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aarkwilde t1_jdxz6gq wrote

Because at that point gps may be gone?

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neoengel t1_jdxzmf4 wrote

Hopefully, a real (end of the) world scenario doesn't test out how effective it will be.

On that tangent, the SR71 Blackbird reconnaissance plane used a high-tech sextant behind the cockpit similarly by using the stars to navigate at the upper atmosphere.

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haveueverseenallama t1_jdy0sae wrote

Cheers. My girl still doesn't care why knowing how to use a sextant is as important as Morse or flags. However I DO!

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AdoltTwittler t1_jdy1dfd wrote

As did the Apollo missions. Same group created the navigation hardware and software

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MongFondler t1_jdy21x2 wrote

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.

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MostBotsAreBad t1_jdy4v5s wrote

Yes, but technically they're flying outside of every planet's atmosphere.

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CheeseSandwich t1_jdy909a wrote

That was the big deal about the MX/Peacemaker missile. It relied on an extremely accurate internal navigational system called AIRS (eventually called IMU) that produced a circular error probable (CEP) around 90 meters. The MX was designed to survive an initial nuclear attack and be capable of being launched and retargeted quickly and accurately. Other American missile systems had a CEP of 160 meters.

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on_ t1_jdzih22 wrote

But how a 60’s 70’s missile “see” the stars. With some photoelectric receiver?

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thousand-grandmas t1_jdzxbtd wrote

Replying to aarkwilde (#2,404,936)

I’m not sure gps would even work up there. GPS satellites are obviously a lot further out than LEO and suborbital missiles, so there should be a signal, but it’s probably designed to work best at surface level.

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Seraph062 t1_je6dz2r wrote

Replying to on_ (#2,412,565)

> But how a 60’s 70’s missile “see” the stars.

TV cameras were a thing back then. The idea of taking a 'video' signal and converting it to an 'electrical' one was a fairly solved problem.

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Seraph062 t1_je6g3ku wrote

Replying to BandidoDesconocido (#2,441,256)

This isn't true.
If you're a monster that just wants to run up a body count you can get away with 'a couple of kms' from your target. But if you want to attack hardened (military) targets, using a warhead you can actually carry on an ICBM, you'll need to get <1km levels of accuracy. If you want to shrink warheads (so you can carry more than one per missile) then you need to be even more precise.

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