Re: SPS/Pulsars

On Mon, 25 Feb 2002, K.H.Ranitzsch wrote:

> > > ----- Original Message -----
> > > From: "Indy" <kochte@stsci.edu>
> > > Well, if the beacons imitate specific real pulsars in their
frequencies
> and
> > > repeat patterns, they could, at least over a limited volume, be
made
> > > indistinguishable from the real ones and make navigation
difficult. Lots
> of
> > > similar cases from fake lighthouse to electronic warfare.
> > >
> > > But the time lag seems a serious problem.
> >
> > That and how do you disguise the real pulsar so it isn't picked up?
> 
> Not really neccessary. If you have one fake, he has 50% chance of
picking
> the wrong one. Make you beacon appear stronger than the pulsar, and
the
> electronics may be dumb enough to go for the wrong one 90% of the
time.

I'll give you that. However...you have to make some assumptions as to
how space nav algorithms would work (unless you do the "cheapest bidder
did your nav design", then you are only going to pick 3 known pulsars
;-).
I would imagine (however wrong this may be) that space nav systems would
(should!) take in as many pulsars as possible for a firm fix of
position,
not just three (that leaves you more vulnerable to potential spoofing
attempts). But maybe it's just me. Maybe the NAC sold out to the
cheapest
bidder and shoot for 3.  ;-)

> > Moreover, I would think that unless you have rearranged where the
pulsars
> > are in space completely, a savvy nav officer is going to pick up on
> > any discrepencies when correlating to other known pulsars. With
hundreds
> > to choose from, how do you know which ones will be picked for
spatial
> > location purposes?
> 
> Right, this would make spoofing hard.
> On the other hand, if he doesn't know where he is, how much
correlation can
> he do to find out where he is ?

Actually, quite a lot. Depends on how many pulsars (and other
astronomical
objects) the nav officer opts to use to fix the ship's location.

> > Fake lighthouses and e-warfare operate in a much tighter realm than
> > that of using pulsars. It's that distance thing you have to overcome
> > when faking out a pulsar (and masking the real one; another daunting
> > task, I would imagine ;-)
> 
> But given the distances involved, even small errors might land you in
> entirely the wrong place.
> 
> Though I guess one would have to do the math to see whether it would
> actually work.

One could. I'm not. It'll be morning there first (already is,
in face - the wee hours). Have fun. I'll await thy results.  ;-)