At this stage. no public funding is involved, but the goal is to allow NASA to purchase transportation services from commercial providers to supply the International Space Station.

Instead, NASA will provide information about its requirements and criteria, allowing SpaceDev, SPACEHAB and Constellation Services International (CSI) "to develop and demonstrate the vehicles, systems and operations needed to transport cargo to and from a low Earth orbit destination."

Similar agreements were signed last year with Transformational Space Corporation (t/Space) and PlanetSpace. By encouraging US companies to address its low Earth orbit requirements, NASA can concentrate its resources on moon and Mars missions.

"This is a significant development," said Scott Horowitz, NASA associate administrator for Exploration Systems. "First there were two, and now there are a total of five private companies cooperating with NASA by dedicating entirely private funding to help establish a robust commercial space transportation industry."