Long-baseline space interferometry for astrophysics: A forward look at scientific potential and remaining technical challenges

Optical and infrared interferometry from the ground has had major successes but will soon meet fundamental limitations. Adaptive optics and creative fringe tracking solutions has the potential to greatly increase the reach of interferometry from the ground, but the factor of 107 in thermal infrared background means that space interferometry with small telescopes is a more cost-effective solution at long wavelengths. Additionally, important spectral windows for high angular resolution astrophysics are only open from space. I will briefly outline the limitations of interferometry from the ground, and make the case for space. In addition to reviewing the historical cases of low fringe visibility (complex) imaging, precision astrometry, high contrast mid-infrared interferometry and far infrared interferometry, I will make the case for wavelength-differential and polarimetric interferometry at visible and ultraviolet wavelengths. A major long baseline interferometry mission will require higher technological readiness levels of key technologies, including interspacecraft metrology, fringe tracking in a space environment and high contrast nulling. For some mission concepts, relatively little new subsystem development is required and tolerances are surprisingly loose. I will argue that in order to fast-track the inevitability of space interferometry, some key subsystem development, whole mission simulation and a pathfinder mission are all required in the near future.