Re-entry

[Flash2001]

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...

[thetimesreader84]

Not an expert, just a guess;


Capsule swinging, distorting the canopy, something like that?

[underfire]

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

[pattern_is_full]

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

[wiedehopf]

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/questions/16793/why-does-the-soyuz-parachute-pulsate