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The use of spherical afterbodies on blunt atmospheric vehicles for dynamic stability.

机译：在钝性大气飞行器上使用球形后车身以获得动态稳定性。

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It has been observed in both ground based tests and in flight data that oscillation amplitudes exist with some of NASA's blunt planetary probes at the low supersonic regime. The presence of this instability pose a threat to the success of missions which rely on blunt atmospheric vehicles to conduct their mission objectives. If the amplitude oscillations were permitted to continue and grow, they would eventually lead to a limit cycle behavior. In 1970, Sammonds published his findings that the use of a spherical afterbody on a blunt vehicle with the center of radius located at the center of gravity eliminated its limit cycle problem. The spherical afterbody configuration was tested on various vehicle designs, and for each case has shown that the limit cycle problems were resolved.; A nonlinear method to assess dynamic stability using Liapunov's main stability theorem was developed to determine the stability of a vehicle. This prediction method was used to assess the stability of trajectories generated from gound-based tests and simulations, where the aeroballistic range at the NASA Ames Research Center was used to perform the ground-based experiments. For the baseline vehicle, the Stardust sample return capsule was selected to test the spherical afterbody design, which is known to have a limit cycle behavior near M = 2.0. Because of the additional volume created from this design, a truncated spherical afterbody design was also developed and studied to facilitate possible packaging constraints. It was found that not only was the truncated spherical afterbody unable to eliminate the limit cycle behavior, but also the vehicle with the spherical afterbody was unable to eliminate the limit cycles. Hence, a blunt vehicle that has a spherical afterbody with the center of radius located at the center of gravity is not necessarily guaranteed dynamic stability.
机译：在基于地面的测试和飞行数据中都已经观察到，在低超音速状态下，某些NASA钝头行星探测器存在振荡振幅。这种不稳定性的存在对依靠钝性飞行器完成任务目标的任务的成功构成了威胁。如果允许振幅振荡继续并增大，则最终将导致极限循环行为。 1970年，萨蒙兹（Sammonds）发表了他的发现，即在半径为重心的钝车上使用球形后车身消除了其极限循环问题。球形后车身的配置在各种车辆设计上进行了测试，每种情况都表明极限循环问题得到了解决。开发了使用Liapunov主稳定性定理评估动态稳定性的非线性方法，以确定车辆的稳定性。这种预测方法用于评估基于基于Gound的测试和模拟生成的轨迹的稳定性，其中使用NASA Ames研究中心的空中射程进行地面实验。对于基线载具，选择星尘样品返回胶囊来测试球形后身设计，已知该球形后身设计的极限循环性能接近M = 2.0。由于这种设计产生了额外的体积，因此还开发并研究了一种截头球形的球体后部设计，以简化可能的包装限制。已经发现，不仅截头球形残体不能消除极限循环行为，而且具有球形残体的车辆也不能消除极限循环。因此，具有半径为中心位于重心的球形后车身的钝车不一定能保证动态稳定性。

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