  We describe the HST ACS Coma cluster Treasury survey, a deep two-passband
imaging survey of one of the nearest rich clusters of galaxies, the Coma
cluster (Abell 1656).
  The survey was designed to cover an area of 740 square arcmin in regions of
different density of both galaxies and intergalactic medium within the cluster.
The ACS failure of January 27th 2007 leaves the survey 28% complete, with 21
ACS pointings (230 square arcmin) complete, and partial data for a further 4
pointings (44 square arcmin).
  Predicted survey depth for 10 sigma detections for optimal photometry of
point sources is g' = 27.6 in the F475W filter, and IC=26.8 mag in F814 (AB
magnitudes). Initial simulations with artificially injected point sources show
90% recovered at magnitude limits of g' = 27.55 and IC = 26.65. For extended
sources, the predicted 10 sigma limits for a 1 square arcsecond region are g' =
25.8 mag/sq. arcsec and IC = 25.0 mag/sq. arcsec.
  We highlight several motivating science goals of the survey, including study
of the faint end of the cluster galaxy luminosity function, structural
parameters of dwarf galaxies, stellar populations and their effect on colors
and color gradients, evolution of morphological components in a dense
environment, the nature of ultra compact dwarf galaxies, and globular cluster
populations of cluster galaxies of a range of luminosities and types. This
survey will also provide a local rich cluster benchmark for various well known
global scaling relations and explore new relations pertaining to the nuclear
properties of galaxies.
