Please consider donating to Behind the Black, by giving either a one-time contribution or a regular subscription, as outlined in the tip jar to the right or below. Your support will allow me to continue covering science and culture as I have for the past twenty years, independent and free from any outside influence.
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 In a later tweet that was subsequently withdrawn, Musk then indicated that “the issue was stiction in the biprop throttle valve, resulting in control system phase lag.”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.