From its ocean-based launch site located directly on the equator at 154 degrees West longitude, a Zenit-3SL launch vehicle will lift the Intelsat 21 spacecraft into an optimized geosynchronous transfer orbit on its way to its final geostationary orbit at 302° East longitude.
The Zenit-3SL rocket will begin its ascent phase of flight. The first stage of the vehicle will separate 2:30 minutes (150 seconds) after liftoff, and the protective payload fairing will be jettisoned 74 seconds later at 3:44 minutes. The second stage will conduct a 6 minute burn, followed by its separation from the Block DM-SL upper stage. The Block DM-SL will begin its first and only burn at 8:41 minutes (521 seconds) into the mission, for the duration of 696 seconds. The upper stage will then shut down for almost 10 minute coast period before spacecraft separation over equatorial South America.