RU2801979C2 - Method for simulation of external heat transfer conditions of space vehicles in thermal vacuum chamber - Google Patents

Abstract

FIELD: thermal vacuum testing of spacecraft.

SUBSTANCE: to simulate the conditions of external heat exchange of spacecraft in a thermal vacuum chamber, a solar radiation simulator is assembled from separate sections of autonomous heaters and placed inside the thermal vacuum chamber together with the test object. In sections of autonomous heaters, an array of point sources of radiation is used. Radiation sources of autonomous heaters are equipped with optical elements and can consist of several types with different spectral characteristics. The test object is brought to hot and cold temperatures using a solar simulator and a cooled grate, respectively. The power of sections of independent heaters is regulated separately by a single control system. A uniform working field is obtained by mixing the radiation of point sources. The control system uses feedback based on the readings of the sensors of the level of energy illumination and the spectrum on the surface of the test object.

EFFECT: increase in the reliability and energy efficiency of thermal vacuum tests, a reduction in time costs and labour intensity in the preparation of thermal vacuum tests.

3 cl, 5 dwg

Description

The invention relates to the field of ground testing of space vehicles (hereinafter referred to as the test object) under conditions of thermal vacuum tests, close to the conditions of open space.

To simulate the conditions of external heat transfer, the test object is placed in a thermal vacuum or thermal vacuum chamber, in vacuum, using cryogenic screens, the conditions of "cold" and "black" space are created, and the thermal state of the test object is obtained, including using a solar radiation simulator.

A known method of simulating solar radiation is described in patent RU 2011112413, in which the simulator contains sources of solar radiation located outside the thermal vacuum chamber - lamps with ellipsoid reflectors and auxiliary spherical mirrors, an entrance porthole in the form of a biconcave lens, a mirror mixer hermetically built into the thermal vacuum chamber housing in the form convex mirror lenses with square profiles evenly located in the plane of contacting their faces, a parabolic collimating reflector located in the thermal vacuum chamber for reflecting simulated solar radiation onto the test object.

There is also known a method for simulating solar radiation in a thermal vacuum chamber (US Pat. RU 2476833 C2), in which the focusing and input of light fluxes from light sources into the thermal vacuum chamber is carried out through a light-conducting porthole hermetically mounted on its body, made in the form of a biconvex lens. A parallel light flux is created on the test spacecraft by means of a parabolic collimating reflector with the provision of flux characteristics with parameters as close as possible to real solar radiation in the spacecraft orbit, followed by its reflection from the mixer with the separation of the light flux into separate light fluxes with the expansion of their incident light spot by parabolic collimating reflector.

The general disadvantages of these analogues are:

- extremely low energy efficiency of solar radiation simulation, due to the location of light sources outside the thermal vacuum chamber, as a result - high losses in a complex optical system consisting of a large number of reflective and refractive optical elements. Even with the most careful manufacturing, adjustment and adjustment of all optical elements, the efficiency of such solar radiation simulators does not exceed 10% (Krat S.A. Improving the efficiency of solar radiation simulators // Siberian Journal of Science and Technology. 2011. No. 2 (35). P. 124-127);

- high overall complexity and cost of powerful light sources, optical elements and other equipment necessary to simulate solar radiation, while a complex optical system requires constant laborious adjustment and confirmation of the required characteristics during operation by qualified personnel;

- re-reflection by a parabolic collimating reflector of the own and reflected thermal radiation of the test object, resulting in an additional component of the error in simulating solar radiation;

- overlapping of the cryogenic screens located on the inner surface of the thermal vacuum chamber by a collimating reflector, as a result of which the time for creating cold temperature regimes or transient temperature regimes at the test object increases;

- heating of the collimating reflector with a high-density heat flux, which requires its forced cooling and additionally increases the time for creating transient modes of thermal vacuum tests from hot to cold temperatures;

- the impossibility of changing the direction of the flow of simulated radiation, which is required, in particular, to simulate the rotation of the test object relative to the Sun. In this case, complex and expensive solutions are used, in particular, rotary mechanisms adapted to the conditions of thermal vacuum tests, or they reinstall the test object under normal conditions, which requires a complete cessation and subsequent resumption of the entire process of thermal vacuum tests and is accompanied by unreasonably high material and time costs. ;

- the impossibility of irradiating individual sections of the working field with different power levels, which is required, in particular, to simulate partial shading of the test object.

As the closest analogue, a method for testing spacecraft, free from these shortcomings, was chosen, disclosed in the patent "Test bench for spacecraft" (patent RU 2172709 C2), including a vacuum chamber with a spacecraft inside it, a solar radiation simulator, a device for cooling the walls of the vacuum chamber, a system vacuuming. The solar radiation simulator is made in the form of autonomous heaters installed on a truss fixed inside the vacuum chamber, while the light sources of the heaters are located at the focus of the parabolic reflectors; the heaters are sectionally divided among themselves, the sections of the heaters are isolated from each other by screens, and the solar radiation simulator itself is equipped with a control unit for switching on (off) in turn and adjusting the power of each section of the heaters; in addition, each light source is made in the form of a quartz halogen heat-emitting lamp.

The impact of the solar flux is simulated by autonomous heaters, which create a calculated temperature field for each individual surface of the SO, which is controlled by the readings of temperature sensors installed on the irradiated surfaces of the test object. All autonomous heaters are divided into sections; All sections of the heaters have autonomous power supply systems, which are combined into a single control unit of the solar radiation simulator, which provides sequential switching on (off) and adjustment of the radiation power of each section of the heaters. Each heater section is equipped with a calculated number of heaters depending on the area and configuration of the irradiated surface and is located at a given distance from this surface.

To prevent irradiation of surfaces from heaters intended for heating other surfaces, as well as to exclude lateral reflection from structural elements and heaters located on it, screens separating the heaters are provided on the truss brackets, made of screen-vacuum thermal insulation (EVTI), covered on both sides with fiberglass with fiberglass stitching around the edges. The outer surface of the mats has a degree of emissivity ε ≥ 0.9, which ensures almost complete absorption of all lateral thermal radiation from the heaters and the truss structure, thereby providing a simulation of a plane-parallel radiation flux.

This analog is taken as a prototype of the invention.

For the claimed method, the following essential features in common with the prototype have been identified: a solar radiation simulator is assembled from separate sections of autonomous heaters and placed inside a thermal vacuum chamber, cold temperatures are obtained at the test object using a cooling device, radiation sources of autonomous heaters are equipped with optical elements, the power of autonomous heater sections is regulated apart.

The disadvantages of the prototype are:

- placement of heaters, screens separating them from EVTI and elements of their suspension between the cryogenic screens of the thermal vacuum chamber and the test object. At the same time, in the cold temperature mode, the thermal radiation of the test object to the cryogenic screens is partially blocked by the specified elements, which increases the time for creating cold temperature or transient modes on the test object and leads to additional consumption of liquid nitrogen;

- completely unremovable non-uniformity of the working field and non-parallelism of the radiant flux created by autonomous heaters at the test object, due to the property of parabolic reflectors to redirect only the side rays of the radiation source and not to redirect the central ones;

- additional non-uniformity of the working field, caused by the placement of autonomous heaters at a distance from each other;

- a significant difference in the spectral distribution of quartz halogen thermal-emitting lamps from the spectral distribution of the Sun in open space conditions. At the same time, the use of reflective or absorbing coatings on the test object, which are spectrally selective in a region different from the spectral range of the lamps used, leads to a significant error in simulating solar radiation;

- the impossibility of controlling the level of energy illumination by temperature sensors located on the test object, the readings of which depend on the reflective or absorbing properties of the applied coatings of the test object;

- the complexity and laboriousness of installation and configuration of the structure of a plurality of autonomous heaters separating the sections of the screen heaters, their fastening elements, the configuration of which is determined in each specific case depending on the geometric properties of the test object and the requirements of the program and test methodology.

The technical problems of the invention are:

- increasing the reliability of thermal vacuum tests;

- improving the energy efficiency of simulating solar radiation;

- reduction of time costs and labor intensity in the preparation and conduct of thermal vacuum tests using a solar radiation simulator.

The technical problem posed is solved due to the fact that in the method of modeling the conditions of external heat exchange of spacecraft in a thermal vacuum chamber, hot temperature conditions are simulated at the test object by a solar radiation simulator, which is assembled from separate sections of autonomous heaters and placed inside the thermal vacuum chamber together with the test object, while the sources radiation of independent heaters is equipped with optical elements, cold temperatures are obtained at the test object using a cooling device, the power of sections of independent heaters is regulated separately by a single control system, characterized in that an array of point sources of radiation is used in the sections of independent heaters, a uniform working field is obtained at the test object by mixing the radiation of point sources, and a cooled grating is placed between the solar radiation simulator and the test object. At the same time, an implementation is possible in which at least two types of point radiation sources with different spectral characteristics are combined, and feedback is used in the control system based on the readings of the sensors of the energy illumination level and the spectrum on the surface of the test object.

The principle of the proposed method is illustrated by drawings, where in Fig. 1, as an example, shows a general view of the simulator of solar radiation, consisting of four sections of autonomous heaters with a cooled grate, in Fig. 2 in a horizontal section shows a diagram of the formation of a directed radiation flux, in Fig. 3 shows a section of independent heaters, in Fig. 4 and FIG. 5 in horizontal section shows the principle of operation of the cooled grate in the modes of creating hot temperatures and cold temperatures at the test object, respectively.

Directly inside the thermal vacuum chamber 1, near the test object 2, a solar radiation simulator is installed, assembled from sections of autonomous heaters 3. In sections of autonomous heaters 3, an array of point radiation sources 6 placed with uniform alternation is used.

As point sources of radiation 6 in sections of autonomous heaters 3, gas discharge lamps, halogen incandescent lamps, phosphor or monochrome LEDs of various wavelengths, as well as assemblies of such LEDs are used. In a particular case, in order to obtain the required spectral range and spectral correspondence, several or at least two types of point radiation sources 6 with different spectral characteristics are combined in an array with uniform alternation. As an example of combination, sections of independent heaters 3 consist of two types of point sources of radiation 6: halogen lamps 7 and LED assemblies 8 of LEDs of different wavelengths.

Point sources of radiation 6 are equipped with their own optical reflective and/or refractive optical elements 9, which form a narrow-angle radiation distribution, in particular, optical elements operating on the principle of total internal reflection (TIR), reflectors, light guides, lenses, or a combination of several optical elements, in as a result, sections of autonomous heaters 3 create a directed radiation flux with a small distribution angle. The optical elements 9 are rigidly fixed in the sections of autonomous heaters 3 and do not require adjustment during operation. On the reverse side of the autonomous heater section 3, electrical and thermal interfaces 10 are located.

Provided that the distance from the point sources of radiation 6 to the test object 2 is several times greater than the distance between adjacent point sources 6 of the array, the formed directed radiation fluxes of all these point sources 6, evenly mixing with each other, form a single working field on the test object 2 with high uniformity. The principle of forming the working field on the test object 2 is shown in more detail in Fig. 2. The required levels of energy illumination in different parts of the working field are obtained by separately adjusting the power of sections of autonomous heaters 3.

A cooled grate 4 is installed between the radiating surfaces of the autonomous heater sections 3 and the test object 2. The principle of operation of the cooled grate is shown in Fig. 4 and 5. Cooling of the lattice ribs 4 occurs due to the circulation of liquid nitrogen through pipelines 5 connected to the lattice ribs 4. In the hot temperature mode at the test object 2, the radiation of each autonomous heater 3, namely, for example, the radiation of point sources 7, 8, The high directivity formed by the optical elements 9 passes through the grating 4 with low losses, passes through the cooled grating 4 and enters the test object 2. In addition, the walls of the grating 4 additionally increase the directivity of the radiation flux due to the absorption of excessively divergent rays.

The level of losses of the radiant flux is directly dependent on the angle of its non-parallelism and can be determined by the formula (Kolesnikov A.V., Serbin V.I. Modeling the conditions for external heat transfer of spacecraft. M .: Information - XXI century, 1997, p. 84 ):

WhereJ(0) - radiation intensity with non-parallelism angleβ at the inlet of the straightening grid;

l and a are, respectively, the depth and size of the side of the square cell of the straightening grating;

J(β) - radiation intensity at the output of the rectifying grating.

Thus, at a non-parallelism angle of 4° and the ratio l/a = 1, the intensity value J(β) will be 0.93 of J( 0 ) , which corresponds to a loss level of 7%.

On the contrary, when creating a cold temperature mode, with non-radiating sections of autonomous heaters 3, the grate 4, due to the cooling of its walls by the circulation of liquid nitrogen, acts as a cryogenic screen. In this case, the thermal radiation of test object 2, which is exclusively diffuse in nature, is almost completely absorbed by the walls of grating 4. Thus, when diffuse radiation passes through a rectifying grating with the same ratio l/a = 1, the loss level will be 88% (Kolesnikov A.V., Serbin VI Simulation of conditions of external heat transfer of space vehicles, Moscow: Information - XXI century, 1997, p. 87, Fig. 4.28). The remaining part is absorbed by the surfaces of sections of autonomous heaters 3 having cold temperatures, and non-radiating point sources 6, due to the small area of the radiating surface, do not significantly affect the heat transfer process.

From formula (1) it follows that the required degree of absorption of thermal radiation of the test object can be adjusted by changing the parameter l , in the simplest case, by adding additional sections of the cooling grid.

Transitional temperature regimes are obtained by the joint operation of the cooling grate 4 and sections of independent heaters 3 at reduced power levels.

The power levels of autonomous heaters 3 are regulated separately by a single control system that controls the independent power supply of the sections of these heaters from separate regulated sources. Due to this, the maximum uniformity of the working field is obtained or different levels of energy illumination are created in different parts of the working field and thus simulate partial shading or rotation of the test object 2 relative to the Sun, and in the case of combining several types of radiation sources with different spectral ranges, the necessary spectral correspondence is obtained. In a particular case, the control system uses feedback using one or more sensors of the energy illumination level 11 and / or spectrum 12 connected to the system, which are placed in the working field of the solar radiation simulator on the surface of the test object 2. In turn, the control system based on readings of these sensors automatically supports such characteristics of the simulated solar radiation at the test object 2, as the level, unevenness of energy illumination and spectral compliance. In addition, the energy efficiency of the solar radiation simulator is additionally increased by the optimal configuration of the autonomous heater sections, as a result of which the geometric dimensions of the working field correspond to the geometric dimensions of test object 2.

Outside the thermal vacuum chamber, such elements of the separate control system are placed, such as power supplies for sections of autonomous heaters 3 with adjustable power and a PC with software or a programmable logic controller, with the help of which these power supplies are controlled by the operator or in automatic mode based on the readings of sensors 11 and /or 12. Additionally, in the case of using radiation sources requiring thermal stabilization, such as LEDs, heat exchangers are installed in the section of autonomous heaters, which are connected to devices that dissipate excess heat from these sources outside the thermal vacuum chamber. For example, in the case of liquid cooling, a radiator or a refrigeration machine (chiller) is used.

The technical results of the invention are:

- increasing the reliability of thermal vacuum tests by improving such characteristics of the solar radiation simulator as uniformity of the working field, parallelism of the radiant flux, spectral range and spectral correspondence;

- increasing the energy efficiency of solar radiation simulation by placing a solar radiation simulator with a simple optical system in close proximity to the test object;

- additional increase in the energy efficiency of solar radiation simulation due to the optimal shape of the working field of the solar radiation simulator;

- reduction of time costs and consumption of liquid nitrogen during thermal vacuum tests due to the placement of the cooling grid in close proximity to the test object;

- reduction of time costs and labor intensity in the preparation of thermal vacuum tests due to the simple design of the solar radiation simulator, which does not require long, laborious installation and adjustment.

Claims (3)

1. A method for modeling the conditions of external heat exchange of spacecraft in a thermal vacuum chamber, which consists in simulating hot temperature conditions at a test object with a solar radiation simulator, which is assembled from separate sections of autonomous heaters and placed inside the thermal vacuum chamber together with the test object, while radiation sources autonomous heaters are equipped with optical elements, cold temperatures are obtained at the test object using a cooling device, the power of the autonomous heater sections is regulated separately by a single control system, characterized in that an array of point radiation sources is used in the autonomous heater sections, a uniform working field is obtained at the test object by mixing radiation from point sources, and a cooled grating is placed between the solar radiation simulator and the test object. 2. The method according to p. 1, characterized in that autonomous heaters combine at least two types of point sources of radiation with different spectral characteristics. 3. The method according to claim 1 or 2, characterized in that the control system uses feedback based on the readings of the sensors of the level of energy illumination and the spectrum on the surface of the test object.