Understanding and predicting the evolving spin states of defunct geosynchronous (GEO) satellites and rocket bodies is important for space situational awareness, active debris removal, satellite servicing, and anomaly resolution. There is clear evidence that many defunct GEO satellite spin states are predominantly driven by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. The YORP effect is spin state evolution due to solar radiation and thermal re-emission torques. Observations are crucial to understand how YORP drives spin states and to validate dynamical models. Unfortunately, GEO satellites are non-resolved from ground-based telescopes and extracting spin states (spin periods, rotational angular momentum vector, instantaneous attitude) from ubiquitous photometric light curve data is challenging. Even for well-known objects, light curve inversion often yields several or more well-fitting spin state solutions within the measurement noise and modeling uncertainty (i.e. detailed satellite geometry, reflective properties, etc.). Also, there is strong evidence that the YORP effect drives satellites from uniform rotation to non-principal axis tumbling. Such tumbling states further complicate the light curve inversion process because the motion is driven by two independent periods rather than one. To aid complete spin state analysis, particularly for the tumbling case, Doppler radar observations collected at NASA Goldstone Deep Space Communications Complex are incorporated. Observing the well-documented retired GOES 8–12 weather satellites, the radar data yielded unambiguous spin period estimates for all targets and greatly narrowed pole solutions, independent of light curve data. Significant changes in spin rates and pole directions were observed over a two month span. These findings are consistent with YORP-driven evolution.

了解和预测已消失的地球同步（GEO）卫星和火箭弹的旋转状态对于空间态势感知，主动碎片清除，卫星服务和异常解决至关重要。有明确的证据表明，许多已失效的GEO卫星自旋状态主要是由Yarkovsky-O'Keefe-Radzievskii-Paddack（YORP）效应驱动的。YORP效应是由于太阳辐射和热再发射转矩引起的自旋态演化。观察对于了解YORP如何驱动自旋状态以及验证动力学模型至关重要。不幸的是，GEO卫星无法从地面望远镜中分辨出来，因此要从无处不在的光度学光曲线数据中提取自旋状态（自旋周期，旋转角动量矢量，瞬时姿态）是一项挑战。即使是知名物体，光曲线反演通常会在测量噪声和建模不确定性（即详细的卫星几何形状，反射特性等）内产生几个或多个非常适合的自旋状态解。同样，有强有力的证据表明，YORP效应使卫星从均匀旋转旋转到非主轴旋转。由于运动是由两个独立的周期而不是一个周期驱动的，因此这种翻滚状态使光曲线反转过程进一步复杂化。为了帮助进行完整的自旋状态分析，尤其是对于翻滚的情况，我们结合了在NASA金石深空通信中心收集的多普勒雷达观测资料。观察到有据可查的退役的GOES 8-12天气卫星，雷达数据得出了所有目标的明确的自旋周期估计值，极解也大大缩小了，与光曲线数据无关。在两个月的时间内观察到旋转速度和磁极方向的显着变化。这些发现与YORP驱动的进化是一致的。