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Watching the NS-11 launch, I noticed that during descent when the main chutes were deployed, the capsule rotated quite a bit, and would rotate back. Was this an issue as well during the Mercury/Apollo/Gemini missions as well? Did they have something to counter it?

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I can't speak for Mercury or Gemini missions, but the Apollo parachute system is documented in NASA Technical Note D-7437, Apollo Experience Report: Earth Landing System. It appears that they designed the parachute system to reduce this phenomenon.

Rotation of the spacecraft during descent is undesirable. It's a landing hazard, and it can cause motion sickness in the astronauts. It also puts extra loads on the parachute system. As development of Apollo continued, the landing system team was asked to design for an ever-increasing weight of the spacecraft, while simultaneously making the parachutes have less weight and volume. During drop testing, the team noted that when

The three ringsail parachutes inflated in a nonsynchronous manner, that is, one canopy inflated rapidly and inhibited the inflation of the lagging parachutes. This behavior was most pronounced during the inflation following disreef. This crowding effect and nonsynchronous inflation, often referred to as cluster interference, was not a new phenomenon but was unusually pronounced with the ringsail design. This uneven load sharing resulted in abnormally high opening loads on the leading parachute of the cluster.

They redesigned the parachute system to ensure that all three parachutes opened at the same time. One pleasant side effect of this change was

The open-ring-configuration main parachutes also reduced the system oscillations of the two-parachute cluster from approximately ±20° to ±6°, causing a reduction in landing hazards.

Dumping the RCS propellant during landing can also directly rotate the spacecraft, as well as potentially lead to a parachute failure as seen in Apollo 15. Such a dump was standard procedure: after confirming that all three main parachutes were fully open, the astronauts would dump the remaining RCS propellant so the hazardous material would be gone during recovery. However, the RCS fuel ignited during Apollo 15, burning through some of the parachute support lines and collapsing one of the already-inflated main parachutes. Later missions skipped the dump, and the propellant was drained after spacecraft recovery.

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