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> Parachutes are hard. I'm surprised to hear this. I've not heard much about parachute failures in Soyuz landings, except Soyus-1 in the 60's. Nasa had a good

> Parachutes are hard. I'm surprised to hear this. I've not heard much about parachute failures in Soyuz landings, except Soyus-1 in the 60's. Nasa had a good track record with parachutes too before they started using the space shuttle. Are there technical challenges unique to SpaceX or Boeing that other systems didn't have to deal with?

Robotbeat 7y ago
Soyuz has a reserve parachute. Also, because Soyuz only has one, large primary chute, you're less likely (by a factor of 3 or 4) to see any failures. And a reliability of 142:143 is not terribly high for a safety-critical system. No US orbital crew fatalities have ever occurred due to parachute failure, but parachute failure has occurred on at least one of the Apollo missions (Apollo 15). One parachute failure out of 61 parachutes for the US[0] versus one (or two, counting the reserve) parachute failures out of 143 (144) parachutes for Russia/USSR. The statistics here are effectively indistinguishible in any meaningful measure. The challenge is these are new, pre-operational crewed spaceflight systems being developed from the beginning. New systems ALWAYS have a higher rate of failure for complex things like this, and also because there are not yet actually crew on board, there's a little bit lower level of mission assurance (which I would argue is optimal!). Nothing in particular special about SpaceX or Boeing. And in many ways, we got lucky that there weren't more parachute-related fatalities. We understand the dynamics significantly better now than in the past. [0](1 parachute on each Mercury and Gemini mission, 3 parachutes on each Apollo capsule)
- avmich 7y ago
  > And a reliability of 142:143 is not terribly high for a safety-critical system. That's a 50+ years ago flight on a system which was being debugged - unfortunately, too hastily. Parachutes subsystem underwent major rework after that catastrophe, and the follow-up flight history attests to it. One can call it "142:143" only as a first approximation.
- joezydeco 7y ago
  Did Shuttle use similar chutes, or were those simpler drag chutes for braking?
  - hollerith 7y ago
    (Like the F-22 and F-35 do) The Shuttle did aerodynamic braking, which is sort of like using the whole vehicle as a parachute, which reduced the speed at which it had to resort to its chute, enabling the chute to be much smaller than it would otherwise have been: https://en.wikipedia.org/wiki/Aerobraking#Aerodynamic_braking https://en.wikipedia.org/wiki/Aerobraking#Aerodynamic_brakin... But even if it didn't do that, it would need a much smaller chute than a capsule of the same weight because gliding greatly increases distance traveled through the atmosphere, which enables the vehicle to bleed off a lot more kinetic energy as drag.
madaxe_again 7y ago
It’s worth noting that it’s not the parachutes that typically fail, rather, the deployment systems. You’re packing (by hand) a large area of fabric and cord into a very small volume. You’re coating that fabric and cord with a variety of anti-stick substances, which have to be stable with extreme temperature and radiation levels, and huge vibrations. Parachutes are deployed in several ways - springs, hydraulics, compressed gas, explosives, drogues, and combinations thereof. For flight tests, parachutes are typically pre-stressed as though they’ve been to orbit and back. This wasn’t always the case. So - there’s a lot of surface area to go wrong purely around the problem of getting it to eject and unfurl, before you even start to think about the parachute itself.

Robotbeat 7y ago

Soyuz has a reserve parachute. Also, because Soyuz only has one, large primary chute, you're less likely (by a factor of 3 or 4) to see any failures. And a reliability of 142:143 is not terribly high for a safety-critical system. No US orbital crew fatalities have ever occurred due to parachute failure, but parachute failure has occurred on at least one of the Apollo missions (Apollo 15). One parachute failure out of 61 parachutes for the US[0] versus one (or two, counting the reserve) parachute failures out of 143 (144) parachutes for Russia/USSR. The statistics here are effectively indistinguishible in any meaningful measure. The challenge is these are new, pre-operational crewed spaceflight systems being developed from the beginning. New systems ALWAYS have a higher rate of failure for complex things like this, and also because there are not yet actually crew on board, there's a little bit lower level of mission assurance (which I would argue is optimal!). Nothing in particular special about SpaceX or Boeing. And in many ways, we got lucky that there weren't more parachute-related fatalities. We understand the dynamics significantly better now than in the past. [0](1 parachute on each Mercury and Gemini mission, 3 parachutes on each Apollo capsule)

avmich 7y ago
> And a reliability of 142:143 is not terribly high for a safety-critical system. That's a 50+ years ago flight on a system which was being debugged - unfortunately, too hastily. Parachutes subsystem underwent major rework after that catastrophe, and the follow-up flight history attests to it. One can call it "142:143" only as a first approximation.
joezydeco 7y ago
Did Shuttle use similar chutes, or were those simpler drag chutes for braking?
- hollerith 7y ago
  (Like the F-22 and F-35 do) The Shuttle did aerodynamic braking, which is sort of like using the whole vehicle as a parachute, which reduced the speed at which it had to resort to its chute, enabling the chute to be much smaller than it would otherwise have been: https://en.wikipedia.org/wiki/Aerobraking#Aerodynamic_braking https://en.wikipedia.org/wiki/Aerobraking#Aerodynamic_brakin... But even if it didn't do that, it would need a much smaller chute than a capsule of the same weight because gliding greatly increases distance traveled through the atmosphere, which enables the vehicle to bleed off a lot more kinetic energy as drag.

madaxe_again 7y ago

It’s worth noting that it’s not the parachutes that typically fail, rather, the deployment systems. You’re packing (by hand) a large area of fabric and cord into a very small volume. You’re coating that fabric and cord with a variety of anti-stick substances, which have to be stable with extreme temperature and radiation levels, and huge vibrations. Parachutes are deployed in several ways - springs, hydraulics, compressed gas, explosives, drogues, and combinations thereof. For flight tests, parachutes are typically pre-stressed as though they’ve been to orbit and back. This wasn’t always the case. So - there’s a lot of surface area to go wrong purely around the problem of getting it to eject and unfurl, before you even start to think about the parachute itself.