The $1 billion satellite is the sixth and final one in the U.S. military's Advanced Extremely High Frequency series.
"Liftoff!" came the call at T-0 minutes, and then ... nothing.
Sunday's failure came after two failed launches of the Payam and Doosti satellites last year.
The SDA is on track to become part of the Space Force the same year it plans to launch a series of tracking satellites.
Early warning capabilities helped protect U.S. troops on the ground.
SpaceX launched 60 more mini internet satellites late Monday, this time testing a dark coating to appease stargazers.
The satellite — called Icon, short for Ionospheric Connection Explorer — rocketed into orbit following a two-year delay.
It was the third flight of a Falcon Heavy rocket, but the first ordered by the military.
An Iranian satellite-carrying rocket blasted off into space on Tuesday, but scientists failed to put the device into orbit.
The Defense Department already tracks over 20,000 objects in space, and that number is expected to increase dramatically.