航天器载信号定时器是美国航宇局激光测距系统的一部分,它装在围绕加州上空飞行的航天飞机上,目的是通过激光测距来测量沿San Andreas断裂层的位移,以及有可能预报地震。(图1) The spaceborne signal timer, part of the NASA laser ranging system, is installed on a space shuttle flying over California in order to measure the displacement along the San Andreas fault by laser ranging and the potential for prediction earthquake. (figure 1)