MarcoPolo-R narrow angle camera: a three-mirror anastigmat design proposal with a smart finite conjugates refocusing optical system

TL;DR

This paper proposes a three-mirror anastigmat optical design for a space mission's narrow-angle camera, enabling high-quality imaging and refocusing from infinity to 200 meters for asteroid surface exploration.

Contribution

It introduces a novel TMA optical system with a smart refocusing mechanism using a single mirror, meeting specific space mission imaging requirements.

Findings

Design achieves 3 mm resolution at 200 m distance

Refocusing capability from infinity to 200 m

Compatible with current manufacturing technology

Abstract

MarcoPolo-R is a medium-class space mission proposed for the 2015-2025 ESA Cosmic Vision Program with primary goal to return to Earth an unaltered sample from a primitive near-Earth asteroid (NEA). Among the proposed instruments on board, its narrow-angle camera (NAC) should be able to image the candidate object with spatial resolution of 3 mm per pixel at 200 m from its surface. The camera should also be able to support the lander descent operations by imaging the target from several distances in order to locate a suitable place for the landing. Hence a refocusing system is requested to accomplish this task, extending its imaging capabilities. Here we present a three-mirror anastigmat (TMA) common-axis optical design, providing high-quality imaging performances by selecting as entrance pupil the system aperture stop and exploiting the motion of a single mirror inside the instrument to allow the wide image refocusing requested, from infinity up to 200 m above the NEA surface. Such proposal matches with the NAC technical specifications and can be easily implemented with present day technology.