Sending humans to Mars is viable but will require a NASA partnership with China, something current U.S. law prohibits for the space agency, a congressionally mandated study released Wednesday has concluded.

The 285-page National Research Council report titled "Pathways to Exploration -- Rationales and Approaches for a U.S. Program of Human Space Exploration" is the culmination of an extensive 18-month review of NASA’s human spaceflight program to determine whether the expense of the program is justified and  if it can be sustained.

It says the space program has achieved a great deal, but that the U.S. government will have to make some changes, including increasing NASA’s budget and allowing international collaboration, if we are to make it to Mars.

Congress required the report under NASA’s fiscal 2010 authorization bill.

“The United States has been a leader in human space exploration for more than five decades, and our efforts in low-Earth orbit with our partners are approaching maturity with the completion of the International Space Station,” Jonathan Lunine, director of the Center for Radiophysics and Space Research at Cornell University and co-chairman of the committee that wrote the report, said in a statement. “We as a nation must decide now how to embark on human space exploration beyond low-Earth orbit in a sustainable fashion.”

Only the U.S., Russia and China are currently capable of manned spaceflight, but several other countries, including India, are actively developing their manned mission programs. China is seen as having the greatest potential for manned space exploration, but the U.S. considers China its space rival and not a potential partner.

Under a 2011 federal law, NASA is barred from cooperating with China on space missions. The law says NASA cannot "develop, design, plan, promulgate, implement or execute a bilateral policy, program, order or contract of any kind” that would make the U.S. and China partners in space exploration.

NASA has already partnered with the French space agency to send a lander to Mars to explore its interior.

For its report, the National Research Council, a policy panel of experts from the National Academy of Sciences and National Academy of Engineering, looked into things like the technologies required for deep space exploration, political support and funding requirements to determine the feasibility of manned spaceflight.

The NRC determined that the costs and human risks of going to Mars are defensible only if the end goal is to put humans on another planet.