# Would Mayak's large solar reflector have produced a stable attitude, or more likely start tumbling or rotating?

update: Answers to Two week mark; has Mayak (Маяк) been spotted yet? Reflector deployed? Astronomy “ruined”? indicate that the reflector did not deploy successfully (more at Mayak, a magnitude -10 (minus ten) satellite; how is the large, delicate reflector expanded?), so I've changed the tense from future to conditional.

In this question I've asked about the possible reflection of UHF radio signals from the recently launched Mayak cubesat once it's large metallized polymer solar reflector would be deployed. However it would certainly be detectable by reflected sunlight and this was one of the primary purposes. The other is to study the large, light-weight expanded structure as a de-orbiter.

You can learn more on the YouTube videos Mayak. No more space debris! and also A tour through the Mayak project.

I thought I'd try to calculate what the reflections might look like and which positions relative to the ground and the Sun are most likely to make it visible. When fully deployed it would have been a very large, very light weight tetrahedron with a 3U cubesat body attached to one corner. See details of the deployed shape below.

The primary satellite from this July 14, 2017 launch is Kanopus-V-IK; 42825U 17042A and the one TLE I can find so far shows 15.194 orbits per day, which corresponds to an average altitude of roughly 500 km. However the cubesat may have been deployed at a different altitude.

EDIT: Now there are many more objects, 2017-042A through 042BZ; almost 80 of them. A is still at 500 km, but there is a group at 460 and another group near 590 km. If these are close to correct, this must have been an interesting launch!

Sooner or later through, even small atmospheric drag on the large surface area to mass ratio spacecraft would have an effect.

My first second guess is that the mass concentration at one corner would lead and the large-area, low-mass reflector would be dragging directly behind it. (Thanks to @Damien_The_Unbeliever for not believing what I originally wrote, which was exactly the opposite!) But I don't know how dense the gas particles in space would have to be for this orientation to establish itself. It would have to be enough to damp any residual rotation other than that necessary to rotate once every 90 or 100 minutes in inertial space.

Even once the symmetry axis were moving tangent to the direction of motion, it could rotate around its axis until that too were damped. What would the final equilibrium orientation be, and how long before it would settle down?

Is this configuration inherently stable, or inherently unstable? Would it have settled down in with the attitude I natively believe, or start oscillating or rotating at some angle, or perhaps tumble wildly and unpredictably?

The NASA Spaceflight article Soyuz 2-1A launches with and over 70 satellites says:

Mayak is a three-unit CubeSat which was built by Tvoii Sektor Kosmosa – or “Your Sector of Space” – an independent, crowd-funded team of engineers in conjunction with the Moscow State University of Mechanical Engineering. Mayak – meaning Lighthouse – will deploy a highly reflective tetrahedral structure.

Each side of this structure has an area of four square meters, or 43 square feet. To ground observers, the satellite is expected to have an apparent magnitude of up to -10, making it one of the brightest objects in the night sky. The structure will double as a deorbit mechanism, hastening the decay of the satellite’s orbit.

Right now the orbit of the primary payload Kanopus-V-IK 2017-042A, 42825 should be a good guess for the rough predictor of Mayak passes, but once it deploys that giant reflector, things should change quickly.

How is this large reflector made from thin polymer film carefully expanded to and maintained in its full size and shape so that its faces are at least somewhat flat?

above: Mayak Reflector – Photo: CosmoMayak, From Spaceflight 101

above: Mayak Artists conception, From NASA Spaceflight

• Why would the mass concentration fall behind? – Damien_The_Unbeliever Jul 18 '17 at 11:19
• @Damien_The_Unbeliever I have no idea why I wrote that - it should be exactly the opposite! Thanks for pointing that out, I've edit the question a bit, take a look. Helpful suggestions are always welcome! – uhoh Jul 18 '17 at 11:48
• Rule of thumb: light pressure overcomes atmospheric drag at altitudes in excess of 1000km; anywhere below any larger surface is more a parachute than a solar sail. – SF. Jul 18 '17 at 13:54