[time-nuts] Spacecraft Timekeeping

[Magnus Danielson]

On 03/09/2011 03:15 PM, jimlux wrote:
> On 3/8/11 11:05 PM, Magnus Danielson wrote:
>> On 03/09/2011 06:08 AM, Kevin Watson wrote:
>>> 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.
>>
>> Why carry the dead weight of something unusable in orbit.
>>
>> Drop the receiver and antenna out of the equation and just provide a
>> timing signal on launch pad...
>>
>
>
> I'm going to guess that you want a GPS receiver on orbit for other
> reasons (like to know where you are, if your IMU or star tracker dies)

Notice his last sentence...

I agree that there are many uses for a GPS onboard a sat... and if one 
wants one it needs to handle the altitude, speed, different amount of 
atmospheric shift, etc. etc. etc.

But if he only wants a GPS for launch pad synchronisation and then 
reverts to other methods, it seems like dead weight to bring it all the 
way up.

Cheers,
Magnus