The main provisions of the methodology for ensuring the resistance of the onboard equipment of spacecraft to the effects of the radiation effects of outer space

During full-scale operation, the spacecraft is exposed to a wide range of space factors, the main of which are radiation effects. Ensuring the radiation resistance of a spacecraft (SC) is a complex task that is solved both at the stage of development of a spacecraft and beyond the stages of development when conducting full-scale experiments and space exploration.

Impact of radiation effects on spacecraft

Work on the study of the influence of radiation effects on spacecraft in the world and in our country has been carried out for several decades. During this time, since the discovery of the Earth's radiation belts, the physical radiation conditions of the orbital functioning of the spacecraft have been studied in sufficient detail, the main methodological principles for protecting the onboard equipment (BE) of the spacecraft from radiation have been developed [1].

Taking into account the fact that each spacecraft contains about 100–200 thousand electronic components, it is obvious that exceptionally high requirements are imposed on the electronic component base of space applications, both in terms of its reliability and radiation resistance. In this regard, the improvement of the methodology for providing the SC BE with a highly reliable ECB of the required level of radiation resistance is of paramount importance for the further development of the space industry.

As a result of many years of cooperation with leading domestic research institutes and universities, ISS JSC has obtained a significant groundwork in the field of studying the levels and mechanisms of the impact of space factors (ISF) and ensuring the resistance of BE and SC to their impact.

The impact of energy particles on the spacecraft leads to the degradation of its functional surfaces and disruption of the operating modes of the active ECB, on the basis of which the BE of the spacecraft is made. The ionization reaction of various types of electronic components is characterized by a wide variety, while failures of most electronic components occur due to ionization effects and structural damage to materials, as well as heat release [2].

In a number of electronic components, the occurrence of failures under the influence of proton and electron irradiation is due to the degradation of characteristics due to the appearance of volumetric radiation effects. Structural damage (the formation of radiation defects inside the crystal lattice) affects the electrophysical characteristics of materials: they reduce the concentration, lifetime, and mobility of charge carriers.

Surface ionization effects are associated mainly with the accumulation of charges in the layers of gate and passivating dielectrics, as well as with changes in the characteristics of the interfaces. These effects mainly determine the failures of modern electronic components under the influence of cosmic radiation.

Along with internal processes in ECB crystals, under radiation exposure, there are accompanying external effects: electrical effects on the leads, leakage between the leads, etc. In particular, the appearance of voltage and current pulses at the ECB leads occurs as a result of electrostatic discharges of dielectric materials due to their radiation charging under the influence of electrons and protons of outer space.

High-orbit satellites for communication, navigation and geodesy, created at ISS JSC, operate on several types of orbits that cross almost all areas of near-Earth outer space (Fig. 1).

Рис. 1. Орбиты, на которых функционируют КА разработки АО «ИСС»

Fig. 1. Orbits on which spacecraft operate, developed by JSC ISS

Full scale tests on the study of space factor

JSC "ISS" has significant experience in monitoring the parameters of the space environment [3–5], dozens of full-scale experiments have been carried out on board the spacecraft, resulting in the refinement of the physics and mechanisms of the impact of the space environment on the spacecraft, the development of methods and means of protection, the use which allows to ensure a long period of active existence of the developed spacecraft (up to 15 years). The table shows the main stages in the development of the space environment monitoring system at ISS JSC.

Obtained in the course of full-scale experiments, including those carried out on board the spacecraft developed at ISS JSC, data on the parameters of the energy spectra of charged particle flows and the dependence of the absorbed dose on the thickness of the structural protection for each operated orbit and the radiation spectrum of a particular types are given in tabular form as a dependence of the absorbed dose on the value of protection [6].

Using the obtained dependences in the development of BE, taking into account the protection provided by the design of the SC and BE, according to the previously developed methodology, the total absorbed dose value for the critical ECP, which is part of the BE, is calculated.

The main stages in the development of a system for monitoring the space environment on a spacecraft developments of JSC "ISS"

Orbit	Experiment dates	Registered parameters of the space environment	Main research results
Circular 1000 km	1968–1971	Flows of electrons and protons	The model of the Earth's radiation belts has been refined, data on the planetary distribution of SCR have been obtained
High elliptical orbit	1968–1975	Fluxes of electrons and protons, absorbed dose
Geostationary orbit	1978–1990	Electron and proton fluxes, absorbed dose, electric fields, external noise environment	The hypothesis about the influence of electrization factors on the spacecraft was confirmed
Geostationary orbit	1983–2003	Electron and proton fluxes, absorbed dose, electric fields, external noise environment	The processes of formation of magnetospheric plasma, the influence of solar activity on the level of radiative forcing
Круговая, 20 000 км	1983–2016	Electron and proton fluxes, absorbed dose, electric fields, potential differences, external noise environment	Refinement of the model of the earth's radiation belts
High elliptical orbit	2001–2003	Electron and proton fluxes, absorbed dose, interference environment	Refinement of the model of outer space
Geostationary orbit	с 2017	Absorbed dose, interference environment, SVA pressure inside the instrument compartment	The model of the Earth's radiation belts is being refined, the parameters of own external atmosphere and electrification are being studied
Circular, 20 000 km	с 2017	Electron and proton fluxes, absorbed dose, electric fields, external noise environment, own external atmosphere pressure	The model of the Earth's radiation belts is being refined, the parameters of own external atmosphere and electrification are being studied

Further, based on a comparative analysis of the calculation results with data on the radiation resistance of the ECB obtained experimentally, taking into account the required safety factor, a conclusion is made about the radiation resistance of the BE.

Data on the radiation resistance of domestically produced ECB should be given in the technical specifications (TS) for each specific type rating by the ECB manufacturer based on the results of experimental studies on modeling facilities (electron accelerators, protons, gamma radiation source) in the form of its group of resistance. However, as shown by a survey of ECB manufacturers, the overwhelming majority of ECB dose tests are performed only once before they are put into mass production, which does not meet modern requirements for the need to periodically confirm the declared level of resistance required in contracts for co-building of modern spacecraft.

It is obvious that in order to solve the problem of ensuring the resistance of a spacecraft to the effects of radiation dose effects, at present in the domestic space industry, special attention should be paid to determining and confirming the actual radiation resistance of the used element base, which is achieved as a result of periodic radiation tests of electronic components [7].

Creation and implementation of a methodology for guaranteeing the radiation resistance of elemental base used to complete the spacecraft developed by ISS JSC

Until the 2000s the basis for the calculation estimates of radiation resistance was the technical specifications (TS) for the ECB. Typical specifications give levels of radiation resistance in the form of limiting values of radiation resistance, at which the values of the criterial parameters are within the normal range. At the same time, for the absolute majority of ECBs, the indicated data were obtained during acceptance tests during the delivery of ECBs to a series and since then they have not been subjected to periodic tests for compliance with the levels of radiation resistance specified in the TS.

As part of work on one of the international projects to create a spacecraft, ISS JSC sent inquiries to 24 manufacturing plants (MP) regarding the frequency of testing produced electronic components for dose effects. Only six plants gave answers about the availability of ECB test protocols. The rest of the plants answered that the tests had not been carried out since the ECB was put into series.

At the same time, for foreign-made ECB (ECB IP) of the “space” quality level, intended for use specifically in the conditions of exposure to the space radiation environment, tests to determine the actual level of radiation resistance (dose effects) are carried out on a sample from each batch.

Testing for dose effects of all batches of active ECB is a rather expensive and time-consuming procedure. Therefore, the world's leading manufacturers of space technology are developing some compromise approaches to the issue of guaranteeing the radiation resistance of onboard equipment. Thus, in order to minimize the financial costs of conducting radiation tests of each flight batch of electronic components for dose effects, it was necessary to carry out a set of works related to the justification and implementation of the frequency of testing the applied electronic components.

As a result of these works, JSC ISS in 2010 issued and approved in the prescribed manner a document regulating the frequency of radiation testing of electronic components, the number of samples for testing and the intensity of irradiation, "Methodology for testing to confirm the requirements for onboard stability spacecraft equipment developed by JSC "ISS" to the impact of dose effects of ionizing radiation from outer space", which establishes the conditions, procedure and frequency of testing for dose effects.

The main provisions of this concept are as follows: given that there is variability in resistance to the total dose in different batches [8; 9], all active elements, during the production of which radiation resistance control is not carried out, must be subjected to radiation acceptance tests of the batch according to a certain frequency.

The frequency of tests can be increased based on the results of tests of specific types of electronic components of a certain manufacturer, which was allowed under the simultaneous fulfillment of the following conditions:

• – unchanged manufacturing technology;

  – confirmation of the level of resistance guaranteed by the specifications for at least three consecutively tested batches.

When developing a system for the frequency of testing ECB for dose effects, the experience of work in the framework of previously completed projects was taken into account. In accordance with the contract requirements for these projects, in order to confirm the radiation resistance of the BE and SC as a whole, for the first time in the cooperation of ISS JSC, a complete control of the radiation resistance was carried out.

For this purpose, at the first stage, radiation tests of 180 types of ECB of domestic production for dose effects were organized.

The results of the first stage of testing confirmed the feasibility of the implemented approach - out of 180 types of ECB of domestic production, subjected to tests on a gamma installation, in 42 types of ECB, a deviation of the controlled criteria parameters beyond the norms of specifications was recorded when dialing a dose lower than declared in the specifications for ECB data [ 10]. Timely determination of the actual radiation resistance of the ECB made it possible to carry out the necessary refinement of the BE and thereby ensure the required radiation resistance of the created spacecraft, and, accordingly, the required ACS of the spacecraft.

The results obtained made it possible to start creating a database of experimental data on the radiation resistance of electronic components, which is used in the work on subsequent projects with its constant updating and replenishment.

Thus, by 2010, in the cooperation of ISS JSC, an effective system for confirming the radiation resistance used in the composition of automatic spacecraft of the element base was developed and implemented, based on periodic radiation dose tests of samples from ECB batches intended for complete set of BE manufactured by spacecraft.

The main provisions of the “Methods for conducting tests to confirm the requirements for the resistance of onboard equipment of spacecraft developed by JSC ISS to the effects of dose effects of ionizing radiation from outer space” were introduced into the next edition of OST 134-1034-2012 “EQUIPMENT, INSTRUMENTS, DEVICES AND EQUIPMENT OF SPACE VEHICLES. Methods for testing and assessing the resistance of onboard electronic equipment of spacecraft to the effects of electronic and proton radiation from outer space according to dose effects” [11].

In 2017, the “Typical methodology for accelerated testing of electronic products for resistance to long-term low-intensity ionizing radiation of outer space by dose effects on a test gamma complex of the Radian type” was developed and implemented. This method fully complies with the requirements of the industry standard and determines the procedure for testing electronic components made using bipolar technology, potentially sensitive to low-intensity radiation, and using low-intensity gamma radiation of 0.01 rad/s.

Creation of an experimental base for the radiation resistance of the element base used to complete the spacecraft developed by JSC "ISS"

Together with the development and implementation of the methodological foundations of the system for confirming the radiation resistance of the elemental base used as part of automatic spacecraft, the cooperation of ISS JSC launched work to create the necessary experimental test base.

In 2001, by a joint decision of ISS JSC, SPC Polyus JSC and Tomsk Polytechnic University, a “Decision on the organization of work to determine the radiation resistance of electronic components on the basis of the Introscopy Research Institute of Tomsk Polytechnic University and SPC JSC” Pole" was worked out.

In this Decision, it was noted that NII IN TPU has a test bench based on the linear accelerator ELU-4 ..., and SPC "Polyus" has a set of certified equipment for monitoring and measuring ECB parameters.

In 2006, a "Decision on the implementation of a system for guaranteeing the radiation resistance of the element base" was developed.

For the subsequent implementation of the elements of the system for guaranteeing the radiation resistance of electronic components and testing flight batches of electronic components for dose effects in Tomsk, an integrated test infrastructure was created on the basis of the Research Institute of Introscopy of TPU and JSC SPC Polyus, including a set of simulating radiation installations, testing and control and measuring equipment, which ensures the rejection of potentially unreliable components and the assessment of the radiation resistance of purchased batches of electronic components manufactured using various technologies, within the time limits determined by the specified duration of the development of the onboard equipment of the spacecraft (Fig. 2).

а                                    б                              в

Рис. 2. Линейный ускоритель электронов ЭЛУ-4 ( а ), гамма-излучатель «Рокус-АМТ» испытательного комплекса «Радиан» ( б ), гамма-излучатель «Рокус-АМТФ» испытательного комплекса «Радиан-2» ( в )

Fig. 2. Linear electron accelerator ELU-4 ( a ), gamma-emitter «Rokus-AMT» of test complex «Radian» ( б ), gamma-emitter «Rokus-AMTF» of test complex «Radian-2» ( в )

The developed test infrastructure includes:

– a linear electron accelerator providing radiation dose rate in the range of 10–300 rad/s;

• – gamma complex "Radian" based on the gamma emitter "Rokus-AMT", which provides selective testing of electronic components for a full dose of ionizing radiation in the dose rate range of 4–0.001 rad/s [12];

• - Radian-2 gamma complex with a set of filters-absorbers based on the Rokus-AMTF gamma emitter, which provides selective tests of EC for a full dose of ionizing radiation in two dose rate ranges: 0.1–0.0001 rad/s and 0.005–0.0005 rad/s.

The facilities are equipped with a rail-mounted, remote-controlled system for changing the dose rate during irradiation, without interrupting the tests; the non-uniformity of the absorbed dose in the ECB sample at gamma complexes does not exceed 10%.

During irradiation, the ECB located on the test boards in the active electric mode is located in (Pb-Al) containers, which provide photoabsorption of the low-energy radiation component and an equilibrium electron spectrum close to the spectrum of electrons in silicon when it is irradiated with high-energy gamma quanta.

The results of the implementation of the methodology for guaranteeing the radiation resistance of elemental base used to complete the spacecraft developed by ISS JSC

According to the developed methodology, input control, diagnostics and control radiation tests were carried out for more than 1800 flight batches of electronic components, more than 570 types manufactured with different technologies. Several dozens of potentially unreliable electronic components of different levels of complexity, manufactured using different technologies, have been found. For 199 ratings (35%), failures were recorded before reaching the level of resistance guaranteed by the manufacturer.

It was found that ECB of bipolar technology under low-intensity irradiation more often, although not always, demonstrate lower radiation resistance than that determined during tests at high irradiation intensity [13]. In addition, the influence of the dose rate on the nature of annealing at elevated temperature after irradiation with the same dose and close dose changes in the ECP criterion parameter was established, which must be taken into account when extrapolating the results to the natural conditions of outer space.

Thus, the solution of the problem of ensuring reliable long-term operation of the onboard equipment of the spacecraft in relation to failures due to dose effects of low-intensity ionizing radiation required the creation of a new test infrastructure, as well as hardware and methodological support in relation to electronic components of various levels of integration.

Conclusion

At present, the integrated test infrastructure that has been created, including the described simulation radiation facilities, test and instrumentation, makes it possible to identify potentially unreliable components and evaluate the radiation resistance of batches of electronic components from supplier enterprises in the required short time.

Based on the results of the tests of ECB flight batches, a unique electronic database was formed, which made it possible to increase the intervals for testing potentially reliable ECBs (currently 40 ratings) and, consequently, to reduce the volume of required tests.

The created test infrastructure and periodic radiation tests of the electronic components of flight parties for dose effects have become an obligatory component of the system for ensuring the radiation resistance of the SC BE developed by the cooperation of enterprises of ISS JSC [14].