
Building a parachute is boggling - pseudolus
https://www.latimes.com/business/story/2019-12-19/boeing-spacex-spacecraft-parachutes
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lostmyoldone
Regarding the missing pin in Boeing's test last month, I find it quite strange
that a physical verification "touch test" wasn't performed by default if it
was/is possible.

This is obviously based on extremely limited information, but given that the
pin seems to be possible to check physically, and wasn't checked, I don't
think I'm speculating too much, as it constrains the issue greatly.

In as mundane activities as rock climbing, adventure courses, and while
working at height it's basically a mantra to physically check anything that
you can check physically, regardless of if it's been checked in some other way
previously. At least in my circles.

Not that physical verification is a panacea, but doesn't it seem borderline
arrogant to not include it wherever possible when it comes to something like a
parachute system?

I am assuming that the cause for omitting a physical check is that it was
decided previous checks - whatever they were - would've been enough.

If failing to check a pin in a parachute system was an _actual oversight_ , I
can only assume the project is under very intense pressured to deliver on
schedule rather than quality. Not a great look for Boeing if that's the case.

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mechhacker
I knew some people who worked near this specialty in aerospace.

From what I remember, it's highly guarded and sensitive due to the rarity of
skills and knowledge required.

The problem is highly nonlinear from both an aerodynamics and structural
perspective. The fabric changes shape, can only really support a load in
tension, and updates of the geometry then feed back into aerodynamics.

I'm trying to imagine how they deal with vibrations/flutter related issues
(they may not even be called that on flexible fabric, I haven't checked) where
everything has to be solved in the time domain to get Real Answers. We're
talking modern day supercomputers and constantly having to reduce time step
size to keep solutions faster than the Nyquist frequency on a huge problem set
where you have to save a lot of the intermediate results somewhere. Then there
are all kinds of other things to worry about that someone more experienced
with compressible flow can talk about, and its associated nondimensional
simulation parameters and issues...

It's hard enough with incompressible liquids in confined spaces with metals
that can only bend and deflect so much. That is an area I'm more familiar
with, and know where to look in handbooks to get initial solutions.

But parachutes? Whew. Complex.

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elteto
SpaceX has been conducting parachute tests for as long as I can remember, they
are finicky beasts. Besides, there's only a handful (literally) of
manufacturers in the world, perhaps one or two in the US. It is no coincidence
that both Boeing and SpaceX are using the same provider.

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njarboe
Elon Musk originally planned for Crew Dragon to land with rockets instead of
parachutes. That way the same spacecraft design could land on Mars and Earth.
Also, it is "how a rocket should land". Then they discovered that NASA safety
concerns were going to slow things down a lot and that a Mars landing craft
could be a lot better with a different design. SpaceX's in-development
Starship is now the craft that will be able to land on any small planet in the
system.

A quote from[1]:

SpaceX now favors another type of recovery.

"The reason we decided not to pursue (powered landings) heavily is it would
have taken a tremendous amount of effort to qualify that for safety,
particularly for crew transport,” Musk said. “And then there was a time when I
thought that the Dragon approach to landing on Mars, where you’ve got a base
heat shield and side-mounted thrusters, would be the right way to land on
Mars, but now I’m pretty confident that is not the right way, and that there’s
a far better approach.”

Musk did not elaborate on the new concept for landing on Mars.

“That’s what the next generation of SpaceX rockets and spacecraft is going to
do, so just the difficulty of safely qualifying Dragon for propulsive
landings, and the fact, from a technology evolution standpoint, it was no
longer in line with what we were confident was the optimal way to land on
Mars,” Musk said. “That’s why we’re not pursuing it.

[1][https://spaceflightnow.com/2017/07/19/propulsive-landings-
ni...](https://spaceflightnow.com/2017/07/19/propulsive-landings-nixed-from-
spacexs-dragon-spaceship/)

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doctor_eval
SpaceX: “You always learn,” [Shotwell] said. “That’s why we test as much as we
do.”

Boeing: ...The company is confident in its parachutes, Barrett said.

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Fetiorin
Boeing: The company is confident in its parachutes, he said, and testing has
shown that they will work in emergency situations.

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joecool1029
In the case of Boeing's mission, the chutes ended up working but they set the
clock wrong so the mission primary was a fail:
[https://www.nytimes.com/2019/12/22/science/boeing-
starliner-...](https://www.nytimes.com/2019/12/22/science/boeing-starliner-
landing.html)

~~~
irjustin
The article is referring to the Nov 4th[0] test where only 2 of 3 chutes
opened but was still a 'safe' touchdown.

[0][https://spacenews.com/boeing-performs-starliner-pad-abort-
te...](https://spacenews.com/boeing-performs-starliner-pad-abort-test/)

~~~
justinclift
Doesn't seem like it. Article is dated 19th Dec, and has this:

> Early Friday, the company plans to launch its Starliner capsule on its first
> ever uncrewed flight to the space station.

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ufmace
Considering all of these stories of how hard parachutes seem to be, it seems
surprising that everyone seemed to be against SpaceX's initial plan to do
propulsive landings of their capsules. I'd like to see them get that worked
out soon, even if only for the cargo capsules at first.

~~~
kibwen
I don't recall anyone being against the idea of propulsive landings on a
technical level. There was no reason to suspect they weren't possible,
although I could imagine someone being skeptical of the cost savings that they
could practically achieve in exchange for lessened payload capacity.

