fiber positioners for spectrographs

In a short research day, I had a very useful conversation about robot fiber positioners for multi-object spectrographs with Peter Mao (Caltech), who is working on the Prime Focus Spectrograph for Subaru. He gave me a sense of the cost scale, the human effort scale, and the technical precision of such systems. This is critical information for the Letter of Intent that I and various others are putting in for the use of the SDSS hardware after the end of the current survey, SDSS-IV. We would like to go really big with the two APOGEE spectrographs, but if we want to do really large numbers of stars (think: millions or even tens of millions) we need to have robots place the fibers.