analysis has been run showing that the  fairing can accommodate the actuator ’s loads during launch and separation. A focus has been on the  fairing’s deformation caused by the actuator ’s force. It has been found that the deformation is negligible for  the developed system as clearance towards possible fairing breathing is ensured during the rotation phase  before jettison.  

The interface brackets have been designed and analysis for a medium launch vehicle. For the qualification  campaign, described in the next section, the full set -up, including the interface joints, has been tested.