WASHINGTON, July 17 -- U.S. space firm SpaceX will on Monday launch supplies to the International Space Station, including a crucial docking port for future American commercial crew vehicles, and then try a second rocket landing on solid ground.

The SpaceX Dragon cargo spacecraft is scheduled for liftoff on the company's Falcon 9 rocket at 12:45 a.m. EDT (0445 GMT) from Cape Canaveral Air Force Station in Florida.

Among the cargo is the first of two international docking adapters, which will allow U.S. commercial spacecraft to dock to the station when transporting American astronauts in the near future.

Its first users are expected to be the Boeing Starliner and SpaceX Crew Dragon spacecraft, which are now in development in partnership with the U.S. space agency NASA's Commercial Crew Program and expected to begin test flights in 2017 and 2018.

The adapter, a metallic ring big enough for astronauts to fit through, also represents the first on-orbit element built to the docking measurements that are standardized for all the spacecraft builders across the world, which means other spacecraft will also be able to dock there in the future, NASA said.

"It's really good we have an international standard now that anybody can build against and come dock to the station or to anything that has the same standard," David Clemen, Boeing's director of Development and Modifications for the space station, said in a NASA statement.

SpaceX tried to deliver one international docking adapter last year, but the equipment was destroyed during a launch accident.

Overall, the uncrewed Dragon spacecraft is loaded with about 5,000 pounds (2,268 kilograms) of cargo for its ninth Commercial Resupply Services mission for NASA.

Included in the payload is a pocket-size device that will allow DNA sequencing in space for the first time. The samples in this first test will be DNA from a virus, a bacteria and a mouse.

Meanwhile, the first stage of the Falcon 9 rocket will attempt an experimental landing on a landing zone, also at Cape Canaveral Air Force Station, minutes after Monday's launch.

"I'm pretty optimistic at this point in time that we land it, but I would always knock on wood," Hans Koenigsmann, vice president of flight reliability at SpaceX, said during a prelaunch news conference Saturday. "That's part of the nature of this maneuver, it's pretty challenging."

The California-based company achieved a soft landing on a land-based pad at Cape Canaveral last year. Since then, it has also had three successful landings on a droneship in the Atlantic Ocean.

Koenigsmann said the reflight of the company's recovered rocket could occur this fall.

SpaceX is one of two U.S. companies that provide space station cargo services for NASA. The other company is Orbital ATK, whose next space station cargo launch is targeted for August.