[time-nuts] tube GPS receivers

[Bob Camp]

Hi

I'm not so sure that "slow" would work. With all the sat's moving various directions all the time, I suspect you need to do a solution fairly quickly. If you don't the stale data messes up the solution. Also you need the correlators to work fast enough to lock on to an essentially unknown code before the sat is out of view. 

Bob

On Jun 23, 2013, at 9:44 PM, Jim Lux <jimlux at earthlink.net> wrote:

> On 6/23/13 10:47 AM, Chris Albertson wrote:
>> Magnetic cores were not invented until the 1950's and realy cam into use as
>> tubes were beibg replaced by SS.  But there isnot reason yu can't build a
>> tube computer with core memory.   I have actually seen and used a computer
>> that had one megabyte of core memory.  The stuff was still in use in the
>> late 1970s   1MB was a lot of RAM in 1975.
>> 
> 
> Lots of rotating drum memory and acoustic delay lines were used back then.
> 
> I don't know that the whole GPS thing is very memory intensive anyway. You've only got a few dozen variables to work with, it's all in the math, but presumably you'd that as a parallel or pipeline implementation, rather than a ALU and memory.  It's not like you're going to be changing the algorithm often (e.g. the programming language is solder)
> 
> The almanac is a bit more of a challenge, but if you allow "externally supplied" that might make it easier.  But even that isn't all that big, 11 or 12 numbers times 32 or so spacecraft.
> 
> 
>> You can have very good reliability with tube circuits.  It was just that
>> few people wanted to pay for it.  Down time was cheaper.  It is not hard to
>> add redundancy to a circuit but it does have a huge cost multiplier effect.
>> 4x or 5x the price.
> 
> Not necessarily.  That is, your redundancy doesn't have to be something like triple modular redundancy.  You can do more efficient error correcting codes, use clever arithmetic, or make use of the fact that your computer can run faster than you need the computation to be done, so you can get temporal redundancy.  Serial computation can also be done.  Remember that the nav message is only coming in at 50 bits/second.
> 
> 
> 
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