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Hi Fred:

On 4 October 1957 when Russia put up the Sputnik some folks at Johns
Hopkins figured out it's orbital parameters by studying the doppler
shift of it's "beep beep" signal.  This gave them the idea that if a
satellite were to transmit it's orbital parameters then someone on the
Earth's surface could figure out where they were (i.e. Navigation).  The
Navy needed a way to update the INS system on boomer subs and TRANSIT
came into being.  http://www.pacificsites.com/~brooke/electron.shtml#Sputnik

The problem with transit was that you need a lab grade local oscillator
in the receiver, making the receiver expensive.  When GPS was developed
it was designed so that a low cost oscillator would work.

Although the Gulf War era Small Lightweight Gps Receiver (SLGR) made by
Trimble doesn't have as impressive a channel count as the more modern
Precision Lightweight Gps Receiver (PLGR) it does have amazingly good
performance and in some ways is superior to the more modern receivers.
Specifically the SLGR family uses a memory keep alive system so that all
of it's RAM acts as ROM when the unit is powered off.  This way at power
up the receiver immediately starts looking for sats.
http://www.pacificsites.com/~brooke/Trimpack.shtml
http://www.pacificsites.com/~brooke/PLGR.shtml

In contrast all the current versions of the PRC-112 survival radio that
have both GPS and beacon capability can not send a position message
until after the pilot has been on the ground for about 15 minutes.  It
would be much better if the radio had a keep alive memory, like the
SLGR, so that it would immediately start tracking when turned on, say
prior to bail out.

Have Fun,

Brooke Clarke, N6GCE

--
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



Fred Hebard wrote:

> GPS integrated into munitions in a significant way only debuted in the
> Afgan War.  In the first Gulf War, the cruise missiles were still
> guided by terrain maps pre-programmed into their memory; it was a big
> hassle both to get the Gulf terrain data and then to load them into the
> guidance systems.  It also was ironic that the down-grading of GPS
> accuracy for civilian use was turned OFF during the first Gulf War
> because the military did not have enough receivers capable of decoding
> the more precise info and had to resort to civilian sets.
>
> There was a recent article on the development of GPS in American
> Heritage's journal, "The History of Science and Technology."  There
> also may have been a separate article on the Navy's Transit system.  As
> I recall, imperfectly, basic navigation was the initial impulse for
> both systems; Transit was a Navy initiative and GPS an Air Force.  I
> very vaguely recall that Transit was used for submarine-launched ICBMs,
> but I believe these were not targeted at hardened sites because of
> their inaccuracy in comparison to land-based missiles.  That inaccuracy
> may have been decreased in the 80s.
>
> Fred
>
> On Jan 5, 2005, at 10:33 AM, Charles Seitz wrote:
>
>> I was told the Army Pershing intermediate range missile employed a star
>> tracker to trim the trajectory.  The Pershing warhead section that I
>> saw was
>> marked secret so I didn't get a
>> chance to examine it closely.
>>
>>
>> ---  CHAS
>>
>>
>> ----- Original Message -----
>> From: "Trevor J. Kenchington" 
>>
>>> The reason for wanting an accuracy better than 100 metres with a
>>> thermonuclear warhead is for when you aim to crack the hardened silo
>>> in
>>> which the other guy's ICBM is (if you are lucky) still waiting to be
>>> fired at your now-empty silo. Outside of the circle of those who
>>> really
>>> know (but won't talk), it is widely supposed that that needs extreme
>>> accuracy.
>>
>
>

   

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