(Thread) Shall we talk a bit about #MarsPerseverance 's EDL sequence? Let's start with the parachute. The design is called a disk-gap-band parachute. Picture below is from Tutt, Lowry, 2019. As you can see, there is a disk of fabric, a gap and a band of fabric. Hence the name!
It's a design already proven on the Viking Mars probes. However, there have been some changes to the original design.
To clarify, a "gore" is a segment of fabric that runs from the center to the rim, shaped somewhat like this:
Yes, that is a highly professional rendering.
Actually, the choice of what kind of parachute to use is quite difficult, as it needs to be quite big and work in a supersonic airstream. Oh, yes, and on Mars, so in an atmosphere that's less dense than our lower atmosphere.
The combination of these three factors makes testing parachutes for the mission very difficult. So some parts of the design need to rely on experience and... extrapolation. That's another way to say, "we need to guess".
If you guess the wrong values, your parachute will end up looking like this:
That's a picture from NASA's LDSD test, from about 2015 or 16. As you can see, even the best computer simulations will not be able to predict the forces on a supersonic parachute correctly.
By the way LDSD was led by @madler , who is also co-author of some compression libraries and a parallel implementation of gzip called pigz which I had the pleasure of using a while ago. Yes, he is a software engineer.
Goes to show "you don't have to be a rocket scientist to be a rocket scientist" (Jay Leno), being a super-skilled IT person may also qualify you for the job. I digress.
Anyway, LDSD cast some doubts on the ability to estimate the forces on a supersonic parachute correctly, so everyone decided to beef the parachutes up, just in case. As a result, #Mars2020 parachutes are a bit stronger than those for #CuriosityRover
The improved design was tested in 2018 with a sounding rocket test at an altitude of 55km.
What's the conclusion? Rocket scientist are geniuses, but it takes several rocket scientists to perform a supersonic parachute scientists' test. Let that sink in.
The parachute was then manufactured by @AirborneSysNA .
Fabric for the parachute was provided by the UK's @Heathcoatfabric
Also, if you're interested, watch this. And upvote.
And this. @ChutesNL
And JPL's video on testing the parachute
So what does the parachute deployment actually look like? This is from JPL's video on the subject.

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More from @AGeeknologist

18 Feb
(Thread) Continuing down the EDL sequence of #Mars2020 #MarsPerseverance, how was the Skycrane phase prepared? Obviously, it worked on @MarsCuriosity , was there anything to improve? Apparently, yes. @ATAEngineering performed studies with @MSCSoftware ADAMS to simulate the phase.
To simulate the event, a technique called multibody simulation is used (ADAMS is a software dedicated to that). Basically it's a physics simulator to perform analyses in time-domain. That's jargon for "it's a sandbox for engineers".
Because we cannot know in advance what the exact conditions for the landing will be, engineers resort to "Monte Carlo simulation". That's jargon for "we are running thousands of calculations with changes on the initial assumptions to cover all cases".
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