[time-nuts] Spacecraft Timekeeping

Chris Albertson albertson.chris at gmail.com
Tue Mar 8 19:41:02 UTC 2011


On Tue, Mar 8, 2011 at 9:57 AM, Kevin Watson <time-nuts at enuuf.com> wrote:
> Hi Jim,
>
> As part of my research into keeping time on rockets and spacecraft, I joined
> this list to see what I could learn from the masters. Of course I'm a
> knuckle-head for not assuming that you'd be one of the resident masters
> <grin>. Anyway, as my accuracy needs are modest (~10uS across many onboard
> computers), have access to GPS most of the time and don't really need to
> worry about relativistic effects (yet, anyway <grin>) or radiation effects
> (due to redundancy), I thought I'd use a GPSDO that can handle a decent
> amount of holdover and then use PTP to distribute time across the vehicle.
> Do you, or anyone else, have a recomendation for the GPSDO? Jackson Labs'
> (http://jackson-labs.com/) DROR seems like it might work, but I wonder if
> there might be better alternatives.

Off hand I'd worry a little about vibration.  How do crystals work
when being shaken with huge amount of mechanical and acoustic energy
during launch?

Cooling.  Almost all commercial off the shelf gear depends on air and
has a maximum altitude at which it will operate.  Off gassing might be
a problem too if there is flux left on the PCB or even fingerprint oil
leftover from assembly.

PTP is a new and not so mature technology so you will need to
characterize it on your own and likey port it so the specialized
processors you use your self


-- 
=====
Chris Albertson
Redondo Beach, California




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