Atlas 5 prepares to launch the NROL 42 payload on Sept. 23, 2017. Photo: ULA.

United Launch Alliance (ULA) successfully orbited a classified satellite for the National Reconnaissance Office (NRO) on Saturday, Sept. 23 from California’s Vandenberg Air Force Base. According to NRO, the mission, dubbed NROL 42, is in support of national security, but the true purpose of the payload remains a mystery.

The payload launched aboard an Atlas 5 Evolved Expendable Launch Vehicle (EELV), which includes a 5-meter payload fairing and four solid rocket boosters. An RD Amross RD-180 engine powered the Atlas booster for this mission, and an Aerojet Rocketdyne RL10C engine powered the Centaur upper stage.

This successful launch marks ULA’s sixth this year. NROL 52, ULA’s next mission, will launch another payload for the NRO on Oct. 5 from Cape Canaveral Air Force Station in Florida.

“Congratulations to the entire team for overcoming multiple challenges throughout this launch campaign. From Hurricane Irma schedule impacts to replacing to a first stage battery this week, the team maintained a clear focus on mission success,” said Laura Maginnis, ULA vice president of government satellite launch.