[time-nuts] Spacecraft Timekeeping

Kevin Watson time-nuts at enuuf.com
Wed Mar 9 00:08:41 EST 2011

Hi All. Thanks for responding. There are quite a few GPS receivers that will 
work outside of the usual commercial-grade GPS limitations, but I'm not too 
sure I need such a receiver. As my application is to just accuratly time-tag 
messages for a data recorder, my thinking is to allow a ruggedized GPSDO to 
stabilize on the pad before launch, and then just before launch force the 
GPSDO into holdover mode and act as the PTP grandmaster for the onboard 
computers until we reach orbit. Once on orbit I have other means to 
synchronize the PTP grandmaster.


----- Original Message ----- 
From: "ehydra" <ehydra at arcor.de>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Tuesday, March 08, 2011 3:02 PM
Subject: Re: [time-nuts] Spacecraft Timekeeping

> There are is a list on a ballooner website with GPS devices working beyond 
> export rules.
> - Henry
> -- 
> ehydra.dyndns.info
> Magnus Danielson schrieb:
>> First thing to consider is that standard GPSes will not meet your needs, 
>> since they have to obey the height and speed limits for export rules.
>> The side-effect is that doppler frequencies may be much higher and both 
>> tracking and acquisition needs to include these more extremer doppler 
>> frequencies.
>> Use of PTP within a rocket or spacecraft may or may not be a good thing. 
>> NMEA + PPS may suffice and be less power-hungry. IRIG may also be an 
>> option.
>> If timing and frequency needs strict correlation with ground, relativity 
>> comes into play due to altitude alone shifts frequency.
>> Cheers,
>> Magnus
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