5 ms·
If the only concern was that your GPS receiver could fail, then you could rely on your backup system. Either a second receiver, or some other system. (TACAN, IN
by ckozlowski 11y ago
If the only concern was that your GPS receiver could fail, then you could rely on your backup system. Either a second receiver, or some other system. (TACAN, INS, etc.)
Their concern seems to be, "What if none of the electronic systems can be trusted?" That wasn't as much a concern when the sextant courses were dropped, but they are now, which is why it seems they're reinstating them.
Curiously, INS (inertial navigation system), which uses gyroscopes, is often turned to as a backup for when GPS can't be used, or is otherwise unavailable. (Many guided systems now can use INS as a backup if the GPS signal is jammed.) Most ships have this as well. Presumably this would be an adequate fallback.
That being said, if my ship were dead in the water with no electrical power, this seems like a no-brainer.
- gregwtmtno 11y agoI wonder how accurate a modern INS system is. I'll bet it's pretty good.
- mikeash 11y agoShould be extremely good over the short to medium term. The trouble with INS is that the error is unbounded, so you have to use some other technique to get a fix periodically to reset it.
- ckozlowski 11y agoI don't know, but I do remember reading that one characteristic issue of them is that the errors compound over time. If you're say, dropping a GPS-guided bomb, and the signal is jammed, then they'll fall back to INS for the rest of the way. The distance between signal loss and impact is pretty short, so there isn't much time for errors to compound. If you're navigating say, a submarine however, the longer you go without a real fix, the more unreliable that INS estimate is going to be, especially if maneuvers have been undertaken. In other words I guess, "it depends". =)
- dingaling 11y agoRing-laser INS still have a drift of a few kilometres per hour. To keep their respective INS in-check, Tomahawk looks down and performs terrain-comparison whereas Trident looks up and does stellar nav... The Kearfott Mk 6 that is used by Trident is the successor a line of stellar nav units they produced for the Navajo, SR-71, Hound Dog and FB-111. And probably a bunch of others I've forgotten. The early models used a sheath of acetate star-chart sheets in a mechanical loader to perform the matching operation!
- toomuchtodo 11y agoI've always wanted to build a hobbyist steller nav system using a CCD and some open source star position comparison software. One day!
- GFK_of_xmaspast 11y agoIf you're dead in the water with no electrical power, do you have anywhere to go that needs navigating.