NASA Administrator Jim Bridenstine wrote in a blog post accompanying the announcement that the plans would not violate a 1967 treaty that holds that celestial bodies and space are exempt from national claims of ownership. The initiative, targeting companies that plan to send robots to mine lunar resources, is part of NASA's goal of setting what Bridenstine called 'norms of behaviour' in space and allowing private mining on the moon in ways that could help sustain future astronaut missions. NASA said it views the mined resources as the property of the company, and the materials would become 'the sole property of NASA' after purchase. Under NASA's Artemis program, President Donald Trump's administration envisions a return of American astronauts to the moon by 2024. NASA has cast such as mission as a precursor to a future first human voyage to Mars. 'The bottom line is we are going to buy some lunar soil for the purpose of it demonstrating that it can be done,' Bridenstine said during an event hosted by the Secure World Foundation, a space policy organization. Bridenstine said NASA eventually would buy more types of resources such as ice and other materials that may be discovered on the moon. NASA in May set the stage for a global debate over the basic principles governing how people will live and work on the moon, releasing the main tenets of what it hopes will become an international pact for moon exploration called the Artemis Accords. This would permit companies to own the lunar resources they mine, a crucial element in allowing NASA contractors to convert the moon's water ice for rocket fuel or mine lunar minerals to construct landing pads. Under the initiative disclosed on Thursday, NASA offered to purchase limited amounts of lunar resources and asked companies to offer proposals. Under contracts whose terms would vary, a company mining on the moon would collect lunar rocks or dirt to sell to NASA without having to bring the resources back to Earth. 'This is one small step for space resources, but a giant leap for policy and precedent,' Mike Gold, NASA's chief of international relations, told Reuters. 'They are paying the company to sell them a rock that the company owns. That's the product,' Joanne Gabrynowicz, former editor-in-chief of the Journal of Space Law, said in an interview. 'A company has to decide for itself if it's worth taking the financial and technological risk to do this to sell a rock.'