NASA just released some interesting preliminary data from their instrumentation onboard the #Mars2020 lander that delivered #Perseverance

Here’s a quick thread w some thoughts

[TLDR: Mars entry is HOT, but we made the heat shield too big (again)]

So to start, let’s turn back the clock to 2012. While you were watching The Walking Dead and the London Olympics, the good folks at NASA were measuring the aerothermal environment of Mars entry for the Mars Science Laboratory (MSL Curiosity) mission
They did this with an instrumentation suite called “MEDLI” which stands for Mars Entry, Descent, & Landing Instrumentation

This contained, among other things, a bunch of heat transfer, pressure, and temperature measurement devices in and around the MSL heat shield
One of my favorite anecdotes about the difficulties of modeling hypersonic heat rates and ablation comes from MEDLI

NASA scientists designed a clever experiment to measure the rate of heat shield recession (it basically burns off) during Mars entry using thermocouples onboard
The idea was that as the heat shield material burned away (this is more technically called ablation) the thermocouples would stop transmitting a signal as they were destroyed. So if you bury the thermocouples at different depths in the heat shield, you measure recession. Smart
The only problem was that we overpredicted the heat transfer rates for MSL & built a heat shield that didn’t lose that much material. So even the first, shallowest thermocouple (8% depth) was not destroyed.

We used <8% of the heat shield!

Figures source: ntrs.nasa.gov/api/citations/…
Take a closer look at this chart

Notice how the thermocouple with the red dashed line (model) falls off but the solid line (measurement) doesn’t? This is showing how the simulations predicted significantly more ablation (and temp rise) from turbulent heating than what occurred
Fast forward to present-day, and NASA released some top-line results from the MEDLI2 instrumentation suite installed on the Mars 2020 capsule

While more publications will surely follow, you can read more in this initial release here: mars.nasa.gov/news/8903/sens…
A lot to unpack here already, but a few things jumped out

1) This thing got really hot! And we would expect that for hypersonic entry on Mars, but it’s still impressive to see temperature measurements made on another planet of 1,000 °C (correlating to vehicle surface T 1,400 °C)
2) We did a good job predicting pressure. This is a little easier to get than say heat transfer, so perhaps expected, but instills some confidence in modeling nonetheless
3) We repeated the same heat shield recession measurement with the buried thermocouples from the OG MEDLI and we STILL didn’t burn up the first thermocouple!

So after two missions we still don’t have recession data and we’re clearly making massive heat shields 🤯
I do wonder how intentional this was. Based on lessons learned from MSL did we try to get away with slimming down the heat shield? Or did we just stick with what worked and accept the weight penalty? I might need to do some reading but it’s curious 🤔
Okay I think they basically used the same design as MSL/Curiosity and were even planning to use the spare heat shield from that mission until it fractured during testing

spaceflightnow.com/2018/04/28/nas…

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More from @DrChrisCombs

20 Feb
Oh my goodness, this is video of the turbofan on a Boeing 777-200–flight #UA328 out of Denver—which experienced a serious engine failure after take-off.

Remarkably sounds like no injuries in the air or on the ground #AvGeek
I mean, just look at these photos...
#AvGeek #ua328
Worth noting, twin-engine aircraft are designed to be able to fly safely with only one engine and pilots are trained for this (seems they did a phenomenal job here!)...but people and homes are NOT designed to withstand falling turbofan cowlings. Miraculous no one was hurt
Read 12 tweets
19 Feb
WOOWWWWW

Check out these images of #PerseveranceRover being dropped from the sky crane (left) and descent with chutes deployed via Mars Reconnaissance Orbiter! Incredible photos!

#Mars2020 #Perseverance #NASAPerseverance #NASA #Mars ImageImage
Folks, we just snapped of a photo of a spacecraft landing (possibly still at supersonic speed) on ANOTHER PLANET from a satellite also orbiting that planet. That is WILD

#NASAPerseverance #NASA #PerseveranceRover #Perseverance #Mars2020 #ScienceTwitter Image
I just can’t believe this image—am I right that we’re seeing some of the dust plume from the retro rockets? This is like a baroque painting Image
Read 5 tweets
18 Feb
NASA is LIVE with coverage of the Perseverance landing, happening around 2:55p US CT, this is the place to be

Percy about to hit the atmosphere at 3.5 miles/sec (5.5 km/s) and create some serious heat
#CountdownToMars #MarsPerseverance #Perseverance

pscp.tv/w/cv11hDFsWkVw…
The extreme velocity of atmospheric entry will heat the surface of the heat shield to nearly 2,400 F (1,300 C) due to intense shock heating and aerodynamic forces
It’s a tricky part of the mission for many reasons, but our ability to predict/model the physics of these atmospheric entry events is currently limited—it’s a “multi-physics” problem which makes it tough even for our best super-computers to handle
Read 5 tweets
23 Nov 20
It’s November which means we’re getting into GRAD SCHOOL APPLICATION SEASON so I thought I’d take a break from my usually #AvGeek/rocket threads & talk some #AcademicChatter with my personal advice for those considering grad school. A thread...

#AcademicTwitter @AcademicChatter
All the usual caveats apply: I’m in engineering and while there are many different paths & perspectives I’ll be giving advice based on my personal experience. With that said hopefully it’s helpful to many of you w/ broad applicability outside of engineering
First: don’t pay to go to grad school. Many faculty have paid research assistantships (GRAs) and will provide tuition + stipend. You’ll still be underpaid but it’s really difficult to economically justify the benefit of grad school vs lost income if you pay your own way
Read 33 tweets
1 Sep 20
THIS IS NOT A SONIC BOOM

Okay folks, it’s been long enough. Time to finally address the biggest point of confusion on #AvGeek twitter: what exactly is going on with vapor cones?

Let’s just say much of what you’ve read is (probably) wrong. Wonder no more: a thread... 1/n
2/n We’ve all seen the photos & videos—whether it’s a jet flying over the beach or a rocket during its ascent—with the beautiful vapor cone (you also hear shock collar or even shock egg). Inevitably the exclamations follow: “sonic boom!” “Mach 1” & “breaking the sound barrier”
3/n And I totally understand. It’s a nuanced concept & a quick Google search brings up all kinds of misinformation. I could not find a single article that seemed to truly “get it”. So no shaming here—it’s debunking time
Read 25 tweets
11 Aug 20
DETONATION ENGINES THREAD

It’s been too long since a good propulsion thread. With enticing potential for supersonic & hypersonic flight, pulsed & rotating detonation engines are an exciting possibility for future high-speed vehicles. Let’s discuss 1/n

🎥 credit @PurdueEngineers
So the top-line big number is the potential 25% theoretical efficiency improvement from pulsed & rotating detonation engine concepts (PDEs & RDEs, respectively) & ISP > 8000s for hydrogen fuel up to hypersonic Mach numbers, far exceeding other air-breathing and rocket engines 2/n
And this is in no way a new concept—detonation engines were theorized way back in the 19th century! With initial RDE experiments performed in the 1950s. But recent advances in experimental and computational methods have started to make this complex problem more tractable. 3/n
Read 26 tweets

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