Wide Field Space Imaging with Off-Axis Freeform Optics

Wide Field Space Imaging Project Overview

Meeting the growing demand for large-area Earth observation requires optical systems that combine wide field of view, high optical performance, and compact design. One such solution is a space camera optical system based on an off-axis four-mirror freeform design, achieving a 70° ultra-wide field of view from a 640 km orbital altitude.

This system demonstrates how freeform optics and advanced integration techniques can unlock new possibilities in spaceborne imaging.

Mission Objectives

This project aimed to develop a space camera system capable of:

Capturing wide-area coverage in a single pass
Maintaining geometric and radiometric accuracy across the full field
Operating reliably in low Earth orbit (LEO)

Designed for applications such as environmental monitoring, agriculture, and large-scale change detection, the system balances field of view and resolution for optimal revisit time and surface coverage.

Optical Design Highlights

Ultra-Wide Field of View: 70°

The system delivers an exceptionally wide 70° field of view, a capability rarely achieved without significant aberrations. This was made possible through the use of an off-axis four-mirror optical configuration, carefully optimized to correct for distortion, coma, and astigmatism across the entire field.

Orbit Altitude and Swath Width

From an altitude of 640 km, the system achieves an 800 km swath width on the ground—enabling coverage of large regions in a single pass. This is ideal for missions where rapid temporal coverage and large-area mapping are priorities.

Ground Resolution

While the system’s 16-meter ground resolution is moderate by current high-resolution standards, it is sufficient for regional scale analysis, including vegetation monitoring, forest mapping, and surface change detection.

Technical Challenges and Solutions

Off-Axis Freeform Optics

The design required precise fabrication of off-axis aspheric and freeform mirrors, which are inherently more challenging than standard rotationally symmetric optics. Each mirror needed tight surface figure tolerances to maintain image quality over the large field. Solutions included:

Advanced CNC polishing and sub-aperture figuring methods
Interferometric testing of off-axis segments using custom null optics

Freeform metrology to measure complex surface shapes

Precision Alignment and Integration

Off-axis systems are highly sensitive to alignment errors. The team implemented:

Kinematic mounts and precision adjustment stages for assembly
Metrology-guided alignment procedures using laser trackers and optical benches

Thermal compensation strategies for in-orbit stability

Outcomes

The camera system has successfully demonstrated:

Reliable imaging performance in orbit
Consistent wide-area data collection
Long-term optical and structural stability

Its architecture remains a reference model for wide-swath Earth observation systems that prioritize coverage and speed over fine spatial resolution.

Key elements

Off-axis freeform designs are critical enablers for wide-field, high-performance space imaging.
Mastery of freeform fabrication and integration is essential to realizing these systems.

A 70° field of view combined with a 640 km orbit and 800 km swath width delivers strategic value for monitoring applications requiring fast revisit and broad coverage.