Falcon 1
Launch vehicle Falcon 1
Launch site Kwajalein Atoll, Marshall Islands
Date/Time 2007-03-21 0110 UTC
Description Second stage failure
Cause Design flaw
Payload DemoSat
Desired orbit circular at an altitude of 685 km and 9 degrees inclination

"There were eight significant anomalies identified during analysis of flight data, the most important being an upper stage control issue. Although the rocket failed to reach orbit as planned, SpaceX CEO Elon Musk called the launch "pretty good" as it had proven 95+ percent of the Falcon 1 systems. However, had this been an actual satellite launch, it would have been a failure.

An oscillation appeared in the upper stage control system approximately 90 seconds into the burn. This instability grew in pitch and yaw axes initially and after about 30 seconds also induced a noticeable roll torque. This roll torque eventually overcame the second stage's roll control thrusters and centrifuged the propellants, causing flame-out of the Kestrel upper stage engine. There is high confidence that LOX slosh was the primary contributor to this instability.

Falcon 1 did not use slosh baffles in the second stage tanks, as simulations done prior to flight indicated the slosh instability was a low risk. Given that in space there are no gust or buffet effects, the simulations did not take into account a perturbation, as occurred due to a "hard slew" manoeuvre after stage separation. Extensive second stage slosh baffles will be included in all future flights, as is currently the case with the first stage.

The "hard slew" manoeuvre occurred after the nozzle of the Kestrel engine made contact with the interstage section as they separated after Main Engine Cut Off (MECO). The re-contact occurred owing to higher than anticipated rotation rates, both of the combined vehicle stack prior to separation, and of the second stage after separation. This rotation was caused partly by the Merlin (first stage) engine pointing slightly off center-of-mass at shutdown. Analysis indicates that a majority of the rotation was caused by increased aerodynamic forces acting on the second stage and fairing, owing to the vehicle being lower than expected during stage separation and at a high angle of attack.

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Last updated: 18 August 2008

Launch Failures Chronology