Nasa is paying SpaceX and Boeing $2.6bn and $4.2bn respectively to build rocket and capsule launch systems to return astronauts to the International Space Station from US soil for the first time since America’s Space Shuttle programme went dark in 2011.

Just ahead of the first scheduled unmanned test flight planned for March 2 under Nasa’s Commercial Crew Programme, Nasa’s safety advisory panel cited four “key risk items” in its 2018 annual report earlier this month.

For Boeing, the report included the capsule’s structural vulnerability when the heat shield is deployed. Also, the report mentioned the redesign of a SpaceX rocket canister following a 2016 explosion and its “load and go” process of fuelling the rocket with the crew already inside the capsule. “Parachute performance” also remained an issue for both companies.

“There are serious challenges to the current launch schedules for both SpaceX and Boeing,” the report said.

Two people with direct knowledge of the programme told the Reuters news agency that Nasa’s concerns go beyond the four items listed and include a risk ledger that as of early February contained 30 to 35 lingering technical concerns each for SpaceX and Boeing.

The same sources also said the two companies would have to address “most” of the concerns stated above before flying astronauts and, eventually, tourists to space.

Furthermore, according to the people familiar with the matter, the Nasa risk database is updated routinely during the space agency’s stringent certification process, which includes data collection, tests and collaboration with SpaceX and Boeing.

Boeing’s and SpaceX’s systems have been delayed several times this year, a common result in the sector given the complexity of building a multibillion-dollar spacecraft.

Nasa spokesman Joshua Finch deferred all technical questions on Boeing and SpaceX systems to the companies, citing confidentiality, but said: “Flying safely always takes precedence over schedule.”

Boeing spokesman Josh Barrett said the company “closed out” the capsule’s structural vulnerability risk when it completed its structural test programme in January. While Boeing is working through several other issues, they “are not driving any major architectural system changes.”

“Our numbers show we are exceeding Nasa’s safety requirements,” said Barrett.

SpaceX spokesman James Gleeson said the company has developed “one of the safest, most advanced human spaceflight systems ever built.”

“There is nothing more important to SpaceX than safely flying crew,” said Gleeson, calling it “core to our company’s long-term goal of enabling access for people who dream of flying to space.”

Nasa is set to conduct a flight readiness review on Friday for SpaceX’s mission without a crew set to take place at the start of March. The space agency will decide whether to approve the test flight without a crew, while SpaceX addresses the issues raised for a human mission.

On 13 February 2019, Nasa made its final attempts to contact its Mars rover Opportunity after it stopped responding eight months ago.

Nasa is paying SpaceX and Boeing $2.6bn and $4.2bn respectively to build rocket and capsule launch systems to return astronauts to the International Space Station from US soil for the first time since America’s Space Shuttle programme went dark in 2011.

Just ahead of the first scheduled unmanned test flight planned for March 2 under Nasa’s Commercial Crew Programme, Nasa’s safety advisory panel cited four “key risk items” in its 2018 annual report earlier this month.

For Boeing, the report included the capsule’s structural vulnerability when the heat shield is deployed. Also, the report mentioned the redesign of a SpaceX rocket canister following a 2016 explosion and its “load and go” process of fuelling the rocket with the crew already inside the capsule. “Parachute performance” also remained an issue for both companies.

“There are serious challenges to the current launch schedules for both SpaceX and Boeing,” the report said.

Two people with direct knowledge of the programme told the Reuters news agency that Nasa’s concerns go beyond the four items listed and include a risk ledger that as of early February contained 30 to 35 lingering technical concerns each for SpaceX and Boeing.

The same sources also said the two companies would have to address “most” of the concerns stated above before flying astronauts and, eventually, tourists to space.

Furthermore, according to the people familiar with the matter, the Nasa risk database is updated routinely during the space agency’s stringent certification process, which includes data collection, tests and collaboration with SpaceX and Boeing.

Boeing’s and SpaceX’s systems have been delayed several times this year, a common result in the sector given the complexity of building a multibillion-dollar spacecraft.

Nasa spokesman Joshua Finch deferred all technical questions on Boeing and SpaceX systems to the companies, citing confidentiality, but said: “Flying safely always takes precedence over schedule.”

Boeing spokesman Josh Barrett said the company “closed out” the capsule’s structural vulnerability risk when it completed its structural test programme in January. While Boeing is working through several other issues, they “are not driving any major architectural system changes.”

“Our numbers show we are exceeding Nasa’s safety requirements,” said Barrett.

SpaceX spokesman James Gleeson said the company has developed “one of the safest, most advanced human spaceflight systems ever built.”

“There is nothing more important to SpaceX than safely flying crew,” said Gleeson, calling it “core to our company’s long-term goal of enabling access for people who dream of flying to space.”

Nasa is set to conduct a flight readiness review on Friday for SpaceX’s mission without a crew set to take place at the start of March. The space agency will decide whether to approve the test flight without a crew, while SpaceX addresses the issues raised for a human mission.

On 13 February 2019, Nasa made its final attempts to contact its Mars rover Opportunity after it stopped responding eight months ago.