Washington, Sep 28 (IANS): After awarding contracts to Boeing Co. and SpaceX to ferry American astronauts to the International Space Station (ISS), NASA has called for the next round of contracts for private sector companies to deliver experiments and supplies to the orbiting laboratory.

The US space agency intends to award contracts to one or more companies for six or more flights per contract.

As with current re-supply flights, these missions would launch from US spaceports and the contracted services would include logistical and research cargo delivery and return to and from the space station through fiscal year 2020, with the option to purchase additional launches through 2024.

Earlier this year, the US administration decided to extend the life of the International Space Station until at least 2024.

The ability to continue commercial deliveries to the station is critical to continuing the use of the station 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 high-quality scientific research and technology development.

"The International Space Station is vital to the US' exploration efforts, a laboratory in orbit where we can work off the Earth, for the Earth," said William Gerstenmaier, associate administrator for human exploration and operations at the NASA headquarters in Washington, DC.

"To push beyond low-Earth orbit and on to Mars, we rely on the American industry to keep the station supplied through cargo deliveries," he added.

The space agency Sep 16 unveiled its selection of Boeing and SpaceX to transport US crews to and from the space station using their CST-100 and Crew Dragon spacecraft, respectively, with the goal of ending the nation's reliance on Russian hardware in 2017.