COPHASING OF A LARGE SEGMENTED TELESCOPE FOR EO EXPRO+

Objective: To develop and validate the different steps necessary for the cophasing of a large Earth observation segmented telescopeDescription: Large telescopes (primary mirror diameter > 2-4m) have strong potential for Earth Observation applications: - persistent monitoring for security and disaster management from GEO - secure remote sensing from higher orbits (> 1200km), avoiding LEO debris impacts - high resolution for infrared missions (for which large pupils are mandatory). - very high resolution from LEO The segmentation of the large primary mirror is extremely useful to drastically improve the manufacturing/polishing schedule (multiyear gain) and to reduce the risk of development of a large monolithic primary mirror, particularly if the segmented mirror is not deployable. Technical maturity is high for ground segmented telescopes but is very low for Earth observation space telescopes, in particular in Europe. The key enabling technology behind the segmentation of a large primary mirror is the cophasing of the telescope segments, allowing to optimize the optical quality of the telescope. This critical technology that must be adapted to space use. In particular, the coarse cophasing must be based on a method and reference equipment that can be used and located on-board the payload. The finecophasing on an extended scene (essential for an EO application) need development as very little literature available on this topic. This activity would prove the feasibility of the full cophasing (coarse + fine phasing on star + fine phasing on extended scene) of a segmented telescope, with measurements on a small scale breadboard (2 to 4 segments) in order to correlate the results. The activity would encompass the following main tasks: - Coarse phasing: simulations and measurements on 4-segment small scale breadboard - Fine phasing on star: simulations and measurements on the breadboard. - Fine phasing on an extended scene: algorithm developments preliminary tests . - Roadmap and way forward.