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Comment by dullgiulio | Hacker News Reader

Perhaps a stupid question, but during the re-entry glide I'd expect the glider to be shrouded by plasma. Doesn't it stop radio signals? How does the glider get information on the route?

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Not a stupid question. What you're referring to is the blackout period during reentry. It's a challenge not just for missiles but spacecraft too. Lots of research has gone into it:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201000...

Beyond the advanced research concepts though, I believe the leading solution is typically inertial navigation (or a variation thereof):

https://en.wikipedia.org/wiki/Inertial_navigation_system

https://ui.adsabs.harvard.edu/abs/2016SPIE10158E..13L/abstra...

I don't know how this system works but US hypersonic missile designs suggest how it could work without requiring radio signals. Inertial guidance gets you into the general area of the target, at which point you switch to active terminal guidance i.e. the missile can identify and maneuver toward the selected target.

This is much more difficult than it sounds. At hypersonic velocities, your entire terminal guidance system is being actively destroyed by atmospheric ablation. Decades of research went into how to make a terminal guidance system that survived just long enough while retaining sufficient precision of control to hit the target. It is an exotic materials science problem.

Does a piece of cork amount to "exotic material science."

Disposable heatshields are certainly used on all of them.

And i always thought the whole point of a missile would be its one time use..

Plasma shield also means no radar to scan for missile defenses, so I guess the maneuvering is just random?

Big bright ball of plasma might also make a great target for said missile defense kill vehicle.

Western sources routinely dismiss claims that plasma stealth is in practical use / is of practical use. We'll have to see of course.

And yes, plasma generated by re-entry fireballs are plenty detectable in other areas of the spectrum.

> Western sources routinely dismiss claims that plasma stealth is in practical use / is of practical

Given that the A-12/SR-71 were designed to use A-50 fuel addition for plasma stealth I am confused by this statement.[1]

[edit: reworded from definitive statement of actual use]

[1] https://www.thedrive.com/the-war-zone/29787/the-sr-71-blackb...

Well, my wording was a little imprecise. Plasma stealth as a physical concept is real, there's little doubt about that. I wasn't aware of the linked application (that's so cool! Thanks for sharing), but I would argue that that demonstrates a limited application of plasma stealth (rear aspect and plume RCS reduciton). Typical claims of plasma stealth involve somehow cloaking the entire fuselage and providing all-aspect stealth.

I guess what I was trying to get at is that western sources typically downplay the threat posed by any mention of plasma stealth, typically usually some combination of "we don't actually know if their systems use plasma stealth in a meaningful manner" and "even if they did, we don't believe that it poses of a significant threat".

It may get last-minute trajectory telemetry during the boost phase, but after that it's all internal measurements and timing by the IMU.

Makes sense. The video simulation shows satellites correcting the glider's path after it has left the booster. They even drew the hot plasma around it...

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