It was originally intended to defend troy, but a faulty slipspace drive kept it from making the jump. Instead it made it's way to Harmony where it was to make the slipsace drive repairs and aid the remaining Troy defenders. But before it's repairs were done, damaged ships slipspaced into the system. The remaining ships from the Troy defense force. Having to get ready for defensive actions faster than originally planned, the Celestia was unable to finish slipspace drive repairs.