[time-nuts] Satelles PNT from Iridium satellites

Mon Aug 10 03:41:12 UTC 2020

Hi  Taka,

 > On more broader sense, was GPS originally designed to provide timing 
service?

Yes, from the beginning GPS was a so-called PNT (Positioning, Navigation 
and Timing) system.

 > Or is it a byproduct of needing to measure location and speed, thus it
 > needed a constant signal, and that using it to sync reference signal
 > is just an ancillary and after-thought use cases?

Precise timing is not so much a by-product but the key feature that 
makes GPS work.

Here's some reading, with an emphasis on the early history and design of 
GPS:

"TIMATION - a GPS Predecessor Program"
https://directory.eoportal.org/web/eoportal/satellite-missions/t/timation

"Pre GPS History of Satellite Navigation", Francis M. Czopek
https://web.stanford.edu/group/scpnt/pnt/PNT08/Presentations/2_Czopek_PNT_2008.pdf

"True Origins and Major Original Challenges for GPS Success (1962 – 
1978)", Brad Parkinson
https://web.stanford.edu/group/scpnt/pnt/PNT09/presentation_slides/13_Parkinson_Creating_GPS.pdf

"Launching the Brick Moon: GPS’ path from the Space Race to Smartphone", 
Aaron Lovell
https://www.wilsonquarterly.com/quarterly/summer-2015-an-age-of-connectivity/launching-the-brick-moon-gps-path-from-the-space-race-to-smartphone/

"GPS Declassified: From Smart Bombs to Smartphones", Richard Easton
http://www.gpsdeclassified.com

"The Origins of GPS", Stephen T. Powers, Brad Parkinson
Article published in May & June 2010 issues of GPS World
https://www.u-blox.com/sites/default/files/the_origins_of_gps.pdf

"Initial Results of the NAVSTAR GPS NTS-2 Satellite", James A Buisson, 
Roger L. Easton, Thomas B. McCaskill
"General Relativity in the Global Positioning System", Neil Ashby
http://www.leapsecond.com/history/Ashby-Relativity.htm

/tvb

On 8/9/2020 6:33 PM, Taka Kamiya via time-nuts wrote:
> I've done some quick research.  I do not see timing as one of the services provided.  I wonder if it can be achieved by just listening into what's already transmitted (like GPS) and do some math on our side.
>
> On more broader sense, was GPS originally designed to provide timing service?  Or is it a byproduct of needing to measure location and speed, thus it needed a constant signal, and that using it to sync reference signal is just an ancillary and after-thought use cases?
>
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>   
>
>      On Sunday, August 9, 2020, 9:21:23 PM EDT, Bob kb8tq<kb8tq at n1k.org>  wrote:
>   
>   Hi
>
>
>
>> On Aug 9, 2020, at 7:03 PM, Tom Van Baak<tvb at LeapSecond.com>  wrote:
>>
>> Hi Stu,
>>
>> There's no problem with a semi-commercial posting here. You've been a member for a decade and frequent contributor plus the subject matter is exactly on-topic. So thanks for posting.
>>
>> I spent a while on your web site and didn't uncover a trove of white papers. If you could post some URL's that would be appreciated. You don't have to worry about being less accurate than GPS. I mean, there are often far more important factors than nanosecond precision.
> To that point ( as accurate as GPS ) ….. GPS is simply a convent comparison system. Saying that
> this or that is better or worse at this or that tau is *not* the same as saying it has more or less value.
> It’s simply a system that is out there to be compared to.
>
> Bob
>
>
>> You didn't mention pricing; it's hard to imagine it's as free as GPS so that seems like another disadvantage to me.
>>
>> Your comment about fewer satellites is spot on. That will be taken care of if you give SpaceX / Starlink a call and join that bandwagon. There are already 597 Starlink [1] satellites up there vs. 82 Iridium [2] satellites, yes?
>>
>> If you have entry-level / hobbyist grade evaluation kits I'm sure a number of us would be very interested to try it out.
>>
>> Thanks,
>> /tvb
>>
>> [1]https://en.wikipedia.org/wiki/Starlink
>>
>> [2]https://en.wikipedia.org/wiki/Iridium_satellite_constellation
>>
>>
>> On 8/9/2020 2:53 PM, Stewart Cobb wrote:
>>> Taka Kamiya and Forrest Christian both asked recently about the alternative
>>> satellite PNT system using the Iridium satellites. That system was
>>> developed by my company, Satelles. It has been commercially available for
>>> more than a year now.
>>>
>>> The biggest advantage is that our signal is at least 30 dB stronger than
>>> GNSS signals (the exact numbers depend on whether you're talking to
>>> engineering or marketing :). You can easily get a usable signal in deep
>>> jungle, or a data center in the middle of a building's basement, or even
>>> inside a locked shipping container. The stronger signal is correspondingly
>>> more difficult to jam or spoof than GNSS, and our signal has anti-spoofing
>>> features as well.
>>>
>>> The biggest disadvantage is that it is not quite as accurate as GPS,
>>> because there are fewer satellites in view at any given time.
>>>
>>> I don't want to quote exact timing numbers here, because they depend a lot
>>> on system integration details, but you can easily steer an OCXO within a
>>> few hundred nanoseconds of USNO time. With a rubidium, you can do
>>> considerably better.
>>>
>>> If you want to know more, our website iswww.satellesinc.com.
>>>
>>> (If this message has been too commercial, I apologize in advance. The
>>> boundary between information and salesmanship is not always sharp.)
>>>
>>> Cheers!
>>> --Stu
>>> _______________________________________________
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