The distinct diffraction spikes in JWST images arise from the hexagonal mirror geometry and secondary mirror struts
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Retrieved literature acknowledges that JWST diffraction spikes and point spread functions relate to the telescope's primary mirror geometry and boundaries, but no single retrieved text fully covers both the hexagonal geometry and the secondary mirror struts as combined causes.
This paper presents an analysis of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE) based on its published optical prescription and system architecture. Using modeling, key optical performance parameters were evaluated, including spot diagrams, footprint diagrams, wavefront error (WFE), point spread function (PSF), Strehl ratio, encircled energy (EE), and modulation transfer function (MTF). The segmented 6.6 m primary mirror was modeled using a User-Defined Aperture (UDA) approach to accurately reproduce the hexagonal pupil geometry and diffraction effects. Results confirm diffraction-limited performance across the evaluated field, with RMS wavefront error well below the Maréchal criterion, high Strehl ratios (≥0.87 off-axis and ≥0.97 on-axis at 1 µm), and encircled energy closely matching the diffraction limit. MTF curves demonstrate strong contrast transfer up to the cutoff spatial frequency with minimal field-dependent degradation.
Additional analyses were performed to assess the impact of individual segment piston and tilt misalignments. Controlled perturbations show that segment-level phase discontinuities significantly degrade WFE, emphasizing the importance of precise segment phasing and wavefront sensing and control (WFS&C).
Analysis of Optical Telescope Element (OTE) used in James Webb Space Telescope (JWST) | Defense and Security Studies Analysis of Optical Telescope Element (OTE) used in James Webb Space Telescope (JWST) Authors Alan Catovic Mechanical Engineering Faculty, University of Sarajevo, Bosnia and Herzegovina Dzan Jasarevic DOI: https://doi.org/10.37868/dss.v7.id309 Abstract This paper presents an analysis of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE) based on its published optical prescription and system architecture.
Using modeling, key optical performance parameters were evaluated, including spot diagrams, footprint diagrams, wavefront error (WFE), point spread function (PSF), Strehl ratio, encircled energy (EE), and modulation transfer function (MTF). The segmented 6.6 m primary mirror was modeled using a User-Defined Aperture (UDA) approach to accurately reproduce the hexagonal pupil geometry and diffraction effects. Results confirm diffraction-limited performance across the evaluated field, with RMS wavefront error well below the Maréchal criterion, high Strehl ratios (≥0.87 off-axis and ≥0.97 on-axis at 1 µm), and encircled energy closely matching the diffraction limit.
How to Cite [1] “Analysis of Optical Telescope Element (OTE) used in James Webb Space Telescope (JWST) ”, Defense and Security Studies , vol. 7, no. 1, pp. 60–88, Feb. 2026, doi: 10.37868/dss.v7.id309 .
To minimize the artifacts in Point Spread Functions (PSFs) of space telescopes such as the 6 major spikes shown in the star image observed by the James Webb Space Telescope, which are caused by the primary mirror outer boundary and the gaps between segments, an alternative method to segmentize large circular telescope mirror is proposed. From the fact that the strong spikes are due to the parallel-ness of all linear boundary edges and gaps in the current hexagonal segmentation approach, the proposed segmentation methodology minimizes such parallel-ness. The proposed method comes with a set of formulas that can assist the design process including the systematic calculation of number of segments and the size of each segment to cover the entire mirror pupil area. Some example PSFs of a few possible segmented mirrors with the proposed formalism will be presented.
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