North Korea conducted at least two rocket engine tests ahead of Monday’s failed military satellite launch, according to NK Pro analysis of imagery, an increase from the amount of testing before last year’s launches that points to intensified preparations likely related to the use of a new engine type.

Planet Labs imagery shows additional vegetation die-off appeared under the vertical test stand at the Sohae Satellite Launching Grounds between May 10 and 12, suggesting North Korea conducted a second engine test after one previously reported by NK Pro at the same location between April 21 and 26.