Space Interferometry Mission System testbed-3: architecture

The Space Interferometry Mission's System testbed-3 has recently integrated its precision support structure and spacecraft backpack (bus) on a pseudo free-free 0.5 Hz passive isolation system. The precision support structure holds a 3-baseline stellar interferometer instrument. The architecture of the instrument is based on the current flight system design, and its main purpose is to demonstrate nanometer class fringe stabilization using the path length feed forward technique. This work describes the overall instrument architecture, brief theory of operation, and preliminary measurements.