Re-entry
 

Yesterday I watched the landing of the Soyuz crew compartment from the ISS. During the parachute phase of the descent, I noticed a rhythmic variation in the geometry of the canopy with about 4 of 5 second period. The maximum diameter seemed to fluctuate with a corresponding inverse variation in the height. Big canopy! Does anyone know why?

After an excellent landing etc...

Not an expert, just a guess;


Capsule swinging, distorting the canopy, something like that?

Looks like even the astronauts cannot resisit jumping up and down on a gondola ride.

I'm going to guess that as the canopy gets taller and narrower, trapped pressure builds up inside the canopy, and begins to leak around the edges, "deflating" the canopy to a wide diameter - which then sweeps up more air per second, reinflating it to tall and and narrow - repeat as needed.

It is sort of the inverse of how "canopy-shaped" jellyfish propel themselves:

https://www.youtube.com/watch?v=rzNI1Yh0F5A

parachute has a central hole for controlled air release.

fast descent: parachute gets wider as more air is captured than released, capsule slows down and pressure in the parachute increases
slow descent: parachute gets narrower as more air escapes than is captured, capsule speeds up and pressure decreases

https://space.stackexchange.com/ques...achute-pulsate