A SpaceX Dragon cargo ship carrying over 5,700 lbs. (2,585 kilograms) of science gear and NASA supplies arrives at the International Space Station on Dec. 8, 2019 during the CRS-19 cargo mission. Another Dragon will launch on the CRS-20 mission on March 6, 2020.

SpaceX has delayed the launch of its next Dragon cargo ship to the International Space Station by at least four days in order to replace part of the mission's Falcon 9 rocket.

The private spaceflight company initially planned to launch the Dragon resupply mission from Florida's Space Coast on Monday (March 2), but is now targeting a March 6 liftoff due to a suspect valve motor on the Falcon 9's upper stage. Liftoff is set for 11:50 p.m. EST on March 6 (0450 March 7) from Space Launch Complex 40 at the Cape Canaveral Air Force Station.

"During standard preflight inspections, SpaceX identified a valve motor on the second stage engine behaving not as expected and determined the safest and most expedient path to launch is to utilize the next second stage in line that was already at the Cape and ready for flight," NASA officials said in an update Tuesday (Feb. 25). "The new second stage has already completed the same preflight inspections with all hardware behaving as expected."

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The Dragon cargo ship is carrying more than 5,600 lbs. (2,540 kilograms) of science equipment, food and other supplies for the three-person Expedition 62 crew on the International Space Station. The spacecraft is carrying gear for a variety of space experiments, "including research on particle foam manufacturing, water droplet formation, the human intestine and other cutting-edge investigations," NASA officials said.

The mission, called CRS-20, will mark SpaceX's 20th cargo run for NASA under a multi-billion-dollar deal as part of the agency's Commercial Resupply Services program.

Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik. Follow us @Spacedotcom, Facebook and on Instagram.