7.7. Complex Dynamic Test Units The main problem which arises in the creation of dynamic test units is the reproduction of the movement of the spacecraft with given inertial and geometric characteristics in weightlessness. To reproduce this movement and the interaction of docking assemblies the test units are divided into two main types: 1) mechanical, using full-scale models of the spacecraft; 2) hybrid, including mathematical models and force tracking systems for displacement of the tested docking assemblies. Models which have the same docked masses, moments of inertia, and configuration of the docking assemblies relative to the center of mass as the spacecraft, with an approximate reproduction of the distribution of mass, rigidity, and other characteristics, are relieved of the effect of the force of weight and are installed or suspended so that their movement occurs by inertia, as in weightlessness. Many other methods are known which are passive and which use auxiliary tracking drives to provide displacements in six (or less) degrees of freedom. 411 of them, especially those with tracking drives, are rather complex and bulky. The experience of use and analysis shows that mechanical test units have definite and obvious advantages (relative simplicity, smoothness, reliability of mass, geometric, and other characteristics of the spacecraft). At the same time complex mechanical test units have a number of drawbacks, mainly their large mass and size, which increases as the dimensions of the spacecraft increase. Also, one must create models for each spacecraft to be tested, and there is a limited reproduction of the actions of the control system. In these units it is difficult to heat and cool the docking assemblies to extreme temperatures. Tn hybrid complex test units the motion of the spacecraft affected by the force of interaction of the tested docking assemblies, and the forces and momenta of the control system are calculated with a computer which controls the tracking drives, making relative movements of the docking devices. The main advantage of this test unit is the independence of the size and construction of the test unit on the mass, dimensions, and configuration of the spacecraft, as well as good reproduction of the effect of the control system. Thus, hybrid test units are promising for testing the docking of heavy spacecraft. The
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