  As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray
Observatory enters its fifteenth year of operation on orbit, it continues to
perform well and produce spectacular scientific results. The response of ACIS
has evolved over the lifetime of the observatory due to radiation damage,
molecular contamination and aging of the spacecraft in general. Here we present
highlights from the instrument team's monitoring program and our expectations
for the future of ACIS. The ACIS calibration source produces multiple line
energies and fully illuminates the entire focal plane which has greatly
facilitated the measurement of charge transfer inefficiency and absorption from
contamination. While the radioactive decay of the source has decreased its
utility, it continues to provide valuable data on the health of the instrument.
Performance changes on ACIS continue to be manageable, and do not indicate any
limitations on ACIS lifetime.
