NROL-45 US secret satellite launch
The National Reconnaissance Office launched a secretive satellite into orbit with a classified missionSeti Institute

The US military has launched a secret satellite into orbit this week and nobody, apart from those involved, knows exactly why or what its purpose is. The classified satellite, called NROL-45, took off from the Vandenberg Air Force Base in California under the cover of darkness at 3.40am local time with the simple mission explanation that it will "support national defence".

Details on its mission are unknown as well as what payload the satellite is carrying but a clue as to what it might be doing up there is its name. The NRO stands for National Reconnaissance Office and, as the name suggests, its business is in keeping an eye out. In fact, it's the US government intelligence agency set up in 1961 that has been responsible for building and operating spy satellites, with multiple reconnaissance satellites already in orbit.

With the motto "vigilance from above" it's likely the NROL-45 will be yet another set of eyes in the sky for the US military's defence department in the form of radar but as to what or who it's looking at will be top-secret information.

However, website Nasaspaceflight.com reported on the launch and theorised to a possible orbit destination and purpose for NROL-45:

"Because it is launching from Vandenberg, Wednesday's mission can immediately be assumed to be targeting a highly-inclined orbit. Navigation warnings in effect at the time of the launch suggest that the rocket will fly to the south-west.

"Recent NRO launches from Vandenberg have targeted sun-synchronous orbits for optical imaging, highly elliptical orbits for signals intelligence (SIGINT) satellites and low Earth orbits for ocean surveillance and radar imaging spacecraft."

It goes on to refer to the NRO's three other radar imaging satellites currently orbiting Earth as part of an imaging programme – the same one Edward Snowden leaked – and suggests this launch could be the fourth satellite of the recon mission.

Watch the skies.