[ntp:questions] frequency adjusting only

David L. Mills mills at udel.edu
Wed May 14 19:33:54 UTC 2008


Evandro,

We didn't account for gravity and time dilation, as the errors in the 
extrapolated ephemeris data dominated the error budget. I am told 
accurate spacecraft navigation needs time to the nanosecond. In 
principle, the Proximity-I protocol and NTP onwire protocol can do that, 
I don't think the transceiver clocks and onboard rover clocks are 
anywhere near that caliber.

Dave

Evandro Menezes wrote:
> On May 4, 2:37 pm, "David L. Mills" <mi... at udel.edu> wrote:
> 
>>On symmetry, etc. There are both gravitational and velocity corrections
>>relative to both Earth and solar system barycentric time amounting to
>>some 15 ms, but current space missions don't worry much about that. The
>>mission times are relative to a clock onboard the spacecraft; nothing
>>else matters. Our Earth-Mars simulations didn't worry about these
>>effects either. I suspect disciplining an orbiter/rover clock to these
>>corrections will be dominated by the frequency noise of affordable
>>oscillators. Maybe not.
> 
> 
> Just curious, but did you have to deal with relativistic effects of
> relative time dilation as the craft speed increased?
> 
> TIA




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