NavList:

Alex,

I found the following on a military history web sight.

"Boeing and Navy Strategic Systems officials say that the electrostatic gyro, first developed in the 1970s, is the world's most accurate inertial navigation system; it meets the extremely stringent standard required for launching nuclear-tipped ballistic missiles after being submerged for long periods without position updates from offboard sources. The WSN-7 and WSN-7A RLG-based systems require updates from the global positioning system (GPS) every 14 days."

So it looks like the inertial systems in the 70's were good for 14 days which means that 6 position updates were needed during a 2.5 month assignment.

Today's subs are using fiber optic gyro navigation (FOGN) which matches accuracies of the older electrostatic system at much less cost, weight, space, and technical support.

Greg Rudzinski

[NavList] Discussion of subs/INS
From: Alexandre Eremenko
Date: 12 Apr 2012 07:17
Richard wrote:
> apologies for helping to continue this somewhat off-topic dialogue.

I also apologize for triggering this submarine discussion,
but let me recall that it started from this important Cel Nav question:

Who needed high precision Celestial Navigation, and was this really ever
needed?

By "high precision" I understand less than 1 nm accuracy.
Ordinary practitioners do not care about this, as was stated on this list
many times. They do not care about dip-meters, for example, the simplest
device to improve the accuracy of ordinary fixes based on altitudes.

I conjectured that high precision was needed for submarine missile launches
when satellite navigation was not available. That is in the US before Transit
system became operational, and for much longer period in Soviet Union.

This is still a conjecture and there is no direct proof of this. However,
there is much indirect evidence.
It seems clear that INS alone, without checks is not capable of the required
accuracy. The question is what checks were available before satellites,
and also what checks are available without surfacing.

Here is one thing which was not mentioned so far:
I read yesterday an interesting paper on whether it is possible to use GPS
under water:
www.math.purdue.edu/~eremenko/Navigation/gps-sub.doc
They mention the following method: disposable satellite receiver
is released from the sub, surfaces, determines its position,
and sends to the sub a sound signal.
If it is near the sub, this is enough.
If not, one need three such buoys; receiving the sygnals from them is
enough to determine the position with high accuracy.
This and other papers confirm that such method was (is) used.
This does not solve the question of what was available before satellites.

There is one more possibility. The region of missiles launch can be equipped in
advance with sound beacons. Either attached to the bottom or floating and
determining their position from satellites. This is again only my conjecture.

Alex.

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