Re: Pulsar Nav accuracy

hal@buffnet.net wrote:

> Hello Roger,
>   See, I'm getting confused myself...
> 
> 
> 
>>Let's see if I can  work my way through this.
>>
>>1.  I know the absolute locations of 3 pulsars (A B C).
>>
>>2.  Knowing two (A B) and their angles to my ship I know my
>>   location on the surface of circle.
>>
>>3.  Pick another pair (B C).	I get another circle.
>>
>>4.  Pick the remaining pair (A C).  Yet another circle.
>>
>>5.  Intersect the three circles.  I now know where I
>>   am.
>>
>>6.  For safety make it 6 pulsars and find the intersection.
>>
> 
> 
> Lets say for the sake of argument, that I attempt to take a bearing on
> Pulsar A.  I get that bearing.  At the same time, I have someone else,
or
> the computer take readings automatically) that gets the bearing on
Pulsar
> B.  For this "exercise" I have the bearings on both known Pulsars,
along
> with their *known* 3d co-ordinates.  From those two known
co-ordinates, I
> should be able to compute the third co-ordinate (my location).  This
is why
> I am confused as to why it should require more than *two* pulsars... 
Mind
> you, I'm not saying "exact" co-ordinates down to precision values, but
> general ball park at least.
> 
>	 Hal
 
Take a look at this diagram:

http://www.wombatzone.com/images/navexample1.gif

This is a side view of your ship.

You have two pulsars to take a reading from, Pulsar Red and Pulsar Blue.

You take a reading on Pulsar Red.  It is 45 degrees below the centerline
of your 
ship.  It is 0 degrees to the left or right of the centerline of your
ship.

You take a reading on Pulsar Blue.  It is 60 degrees above the
centerline of 
your ship.  It is 0 degrees to the left or right of the centerline of
your ship.

You attempt to determine your location.  As you can see, there are two
possible 
locations on this diagram (marked A and B) where Pulsar Red is 45
degrees below 
the ship and Pulsar Blue is 60 degrees above the ship.

Without a third point of reference, to tell you which way the ship is
pointing, 
there is no way to determine if you are at point A or B.  Even if you
know the 
distances from your ship to each pulsar, and the distance between the
pulsars, 
you could still be at either point.

Now, in actuality, the range of possible locations would be a circle of
all the 
points that lie such that Pulsar Red is 45 degrees below and Pulsar Blue
is 60 
degrees above.

--