The US successfully launched a secret spy satellite on Sunday (24 September). The NROL-42 satellite was carried into space by an Atlas V rocket. The spy satellite is the latest addition to the fleet of satellites developed and operated by the NRO (National Reconnaissance Office).

Since NRO missions are classified, it is unclear what path the spy satellite's orbit will take and what kind of mission the spacecraft will be involved in while orbiting the Earth. It also remains uncertain as to how long the NROL-42 is slated to remain in orbit.

The NRO's mission patch for the spy satellite displays a grizzly bear, 10 stars and an impression of the Atlas V rocket ascending to orbit, Nasa Spaceflight reported.

"This launch is the culmination of many months of work by United Launch Alliance, the National Reconnaissance Office and the 30th Space Wing," Air Force Col Gregory Wood, 30th Space Wing vice commander at Vandenberg, said in a prelaunch statement. "All of Team Vandenberg is dedicated to mission success and proud to play a part in delivering these capabilities to our nation."

"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. "NROL-42 marks the 25th ULA-launched NRO mission, building upon our legacy of partnership with the NRO in providing reliable access to space for our nation's most critical missions."

ADVISORY: Vandenberg AFB @30thSpaceWing just successfully launched #NROL42 #AtlasV rocket. *May* have been visible. No need to call 9-1-1 — LAFD (@LAFD) September 24, 2017

The launch was reportedly visible to some residents of Los Angeles and other parts of California and sparked several Twitter users to wonder if the bright light in the sky was caused by a missile launch. The LA fire department tweeted out an advisory, alerting the public about the launch and advising them against calling the emergency response number 9-1-1.

Tonight's @ulalaunch #NROL42 #AtlasV launch as seen from La Crescenta, CA...a thing of beauty in the night sky pic.twitter.com/AAbf6XBP90 — Mike Seibert (@mikeseibert) September 24, 2017

The spy satellite marked the third NRO payload to be launched in 2017. Two more NRO missions are reportedly slated to be launched by the end of this year, with yet another satellite, NROL-52, expected to be launched via an Atlas V rocket in October.