This article considers the solution of the problem of dynamic loading of the pipeline [1], which is necessary to supply fuel to the booster engine. The method of calculating the dynamic loading [2] of the pipeline is described. Its equation of motion is decomposed into components and loads are calculated for harmonic vibrations of the launch vehicle. The accelerations of the propulsion system and pipeline attachment points obtained from solving a general dynamic problem for estimating the hydrodynamic force for a launch vehicle were set as initial data for dynamic load calculation. At this stage, the load on the pipeline was calculated taking into account the hydraulic shock of the liquid mass in the event of the launch vehicle flight, as one of the most loaded for this system. Nonlinear dynamic analysis was used to calculate pipeline loads [3]. As a result of the calculation, the forces in the attachment points of the structure under consideration, as well as the forces distributed along the length of the pipeline, were obtained. The method of calculating the dynamic loading of the pipeline is described. Pipeline loads consist of quasi-static components, which usually include trajectory overloads and low-frequency dynamic components [4] from transient processes such as start-up, as well as additional loads from vibration and acoustic influences. Quasi-static and low-frequency dynamic components in loads [5] usually have a fairly high degree of certainty and, as a rule, are estimated by calculation using appropriate RCN models and attachments. The loads obtained in this way cover the low-frequency part of the spectrum up to 20-30 Hz. Spatial beam models[6] with elastic supports and kinematic connections with tank bottoms and propulsion system are usually used for pipelines. When calculating the force factors in the sections of pipelines (longitudinal and shearing forces, bending and torques, forces in the support nodes), the fuel is allowed to be considered frozen (without taking into account the speed of movement). The fluid velocity should be taken into account when assessing the pressure of hydraulic shocks in pipelines to calculate the stress-strain state of pipelines from internal pressure.

Obviously, there are no constructs in nature that describe linear dynamic behavior. However, it is customary to conduct research on such systems, with some exceptions, using the principle of linearization. Nevertheless, with the growth of requirements for modern space technology, a decrease in their mass and size, and a reduction in the time of their ground-based experimental development, it is not permissible not to take into account the nonlinearity in the design, since they become more nonlinear. As you know, rocket and space technology at the stages of transportation to the operating organization, during launch, in orbit, is subjected to dynamic loads. To ensure the smooth operation of space technology, it is necessary to develop the most reliable, that is, accurately describing a full-scale object, a finite element model. It will serve, in turn, for load calculations and strength calculations. This article discusses an experimental study of the nonlinear dynamic behavior of the structure of a small spacecraft. At the initial stage of the work, the amplitude-frequency characteristics of the research object were determined for forward and backward scanning. This approach did not reveal any obvious nonlinearity in the design of the small spacecraft. Then, having previously selected the proposed installation locations for the sensors, a number of experiments were carried out at the resonant frequencies of the small spacecraft, during which the values of the overloads were obtained for different modes of exposure. The results of overloading individual instruments and most of the small spacecraft design did not show convincing nonlinear dynamic behavior. However, experimental data at local locations in the structure revealed a clear non-linear dynamic behavior. These results will serve in the future when validating the finite element model of a small spacecraft for a more reliable determination of the loads on the structure.