NavList:

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Frank. The fact that you even came up with this notion makes me wonder if you are a diabolical super-villain in the making.

 

I have to agree with Brad. I buy my NA from the US Gov't publishing office and it is therefore hard to break that chain of custody.

 

That being said, I think spoofing the NA would have to be subtle but you would also need your own publishing and printing equipment to reproduce an NA that would be physically identical to the real thing.  How would I do it?  Just off the top of my head, I would reverse the declination of all of the celestial bodies and for good measure, add or subtract about 2 - 3 degrees to/from each. If I wanted to go the whole way, I would also alter the GHA by several degrees.

 

As Brad has correctly pointed out, these changes would have to be done incrementally; in such a way that the ephemeris data for the start of the trip is correct and subsequent data would be degraded as the days wear on.

 

Now you have to have a team of black-suited Ninjas to get into each and every yacht to switch out the NAs. And to do that, I would set up a large celebratory banquet for the racers in order to get them all away from their yachts so that my Ninja team can do their dirty deed.

 

You mentioned that our perspective sailors only have a working knowledge of nautical astronomy so I would -- as the maniacal villain -- hope that they would not detect the subtle changes and presto: they are sailing towards oblivion.

 

This is just off the top of my head. I have not actually done any calculations to see what would be the effect of my mischief.

 

But again, this would require one to have access to appropriate publishing and printing equipment.

 

A very interesting concept Frank, or should I refer to you as "Snidely Whiplash"?  Bwaahaahaa!

 

Robert

----- Original Message -----

From: Brad Morris

To: enoid{at}northwestel.net

Sent: Friday, August 02, 2013 9:51 PM

Subject: [NavList] Re: Spoofing celestial navigation

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1) I buy my NA directly from the government publishing office.  Others may do so too.  Awfully hard to break that chain of custody at the Post Office to my door.
2) Suppose you did have a bogus Nautical Almanac.  You would get 'unusual' results, which may cause you to compare your NA with others, leading to discovery.
3) In order for the 'dastardly' plan to work, you would have to cause significant change such that landfall sight would be eliminated.  That's a big change, requiring either a single jump in the data (which would be self evident when detected) or an entire offset in the bogus NA (which would be self evident at the start of the race, because the know point of departure would not agree with the first celestial observation.
4) Of course, you say, it could be right at the start of the trip and meander away from the truth incrementally until at the end it was significantly wrong.  While feasible, its just not practical for pirating or for military purposes, ala GPS spoofing.

Sadly, I just don't think that's a practical way to spoof celestial. 

How about spoofing the time signal?  Just provide a stronger radio time check than the real one at the appropriate frequency (to swamp the true signal) and shift the time.  That will do it.

Brad

On Aug 2, 2013 8:56 PM, "Frank Reed" <FrankReed{at}historicalatlas.com> wrote:

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We joked a bit a few days ago about spoofing celestial navigation. But now I would like to propose a (slightly) more feasible scenario...

Let us suppose that some wealthy yachtsmen are prepared to race by sailing vessel from Hawaii to Tahiti using only traditional twentieth century celestial navigation and necessarily also traditional dead reckoning. The teams will race with absolutely no access to GPS and in complete radio silence except in the event of an emergency. They can, of course, see all the traditional signs of the ocean. Let's assume we know the date of departure. Make it tomorrow, August 3, 2013 for a specific. And let's assume that they take their departure (last clear sight of land at a known distance) from the southernmost tip of the Big Island. From there they will sail to Tahiti using only DR and celestial. The race is fair, but you are a diabolical super-villain wannabe --a teenage "hacker"-- with a need to embarass the wealthy captains of the yachts. So by a little trickery, you will arrange to "spoof" the celestial navigation and send them to Easter Island instead of Tahiti.

Both GPS and celestial navigation depend on data from "on high" that is largely out of the navigator's control. Data which the navigator must accept, more or less as a matter of faith. In the case of GPS, that is obvious: it is the signals themselves. For celestial navigation, that data which the navigator must trust as a matter of faith is, of course, the Nautical Almanac (and its equivalents). And that is our target. SPOOF the Nautical Almanac!

Could you do it? How would you modify the data in a counterfeit almanac to send these racing yachts to the wrong corner of the vast Pacific Ocean? How well would this subterfuge work? How might they detect that something is wrong? To be fair to the spirit of the challenge, you can assume that these navigators are not rocket scientists. You can assume that they are skilled and confident and equipped with excellent sextants and chronometers, but they have only a "working knowledge" of nautical astronomy.

I think this trick could be pulled off at a cost of less than five thousand dollars. So why didn't anyone try this in the long history of celestial navigation?

-FER

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