Monday, 10 February 2003
Weather Support for the X38 131R Free Flight 3: December 13, 2001
The third Free Flight test of NASA's X38 131R vehicle occurred December 13, 2001 at Edwards AFB, California. The X38 vehicle landed successfully. There was a significant wind shear that developed late in the mission countdown and launch. The rawinsonde observations taken during the preflight, including observations up to the 1915Z balloon, did not indicate any significant wind shear or turbulence. In addition, the forecast model "point" data did indicate a brief increase in jet stream winds during the time of the X-38 launch, however, the model data under predicted the wind speed intensities of the maximum jet. There were no PIREPS that mentioned turbulence in the area. Although the original forecasts were updated and amended, there were no indicators that turbulence would have developed. Two Programmed Test Inputs (PTIs) were lost initially due to the encountered wind shear. One was regained as a result of the wind changes since the vehicle responded as if encountering a wind gust. The X-38 vehicle was released from the B52 well within the planned tolerances, and the hatch door, pilot chute, and drogue chute all landed well within the range safety ellipse computed with the 1745 GMT planning wind. The X-38 and the B-52 were never in danger due to the existence of turbulence. The X-38 operated nominally and the B-52 pilots did not report any problems with stability and control during the descent through the shear. This paper describes events in the mission countdown and atmospheric conditions that were present for the X-38 and B-52 descent over the Edwards AFB lakebed.