  Virtual Super-resolution Optics with Reconfigurable Swarms (VISORS) is a
distributed telescope mission for high-resolution imaging of the Sun using two
6U CubeSats flying in formation in a Sun-synchronous low-Earth orbit. An optics
spacecraft carries a photon sieve acting as a high-resolution lens in the
extreme ultraviolet spectrum, while the image passing through the sieve is
focused on a detector spacecraft. This paper presents the newly conceived
design of the on-board guidance, navigation and control (GNC) system, which is
highly autonomous, robust, passively safe, and validated under realistic
mission simulations. The primary objective of the GNC system is to establish a
passively safe and high-precision formation alignment at 40-meter separation,
with sub-centimeter relative navigation and position control accuracy, over
repeated observations of 10-second duration. Science mission success rates are
assessed via Monte-Carlo analyses under realistically modelled uncertainties
stemming from sensing errors, maneuver errors, unmodelled dynamics, and
erroneous knowledge of internal spacecraft components. Precise real-time
relative navigation is achieved by carrier phase differential GPS with integer
ambiguity resolution. Precise control over short baselines is achieved via
closed-loop optimization-based stochastic model predictive control with
centimeter-level accuracy. Control at far range and during approach is achieved
by closed-form impulsive control with meter-level accuracy. Passive safety is
enforced throughout the mission to mitigate collision risks even under critical
subsystem failure. Beyond VISORS, this work also realizes the crucial insight
that the described GNC architecture is generalizable to other distributed space
missions where accuracy and fault-tolerant safety are key requirements, such as
rendezvous, proximity operations, and swarming missions.
