Enabling design concepts for a flight-qualifiable optical delay line

In an interferometer, an Optical Delay Line (ODL) must be able to inject a commanded pathlength change in incoming starlight as it proceeds from a collecting aperture to the beam combiner. Fringe visibility requirements for space interferometry prescribe that the optical pathlength difference between the two arms must be equal and stable to less than 5 nm RMS to a bandwidth of 1 kHz. For a space mission, an ODL must also operate in a vacuum for years, survive temperature extremes, and survive the launch environment. As part of the Interferometer Technology Program (ITP) at Jet Propulsion Laboratory, a prototype ODL was designed and built to meet typical space mission requirements. It has survived environmental testing at flight qualification levels, and control design studies indicate the 5 nm RMS pathlength stability requirement can be met. The design philosophy for this ODL was to create as many design concepts as possible which would allow a priori attainment of requirements, in order to minimize analysis, testing, and reliance on workmanship. Many of these concepts proved to be synergistic, and many attacked more than one requirement. This paper reviews the science and flight qualification requirements for the ITP ODL and details design concepts used to meet these requirements. Examples of hardware implementations are given, and general applicability to the field of optomechanics will be noted.