Securing the survival of humanity is just one of several reasons why NASA should focus on sending people to Mars. The trouble is, the space agency will find it tough to afford the trip.

That's the conclusion of a sweeping review of the value of the US human space flight programme released today by the National Academy of Sciences. Suggested solutions include practice trips to an asteroid to test Mars technology, and increased collaboration with international partners – most importantly China.

According to the report, a human space flight programme is not just important for technological innovation. It is also vital for the long-term survival of humanity, acting as an escape rope in case of a catastrophe on Earth. Having an inspirational goal – such as Mars – is key because then setbacks or accidents in a particular mission are less likely to derail the broader scheme.

However, the report cautions that a human Mars mission won't happen unless NASA's budget increases substantially and the government makes a long-lasting commitment to the plan. Achieving those goals could be tough because the benefits of space flight are hard to demonstrate and public support for human missions is modest.

Here are the report's main recommendations for how NASA can one day put human boots on Mars:

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