Clouded in secrecy, a Delta IV-Heavy rocket (the world's most powerful) on June 11 lofted into orbit a massive 5,200 kilogram Mentor or Advanced Orion spy satellite analysts say is now the largest satellite ever placed into orbit.

This spy satellite with the designation NROL-37 blasted-off from Cape Canaveral, Florida aboard a United Launch Alliance Delta IV Heavy rocket at 1.51 p.m. The U.S. government only said the satellite was launched "in support of national defense."

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Apart from not commenting about the satellite, the government cut a live feed of the launch after some six minutes to maintain the payload's secrecy. The manufacturer or manufacturers of Advanced Orion also remain unknown.

What observers do know is that NROL-37 is an Orion, otherwise known as Mentor or Advanced Orion, which is a class of U.S. spy satellites that collect signals intelligence (SIGINT) from space. NROL-37 will enter its designated geostationary orbit over the Equator in a few days.

NROL-37 or Mentor 6 is operated by the secretive National Reconnaissance Office (NRO) that designs, builds and operates all U.S. reconnaissance satellites. NRO provides the SIGINT collected by its satellites to the National Security Agency, which is responsible for the U.S.' global SIGINT effort.

NROL-37 was developed with input from the Central Intelligence Agency (CIA).  It is the sixth Advanced Orion spy satellite launched from Cape Canaveral since 1995. The last Advanced Orion spysat orbited was NROL-32 in November 2010.

At the time of its launch, NROL-32 was also "... the largest satellite in the world," according to former NRO director Bruce Carlson. Carlson was referring to the spysat's enormous 100 meter diameter main antenna.

On the other hand, the main antenna of NROL-37 is most likely larger, making this spysat the largest satellite ever placed in orbit. The Advanced Orion satellites are so huge they look like stars when viewed through telescopes. One of these satellites, NROL -26 launched in 2009 is as bright as a magnitude +8 star.

Advanced Orion intercepts electronic signals from ships, aircraft, ground sources and other satellites. Analysts believe these signals are processed aboard these spysats, encrypted and transmitted back to NRO.

Delta IV-Heavy has only flown nine times since 2004. Three of these flights have been for the NRO, as far as is known.

TagsDelta IV-Heavy, Advanced Orion spy satellite, NROL-37, National Reconnaissance Office