Recent developments in the construction and operation of high-altitude platforms (HAPs) close the gap between airborne and spaceborne remote sensing. The possibility of permanent monitoring of regions from the stratosphere offers new fields of application requiring bespoke instruments for operation on HAP carriers.The MACS-HAP aerial camera system was developed specifically for platforms operating in the stratosphere. Based on a refractive optical design, it captures aerial images with 127 megapixels per image and achieves a ground sampling distance of 15 cm per pixel at 20 km altitude. One of the special system features is the embedded onboard processing hardware with specific algorithms for real-time information extraction.This paper presents an overview of the instrument and the current state of development. Technical solutions to meet the specific payload requirements are described, such as stress-optimized design and the lightweight optical system with its capabilities for automatic onboard image processing.