Photos: Tuesday’s Atlas 5 rollout

SpaceX is replacing two engines on the Falcon 9 booster set to launch four astronauts next month on the company’s first operational Crew Dragon flight to the International Space Station, following an investigation that revealed a subcontractor failed to adequately clean out narrow vent ports on multiple engines across the company’s fleet, officials said Wednesday.

Loaded with three commercial satellites, a European Ariane 5 rocket returned to its launch pad in French Guiana Thursday after a two-week launch delay to resolve a technical issue that forced an abort to a countdown July 31. Arianespace says the mission has been rescheduled for launch Saturday due to unfavorable upper level winds in the forecast for Friday.

America’s next Mars rover, a $2.1 billion nuclear-powered vehicle to search for evidence that life once existed there, will be launched to the Red Planet in the summer of 2020 by a powerful Atlas 5 rocket.