On 1/9/15 4:57 PM, Henry Hallam wrote:
Such slewing solutions are OK for Google. They wouldn't work well for one of the systems I work with, which uses system time to calculate the position of a LEO satellite for purpose of pointing a 7.6 meter X-band dish. Half a second of error corresponds to a pointing error of 0.5 degrees, well outside the main lobe of the antenna beam.
Which is why we use TAI in the space business and don't fool with this "Greenwich Mean Time" or "Coordinated Universal Time" which is discontinuous and potentially non-monotonic.
We DO need to compensate for the earth's varying rotational speed, though, but that's just handled as a separate model for deep space, or for LEO, where the coordinate system is Earth Centered, absorbed into the spacecraft orbital elements.. nobody is going to use 1 year old ephemerides)
I do find myself explaining exactly WHY we can't just use PC system time, etc. and periodic leap seconds are an object lesson in why not.
(or, you can arrange to not being doing any operations at the moment of leap...that's been done too)
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