In article ,
says...

From J. Clarke:
snip

Just a reminder, GPS was originally not for targeting, it was for
positioning the launcher accurately. With three hundred 400KT warheads
close counts.

I'd be interested to know where you got that idea from. If all that was needed was precise coordinates for launching mobile systems, you could simply hire teams of surveyors, at little more than minimum wage, to paint a bunch of 'X's on the ground at potential launch sites. This is a *far cheaper* solution than a multi-billion dollar satellite constellation, especially if you wait til the Glidden paint buckets go on sale.


The reason why GPS was developed and implemented was very straightforward:
Inertial Nav Systems (INS) are inherently prone to errors that can run away in a huge way. ALL THREE legs of the nuke triad depended on INS - the bombers, sub-launched and land-based missiles.

INS's measure acceleration, so you have to go through two integrations to get position, and that's only after you've initialized it to an accurate position by some other means - taken a fix. After feeding the INS an accurate fix, errors can still go wildly out to lunch.

GPS measures position (and velocity) directly, so the entire nav problem is *solved*. This is the reason why DoD knew that what GPS offered was worth megabucks, in order to get those megatons on target reliably and precisely.

GPS offered a way to cover nav for the full trajectory of those nukes as the warheads found their way to their targets, not merely fixing launch coordinates (a much easier problem to solve).

You're correct that with a fixed site, things like satellite images and
traditional surveying methods could determine the position of a launch
site. But, do not forget that with subs and bombers, the launcher
itself is not fixed (subs especially), which makes determining the
position of the missile before launch a bit harder than with a fixed
missile launch site.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer