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Masao Dahlgren Profile picture
@masao_dahlgren
Feb 1, 2022 • 13 tweets • 7 min read • Read on X
Scrolly
Reentry vehicle nosetip after flying through rain at Mach 10, Sandia photo. One of the many engineering challenges to consider when designing hypersonic weapons. Image
Table of impact energies and speeds for water-density particles, courtesy B. Carmichael, Southern Research. Image
Hypersonic thought leaders emphasize there's much left to understand. At ISEC 2021, AFOSR high-speed aero lead Dr. Sarah Popkin noted that particulates were "highly suspected to impact boundary layer transition" (sudden turbulent flows on vehicle).

Image
I'd add @DrChrisCombs has a couple tweets talking about boundary layer transition.

From the forthcoming report: just some of the many phenomena at play in these conditions. Adapted from Anderson's Hypersonic and High-Temperature Gas Dynamics (2019). Image
From a presentation at this 2021's TTC:
"turbulent boundary layers are a challenge, they can have 5 times or greater heating than a laminar boundary layer...But an equal challenge is dealing with the uncertainty associated with predicting that boundary layer transition..."
"...And because of that, sometimes it's easier to trip a boundary layer early and deal with that heating, even if it may increase the size of the thermal protection system, and just not having to figure out exactly where transition is going to occur." Image
This and more in our forthcoming report dropping Monday. Release will feature some of the biggest thinkers on this: Gillian Bussey (JHTO), Mark Lewis (NDIA), Kelley Sayler (CRS), Stan Stafira (MDA), & Tom Karako (CSIS), mod. by @TheDEWLine.

csis.org/events/complex…
Since some questions are coming in: the original photo doesn't say what material the nosetip is. From the looks I'd guess some variety of 3D carbon-carbon? Have a lot of past threads on the US' decadeslong RV nosetip efforts, see:

ImageImageImage

Some more C-C nosetip diagrams:

ImageImageImage

Also will note: @Casillic routinely finds and tweets interesting material from Sandia docs, including that photo. Some relevant tweets:



Also tossing this in the thread since it was asked:

For general interest, some more "environmental" factors warheads might encounter. Clockwise from left:
1) X-ray radiation damage on test RV (Sandia)
2) Natural charring of RV ablative heat shield after reentry (Sandia)
3) Simulated kill vehicle impact with test RV (LLNL) ImageImageImage

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More from @masao_dahlgren

Masao Dahlgren Profile picture
Oct 7
Old news, but man, RU munitions look ancient:
🧨 Obsolete through-hole construction (wire leads connect components to board surface)
🧨 Thin, slathered-on encapsulation compound (red, used to insulate/protect parts)
🧨 No potting (filling empty space w/ shock-cushioning plastic)
For comparison, some early 2000s NDIA slides on the U.S. GMLRS system electronics. SMT instead of through-hole components, which are hermetically sealed in metal and plastic potting material. Image
Image
Lot of gold in the replies. The broader significance here: these choices have disproportionate impact on the whole design. They limit maneuverability: under 100G maneuvers, each 4-gram capacitor becomes nearly a pound, stressing the leads. Potting helps you survive that.
Read 5 tweets
Masao Dahlgren Profile picture
Apr 28
USAF Chief Scientist Victoria Coleman later noted ARRW was "the most mature weapon that we have" Disclosed prev. unreported successful Tactical Boost Glide flight test on Dec 8, 2020, over the Pacific, "an amazing day." Was coy on whether ARRW was fully zeroed out
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Progress continuing on HACM, Congress and Global Strike Command apparently "huge fans and can't wait" for it to be in inventory. flight test next year will happen in Australia. This is why AUKUS matters.
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Here's the top-level portfolio from Dr. Weber on current hypersonic acquisition programs. Image
Read 6 tweets
Masao Dahlgren Profile picture
Apr 15
[1/3] Real vs. AI-generated images: check out the Fourier patterns yourself. At right: the FFT output, which captures info on repeating patterns in images. You can generate them easily with ImageJ, as I've done here.
Fake:

Image
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[2/3] Load in 4K and zoom for best results.
Real:
Image
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[3/3] Real at left, fake on right. Can you see the difference?
CC @dicooke34 @SpauldingSez
Image
Image
Read 5 tweets
Masao Dahlgren Profile picture
Dec 10, 2023
Left: the infrared scene data we imported into our simulation. Right: a more detailed pic of the hypersonic model, with diff temps assigned to the leeward & windward sides, leading edges, and rear. It's not just distance; the diff in viewing aspects are modelled in.

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It won't just be IR. @tomkarako and I have prev said that hypersonic weapons have unique kinematic vulns. But they also have unique, exploitable signatures. We don't model those, but see slide from Dr. Iain Boyd—complex interactions on vehicle surface => novel plumes & sigs. Image
@tomkarako @HyTASP_TC @lizvstein @DrChrisCombs @Missile_Defense Cc @nktpnd @Kaitlyn_Johns0n @Aaron_MatthewIL @shashj @ThrustWR @AirPowerNEW1 @zebulgar @_MakenaYoung @dex_eve @wslafoy @rena_in_dc @heatherwilly @ThomasGzRoberts @ferencdv @RocketSchiller @Casillic @RejaYounis @ctjlewis @Ascii211
Read 4 tweets
Masao Dahlgren Profile picture
May 7, 2023
There's so much buzz around new missiles; rockets are inherently attention-grabbing. But over time, you learn that it's everything upstream—the sensors, battle management systems, comms, command & control—that matters most.
defensenews.com/opinion/commen…
But those things are murky. There's no easy way to prove to adversaries that you have software that speeds up your targeting cycles, or EW/cyber that bogs up theirs. Russia could see Ukraine's meager missile stocks, but couldn't see the murky stuff that actually wins wars.
Massive stakes on the assumption that deterrence works. As wars are increasingly decided by the murky stuff, that gets harder. The fact Russia was caught unprepared represents a failure of deterrence; their failure to understand they'd lose, our failure to show why we'd win.
Read 8 tweets
Masao Dahlgren Profile picture
Jan 27, 2023
Thread on post-Cold-War glow-ups. In 1993, Russia converted some Topol ICBMs to civilian space launch vehicles: "Start" and "Start-1". They took the same mobile missile launcher (left) and added a spiffy paint job. Could lift ~360 - 450 kg to LEO. ImageImage
Before/After: The Fukuyama edit. Military version (left), civilian version (right). Both the 4-stage and 5-stage SLVs had a 5 km altitude, 2.5 s period, and 6 MoA inclination orbital injection accuracy. ImageImage
Before/After: Armageddon (left), cool and normal satellite launch (right). The Topol missile (SS-25) still remains in service but is slated for replacement by Russia's new Topol-M and Yars ICBMs. ImageImage
Read 6 tweets

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