It’s interesting that an MIRVed ICBM fired from one country at a target follows a suborbital trajectory that takes the missile up to about 900 miles above Earth and at velocity approaching 17,000 mph. Shortly before reentry, the independent warheads are seperatly targeted and fired from their launch “bus” and simultaneously spun up or rotated to tremendous velocity, similar to bullets fired from a rifle, for increased stability and accuracy, and then the separated warheads race toward their targets. One source notes, “in advanced MIRV systems, rotational velocities could potentially reach several thousand RPM or more. Higher rotational speeds enhance stability and control during reentry, particularly in scenarios where the warhead needs to navigate through varying atmospheric conditions or when high precision targeting is required.”
A nuclear missile spinning at several thousand RPMs? Surely this is a typo.
Are the warheads launched nearly simultaneously or can there be a delay between their firing? At 17,000 mph, a few seconds delay per launch can translate to a lot of ground covered between warheads A, B, C, D, and E.
MIRV warheads are typically distributed on a bus, the capabilities of which varies depending on missiles. I know the US Trident SLBM MIRV bus spins around to eject MIRVs on different paths, one at a time. Depending on the capabilities of the missile you’re looking for a potential MIRV spread anywhere from like 80 miles to around 1000.
“Rotational speeds for spin-stabilized warheads can indeed vary widely based on specific design requirements and the characteristics of the missile system. While I mentioned that typical ranges could be from around 10 RPM to 100 RPM as a general estimate, there are scenarios where rotational speeds can indeed be higher, potentially reaching into the hundreds or even thousands of RPM.”
One would think a rotational velocity of “thousands of RPM” would seriously degrade the warhead’s performance, rather than improve it. Or perhaps tear it apart. I know that missiles fired from, say, an F-22 fighter do not spin or rotate, although they only travel at about mach 4 versus about mach 22 for an ICBM.
Missiles launched from an F-22 are guided and steered with the fins on their rocket. MIRV warheads do not guide or navigate themselves and have no control surfaces. The MIRV bus can guide their launch point, but they’re closer to being a bullet than an air to air missile in that way.
The internals of a nuclear weapon are symetrical and solid metal, generally speaking. I don’t see spinning at a high RPM necessarily has to impact their performance. They’re solid assembly with few to no moving parts.
We’ve also put nuclear weapons into artillery shells, which spin at several thousand RPM, so it may be referring to those, or at least that indicates that nuclear warheads can be spun very fast by design.
Remember that chatGPT isn’t a “source”; it got that info from someplace.
Or maybe it “pasted” together a fact about artillery shells from one article into an unrelated paragraph about MIRVs from another article. With zero awareness it was talking about two things that are completely unrealed. This is what makes these LLM "AI"s so dangerous.
In this you’re mixing the rotation rate of “missiles” with “warheads”. Two very different things.
Mach numbers are inherently a very misleading unit of measure for speed when you’re thinking about inertial forces. The same exact speed can be wildly different Mach numbers depending on the atmosphere or lack of it where the measurement is taken.
It is a very valuable unit of measure for aerodynamics. But is often misapplied by amatuers in other realms.
I’ve seen CHAT GPT make some ridiculous and demonstrably false claims of fact, so anything it says should be taken with a grain of salt. Can you point to a non-AI source confirming that nuclear MIRV warheads spin enroute to their target?
ISTM that if a nuclear warhead/vehicle is spinning at several thousand RPM, you won’t be able to apply steering corrections; you’ll have to have it perfectly aimed before it starts spinning, and you’ll have to assure that your spin-up mechanism doesn’t alter its course during spin-up.
I may be incorrect but I believe that warheads do not steer themselves at all. They have no control surfaces. A trident’s MIRV bus looks like this. The warheads are just cones.
The aiming is mostly just rocketry - knowing where you launch, where you want to go, and dialing in the correct sub-orbital path to get there. A big part of the challenges of early sub-launched ballistic missiles was getting a navigational fix on the sub’s location. A significant amount of space was dedicated to early navigational computers for this purpose.
The warheads are moving so fast that some drifting by prevailing winds will be relatively insignificant. Maybe they’re designed to spin to stabilize the trajectory like a rifle - that’s plausible enough. The MIRV bus does have some ability to navigate in space and correct for errors in the suborbital path as well as maneuver to allow MIRVs to hit far apart targets. Since they can’t rely on satellite or other navigation systems to be working during a nuclear war, they actually designed a system to sight stars for navigation which is really quite remarkable. But once the MIRV bus releases the warhead, as far as I know, it’s just dumb warhead travelling on a ballistic trajectory to its target.
The gyroscopic stability of a cone will depend on a number of factors like the square of the spin rate, the ratio of the axial and transverse moments of inertia, its diameter, velocity, the density of the air, etc.
For all of which we can make up some “reasonable” figures to come up with an order of magnitude, but to get a chatbot to do it… well, you can see the results for yourself.
Also keep in mind that the warheads don’t need very much precision. As the saying goes, “Almost is only good enough in horseshoes, hand grenades, and nuclear war”.
Precision helps to kill hard targets (we don’t bother to use the nuclear complex at Cheyenne Mountain anymore because Russian missiles are accurate enough to kill it) but also allows you to use smaller weapons to destroy your targets reliably. Nuclear warheads are far less powerful than the average person seems to think (I often see people talk as though a nuke would take out half a state rather than half a city). Average yield of warheads is down significantly from where it was in previous decades because modern missiles are precise enough to destroy their targets with 200-450kt warheads rather than multi-megaton warheads, which allows you to pack more warheads on each missile.
Advanced (US) missiles actually land their warhead within 100m of the target half the time, which is an amazing number when you consider that they travel for thousands of miles based on inertial and stellar navigation. Russian missiles are an order of magnitude or two worse, and for that reason they still tend to use bigger warheads.
This video shows non-armed MIRVed ICBM warheads hurtling toward their practice targets during re-entry phase. In one of these scenes, you can hear people cheering.
Are these warheads glowing because of friction from re-entry? Clearly, these warheads are moving at terrific speed. As they enter the atmosphere, do they create sonic booms … before the somewhat larger boom?
Not friction, but compression. The air in front of the vehicle gets compressed and undergoes adiabatic heating, just like the air in a diesel engine combustion chamber: you squeeze it, and it gets hot. Really hot. For a hypersonic object, hot enough to glow. On a supersonic/hypersonic object, the hottest areas are the forward-facing surfaces (where the air is slowest and most-compressed), not the lateral surfaces (where air is subject to friction as it slips past the object).
I prefer to call them “bullshit engines”. They’re like Cliff from Cheers: Ask him any question, and he’ll immediately come up with a plausible-sounding answer. And he does actually know a lot, so very often his answer will be correct. But even if he doesn’t have a clue, he’ll answer just as quickly and just as confidently. He’s a bullshitter. And so, even if his answers are often correct, you can never be sure which of his answers are correct.
In this video of the flight sequence of a Minuteman III ICBM, Northrop Grumman pretty much gives Pyongyang the entire recipe book. Here, President Kim can see how “the post-boost vehicle is maneuvered to pre-determined launch window in space” and then “spin-gas generators” stabilize and guide the warhead as it speeds toward the target. This appears to be a non-MIRVed missile.
There’s a terminology issue, here. “Friction” can sometimes be used to mean any dissipative force that opposes the motion of an object, in which case aerodynamic drag is a form of friction, despite acting almost entirely on the front surface of the object. But it can also sometimes be used to mean specifically shear forces on lateral surfaces, in which case an object moving through a gas has almost no friction.
