Abstract:
Extremely Large Telescopes (ELTs) have precision requirements of a few tens of micro-arcsec for differential
astrometry science cases. Each ELT project has its own astrometric error budget taking into consideration the
specific design parameters of the observatory. A version of the Thirty Meter Telescope (TMT) astrometry error
budget has previously been established and the details were presented at SPIE 2016.1
In this paper, we briefly
revisit this error budget analysis. The main focus of this paper is a new python-based astrometry calculator
which was developed for a more user-friendly application of the error budget. It facilitates direct evaluation of,
and comparison between different scenarios such as absolute vs differential astrometry; dense vs spare observation
fields; science fields with and without reference objects, etc. The details of the astrometry calculator and its
general functions are described. A few example science sensitivity studies are presented and the procedure of
estimating astrometric errors for other observatories is outlined.
