Throttle Issue Blamed for Falcon’s Hard Landing

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WASHINGTON — SpaceX Chief Executive Elon Musk confirmed a throttle issue was the cause of failed landing attempt of a Falcon 9 first stage last week, and that it plans to make another landing attempt in June.

Musk, in a tweet late April 18, said that “slower than expected throttle valve response” caused the first stage to come down hard on its mobile landing platform in the Atlantic, toppling over and exploding seconds later.

Musk originally suggested a throttle problem was the root cause hours after the April 14 landing on the company’s “autonomous spaceport drone ship” in the Atlantic Ocean. “Looks like the issue was stiction [static friction] in the biprop throttle valve, resulting in control system phase lag,” he wrote in a reply to John Carmack, the software developer who formerly ran Armadillo Aerospace. Musk deleted that tweet hours later.

Musk said that the next landing attempt would be in two months, which would correspond with the scheduled June 19 launch of another Dragon cargo spacecraft to the International Space Station. Company officials previously stated that this launch would be the next opportunity to attempt a landing.

Musk did not say whether SpaceX would attempt to land the stage on its ship or on land. In an interview at the 31st Space Symposium in Colorado Springs, Colorado, April 14, SpaceX President Gwynne Shotwell said that the company could attempt to bring the first stage back to land on that June mission to the ISS, or on a scheduled July launch of the Jason-3 satellite from Vandenberg Air Force Base in California.