Salute!
Good question, Blacksheep, and I thot I had answered some of it without going into minutiae.
Your system uses present position for the Kalman or other algorithm to compare predicted body rates and accelerations with what the inertial sensors are actually detecting, whether they are gyro-stabilzed like the old days or bolted on your airframe. The old ones assumed you were stationary on the ramp, huh? If you had an alternate means of providing movement over the earth like a doppler, things got easier. If you had postion data like from a GPS, even without velocity, things got easier. So for our aviation use navigating across the earth, initial position for alignment is a biggie. For systems lile the AMRAAM and other weapons, not so much. JDAM was provided persent position, aircraft velocity thru space and rough attitude, as they could be loaded on various store stations. That allowed it to get its own posiiton quickly and begin the hunt.
- Good first question, and I mentioned that providing attitude will speed up the alignment process, especially for Earth coordinate referenced systems concerned with true north. But for some of the strapdown systems we don't have to be at a specified attitude like st-and-lvl or wait for the "platform" to "settle" like we used to. Even with a rough attitude to start with, the doggone things nowadays eventually figure it out. When I say "eventually", that could range from seconds to several minutes depending on your set. I'll have to get with the sfwe troops, but my hunch is that orientation of the fixed sensors WRT the airframe is the primary requirement for your navigation not orientation WRT the Earth-referenced coordinate system. In other words, the overall nav system applies a bias to the sensed data, Gotta hit the books.
Gums sends..