When solving the problem of on-board equipment (OE) arrangement in spacecraft compartments, one of the efficiency indicators is the layout density, and one of the particular efficiency criteria is its maximum. In practice, its application in design calculations and in construction begins to acquire differences, which can be seen, for example, in the use of different formulas and dimensions. Therefore, in this paper, it is proposed to distinguish between the concept of layout density depending on the type of the problem being solved, in order to help designers and engineers choose one or another value of this parameter for the sake of convenience of engineering.
In total, there are three types of layout density, based on the dimensions used — dimensional, mass and relative. Further, it is proposed to describe each of them in more detail.
The dimensional density of the layout is a value that is the ratio of the unit of mass of the OE to the unit of length (kg/m) or surface area (kg/m2), or the volume of space (kg/m3) of the compartment. Traditionally, it is determined averaged in order to take into account with some accuracy the heterogeneity of product materials, and is used in calculating the mass-dimensional design characteristics of the spacecraft . Also, these distributions of mass along the length, area and volume are used to calculate the loads acting on the spacecraft and its compartments at various stages of operation, to calculate the dynamics of vibrations of outboard structures and dynamic calculations of the spacecraft in flight as a whole .
The mass density of the layout is the reciprocal of the ratio of the unit of the volume of the EO to the unit of its own mass (m3/kg). It shows how much space in the space of the compartment falls on a kilogram of equipment to be placed. In this form, this characteristic is useful when developing a layout for the EO in a compartment, so that, with a known total mass of objects, to estimate in a first approximation the main condition for the existence of a layout (capacity condition). And if in the first case the criterion of efficiency is the maximum of the measured density of the arrangement, then here it is vice versa. That is, the less volume is allocated to each product, the more compact the result .
The relative density of the layout is a dimensionless quantity defined as the ratio of the lengths of the dimensions or volumes of the spacecraft assembly to the spacecraft compartment. This interpretation makes it possible to assess the presence of the formed voids, their nature and location in space . Or, if the installation of objects is carried out with the division of the compartment into racks according to its height, then it becomes possible to take the minimum height of the arrangement area as the criterion of efficiency .
It is important to note that the density of the layout in any of the three types cannot be the only argument of the target function of arrangement, because in practice, the relationship between the target indicators and the design, cost, etc. parameters of the spacecraft is rather complicated . Therefore, this parameter is proposed to be used in conjunction with the mass-centering and inertial characteristics of the spacecraft.
Thus, when solving the problem of placing the EO in the spacecraft compartments at different stages of operation, the dimension of the density of the layout may technically differ. If you need to determine the dimensions and masses of devices, then the measured density of the layout is suitable for this. If these parameters are known in advance, then by multiplying the total mass of the devices by the mass density of the layout, you can quickly find out how much volume the final layout can take. If you need to evaluate the efficiency of the solution, then the relative density of the layout will come in handy, which will show the percentage of filling the compartment with devices and the existence of voids in it.