Ring-field TMA for PRISMA: theory, optical design, and performance measurements
Luciano Calamai ; Stefano Barsotti ; Enrico Fossati ; et al. ; - ASI Sponsor
Sep - 2015
DOI: 10.1117/12.2191286

Event Title : Optical Systems Design 2015: Optical Design and Engineering VI
Published in: Proc. SPIE 9626, Optical Systems Design 2015: Optical Design and Engineering VI
Publisher: SPIE
type: Conference Proceedings

PRISMA (PRecursore IperSpettrale della Missione Applicativa) Hyperspectral Payload is an Electro-Optical instrument developed in Selex ES for the dedicated ASI (Italian Space Agency) mission for Earth observation. The performance requirements for this mission are stringent and have led to an instrument design that is based on a Ring-Field Three Mirror Anastigmat (Ring-Field TMA), a two channel prism dispersion based spectrometer (VNIR and SWIR), and a Panchromatic Camera. The Ring-Field TMA contains three mirrors (two conics and one conic with some higher order correction). Exceptional performance has been achieved by not only introducing 3rd order astigmatism to balance the 5th astigmatism at the ring field zone as is traditional in an Offner-type design but, additionally, 3rd order coma has been controlled to align the balance of the linear and field cubic coma terms at the same ring field zone. The predicted wavefront performance of the design over the field of view will be highlighted. An assembly and alignment procedure for the Ring-Field TMA has been developed from the results of the sensitivity and tolerances analysis. The tilt and decenter sensitivity of the design form is nearly exclusively determined by 3rd order binodal astigmatism. The nodal position is linear with perturbation, which greatly simplifies the decisions on alignment compensators. The manufactured mirrors of the Ring-Field TMA have been aligned at Selex ES and as will be reported the preliminary results in terms of optical quality are in good agreement with the predicted as-built performance, both on-axis and in the field.

keywords : Alignment procedures ; Cameras ; Dispersion ; Equipment and services ; Mirrors ; Monochromatic aberrations ; Optical design ; Prisms ; Short wave infrared radiation ; Spectrometers

Notes : Acknowledgements "The instrument is the focus ofthe PRISMA mission, fully funded by ASI (Agenzia Spaziale Italiana)".