
Seeing stars again: Naval Academy reinstates celestial navigation - curtis
http://www.capitalgazette.com/news/naval_academy/ph-ac-cn-celestial-navigation-1014-20151009-story.html
======
dpeck
For anyone interested, I taught myself the basics of celestial navigation a
few years back after being interested in it for years. Something just feels
right and maybe a bit primal about knowing where you are relative to the
heavens.

I used the book [http://smile.amazon.com/Celestial-Navigation-GPS-John-
Karl/d...](http://smile.amazon.com/Celestial-Navigation-GPS-John-
Karl/dp/0939837757) and really enjoyed it. Fun to do with kids too.

Edit: And the [http://smile.amazon.com/Davis-Mark-3-Marine-
Sextant/dp/B0014...](http://smile.amazon.com/Davis-Mark-3-Marine-
Sextant/dp/B0014476FI/ref=sr_1_1?ie=UTF8&qid=1444844189&sr=8-1&keywords=davis+mark+3+sextant)
makes a fine sextant to start with.

~~~
wyclif
I'd be interested in more book suggestions.

~~~
Luc
John Karl's book is very good.

My favourite is 'Self-contained Celestial Navigation with HO 208' by John
Letcher. It's out of print but used copies show up on abebooks for a
reasonable price at times. It's often recommended.

I also like 'The Sextant Handbook' by Bruce Bauer. Also out of print.

A very nice modern coffee-table book about the history of celestial navigation
is 'Finding Longitude' by Richard Dunn e.a. :
[http://www.amazon.com/dp/B00HPMW95A](http://www.amazon.com/dp/B00HPMW95A)

Finally, you could subscribe to NavList at fer3.com. There's enough in the
archives to fill several books and the people there really know their stuff
(well, not me so much, but others do!).

------
maze-le
It is always good to have a backup system, in case the primary system (GPS)
fails. Celestial navigation has a proven track-record for centuries.

I wonder more why it was dropped in the first place...

~~~
ckozlowski
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
I wonder how accurate a modern INS system is. I'll bet it's pretty good.

~~~
dingaling
Ring-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
I've always wanted to build a hobbyist steller nav system using a CCD and some
open source star position comparison software. One day!

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xg15
I wonder if, with the use of image analysis, it would be possible to create a
"robo-sextant" \- i.e. a system which scans the sky in certain intervals,
locates the waterline, sun or other celestial bodies and performs the
necessary calculations. Such a system could be used to e.g. detect GPS
manipulation quickly

~~~
mninm
Trident missiles (a type of ICBM currently being carried aboard US submarines)
do just that.

Once launched a Trident, using a camera, gets a fix on a single specific star.
It then uses the data on that star's position to correct for any errors in its
internal guidance system.

See:
[https://en.wikipedia.org/wiki/Trident_(missile)](https://en.wikipedia.org/wiki/Trident_\(missile\))

~~~
ju-st
There are also star trackers in use by spacecrafts.

[https://en.wikipedia.org/wiki/Star_tracker](https://en.wikipedia.org/wiki/Star_tracker)

------
joshuaheard
I'm surprised they gave it up. It is still best practice in yachting to have
at least one crew member on an ocean crossing be able to do celestial
navigation. You can't count on electricity, and thus GPS, so you have to
return to the basics as a backup.

~~~
Perdition
On a modern naval vessel if you lose all the electronics the ship is going to
be drifting anyway.

Still it seems smart to keep the skill around as the GPS system can be locally
jammed and in WWIII could be completely knocked out.

~~~
zappo2938
Maybe not. Marine diesel engines can run without the computers attached using
mechanical throttles. There has been instances where the yacht's wheelhouse is
flooded with water and all the navigation computers and electronic controls
are lost. The captain and mate stationed in the engine room coordinate by
controlling the manual throttles on each engine. Move one throttle more to
turn.

~~~
scrumper
Depends on the ship of course, but this wouldn't have worked on at least one
of the naval vessels I've visited. Common on newer ships are electric drives,
where diesel or gas turbine engines are connected to generators instead of
prop shafts.

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csense
Isn't the GPS signal fairly low-power, and thus, trivial for an enemy to jam?

Or would they have to get their jammer close enough to be in range of the
ship's guns (and presumably its loud radio broadcasts would give away its
position)?

~~~
tonyarkles
Apologies for the brevity, I'm on a tablet with an annoying keyboard.

There's two things that make GPS trickier to jam:

\- it's spread spectrum with relatively hign coding gain. The signal itself is
pretty much imperceptible above the noise floor until you phase lock onto the
signal and despread. A really effective jammer would likely need to send out a
similar but corrupted signal, not just noise.

\- we know where the signal will be coming from. First that it will be coming
from the sky, and once we have a copy of the almanac, we've got a pretty good
idea where in the sky each SV will be. Directional antennas could further
mitigate the jamming.

You're not wrong about it being jammable, but it's not trivially simple.

p.s. (because kb sucks) While the spreading codes for the civilian signal are
commonly available and could be replicated in a jammer, the military spreading
codes are not available. A well-funded adversary might be able to get ahold of
them anyway, but it'd take some effort/treason.

~~~
jessaustin
I'm sure you're correct, but this account seems to contradict all the horror
stories we heard about LightSquared a few years ago. Is the explanation simply
that civilian GPS uses crap radios and military GPS does not? I always sort of
felt sorry for LightSquared, because they were obviously victims of regulatory
capture.

~~~
tonyarkles
I just read through the LightSquared story and am pretty intrigued!

One of the fascinating demonstrations of the fact that GPS is relatively
interference robust is that Galileo (ESA GNSS system) runs on the same
frequencies as GPS; the different spreading codes mean that receivers can
choose which signal to listen to.

Reading about the LightSquared system though, they do talk about a quite real
concern: overloading the receiver's frontend entirely. That's one of the
concerns that would be addressed by using directional antennas (if you're
receiving interference, rotate your antenna so that the source is in an
antenna null). As far as I know, most civilian receivers wouldn't have a
directional antenna, they'd have an omni so that they work in any orientation;
it'd suck if your iPhone could only receive GPS signals if it were sitting
flat. On a military vessel, it'd make a lot more sense to mount an upward-
cone-looking antenna high up on a mast to avoid sources of surface
interference.

I'm super curious now though! I've got a software GPS receiver set up, I'd
like to try injecting noise into the (virtual) signal chain and see how much
noise power is necessary to lose lock. If anyone's curious, GNSS-SDR works
great with $20 RTLSDR radios: [http://gnss-sdr.org/source-code](http://gnss-
sdr.org/source-code)

Edit: I did a bit more research, and it sounds like overloading the front-end
is the most common approach to jamming. People are turning on multi-watt
transmitters in their vehicles (e.g. to block fleet management GPS from
detecting their location). Despite the amount of power they're putting out,
they seem to be limited in range to around 50 feet.

It's also pretty satisfying to see
[http://www.novatel.com/assets/gajt/pdf/gajt-white-
paper.pdf](http://www.novatel.com/assets/gajt/pdf/gajt-white-paper.pdf) which
indicates that the solution I came up with (directional antennas with nulls
pointed at the interference sources) is a solid strategy for mitigating
jamming.

------
DrJokepu
Do commissioned officers actually do any navigation at all? I understood that
this is mostly done by enlisted quartermasters (QM) an navigation electronics
technicians (ET).

~~~
Nrsolis
You bet they do.

Commissioned officers are responsible for the boat and the crew. That doesn't
mean that they do all the work, but they are responsible for making sure it's
done correctly and getting it done correctly if the crew can't. They are also
responsible for training the crew to the highest standards.

Source: spent two years at the Naval Academy and one tour on a nuclear
submarine during the summer.

------
gchadwick
I wonder if they also asked trained officers to do regular practise? The
theory behind celestial navigation is fairly trivial (I've almost forgotten it
all but give me an alamnac and an hour and I'm confident I'd work it all out).
The successful use of a sextant for a decent fix however requires training,
practise and regular use to keep your skills sharp.

~~~
Tepix
Moxie Marlinspike's documentary "Hold fast" (2010) [1] inspired me to learn
how to use a sextant. Most of the sextants you can get on eBay these days are
just for decoration, however.

[1] "Hold Fast: Stories of maniac sailors, anarchist castaways, and the voyage
of the S/V Pestilence..."
[https://vimeo.com/15351476](https://vimeo.com/15351476)

~~~
Luc
> Most of the sextants you can get on eBay these days are just for decoration,
> however.

Ugh, these things are a plague. There's a factory in India pumping out most of
these. They do a whole bunch of variations, boxes, antiquing, etc. Some
sellers on eBay list them as genuine antique instruments, which is straight up
deception.

The replicas of box sextants (small pocket instruments in the shape of a round
box) are especially hard to spot if the seller is dishonest.

------
yread
RYA Yachtmaster course requires celestial navigation and some schools even
require candidates to perform the navigation on the qualifying passage (couple
hundred nm) without GPS.

~~~
gchadwick
It's the Yachtmaster Ocean, and as far as I know you're allowed to use GPS on
your qualifying passage you simply have to take some sights whilst on passage
to present to the examiner. I think they also allow for cloudy weather
preventing any sights from being taken and allow you to present some from
another trip.

There's some controversy there too as to whether it should be left in the
syllabus. Personally I think it's a nice thing to do, there's something very
pleasing about producing a fix especially when you do fun things like
producing a running fix from sun and moon sights.

~~~
Robadob
> I think they also allow for cloudy weather preventing any sights from being
> taken

Is there not a modern equivalent of the medieval 'sun stone'?

[https://en.wikipedia.org/wiki/Sunstone_(medieval)](https://en.wikipedia.org/wiki/Sunstone_\(medieval\))

~~~
sethrin
Knowing the direction of the sun to within a few degrees is unlikely to help
much. For one thing, you have no other "fix", and for another, an error factor
of a few degrees probably represents an error of a few hundred (nautical)
miles. You should probably read a bit more about celestial navigation to
understand the problem.

------
SCAQTony
I am presuming an even darker scenario. GPS signals would not be jammed by the
enemy but rather satellites would be obliterated wholesale as a result of a
limited nuclear exchange. Thus sailing the old fashion way: Sextant, watch,
and maps are the only way home.

~~~
JulianMorrison
Or Kessler Syndrome. Deliberate or otherwise.

~~~
simonh
Kessler Syndrome is mainly a Low Earth orbit issue. GPS sats are at 20,000 km
altitude so aren't particularly vulnerable to it. They're probably far enough
away to not be vulnerable to EMP either, unless someone were to lob a nuke out
pretty far.

------
VLM
One interesting side effect of learning celestial nav is you can't avoid
learning some astronomy and keeping up to date on the night sky.

Another side effect is its a filter on people who can't handle math or can't
handle complicated written procedures. Its unclear how important that is, but
it is clear its a very good filter if you value those skills for other
reasons.

With respect to situational awareness, its very easy to own a GPS while
confusing that attribute of ownership with understanding where you are, but
its very hard to mentally do celestial nav without understanding where you
are, what are the present sea and weather conditions. Also there is a
difference between merely owning a (possibly GPS accurate) clock or
chronometer and understanding what time it is. "I own things that could
provide accurate 4 dimensional situation, were I to actually understand the
outputs" is a lot different from "I can perform extensive labor and
calculations with the result of being deeply aware of my 4 dimensional
situation"

~~~
dfc
> its a filter on people who can't handle math or can't handle complicated
> written procedures.

Do you think that the USNA admissions process and or the Academy's graduation
requirements do not provide an equivalent filter?

~~~
VLM
Conversely if the upstream filters are working, then its not going to hurt
anything to implement, is it?

I agree its a much more useful discriminator for civilians than naval officers
or professional sailors.

------
dctoedt
I sort-of learned celestial navigation during Navy ROTC training 40 years ago.
I remember the Nautical Almanac being something of a pain to work with. It
would have been so nice to have the modern-day mobile-device apps that will
take the sextant data and do the table-lookup number crunching.

~~~
tribe
Even with a mobile app, it may still be worth knowing how to navigate the old
fashioned way. I would imagine that books / hand calculations are more
resistant to power failure than apps and GPS are.

~~~
chiph
Or in the case of military applications, proof against EMP.

~~~
Nrsolis
On my boat, we still did firing solutions for torpedoes using a slide ruler.

The military is quick to embrace new technology but slow to completely rely on
it to the exclusion of other methods. The great fear is that technology will
let you down at a critical moment via failure or damage. That's why they teach
the old methods alongside the new ones.

~~~
chiph
Agree. When I was in the USAF, we had micro-processor controlled communication
systems, but also still had the 1950's Teletypes as backups. Running a war at
75 baud...

One time we bolted some backpack straps to one, painted it camo, and called it
our Tactical Teletype. The joke was that it was 350 pounds of steel parts and
electric motor...

~~~
knodi123
I wonder if modern fighter pilots still need to learn old NDB and ADF radio
beacon navigation? In a modern jet, I assume that if your computer-aided nav
systems are non-functional, the plane is probably non-functional as well?

~~~
chiph
In a fighter, the cockpit is too cramped and the weight/balance figures too
tight to allow for backup nav systems, other than a compass. With it, they
could drop down and follow a road or power-line home (at the expense of
greater fuel consumption and exposure to hostile ground fire). But if they
still have an operating radio, they'd probably call air traffic control or an
E-3 Sentry for directions. Larger planes like the B-52 might still have their
radio beacon equipment installed.

~~~
knodi123
What I was asking, though, was do the pilots still have to learn it?
Considering the limitations we both pointed out, I wonder if it has been
removed from ground school and basic pilot instruction.

~~~
Nrsolis
You always learn the basics. I've not been USAF but you're always taught the
"hard" way or "old" way before they teach you the "new" or "easy gizmo" way.

How _long_ you spend on the topic and whether you have to prove proficiency is
a different question.

------
w8rbt
This is also why non-network based communication backups are important. HF
radios, NVIS and Morse Code are very efficient and effective when network
packets are not flowing.

------
hackuser
My impression, based on very limited knowledge, has been that inertial
navigation was the backup to or even replacement for GPS. Does anyone know
more about it?

------
moosetafa
Now, if the Navy wanted their sailors to be truly hardcore navigators and be
totally immune from cyber hacking, they'd have them use an abacus for
calculations rather than a calculator or computer.

~~~
tonyarkles
Slide rule... we're not cavemen!

