Earth Observation (EO) imagery from nano-satellite platforms can revolutionize its scope. The typical CubeSat designs with standard sizes 1U to 3U, enable low costs, a high temporal resolution and rapid development cycles. This supports cost-effective constellations and a breakthrough in the market price compared to existing constellations such as Rapid Eye, DigitalGlobe and GeoEye. It allows for dedicated EO missions that are accessible to (scientific) institutions and smaller organizations. A roadmap for this development has been defined and actively pursued since 2011.
A number of camera concepts as enablers have been developed. The 1.5U to 2.0U plug-and-play cameras enable cutting-edge Cubesat constellation EO system designs. The instruments contain folded light-paths instead of deployable optical systems and ultra-stable opto-mechanical-thermal performance. The three light-weight, small-volume camera structures comply with 3U Cubesat concepts:
The Advanced Nanosat Telescope 2a (ANT-2a) VIS camera captures high to medium spatial resolutions, i.e. 5 to 10 m, depending on the altitude. The design is based on a Ritchy-Chretien Cassegrain (RCC) system with a much larger aperture and an mproved Signal-to-Noise Ratio (SNR). An increase in wavelength bandwidth was achieved by using more mirrors. The incorporation of a MEMS calibration subsystem is foreseen.
The ANT-2b is based on a Three Mirror Anastigmat (TMA) system to serve applications which require a large coverage. It offers a ground resolution of 25 meters at 500 km altitude. The larger relative aperture enables a higher SNR to capture multiple narrow wavebands and multi-spectral imaging performance.
The Advanced Remote-sensing CubeSat Thermal Infrared Camera (ARCTIC-1) offers a unique off-the-shelf IR camera solution to comply with the CubeSat standard and UAV’s platforms. The passively cooled ARCTIC concept fills the IR void and adds a technology to extend EO monitoring and science within the deep IR spectrum 9 to 11 μm. Due to the diffraction limit at these wavelengths, the ground resolution remains limited at 65.8 m at a Low Earth Orbit (LEO) altitude of 500 km at a NEDT of about 100 mK.
The instruments are healthy phase-A concepts to support niches in the EO market. The application of multiple CubeSats, supplied with the three instruments and placed in a single orbit or in different orbits as part of a (hybrid) constellation, can provide with both different selectable spectral bands as well as tuneable revisit times (high temporal resolution).
A Very Low Earth Orbit (VLEO) 288 km CubeSat camera design with aerodynamic drag compensation was most recently defined as part of a promising EO constellation architecture.
The research focusses now on designs to improve the limited spatial resolution by deployable (synthetic) apertures and image stitching solutions.