While the dust is far from settling over the -- court-challenged -- selection of Boeing and SpaceX to transport astronauts to the International Space Station, the search is already on for new suppliers to the orbiting lab.

The National Aeronautics and Space Administration has released a request for proposals, or RFP, for the next round of contracts with private-sector companies to deliver experiments and supplies to the ISS.

Under the "Commercial Resupply Services 2 RFP," a NASA news release explains, the space agency intends to award contracts with one or more companies, each for six or more flights.

Like the current resupply mission, the new wave of flights would launch from spaceports in the United States, would include logistical and research cargo delivery and would go to and return to Earth from the space station through fiscal year 2020, with the option for NASA to purchase additional launches through 2024.

The life of the ISS was extended at least until 2024 through a decision by the Obama Administration earlier this year.

The ability to continue commercial deliveries to the station is critical to continuing the use of the station, NASA said in a statement, "as a platform for discovery that improves life on Earth, expands the commercial use of low-Earth orbit and helps advance America's journey to Mars" through ongoing scientific research and the development of new technologies.

"The International Space Station is vital to the United States' exploration efforts, a laboratory in orbit where we can work off the Earth, for the Earth," William Gerstenmaier, associate administrator for Human Exploration and Operations, said in the statement. "To push beyond low-Earth orbit and on to Mars, we rely on American industry to keep the station supplied through cargo deliveries."

The new commercial delivery RFP is open to companies that are able to demonstrate safe, reliable launch and rendezvous capabilities with the station.

The goal of the RFP is to foster a full and open environment of competition "that provides the most complete set of services, providing the best value to American taxpayers," NASA said.

Proposals for the new RFP are due in to NASA by Nov. 14, while transport company selection is expected by next May.

A little more than a year after the Space Shuttle program ended in 2011, NASA began flying Space Station cargo resupply missions under two contracts -- one with Orbital Sciences Corp. of Dulles, Virginia, and one with Space Exploration Technologies Corp., or SpaceX, of Hawthorne, California.

At the time of contract awards, NASA ordered eight flights valued at about $1.9 billion from Orbital and 12 flights valued at about $1.6 billion from SpaceX through December 2016.

SpaceX has so far completed three of the contracted delivery missions, with a fourth currently underway, and Orbital has completed two.

On Sept. 16, NASA picked Boeing and SpaceX to transport human crews to and from the space station and thereby lead the effort to once again send U.S. astronauts to the ISS with U.S. spacecraft.

Nevada-based Sierra Nevada Corporation, one of the program's two contending outfits not selected, is challenging the contract awards legally, contending the contract selection process was flawed.