As a (former) Naval Officer, I will tell you that a competent mariner
should always be using and cross-checking /all /sources -- GPS, radar,
dead reconing, /looking out the window/, and even celestial in open ocean.
(I frequently had to remind my junior officers that nobody ever ran
aground or collided with another ship from spending too much time
looking out the window. Way too easy to get their heads stuck in the
radar or the GPS map.
73,
Jim
wb4...@amsat.org
On 7/27/2013 9:43 AM, Scott McGrath wrote:
Key here is how does the captain know that GPS is no longer providing an
accurate fix? You need 2 or more independent systems to cross check each
other.
Sent from my iPhone
On Jul 27, 2013, at 12:21 AM, Jim Lux <jim...@earthlink.net> 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 <j...@quikus.com> 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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