BTW I thought about trying to somehow use `replicate` to avoid this hardcoding of the relevant attributes.  The problem here is that the `_delta_*` attributes should not be copied because they get invalidated by the arithmetic.  Thus you end up with a net gain of several lines of code, although that solution would be more future-proof to the addition of attributes in the future.  Something like this *might* work:
```
tai = self_time.replicate()
tai._time.jd1 = jd1
tai._time.jd2 = jd2
tai._time.scale = scale
tai._delta_ut1_utc = None
tai._detla_tdb_tt = None
```
Anyway, just thinking out loud.