Space X and Boeing design risks threaten US access to the International Space Station

Nasa has warned Space X and Boeing about safety concerns for their competing astronaut launch systems, threatening to delay US plans to revive its human spaceflight programme later this year.

Nasa forged agreements with Space X for $2.6bn (£2bn) and Boeing for $4.2bn to build rocket and capsule launch systems to take astronauts to the International Space Station, after its Space Shuttle programme shut down in 2011.

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Earlier this month, Nasa’s safety advisory panel highlighted four “key risk items” in Space X and Boeing’s systems, just days before the first scheduled test flight under the space agency’s multi-billion-dollar commercial crew programme was meant to take place on 2 March.

But according to two people with direct knowledge of the programme who spoke to Reuters, Nasa’s concerns go beyond the four items listed and includes a risk ledger that as of early February contained 30 to 35 lingering technical concerns for Space X and Boeing.

Sources familiar with the matter told Reuters that the companies must address “most” of these concerns before flying astronauts, and eventually tourists, to space.

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If the issues are not resolved soon, it could spell further delays and put US access to the International Space Station at risk.

The US is currently paying Russia about $80m per ticket to ferry its astronauts to the space station. There are no seats available for US crew on Russian spacecraft after 2019.

Nasa said it is considering paying for two more seats to the space station for this fall and spring 2020.