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From: Frank Reed (no email)
Date: Wed Oct 13 2004 - 02:35:08 EDT
Herbert Prinz wrote:
"In my admittedly very limited experience of ten thousand off shore miles
over the last
ten years I have not ONCE been in a situation where GPS didn't work, but cel
nav
would. In fact, I have not once been in a situation at sea where GPS didn't
work.
Full stop. But I have REPEATEDLY been in situations where celestial was
unavailable for several days in a row and GPS was the only position finding
tool
available. Conclusion: Celestial is not even a backup!"
When asked the question "What's the best backup for GPS?", probably the best
answer is "Another GPS!".
There is an ambiguity in the above Q&A that may be worth pointing out. The
obvious interpretation is that a sailor should carry a spare GPS receiver
onboard in addition to the main GPS system. This spare (and maybe a spare for the
spare) should be stowed securely in an emergency kit and checked occasionally
just as you would check all other emergency gear. But there's another
interpretation. What's the best backup for the GPS system itself? And the answer there,
too, is another GPS --the whole system. The Europeans, if I remember
correctly, are gearing up to spend a small fortune launching an independent GPS-like
system. There are plenty of reasons for this, but the most basic is that ANY
system should have a backup. And I should note that there is already a similar
Russian system, but it seems to be less relevant for practical applications.
I think there's a strong analogy in this current situation to the final days
of lunars in the latter half of the nineteenth century. Back in 1850 the
question would have been "What's the best backup for a ship's chronometer?" And the
answer most navigators had settled on by that date was "Another
chronometer!". Some small number of navigators continued to count lunars as their emergency
backup, but in truth, were they shooting lunars for the same reasons that we
shoot lunars today? For fun and challenge and a connection with the past.
I think there's something poetic about GPS in the context of the history of
the quest for longitude. In the late eighteenth century, the problem of
navigation was seen as a great contest between machine and nature, between
chronometers and the Moon. Machines won out, of course. GPS rules the world. But a GPS
satellite is little more than a an amazingly accurate chronometer, an atomic
clock, contained within a tiny artificial moon, a satellite. It's a bit of an
unholy union, and yet lunars and chronometers are united in those orbiting
clocks.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
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