But in the case of balloons , the descent sometimes comes sooner than expected .
但是就热气球来说，有时候它下降时比预想要来的快。
After traveling roughly 80000 kilometers ( 50000 miles ) , the spacecraft deployed its initial chutes to stabilize and slow its descent .
在飞行了约八万公里（约五万英里）后，飞船启用了第一批降落伞来稳定机身并减缓下降速度。
Researchers have observed , for example , that long-haul pilots who sleep during flights perform better when maneuvering aircraft through the critical stages of descent and landing .
Each nonterminal in a parsing expression grammar essentially represents a parsing function in a recursive descent parser , and the corresponding parsing expression represents the " code " comprising the function .
