Presented here is CHAFF (CubeSat Hyperspectral Application For Farming), a design concept for a CubeSat-based Hyperspectral Imager (CHSI) intended to supply high quality hyperspectral image data cubes to the agricultural community. CHAFF has been designed holistically as a system, considering all design and operational characteristics of a CHSI instrument and platform together: including the re-stricted payload mass and volume associated with CubeSats, the platform pointing stability/accuracy limitations, and the restricted downlink data budget. To this end, CHAFF will employ optically aided geometric co-registration methods, which will allow on-board construction of the hyperspectral data cube. This allows the use of powerful lossless data compression schemes to mitigate the downlink data budget limitations. In addition, a calibration methodology using a tuneable laser source at NPL, will be employed pre-flight to achieve rapid and accurate spectral and radiometric calibration, essential for the production of science-grade data sets from the proposed CubeSat constellations. A benchtop prototype has been constructed and a promising spectral resolution of 3nm at around 625nm has been achieved. In addition the auxiliary imager for the optically-aided geometric co-registration has been demonstrated.