SpaceX launches used Dragon capsule on 18th commercial resupply to space station

The successful launch marked the 18th mission under SpaceX's commercial resupply contract with NASA.

The SpaceX Dragon spacecraft successfully launched its third resupply mission — the eighteenth commercial resupply mission, to the International Space Station. SpaceX used a Falcon 9 rocket to launch a twice-used Dragon capsule carrying 2.5 metric tons of supplies to the orbiting laboratory.

The Falcon 9 was scheduled to liftoff from launchpad SLC-40 at the Cape Canaveral Air Force Station, Florida on 24 July in an instantaneous, one-second launch window. This plan was scrubbed due to unseasonably strong winds, predicted showers and thunderstorms around the designated launchpad in Florida.

Of all the previous launches under the contract, this is the seventh mission to feature a reused Dragon capsule — and the first time a Dragon capsule has run three prior resupply missions: the CRS-6 mission in April 2015, the CRS-13 mission in December 2017 and now, the CRS-18 mission.

A slightly-modified Falcon 9 lifts off on CRS-18 resupply mission to the ISS. Image: SpaceX

CRS-18 was the first time a twice-used Dragon has flown to the space station, but it may not be the last. Each of the next two resupplies — the CRS-19 mission planned for and CRS-20 planned for — will also be on Dragon capsules that have been similarly twice-used. Each Dragon cargo spacecraft is certified to fly three times before it needs to be retired, SpaceX officials told SpaceX currently has a fleet of 13 Dragon capsules, each of which is scheduled for a flight approximately every year and a half.

SpaceX Dragon with depictions of two space station logos for two successful resupply missions prior. Image: SpaceX

SpaceX Dragon with depictions of two space station logos for two successful resupply missions prior. Image: SpaceX

The Falcon 9's first stage was modified slightly in an experimental feature to study and test the thermal properties of the Falcon 9's second-stage propellant tank. The Falcon 9 also looked a little different from previous versions, with a gray stripe just above the black 'interstage' that connects the rocket's two stages.

The CRS-18 mission was chosen to test out the new addition to Falcon 9 because SpaceX has carried out second-stage burn tests on earlier CRS missions and has a good baseline to compare the new modification to. Depending on how the tests go, the Falcon 9 could retain the gray stripe as a permanent addition, said.

The last SpaceX resupply mission to the ISS was nearly a month ago on 25 June, with the third flight of the Falcon Heavy rocket carrying a rideshare sponsored by the US Air Force.

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