United Launch Alliance called off a test-firing of the company’s first flight-rated Vulcan Centaur rocket at Cape Canaveral Thursday to troubleshoot a problem with the booster’s engine ignition system.

Weeks after the launch of an earlier trio of Chinese military satellites, another spacecraft triplet successfully took off Feb. 24 aboard a Long March 4C rocket on a clandestine mission that analysts believe may involve spying on foreign naval forces.

Scientists eager for answers to long-standing questions about the geology of Mars will get a lift Saturday with the blastoff from California of an Atlas 5 rocket with NASA’s InSight mission, a robotic landing craft that will take the pulse and temperature of the red planet.