Re: SPS/Pulsars

----- Original Message -----
From: "Indy" <kochte@stsci.edu>
To: <gzg-l@csua.berkeley.edu>
Sent: Monday, February 25, 2002 10:58 PM
Subject: Re: SPS/Pulsars

> "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.

> 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 ?

For a workable scheme, perhaps give priority to faking the locally
strongest
pulsars ?

> 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.

Greetings