[time-nuts] GPS disciplined Mars clock

jimlux jimlux at earthlink.net
Sat Jul 9 17:59:54 EDT 2016

On 7/9/16 1:40 PM, Joe Fitzgerald wrote:
> On 7/9/2016 3:00 PM, jimlux wrote:
>> TAI my friend, TAI...
> Hmm,  gravitational time dilation it might complicate things ...  I
> suppose it depends on whether your Mars clock is on the surface of Mars,
> Earth or somewhere else.
> On 7/9/2016 3:34 PM, Hal Murray wrote:
>> How good is the data on the rotation rate for Mars?  Is it good enough so
>> that they would need leap seconds?
> Without an ocean or significant atmosphere I bet the rotation rate would
> be more predictable than Earth - once good measurements were made.  The
> dearth of observatories on Mars suggests the current error bars on
> current rate estimates pretty wide.

I'd guess the rate estimate is quite good.  Wikipedia says
88,775.24409 seconds/sol

We can do very good ranging to MER and MSL.  Phoenix didn't carry a 
direct to earth transponder.

We can also do ranging from rovers to MRO, and then from MRO to Earth. 
I don't know how much ranging we've done at UHF, though.  The radio 
wasn't really designed for it, so the math gets a bit complex, and I'm 
not sure you can back out all the higher order terms.  The UHF radio on 
MRO does have a USO driving it, so it's timing performance should be 
quite good in "open loop record" mode.

The uncertainty in the MRO range & range rate is probably less than for 
the rovers, because the SNR is much better (big multi-meter antenna on 
MRO helps a lot).

> Fun to think about that's for sure.
> -Joe
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