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Project: VIrtual Super Optics Reconfigurable Swarm (VISORS)

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The VIrtual Super Optics Reconfigurable Swarm (VISORS) mission is a first-of-a-kind nano-satellite segmented telescope with a 40 meters focal length for high-resolution imaging of the solar corona. Due launch in 2024, it is expected to operate in a near-circular sun-synchronous low Earth orbit. VISORS was firstly proposed in the National Science Foundation's IdeasLab to obtain images of active regions of the Sun coronal area in the extreme ultraviolet spectrum with unprecedented resolution. This unprecedented scientific data is expected to improve the current thermodynamic models of the solar corona itself.

The space segment of the VISORS mission is a distributed telescope consisting of two 6U CubeSats. In particular, one spacecraft (OSC) contains the optical payload, whereas the other (DSC) contains the detector. The OSC hosts a photon sieve payload that acts as a high-resolution lens in the extreme ultraviolet spectrum. The deployable solar panels double as a sunshade, blocking most of the light from regions outside the area of interest from reaching the DSC. The DSC hosts a detector payload that collects focused images produced by the photon sieve.

Each VISORS spacecraft consists of two parts: a spacecraft bus provided by Blue Canyon Technologies and a payload provided by the project team. The project team is a multi-institution collaboration including: University of Illinois Urbana-Champaign, Georgia Tech, NASA Goddard Space Flight Center, Stanford University, University of Colorado Boulder, Purdue University, New Mexico State University, Washington State University, Montana State University, Ohio State University and University of California San Diego. In which, the guidance navigation and control (GN&C) subsystem is developed by the Stanford’s Space Rendezvous Laboratory.

The GN&C software will be hosted on the bus avionics board and provides two main functions: navigation and maneuver planning. The navigation software is required to provide absolute and relative orbit estimates with sufficient accuracy to enable science observations and ensure safe operations. The navigation algorithm used is the Distributed Multi-GNSS Timing and Localization (DiGiTaL) system, which uses differential carrier-phase measurements with integer ambiguity resolution (IAR) onboard in real-time to achieve maximum relative state estimation accuracy during observations. The maneuver planning functions provide maneuver commands for station-keeping, formation reconfigurations, and collision avoidance. The maneuver planning algorithms envisioned are a mix of closed-form impulsive control solutions with extensive flight heritage and novel numerical optimization-based model predictive control algorithms with no flight heritage.

The VISORS mission is challenging because the relative motion of the spacecraft must be autonomously controlled with higher accuracy than other distributed telescopes such as Proba-3 or the miniaturized distributed occulter/telescope (mDoT) using smaller and less expensive spacecraft. In particular, over the 10 seconds of observations the spacecraft must keep millimeter level-accurate alignment using autonomous navigation and control.

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Related Publications

Guffanti T., D'Amico S.;
Multi-Agent Passive Safe Optimal Control using Integration Constants as State Variables;
AIAA Scitech 2021 Forum, Virtual Event, January 11-15 & 19-21 (2021). DOI: 10.2514/6.2021-1101

Guffanti, T., D'Amico, S.;
Robust Passively Safe Spacecraft Swarming via Closed-form and Optimization-based Control Approaches;
American Control Conference, Atlanta, Georgia, June 8-10 (2022).

Koenig A. W., D'Amico S., Lightsey E. G.;
Formation Flying Orbit and Control Concept for the VISORS Mission;
AIAA Scitech 2021 Forum, Virtual Event, January 11-15 & 19-21 (2021).

Giralo V.;
Precision Navigation of Miniaturized Distributed Space Systems using GNSS;
Stanford University, PhD Thesis (2021).

D'Amico S.;
Distributed multi-GNSS Timing and Localization System (DiGiTaL);
NASA Fact Sheet, Stanford Space Rendezvous Lab (SLAB), July 16 (2019).