United Launch Alliance

In an image that looks like a van Gogh painting, the Delta IV Heavy rocket launches on Saturday afternoon.

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After the space shuttle retired in 2011, the Delta IV Heavy became, by default, the world’s most powerful rocket. Standing 71.6 meters tall, fully 15 meters taller than the full space shuttle stack, the rocket built by United Launch Alliance can deliver up to 28.4 tons of mass to low-Earth orbit.

On Saturday, under splendid blue-and-white Florida skies, the rocket made one of its rare launches by delivering a spy satellite payload, NROL-37, for the National Reconnaissance Office into orbit. The agency has released no information about the satellite, but from the Delta IV Heavy’s use we can conclude that it likely was one of the spy office’s Advanced Orion satellites, which measure radio signals from the vantage point of geostationary orbit.

The Delta IV Heavy rocket has not flown since December, 2014, when it launched NASA’s Orion spacecraft into a two-orbit test flight around Earth, reaching a peak altitude of 5,800km. In its entire history since 2004, the rocket, which uses three common booster cores to power its ascent, has flown only nine times. One of the reasons the Delta IV flies so infrequently is its cost—up to about $400 million per flight.