The Chandra X-Ray Observatory is about to start its 10th year of operations. Over the time of the mission, the Science
Operations Team, ACIS (Advanced CCD Imaging Spectrometer) Operations group, has participated in spacecraft
command load reviews. These reviews ensure the spacecraft commanding is safe for the instrument and the ACIS
configuration matches the planned observation. The effectiveness of spacecraft command load reviews for ACIS
depends on the ability to adapt the software as operations change in response to the aging of the spacecraft.
We have recently rewritten this software to start incorporating other spacecraft subsystems, including maneuvers and
hardware commanding, to ensure the safety of ACIS. In addition, operational changes that optimize the science return of
the spacecraft have created new constraints on commanding.
This paper discusses the reorganization of the code and the multiple changes to the philosophy of the code. The result is
stronger, more flexible software that will continue to assist us in protecting ACIS throughout the Chandra mission.
The gain of the Advanced CCD Imaging Spectrometer (ACIS) instrument has changed over time since the
Chandra X-ray Observatory launch in July 1999. The calibration and data analysis teams have addressed this
issue, but it has only been recently that the operations team has examined how the commanding of the instrument
could be altered to partially compensate for these changes. This paper will address the changes in the gain, the
impact on science data and the changes the operations team has considered to improve the science return. We
also discuss the restrictions imposed by the commanding software on our response.