LORAN can be good to 60 ft.
On 7/27/13 12:21 AM, Jim Lux wrote:
On 7/26/13 8:45 PM, J. Forster wrote:
I gather from the article, the GPS position was spoofed and the
autopilot,
in bringing it back to where it was supposed to be, actually took it off
course.
There are places where a few hundred feet makes a big difference,
viz. the
Costa Concordia.
IMO, this is a very convincing reason for something like LORAN.
I think it's a convincing argument for a captain who pays attention to
the other navigation instruments and doesn't blindly follow the GPS.
It's also a convincing argument that shipboard
automation/autopilot/autocontrol vendors need to make more
sophisticated software (which I suspect they do, particularly on 200+
foot ships.. I would imagine that there are some aspects of this demo
that are contrived.) The ship making and driving business is pretty
unregulated. It's all about what the owner of the ship is willing to
pay (or what he needs to get liability insurance, if he wants).
There's nothing even remotely like DO-178 for shipboard stuff.
The folks doing stabilized oil rigs probably have sophisticated
systems, but they're also using IMUs and other stuff. Ditto for high
value things (oil tankers, warships). Molasses tankers? They're
probably lucky to have a functioning compass and some old charts.
I'm not sure, though, that looking at the big picture, whether your
tax dollars are better spent on LORAN, or on some other precision
navigation method or on making jam resistant GPS receivers (which do,
in fact exist, and make use of things like direction of arrival of the
signal..)
Note that a GPS system with 3 antennas (as is common in systems that
use GPS to derive attitude/orientation) would be extremely difficult
to spoof, and would be VERY inexpensive to implement. Either the
carrier phases and code phases are consistent for all the received
signals or they're not. A jamming signal coming from the wrong
direction will not have the right direction of arrival relative to the
platform orientation. One wrong signal might be tolerable (multipath,
etc.) but with a multi satellite fix, I suspect it would be hard to do
it.
Sure, one could throw up N pseudolites on a bunch of UAVs, etc., but
that's getting to be a bit noticeable.
For what it's worth, I don't know that LORAN has the performance to
avoid a Costa Concordia type foul up (assuming they were crazy enough
to do the near pass in the fog, so visual navigation didn't work)
I seem to recall that LORAN had 1/4 nmi kinds of accuracy. it would
get you to the channel or mouth of the harbor, but not get you into
your berth. You might be familiar with the local propagation anomalies
and get better accuracy with experience in your local waters.
-John
=================
I boat? The backup is a competent captain. He'd see the compass
heading
move and quickly disengage the autopilot. I had a boat for years I'd
notice a 5 degree change. Mine was a sailboat so I'd be more
sensitive to
heading changes than a power boater but still the human is the backup.
Most autopilots don't directly follow GPS, they use GPS to determine a
heading, follow it then use GPS to detect drift and re-compute the
heading.
the heading would be held by a compass sensor in a low-cost setup
or in a
larger setup a lazer ring gyro backed up by a compass. So a spoofed
GPS
would cause the autopilot to "think" there was a bigger crooswnd or
current
and make a bigger heading change.
I bet you could hijack a drone not a manned vehicle the pilot is
trained
to
monitor the automation and he'd very quickly turn it off thinking it
was
broken.
On Fri, Jul 26, 2013 at 8:41 AM, J. Forster <[email protected]> wrote:
Prof. Humphry from Texas just reported being able to spoof GPS in the
Med
and take over the nav system of a luxury yacht. He's done this before
with
a drone in the US.
LORAN as a backup, at least?
-John
==============
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--
Chris Albertson
Redondo Beach, California
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