Words of Advice:

"If Something Seems To Be Too Good To Be True, It's Best To Shoot It, Just In Case." -- Fiona Glenanne

"Flying the Airplane is More Important than Radioing Your Plight to a Person on the Ground
Who is Incapable of Understanding or Doing Anything About It." -- Unknown

“Never argue with stupid people, they will drag you down to their level
and then beat you with experience.” -- Mark Twain

"Colt .45s; putting bad guys underground since 1873." -- Unknown

"Stay Strapped or Get Clapped." -- probably not Mr. Rogers

"Let’s eat all of these people!” — Venom

"Eck!" -- George the Cat

Wednesday, October 27, 2021

Hypersonic Weapons: Not Buying the Hype

China recently conducted a “very concerning” test of a hypersonic weapon system as part of its aggressive advance in space and military technologies, the top U.S. military officer says.
...
“What we saw was a very significant event of a test of a hypersonic weapon system, and it is very concerning,” [Gen. Mark Milley, chairman of the Joint Chiefs of Staff] said on “The David Rubenstein Show: Peer-to-Peer Conversations” on Bloomberg Television.

“I think I saw in some of the newspapers, they used the term Sputnik moment,” he added. “I don’t know if it’s quite a Sputnik moment, but I think it’s very close to that. So it’s a very significant technological event that occurred, or test that occurred, by the Chinese. And it has all of our attention.”

I'm not an aerospace engineer, so take what I am writing with an appropriate degree of skepticism.

I'm not buying the hypersonic missile hype. First off, the damn things are launched by a rocket. I think it's safe to presume that we have a continuous overwatch on China for such activity. If a bunch of large rockets are launched, we're going to be at a high Defcon before the second stages burn out.

Second, even if they actually work, they aren't exactly sea-skimming aircraft. They will be well up where radar can spot them. They are not exceptionally maneuverable, a missile traveling at 4,000 mph will have a turn speed of about 2 degrees a second.

Third, those things are gliders, so a lot of steep turns will scrub off their speed.

Fourth, if China does deploy these things, then I would expect that the reaction upon detecting a series of rocket launches will be for the silo covers on the Minuteman fleet to open up. They will be primed to launch. The chances of a Chinese strke taking out all 400 or so silos is rather small and even a ten percent launch of a retaliatory strike will devastate much of China, and that's before the SLBMs begin flying.

Which they will.

So forgive me if I hold the cynical opinion that the soon-to-be-proclaimed hypersonic missile gap is as much a military fundraising gimmick as was the "bombr gap" and the "missile gap" of the 1950s.

8 comments:

Jones, Jon Jones said...

I think the basic problem is orbiting nukes that can be targeted on short notice. Re-entry is an issue for sure. Russia couldn't do it. Something like this could do it:
https://en.wikipedia.org/wiki/Boeing_X-37

Dark Avenger said...

Designers of hypersonic vehicles face a daunting adversary: drag, the resistance a fluid offers to anything moving through it. The drag on a flying object increases in proportion to the square of its velocity, making it particularly debilitating at hypersonic speeds. A glider at Mach 5 is subjected to 25 times the drag force than when it flies at Mach 1, for example, and one at Mach 20 faces 400 times the drag of when it is at Mach 1.

Even more severe is the energy drain from an aircraft as it pushes the molecules of air forward and aside: it increases as the cube of the velocity. So a glider flying at Mach 5 will lose energy 125 times faster than at Mach 1; one flying at Mach 20 will lose energy 8,000 times faster. Just as problematic, the kinetic energy flowing from the glider to the surrounding air transforms to thermal energy and shock waves. Some of that energy transfers back to the vehicle as heat: leading edges of boost-glide weapons flying at Mach 10 or above can reach temperatures above 2,000 kelvins for sustained periods. Protecting a vehicle from this intense heat is one of the biggest problems facing engineers.
At the same time, like any other glider, a hypersonic one must generate lift—a force perpendicular to its direction of motion—to stay aloft and to turn. (A glider turns by banking or otherwise inducing a horizontal component of the lift force.) As it happens, lift is also proportional to the square of the velocity. Moreover, the aerodynamic processes that produce lift also unavoidably generate drag. The ratio of the lift force, L, to the drag force, D, is called the lift-to-drag ratio, L/D, a key marker of a glider’s performance.
Achievable values of L/D for hypersonic vehicles are much lower than for conventional aircraft. For subsonic aircraft, the ratio can be 15 or larger. Yet after decades of research and development, U.S. hypersonic weapons tested in the past decade appear to have L/D values less than three. Such low L/D ratios mean low lift and high drag—which limits the speed and range of a hypersonic glider, reduces its maneuverability and increases surface heating.
As if that were not enough, the physics and chemistry of air flowing past an object become radically different at hypersonic speeds. Heated to thousands of degrees, the surrounding air dissociates, converting molecular oxygen into free atoms that can ionize and scour away the surface of the vehicle. Even if the missile survives the roasting, the heating produces a bright infrared signal that satellites can see.

https://www.scientificamerican.com/article/the-physics-and-hype-of-hypersonic-weapons/

Tod Germanica said...

Great synopsis DA.

dan gerene said...

So does this mean that China has replaced Russia as the main boogeyman to justify spending hundreds of billions of dollars to feed the military industrial complex? It just looks like they are ramping up with some fear to justify spending for more super expensive high tech projects that don't work so good while neglecting the basics.

Comrade Misfit said...

Dan, no shit. The Army pretty much was equipped to refight WW2 until the 1960s.

bearsense said...

Small correction: The launcher closure of a Minuteman launch facility remains closed until the missile is in terminal countdown. It opens just before the first stage ignites. …. and yess, that 110 ton closure clears the silo in two swconds.

CenterPuke88 said...

Actually, the biggest problem for “on station” deployment of nukes in orbit is debris. Geo-synchronous placement of the nukes makes little sense, as it voids most of the advantages of orbital placement, provides a stable target, but reduces space junk issues. Low earth orbit increases the protections aspect, and introduces a huge space junk threat…and as DA effectively notes, a grain of sand can damage a heat shield quite enough to void the ability to successfully deploy the weapon. Add to the cold sink effects on ceramics, and the question of how you recover your unused nukes after their effective lifespan…

Dark Avenger said...

For clarification, I merely excerpted from the article I linked to, putting together the parts that would make sense even to a layman like me, who knows little to nothing about it the intricacies of flight. Credit is due to the authors before I can take a bow, IYNWIM.