If you were in Southern California on Thursday afternoon and happened to notice what looked like a skyscraper darting across the sky, you weren’t seeing things. That was the Delta IV Heavy Launch Vehicle, the largest rocket ever to launch from the West Coast.

Since the craft is 235 feet tall — roughly 23 stories — officials were worried that the force of the liftoff blast might break windows or spread earthquake fears in the area, the Los Angeles Times reported.

The launch took place at 1:10 p.m. Pacific time at Vandenberg Air Force Base in Santa Barbara County, near Lompoc.

The three-engine rocket is thought to carry a top-secret U.S. spy satellite, the Times said, that is “capable of snapping pictures detailed enough to distinguish the make and model of an automobile hundreds of miles below.”

It was the fifth launch of a Delta IV, AP reported; the four others were from Cape Canaveral in Florida.

Vandenberg launch preparations lasted for three years and cost $100 million, according to AP. The launch complex used to be configured for West Coast space shuttle launches, but those were canceled after the 1986 Challenger disaster.