To risk being pedantic, US SLBMs (Tridents) indeed use stellar updates for their inertial guidance system.

Our ICBMs have no update mechanism at all. Once they're out of the silo, they're completely on their own.

ICBMs would be more confident in their starting position and orientation, though, at least. SLBMs would necessarily have more uncertainty in the initial conditions.

You can create nuclear load so powerful it won't matter where it hits.

Teller, is that you ?

"close only matters in horseshoes and nuclear strikes"

The BM part means "Ballistic Missile", which sounds like they're basically "thrown" into a parabolic path towards their target, like a falling rock.

Or am I over-interpreting the name?

Have a read of how MERV part of some ICBMs works. Lots going on as far as targeting goes. Also take a look at Trident 2 which can use GPS for course correction but isn’t reliant on it.

That's exactly the right interpretation. You chuck them into space and after the rocket quits, Isaac Newton takes over.

Contrast hypervelocity weapons, which -- contrary to the name -- don't really go faster but they can maneuver in the atmosphere at that speed.

The missile knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where it is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't.

In the event that the position that it is in is not the position that it wasn't, the system has acquired a variation, the variation being the difference between where the missile is, and where it wasn't. If variation is considered to be a significant factor, it too may be corrected by the GEA. However, the missile must also know where it was.

The missile guidance computer scenario works as follows. Because a variation has modified some of the information the missile has obtained, it is not sure just where it is. However, it is sure where it isn't, within reason, and it knows where it was. It now subtracts where it should be from where it wasn't, or vice-versa, and by differentiating this from the algebraic sum of where it shouldn't be, and where it was, it is able to obtain the deviation and its variation, which is called error.

Why is this meme always pasted in to threads about missile guidance?

Because it’s a classic gag, even if it’s out of place on HN

https://youtu.be/bZe5J8SVCYQ?feature=shared

Not just an online gag, that's related to an excerpt of an alleged December 1997 issue of "Association of Air Force Missileers" on the GLCM Guidance System. Likely submitted in jest.

https://web.archive.org/web/20050514035446/http://www.afmiss...

that is so romantic. Rockets looking at the stars one last time before obliterating $cityname

Observing distant nuclear fusion, before unleashing it locally.

fission != fusion, but yeah

I’ve got some bad news for you about modern nuclear weapons.

h-bombs do both

fission + fusion

The fission primary is used to trigger a secondary fusion reaction in modern weapons.

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

All fusion weapons are fission weapons first (like a few nanoseconds first).

All fission weapons are not necessarily also fusion weapons. But probably most are nowadays.

Every nuclear weapon in the active US stockpile has a secondary fusion stage, the last pure fission weapons were removed from service and dismantled in 1992.

Most of the cost in a nuclear weapon is in the primary. It only makes sense to build pure fission weapons when you want very low-powered nukes for close range tactical use; the DoD has determined that don't see enough use for them to justify the upkeep of specific weapons.

i've been to $cityname many times. there are lot of available single women there near me in $cityname

This form of navigation is probably only accurate enough for nuclear weapons, you’re not going to get meter-Range CEPs with that. You probably have to select a city you want to hit.

This is a very good read on the state of the art when it comes to submarine-launched missile accuracy, which are presently inertially guided with a stellar update during flight.

https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...

Thanks for the link, very interesting. So CEP is estimated to be around 100m. Better than I thought but I wouldn’t call it hitting a specific house yet.

What do you consider the primary benefit of pinpointing a particular house in nuclear war?

I don’t know if it matters now but at some point certain targets were hardened to near misses of certain sizes but not direct strikes. So the better your accuracy the smaller the weapon (or fewer) you can use to take out those targets.

So you could say the use would be increased certainty your enemies command and control and other bunkers would be destroyed increasing the odds of “winning” whatever happens afterwards.

There is no "winning" in global thermonuclear war... :/

That’s why I said the guidance is only really usable for nuclear weapons. I wasn’t saying the guidance is bad, I was saying it’s not accurate to a few meters.

https://news.ycombinator.com/item?id=43393504

Oh you're right, my bad. I got lost in the conversation and looking into the types of guidance systems and I forgot that was your original point.

While you probably can't target a cigarette butt on the street, you could definitely hit a building. Especially if the ICBM is paired with image recognition (which it has already for star nav) and/or backup positioning mechanisms like cell tower locations or well-known broadcasting tower locations (think television stations).

An ICBM is coming in at hypersonic speeds in the terminal phase, you’re not going to guide it anywhere using cell tower signals. The guidance is done much earlier.

And I would doubt image recognition for ground features would make it that accurate, too. Before reentry, you’re very high and fast and reentry isn’t that predictable to get you accurate enough to hit a house. And during reentry, you’re not going to see anything though plasma. And after reentry, you probably don’t have enough time and control authority to still guide into a specific house.

ICBM guidance is very different from cruise missiles.

> An ICBM is coming in at hypersonic speeds in the terminal phase, you’re not going to guide it anywhere using cell tower signals.

Hypersonic glide ICBMs have been successfully tested by China, and are under development in the US, so it's entirely possible to maneuver, and optionally guide them in the terminal, though perhaps not advisable on a jammable channel, except perhaps as an anti-radiation weapon.

Yeah that would work for drones and slow cruise missiles but not ICBMs.

Quantum navigation is likely to be more precise.

Down to the Planck scale?

well there is this now as well - you don’t need to use the stars when you already have detailed aerial images of the earth - https://www.spectacularai.com/gps-free

Can you imagine if someone just turned off the sky?

Who are you? Cixin Liu?

The universe winks for thee.

Spin by Robert Charles Wilson is based on this premise.

Singularity Sky

Nine Billion Names of God

Damn guess we have to blow up the stars

…you know, for defense

Or create a lot of artificial ones to confuse the missile.

Swarms to block the cameras maybe?

At this point though, couldn’t you just blow up your own country and thus accelerate warming so much as to doom the rest of humanity in a dozen years? I might have read the wrong article on that though so don’t quote me.

Aperture Science would do it.

They still owe me some cake

I have terrible news regarding said cake.

This makes me wonder how many fake stars an adversary would have to put up (and for how long?) in order to confuse a celestial navigation system.