SpaceX President Gwynne Shotwell said on Monday the company is still a couple of months away from returning the Falcon 9 booster to flight following the launch failure on June 28.

The investigation of the accident is taking longer than originally planned, Shotwell said during a panel discussion at the AIAA Space 2015 Conference in Pasadena. The company is doing a review of its supply chain.

The company has blamed the failure of a strut in the upper stage for the failure, which destroyed a Dragon cargo ship headed for the International Space Station.

The return to flight will feature the first test of the upgraded Falcon 9, which is being tweaked to improve its performance. Shotwell admitted this flight was keeping her up at night.

She said a customer has been identified for the return to flight but would not identify it.

Editor’s Note: I’ve been hearing reliable reports that something more than the strut was the cause of the accident in June. The last I heard, they were still trying to figure out exactly what happened.