SpaceX has received $ 10 billion from NASA to build a spacecraft to transport astronauts to the International Space Station (ISS) in 2014. Several delays, including an explosion during a Dragon Test capsule test in July, have reset SpaceX. As a result, NASA continues to rely on the Russian Soyuz rocket to bring US astronauts to the ISS.
NASA is unhappy that Mr. Musk and SpaceX have not revealed the Starship missile while their promises with the space agency have been breached.  Mr. Bridenstine tweeted: "The trading team is years behind schedule.
"NASA believes the US taxpayer's investment is just as enthusiastic. It is time to deliver. "
However, Mr. Musk struck back from Mr. Bridenstine, claiming that the delays reflected the industry as a whole.
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South African-born billionaire told CNN: " Everything in the aerospace industry is eight years back.
"Most of the work required by NASA astronauts from now on is a long line of security checks, so it's not really hardware related and it's really going as fast as we can.
"If there's a way to make it faster, I'd make it faster.
Mr. Musk added that the commercial crew could supply astronauts to the ISS within three to four months.
The war of words calmed down and Mr. Bridenstine tweeted that he had a "great call with Elon Musk had week, and I'm looking forward to visiting SpaceX in Hawthorne (California) Thursday.
Following the tour, SpaceX will hold a press conference with Bridenstine, SpaceX Chief Engineer Elon Musk and NASA astronauts Bob Behnken and Doug Hurley ̵
] This will be streamed live on Mr Bridentine's Twitter account on October 10, 5:00 pm CET (10:00 pm CET). [Saturday, September 28]Mr. Musk unveiled a prototype of the Mk1rocket spacecraft that will take people to the Moon, Mars, and the Moon "Beyond."
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Ton or 1,400 tonnes at full load, SpaceX Starship, Mr Musk said that the rocket will be in use of six months into orbit to test the machine.
The Starship prototype, shown alongside the original Spacecraft Falcon 1 rocket on Saturday, features eye-catching stainless steel instead of carbon fiber or aluminum materials.  This gives the SpaceX Starship "exceptional thermal properties" and lower costs.
A refined Starship in combination with a SpaceX Super Heavy Booster level increases rocket height to 117 m and can carry 220,000 pounds.
The spacecraft will also include the "orbit refill" capabilities that can be used to transfer fuel from spacecraft to orbiting spacecraft – something Musk says is easier than docking at the International Space Station (ISS).