Global sky observation campaign with the intensity interferometer

The intensity interferometer was developed by Hanbury Brown and Twiss to use correlations between intensity fluctuations in order to measure the coherence between light waves. Correlating the intensities of the waves and not their amplitudes can overcome the main disadvantage of the Michelson Stellar Interferometer in a space environment, which is the present inability to maintain the required sub-micron stability in the optical path difference through apertures which are located on different spacecraft. However, since an intensity interferometry could today measure correlation between fluctuations on a time scale of 5.10^-10sec, stability of the order of cm is required, and this is achievable at the present time. We show that intensity interferometry should be applicable to stellar sources as weak as 8^th magnitude, using techniques which are theoretically feasible today. In order to optimize the use of interferometric measurements, we propose two approaches for a global sky observation campaign. In the first approach we minimize the fuel consumption taking into account the required constant inertial relative position between the spacecraft. In the second approach we introduce the computational interferometry observation method which enables us to observe the full sky from a single orbit. Several concepts of computational interferometry are addressed. Moreover, for each global sky observation campaign approach, control laws were designed to relocate a spacecraft into the required constant inertial relative position and to maintain it.