An Engineering Analysis of the Falcon 9 First Stage Landing Failure

schwit1 writes: AviationWeek has posted an analysis of SpaceX's latest attempt to land its Falcon 9 rocket on an ocean barge. Quoting: "SpaceX founder and chief technology officer Elon Musk tweeted that "excess lateral velocity caused it [the booster] to tip over post landing." In a later tweet that was subsequently withdrawn, Musk then indicated that "the issue was stiction in the biprop throttle valve, resulting in control system phase lag." In this statement, Musk was referring to "stiction" — or static friction — in the valve controlling the throttling of the engine. The friction appears to have momentarily slowed the response of the engine, causing the control system to command more of an extreme reaction from the propulsion system than was required. As a result, the control system entered a form of hysteresis, a condition in which the control response lags behind changes in the effect causing it.

Despite the failure of the latest attempt, SpaceX will be encouraged by the landing accuracy of the Falcon 9 and the bigger-picture success of its guidance, navigation and control (GNC) system in bringing the booster back to the drone ship. The GNC also worked as designed during the prior landing attempt in January, which ended in the destruction of the vehicle following a hard touchdown on the edge of the platform." In related news, SpaceX is hoping to attempt its next landing on solid ground.

Comments

Re:I wonder why he bothers...

[bledri]

In a later tweet that was subsequently withdrawn, Musk then indicated that "the issue was stiction in the biprop throttle valve, resulting in control system phase lag."

Anything he leaves for more than 0.5 seconds is going to be reported, retweeted, screenshotted and several articles posted. Just google "musk stiction biprop" and you get plenty hits, no real "undo" button for such a public figure.

He's tech savvy enough to know it's not scrubbed from the internets nor the collective consciousness. This just seems to be how he uses twitter. He regularly tweets things he leaves up, but he also uses twitter to have conversations with people and then he deletes those tweets after the conversation is over. One theory is that he likes a "clean" twitter history. But who the hell knows?

Re:Video from the barge

[bledri]

So, I asked this in the last thread but the discussion there was already mostly dead: what would it cost (presumably mostly a matter of weird) to upgrade the nose thrusters? These are cold-gas (nitrogen) thrusters, and I can't imagine they have a lot of power.

The Dragon uses hydrazine-based "Draco" thrusters for its RCS system; ...

Thoughts?

You, like many people, are trying to solve the wrong problem. Fix the over-correction and there is no need for rocket powered thrusters in place of the cold gas thrusters. Fix the root cause, don't mask it with a heavy/expensive kludge that will come with a host of it's own failure modes.