Taking a High-Resolution Ultraviolet Image of the Sun’s Corona Will Require VISORS

Sometimes, brainstorming does work. In 2019, America’s National Science Foundation (NSF) held the CubeSat Ideas Lab, a shindig that brought together some of the world’s best CubeSat designers. One outcome of that shindig is the Virtual Super-Resolution Optics with Reconfigurable Swarms, or VISORS, mission. Expected to launch in October, this mission will be a proof of concept for many swarming technologies in CubeSats. Hopefully, It will also capture a pretty impressive picture of the Sun’s corona.

VISORS was formally defined in a paper in 2022, with input from experts at nine different academic institutions, one NASA lab, and one private lab. The concept of operations (or ConOps in the paper) is easy enough – fly two separate 6U CubeSats in formation and take an extreme ultraviolet picture of the Sun. 

The obvious question is—why do you need two CubeSats to do that? A single spacecraft could do the job, but the science goal of the VISORS missions is to take an image at a very high resolution in a very specific extreme ultraviolet wavelength. To do that, the mission would need an optical mirror diameter of around 40m.

That is beyond humanity’s current capability to fit onto a rocket fairing and blast into space. So, VISORS will actually consist of two spacecraft. One, known as the Detector Spacecraft (DSC), will house an ultraviolet detector, and one, known as the Optics Spacecraft (OSC), will act as an optical system that mimics the characteristics of a 40m diameter mirror.

However, the secret sauce of the VISORS mission lies in the coordination between the DSC and the OSC. They will fly in formation with each other, about 40 m apart, with the OSC placed between the Sun and the DSC. The light from a specific region of the Sun’s corona will pass through a photon sieve on the OSC and be directed into the detector of the DSC 40 m away, effectively creating the effect of a 40m wide mirror without the need for a continuous surface.

The only problem is that this type of coordinated alignment between CubeSats has never been done before. So, really, the VISORS mission could be looked at as a technology demonstration mission for CubeSat swarm formation rather than a heliophysics one. The mission statement in the ConOps paper states that the mission will be considered successful if it captures one ten-second image over the course of a six-month primary mission duration.

Ten seconds out of almost 16 million may not seem like much, but it shows the difficulty of getting CubeSats to align properly at the right time. To do so, researchers at the Space Rendezvous Laboratory at Stanford have created novel Guidance, Navigation, and Control (GNC) software based on a concept familiar to any controls engineer—a state machine.

In software, a state machine is defined by various variables that will change the software’s behavior based on the values of those variables. In the case of VISORS, there will be five different states. Standby is pretty self-explanatory – wait in your current orbit for further instructions. Transfer is an attempt to move into formation to allow the system to capture an image. Science is when the mission will attempt to capture that ten-second image. But if something goes wrong, it also has two recovery states – Safe mode is pretty standard for all spacecraft, but Escape mode is unique for VISORS. This would move either spacecraft out of the way of the other, and collision between the two is one of the primary risks of the mission architecture and one of the things the GNC algorithm is designed to avoid.

Development of that software appears to be ongoing, though the planned launch date for the mission is only three months away. If all goes well and VISORS is successfully deployed and takes at least one picture, that proof of concept will shortly enable plenty more CubeSat swarm missions. It might even inspire more successful brainstorming Idea Labs.

Learn More:
Lightsey et al – CONCEPT OF OPERATIONS FOR THE VISORS MISSION: A TWO SATELLITE CUBESAT FORMATION FLYING TELESCOPE
UT – What a Swarm of Probes Can Teach Us About Proxima Centauri B
UT – Tiny Swarming Spacecraft Could Establish Communications with Proxima Centauri
UT – A Pair of CubeSats Using Ground Penetrating Radar Could Map The Interior of Near Earth Asteroids

Lead Image:
Artist’s depiction of the VISOR spacecraft flying in formation.
Credit – Simone D’Amico

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