Development of a Dual Mode D-Strut@ Vibration Isolator  for a Laser Communication Terminal  Dale T. Ruebsamen’, James Boyd*, Joe Vecera. and Roger Nagel’  Abstract  This paper provides a review of the development by Honeywell of a dual mode D-strut@ vibration isolator  for long range communication instrument. This paper reviews the basic design requirements for the dual  mode isolator, the D-strut’ isolator design drivers, the prototype D-strut’ isolator design, and the results of  prototype D-strut’ isolator testing.  Introduction  Honeywell is developing a dual mode D-strut@ vibration isolator to isolate the sensitive instrument from  the spacecraft bus during launch vibration and during in-flight operation (spacecraft bus vibration  distubances). This paper will describe the design challenges that led to a new isolator design meeting the  stringent requirements of this sensitive instrument, and the issues that were identified as a result of  testing a set of prototypes of the new design.  Two isolator design options were considered for this application. The first option was to launch lock mount  the instrument to the spacecraft and design the instrument to survive the launch loads, and then release  the instrument once in flight allowing the isolator to isolate the instrument from the spacecraft bus  disturbances. The second (dual mode) option uses the same isolators to isolate the instrument from the  launch environment and the spacecraft bus disturbances. In both cases, the isolators are configured in an  optimized hexapod configuration (also know as a “Stewart Platform”) to provide the desired isolation. The  dual mode isolator configuration was chosen to minimize the loads into the instrument due to launch and  still provide the required in flight isolation due to the spacecraft bus disturbances.  There are several requirements that define the new isolator design. The requirements for the D-strut@  isolator are that the weight of the isolated system is 48.1 kg (106 Ib) maximum; the quasi-static  acceleration is 16.25 g’s maximum during launch. The vibration requirement means that the peak axial  load into each D-strut@ isolator is approximately a factor of over 2.0 times the previous dual mode design.  The higher loads also required that the stroke in each isolator increase by almost a factor of 1.6. These  increased loads and strokes needed to be accommodated without changing the length of the isolator.  The D-strut@ isolators are three parameter isolation systems. The parameters defined for the three  parameter isolators are static stiffness (Ka), dynamic stiffness (Ka + Kb), and damping factor (Ca). These  are the parameters Honeywell uses to size the main machined spring, the tuning spring, and the damper  annulus gap filled with the proper damping fluid.  Honeywell has submitted a patent application for a new isolator design that meets the load and stroke  requirements needed to support the instrument. In the new isolator design, the sealing bellows in the  damper assembly are externally pressurized instead of internally pressurized. The new configuration  allows for a significant increase in the load capacity and stroke of the isolator without increasing the  overall length of the isolator. To demonstrate that the new isolator design would meet the requirements,  Honeywell built two complete isolator assemblies to measure the isolafor parameters and fabricated the  fixtures needed to test the isolators in a bipod configuration up to the maximum quasi-static accelerations.  Honeywell, Defense and Space, Glendale, AZ  Proceedings of the 38 Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2OC6  141