International Launch Services (ILS) has delayed the launch of SES Americom’s AMC-15 communications satellite to perform additional tests on the Russian-built Proton launch vehicle, ILS announced Sept. 9.

The spacecraft was slated to launch from the Baikonur Cosmodrome in Kazakhstan Sept. 23, but engineers want to do additional checks on the avionics subsystems aboard the vehicle’s Breeze M upper stage, ILS said. The subsystem is being returned to the manufacturer, and a new launch date will be set after the testing is completed.