51 U.S. Code § 20302 - Vision for space exploration
(a) In General.— The Administrator shall establish a program to develop a sustained human presence on the Moon, including a robust precursor program, to promote exploration, science, commerce, and United States preeminence in space, and as a stepping-stone to future exploration of Mars and other destinations. The Administrator is further authorized to develop and conduct appropriate international collaborations in pursuit of these goals.
(b) Milestones.— The Administrator shall manage human space flight programs to strive to achieve the following milestones (in conformity with section 70502 of this title):
(3) Increasing knowledge of the impacts of long duration stays in space on the human body using the most appropriate facilities available, including the International Space Station.