Comprehensive Detection of Particle Radiation Effects on the Orbital Platform of the Upper Stage of the Chinese CZ-4C Carrier Rocket

Abstract

Based on the characteristics of space particle radiation in the Sun-synchronous orbit (SSO), a space particle radiation effect comprehensive measuring instrument (SPRECMI) was installed on the orbital platform of the upper stage of the Chinese CZ-4C carrier rocket, which can acquire the high-energy proton energy spectra, linear energy transfer (LET) spectra of particles, and radiation dose rate. The particle radiation detection data were obtained at 1000 km altitude for the first time, which can be used mainly for scientific research of the space environment, in-orbit fault analysis, and the operational control management of spacecraft, and can also serve as reference data for component validation tests. After SPRECMI’s development, accelerator calibration and simulations were conducted, and the results demonstrated that all the measured indicators, including the high-energy proton spectra (energy range: 21.8–275.0 MeV, precision: <3.3%), total radiation dose (dose range: 0–1.04 × 10⁶ rad, sensitivity: 6.2 µrad/h), and the LET spectra (range: 0.001–37.20 MeV/(mg/cm²), >37.2 MeV/(mg/cm²)), met the relevant requirements. Furthermore, the in-orbit flight test revealed that the detection results of the load components were consistent with the physical characteristics of the particle radiation environment of the spacecraft’s orbit.

1. Introduction

To date, most of the space environment’s exploration activities rely on in-orbit satellites, including low-orbit (e.g., the International Space Station [1,2], China’s space station [3,4], the NOAA/POES satellite [5,6], FengYun-3 [7,8]) and medium/high-orbit satellites (e.g., NOAA/GOES [9,10], Feng Yun-4 [11,12]), and the monitored parameters comprise solar activity, charged particles, the upper atmosphere, surface potential, radiation dose, radiation effects, and single-event effects (SEEs). The detection results provide a preliminary understanding of the state of the space environment in each orbit [13,14], which can play an important role in the in-orbit operational control management and fault analysis of spacecraft. Nevertheless, due to inherent spatial and temporal variation in the space environment, the exploration of its regular characteristics and operational applications requires detection over a vast spatial area as well as long-term data accumulation, which is referred to as real-time and wide-area demand. Currently, only a small number of satellites carry detection loads for in situ exploration of the space environment, but their spatial coverage or temporal resolution is still insufficient.

The orbital platform of the upper stage is an integral part of the actual orbit entry of the carrier rocket. After the launch, the upper stage and its components can be operated in the orbit for a long time, which is suitable for space flight tests [15,16]. Further, compared with conventional spacecraft, the upper stage, supported by the current high-density launch missions, can provide more opportunities for exploring new space technologies while greatly reducing the experimental cost. Therefore, the spatial coverage and temporal resolution of space environment detection can be improved by utilizing a large number of retained orbits and a wide distribution of orbits in the current upper stage. Meanwhile, based on the high-frequency and short-cycle mission characteristics and the advantages of various types of on-board installations on the upper stage, it is convenient to rapidly validate the flight procedure under various new types of exploration loads and applications.

For measuring the radiation effects of space particles, CR-39, TLD, and PMOS detection techniques are widely used now [17,18]. But this paper proposes a space particle radiation effect comprehensive measuring instrument (SPRECMI), which is installed on the orbital platform of the upper stage of the CZ-4C carrier rocket. For the first time, the high-energy proton energy spectra, linear energy transfer (LET) spectra of particle radiation, and radiation dose rate are detected in about 1000 km SSO, which can improve the radiation-monitoring capability in the orbital space environment and ensure the safe operation, fault analysis positioning, and in-orbit management of spacecraft. At the same time, it can provide input conditions for component test verification.

2. Application Objective

The orbital platform of the upper stage of the CZ-4C carrier rocket mainly operates in about 1000 km SSO, where the distribution of spatial geomagnetic cutoff stiffness is shown in Figure 1, with a maximum geomagnetic cutoff stiffness of 11 GV.

The particle radiation environment in this orbit is mainly composed of Earth radiation belt particles [19,20], galactic cosmic rays [21,22], and occasional solar energetic particles [23,24]. The Earth’s radiation belts, including the outer and inner radiation belts, are stable particle-rich regions. Among them, the inner radiation belts are distributed in the equatorial plane in the altitude range of approximately 1.1–3.3 Re, and the particle species mainly include electrons and protons. The galactic cosmic rays are high-energy charged particles, including electrons, protons, and heavy ions, which are generated in the extrasolar Milky Way and are normalized to cover the entire space. The solar energetic particles are episodic and random, and they are generally encountered by LEO satellites (<3000 km) in the polar region.

The orbital platform of the upper stage encounters radiation effects caused by the various particles mentioned above, including single-event effects (SEEs), the total ionizing dose (TID) effect, and charging and discharging effects, among which the charging and discharging effects needs to be investigated by considering the data of high-energy electrons. The SEEs and particle radiation LET spectra are closely related, while the TID effect is caused by the total radiation dose accumulated by devices or materials in the orbit [25,26,27]. This study focuses on the particle radiation LET spectra and the TID, which are the main causes of satellite failures and malfunctions.

As one of the most dangerous radiation effects on the electronic systems in spacecraft, SEEs can cause soft or hard errors in the logic state of the electronic devices, circuit disorder, error in the processed data, instruction error, program “run-away”, computer paralysis, and the burning of silicon CMOS devices by their induced high current, causing satellite anomalies or malfunctions, even leading to serious accidents. The occurrence of SEEs in spacecraft is related to both the characteristics of the particles that hit the devices and the intrinsic features of spacecraft.

Galactic cosmic rays, solar cosmic rays, and the Earth’s radiation belt particles are the main sources of high-energy particles in orbital space, which may cause SEEs [28,29]. The LET value, which is the average amount of energy lost per unit length when charged particles are incident on a material, is used to assess whether the high-energy particles can lead to SEEs. The LET values of different types of incident particles with varied energies are different for different materials. Figure 2 shows the distribution of the LET values of the main components of the galactic cosmic rays calculated by the TRIM software package. Indeed, the evaluation of SEEs in a spacecraft requires orbital-space LET spectra and the intrinsic features of the devices as the input [30,31,32].

The radiation dose effect refers to the ionization of radiation particles by the atoms and molecules in spacecraft devices and materials, which transfers energy to the irradiated materials, thereby affecting the properties of the devices and materials. This effect is mainly caused by high-energy protons, electrons, and heavy ions, which are capable of both ionization and displacement. When the radiation dose of spacecraft devices and materials reaches a certain value, it can cause degradation and component failure. The in-orbit detection results for the radiation dose rate can be directly provided to the ground evaluation system as an environmental input for component validation tests.

The lack of understanding of space particle radiation effects makes it impossible to accurately identify the actual environmental triggers of satellite anomalies. Therefore, to efficiently evaluate the in-orbit performance of spacecraft, accurate LET spectra and radiation dose data of space radiation are needed. Additionally, the mechanism, characteristics, triggering conditions, and hazard level of space radiation effects must be further investigated.

3. Technical Index

The SPRECMI was installed on the orbital platform of the upper stage of the CZ-4C carrier rocket for measuring the high-energy proton energy spectra, particle radiation LET spectra, and radiation dose rate of the SSO. The main technical indexes of the SPRECMI are summarized in

Table 1. Main technical indexes of the SPRECMI on the orbital platform of the upper stage.

Item	Measuring Range	Accuracy/Sensitivity	Calibration Method	Evaluation Criterion
High-energy proton	20–250 MeV	<10%	Particle accelerator, standard radioactive source, combination of equivalent signal generator calibration and simulation analysis	Meet the requirements of accuracy or sensitivity
Radiation LET spectrum	0.1–37 MeV/(mg/cm2), >37 MeV/(mg/cm2)	5% (ΔN/N)
Radiation dose	0–105 Rad (Si)	20 µrad/h

.

The description of the indexes in this table can be found in the relevant literature [33,34]. During the ground development phase, detailed calibration was conducted on all technical indexes to ensure that they met the design requirements. The specifics of the parameters measured, the methods used for measurement, and the criteria for evaluation are further described in Chapter 5 of this paper.

4. Instrument Design

4.1. Principles

4.1.1. Detection of LET Spectra

The core materials of large-scale integrated circuits are usually made of silicon, so the basic principle of a silicon semiconductor detector, to measure the linear deposition energies of different particles in silicon materials, i.e., the LET spectra [35], is also used for the load design. A particle incident on a silicon semiconductor detector loses energy ΔE (keV). If the detector thickness is d (μm), the LET value (keV/μm) of the particle in the silicon material is expressed as follows:

$$\mathrm{L}\mathrm{E}\mathrm{T}=\frac{\Delta \mathrm{E}}{\mathrm{d}}$$

(1)

High-energy charged particles penetrate the satellite’s bulkhead and are incident on the silicon detector. The particles are incident on the first silicon detector and deposit part of their energy, and the LET value of the particles can be directly calculated from the above equation. However, some particles deposit all the energy and are blocked in the first sensor, and the actual path length is less than the thickness of the sensor. In this case, the LET value needs to be obtained by inverting the ground data according to the energy of the incident particles. The detected elements need to recognize whether the particles pass through the sensor. The detection principle of LET spectra is shown in Figure 3.

4.1.2. Detection of Radiation Dose

The radiation dose, which is the total energy deposition of particles per unit mass, is expressed as follows:

$$\mathrm{D}=∆\mathrm{E}/∆\mathrm{M}$$

(2)

where ΔE is the energy loss of incident particles to the silicon detector (keV), and ΔM is the unit mass of the detector (g).

The radiation dose rate, i.e., the cumulative dose per unit time, can be measured as follows:

$$\mathrm{H}=\mathrm{D}/\mathrm{t}$$

(3)

Since the key devices in the satellite are all made of silicon, silicon materials are used as the target material for radiation dose rate measurement [36,37]. The particles lose energy in the silicon detection material, and the energy loss value ΔE of the particles is recorded by electronics.

4.2. Systematic Scheme

The SPRECMI has an independent load comprising a sensor unit, an electronic unit, and a chassis structure. The core component is a sensor unit composed of three silicon semiconductor detectors and one typical device to be tested. The electronic unit mainly includes electronic circuits to process the measurement signal output by the sensor unit and data downlink.

Figure 4 illustrates the systematic measurement scheme of the space particle radiation effect gauge. It comprises a sensor unit of three silicon semiconductor detectors (D1, D2, and D3), where the typical device [38,39] to measure SEEs is located between D2 and D3.

The front-end detectors D1 and D2 mainly measure the high-energy protons and classify their energy spectra by the amplitude information from D1. D2 is used to identify the high-energy protons and measure the radiation dose rate. Specifically, the dose rate is measured by the total energy transfer of particles in D2 per unit time and the mass of D2.

The device to be tested is located between D2 and D3. D2 and D3 form a semiconductor telescope for the measurement of LET spectra. D2 is used for amplitude analysis to measure the LET value of particles. D3 is used for particle positioning to determine whether the particle hits or penetrates the device to be tested.

Once the SPRECMI was switched on, the above tests were performed simultaneously. The in-orbit real-time radiation dose rate and LET spectra could be directly provided to the ground evaluation system and used as the environmental input for the component validation test. Additionally, the measured in-orbit flip data of the typical device could be analyzed in conjunction with the in-orbit LET spectral data.

4.3. Design of Sensor Unit

The sensor unit measures the energy loss of the charged particles in the semiconductor detector and converts it into electrical signals for subsequent analysis by the electronic circuit. For the sensor unit design, it is necessary to incorporate the flight attitude and direction of the satellite as well as the design goals of miniaturization and weight reduction. The sensor unit configuration is shown in Figure 5, where three silicon-based semiconductor detectors are fixed to the front and back sides of the PCB with screws, and the device to be tested is installed below the sensor’s sensitive surface. The entire sensor unit is installed inside the SPRECMI, which was fixed in the satellite cabin through its mounting surface.

The silicon semiconductor detectors receive the injected charged particles. In terms of the linear response range, energy resolution, spatial applicability, etc., the ion implantation-type silicon semiconductor sensor is the best detector. The LET spectra are measured using two silicon semiconductor detectors (D2 and D3) to form a telescope system. D2 detects the energy deposition of the particles in the detector, while D3 is used to record whether the particles penetrate the detector or not, and the LET value of the particles that penetrate the detector can be obtained by dividing the deposition energy in D2 measured by the detector thickness. At the same time, a typical device to be tested is installed between the two silicon detectors, and SEEs in the device are monitored by the electronic unit. In this way, the incident particles and SEE information of the device can be simultaneously monitored, which is helpful to obtain the relationship between the two.

The radiation dose is measured by the total deposition energy of incident particles into D2. The minimum and maximum measurable energies by D2 are designed to be 100 keV and 3 GeV, respectively.

The geometric factor of the detection load (i.e., the ability of the load to accept particles) is also an important parameter for measuring the performance of space particles. It is a necessary parameter for data normalization and data comparison. Assuming that the particle flux is isotropic, the counting rate output of the payload and the particle flux in the environment can be described as follows:

$$\mathrm{M}\left({\mathrm{c}\mathrm{m}}^{-2}{\mathrm{s}}^{-1}{\mathrm{s}\mathrm{r}}^{-1}\right)=\frac{\mathrm{N}(\mathrm{c}\mathrm{o}\mathrm{u}\mathrm{n}\mathrm{t}\mathrm{s}/\mathrm{s})}{\mathrm{G}\left({\mathrm{c}\mathrm{m}}^2\mathrm{s}\mathrm{r}\right)}$$

(4)

where M is the measured payload flux, N is the counting rate, and G is the geometric factor [40].

It is clear that the measurement range of the load flux is related to the counting capacity per unit time and the geometric factor. The geometric factor determines the capacity of the load to accept space particles as well as the final counting rate of the load. A reasonable design of the geometric factor not only ensures that the counting in each instrument channel is not saturated but also avoids a low counting rate, which can lead to a large statistical drop.

According to the design structure of the sensor unit of the space particle radiation effect gauge, the detection angle of each object of measurement can be determined, as shown in Figure 6. Combined with the internal design of the load, the detection field of view composed of D1 and D2 can be used to measure the proton energy spectra. D2 alone measures the radiation dose, and D2 and D3 measure the LET spectra within a large field of view.

4.4. Design of Electronic Unit

The electronic unit of the SPRECMI mainly consists of front-end and back-end electronic circuits. The front-end electronic circuit, which includes a multi-channel charge-sensitive pre-amplifier, filtering and shaping amplifier, main amplifier, and peak-keeper circuits, primarily preprocesses the output charge signals from the sensor unit. The back-end digital electronic unit performs analog-to-digital converter (ADC) sampling, field-programmable gate array (FPGA) data processing, packet storage, and satellite bus interfacing for the front-end analog signals. Additionally, the electronic unit includes power conversion, sensor bias, and engineering parameter detection circuits. The principle of electronics for the space particle radiation effect gauge is shown in Figure 7.

5. Ground Calibration Results

The main purpose of the SPRECMI is to verify and accurately provide the actual measurement specifications of the load, including the channel accuracy, dose range, sensitivity, LET spectra range, and flux accuracy. Due to the limitations of the beam conditions of the ground accelerator, a combination of a standard radioactive source, equivalent signal generator calibrations, and simulations were used for cases that did not meet the calibration requirements.

Table 2. Calibration methods and results of the SPRECMI.

Parameter	Method	Expected Results	Achieved Results
High-energy proton distribution	Huairou electron accelerator (100–500 keV) at CAS; Heavy Ion Accelerator at Peking University (beam conditions: 2.2–20 MeV); standard radioactive source 241Am; other energies are analyzed using the combination of equivalent signal generator calibration and simulation analysis	Energy range: 20–250 MeV Linearity: <10% Energy-level precision: <10%	Energy range: 21.857–275 MeV Linearity: <1.88% Energy-level precision: <3.2%
Total radiation dose		Dose range: 0–105 Rad Dose sensitivity: 20 µrad/h	Dose range: 0–1.04 × 106 rad Dose sensitivity: 6.2 µrad/h
LET spectra range		0.1–37 MeV/(mg/cm2), >37 MeV/(mg/cm2)	0.001–37.20 MeV/(mg/cm2), >37.2 MeV/(mg/cm2)

lists the main calibration methods and results. The specific methods and processes can be found in the relevant literature [41,42]. And the experimental data come from the accelerator tests used by the Chinese Academy of Sciences and Peking University and the radioactive source ²⁴¹Am.

According to the ground calibration results, it can be seen that the achieved results of the energy range, dose range, and LET spectra range fully covered the expected values. The linearity and energy-level precision of high-energy protons and the dose sensitivity were better than the expected values. Through quantitative analysis of calibration data, all actual measurement values met the technical index’s requirements.

6. Preliminary In-Orbit Detection Results

The SPRECMI was successfully launched with the orbital platform of the upper stage on 17 March 2022. On 7 April 2022, after the SPRECMI was turned on, all telemetry parameters were normal and preliminary detection data were obtained, as described below. But, about one year later, it was turned off because of the platform’s energy issue.

6.1. Proton Detection

Figure 8 and Figure 9 show the in-orbit detection results of the high-energy protons and the AP-8 simulation results in the orbit environment of the rail section of the upper stage during 7–15 May 2022, respectively. The horizontal axis represents longitude, and the vertical axis represents latitude. Different colors represent the proton flux of different energies measured by the SPRECMI. It can be seen that the high-energy protons are concentrated in the South Atlantic Anomaly (SAA), and the measured high-energy proton distribution is in excellent agreement with the simulation results. The maximum flux of protons is of the order of 10³, which is also very consistent with the model simulation.

6.2. Radiation Dose

Figure 10 and Figure 11 show the global distributions of the measured dose rate under no and medium geomagnetic storms, respectively. The horizontal axis represents longitude, and the vertical axis represents latitude. Different colors represent the spatial dose rates measured by the SPRECMI. It is clear that the high dose rates are mainly distributed in the SAA and north/south high latitudes. The high dose rates in the SAA are primarily caused by protons and electrons in the radiation belts, while the high dose rates in the north/south high latitudes are mainly ascribed to the electrons and plasma in the radiation belts. It can be seen that the dose rates in north/south high latitudes are significantly enhanced during the storm. This is because the rail section of the upper stage in orbit in the north/south high latitudes is located at the edge of the outer radiation belt, and the high-energy electron burst after the geomagnetic storm increases the overall electron flux in the outer radiation belt, with more electrons then entering the SPRECMI’s sensor and being accepted compared to the calm period, thereby resulting in an increase in the dose rate.

6.3. LET Spectra

Figure 12 shows the LET spectral line and simulation results obtained by SPENVIS in the north and south polar regions during different time periods. The gray solid line represents the LET spectrum of the galactic cosmic ray simulated using ESA’s SPENVIS website under the same period, orbit, and shielding conditions. The galactic cosmic ray model is CREME96. The red and blue dots, respectively, represent the space LET spectrum measured by the SPRECMI. It can be seen that the LET1 and LET2 detection results are in good agreement, and the two spectral lines are basically coincident. The variations in the measured and simulated spectral lines are basically the same and follow a power law. Further, the LET spectra are stable during the test period, and the shape and intensity of the LET spectral lines do not change significantly from one period to another.

7. Conclusions

The orbital platform of the upper stage is suitable for future large-scale, systematic, and long-term sustainable space environment monitoring and detection engineering. In this study, the SPRECMI was installed on the orbital platform of the upper stage of the CZ-4C carrier rocket for measuring the high-energy proton energy spectra, particle radiation LET spectra, and radiation dose rate of the SSO. The results have been successfully applied to the in-orbit operational control and management of satellites and can provide useful data support for the design of anti-irradiation reinforcement for spacecraft. For example, they have been used for analyzing single-particle event anomalies in satellite platform processors, and for providing a particle radiation data source input for on-board component test payloads.