X-48B屁股后面的毒刺是干什么用的？

好像是防止飞机失速，如果发生失速就会放出减速伞，等飞机姿态恢复后，自动切断这个伞，飞机继续飞行。但之前没听说过这东西，不敢确定。另外也搞不清为何要这么长，短点不行吗？给出一段文字供大家参考：
A spin recovery system built into the test aircraft would allow the vehicle to be flown to its maximum angle of attack and as slow as its stall speed. The system will be used to deploy a parachute if the vehicle begins an uncontrollable descent, such as an unrecoverable spin. The parachute attach line would be cut, separating the vehicle from the canopy as soon as stabilized flight could be resumed.
好像是防止飞机失速，如果发生失速就会放出减速伞，等飞机姿态恢复后，自动切断这个伞，飞机继续飞行。但之前没听说过这东西，不敢确定。另外也搞不清为何要这么长，短点不行吗？给出一段文字供大家参考：
A spin recovery system built into the test aircraft would allow the vehicle to be flown to its maximum angle of attack and as slow as its stall speed. The system will be used to deploy a parachute if the vehicle begins an uncontrollable descent, such as an unrecoverable spin. The parachute attach line would be cut, separating the vehicle from the canopy as soon as stabilized flight could be resumed.