Design of a comprehensive test system for spacecraft dynamics environmental testing

0 Introduction

In the process of spacecraft development and finalization production, a large number of dynamic environment simulation tests are required. In the evaluation of test effectiveness and the quality assurance of spacecraft products, test data acquisition and data processing play an important role. At present, in the field of test systems for spacecraft dynamic environment tests, the development level of dynamic integrated test systems represents the technological leadership of a country in this field. Therefore, it is necessary to develop a comprehensive test system for spacecraft dynamic tests.

1 Principle, composition and key technologies of the comprehensive test system for dynamic environmental testing

1.1 Principle of the comprehensive test system

In the spacecraft dynamic environment test, various dynamic responses of the structure such as acceleration, velocity, displacement, force, sound and other physical quantities are converted into dynamic electrical signals through relevant sensors. These weak electrical signals are input into the test system after conditioning, shaping, amplification and other measures. The test system with logic processing function dynamically collects the dynamic signals in real time and processes them. The comprehensive test system in the dynamic environment test should have high data collection frequency and large data flow, so the system requirements for meeting the use are relatively stringent.

1.2 Main performance indicators of the comprehensive test system
128-channel A/D synchronous sampling; 4-channel D/A output; the maximum channel sampling rate is 51.2KSa/s; the channel sampling data conversion accuracy is 16 bits.

1.3 Composition of the comprehensive test system
According to the functional division, the spacecraft dynamics comprehensive test system can be composed of data collection, data transmission, data processing, storage, etc. According to the structural composition, the spacecraft dynamics comprehensive test system can be divided into the following three parts:

(1) Computer software with various dynamic signal testing and analysis functions: random signal analysis, positive rotation signal analysis, impact signal analysis, etc.;

(2) Computer host platform and accessories: including various high-performance processors with powerful processing capabilities and memory, high-throughput computer
storage, high-resolution displays and their accessories;

(3) Test signal testing and acquisition device: including sensor, preamplifier and data acquisition system. [page]

1.4 Key technologies for integrated test system design

The development of a comprehensive test system for spacecraft dynamics environmental testing requires the following technologies to be met:

(1) Optimal design, structural composition, and flexible configuration technology of the dynamics comprehensive test system:

(2) High-speed data synchronization acquisition technology for integrated test systems;

(3) Large-capacity data real-time transmission technology;

(4) High-speed data storage technology;

(5) Various data processing technologies that meet usage requirements:

2 Architecture of the integrated test system for spacecraft dynamics environmental testing

The purpose of developing a comprehensive test system for spacecraft dynamics environmental testing is to carry out engineering design at a lower cost, shorten the development time of the comprehensive test system, and reduce risks to a minimum. Therefore, the most advanced and mature international industrial standards must be adopted in the design of the hardware system to maintain the compatibility of functional modules and directly absorb the results brought about by the development of modern science and technology; software design should make extensive use of application software frameworks to maximize the adaptation to changes in system scale, parameters, etc.

The spacecraft dynamics environmental test integrated test system consists of two parts: hardware platform and software system. The choice of hardware platform is determined by the test system structure adopted. Specifically, the dynamics integrated test system structure includes control mode, bus system configuration, distributed chassis structure, multi-bus composite system architecture, etc. The software system is the core of the test system, including software (i.e. driver, soft panel) operating environment and test-oriented application software.

The integrated test system architecture is the core technology for building a test system, including the test system structure, hardware platform, software system framework selection, etc. Selecting a general hardware platform and a general software framework is a good way to build a general dynamics test system. This article mainly focuses on the hardware level.

3. Hardware system structure selection of integrated test system for spacecraft dynamics environmental test

Currently, the instrument bus platforms that are relatively mature in technology and widely used in the market are divided into VXI bus and PXI bus[4].

As an open bus technology, VXI technology embodies the system requirements of standardization, modularization, serialization, and generalization. The open structure can realize the sharing of system resources, software resources, and hardware resources. The system channel is easy to upgrade and expand to meet the needs of various occasions, and it is convenient to reorganize the system. It can also adapt to the development of computer technology and integration technology, adopt the latest achievements of computer technology and integration technology, maintain the advancement and compatibility of the system, and improve the accuracy and reliability of system testing.
In addition to having many characteristics similar to VXI bus technology, PXI bus technology also has higher data transmission rate, miniaturization, and lower price.

(Low-end systems are usually more than $10,000 cheaper than VXI systems, and the price difference between mid- and high-end systems is smaller). At the same time, PXI bus has the advantage of being directly connected to computers compared to VXI bus. However, PXI bus technology has only been around for a short time and needs to be improved on the technical level. At the same time, it lacks the full support of the most influential manufacturers in the instrument field, the product variety is not rich enough, and there is a lack of strong technical support. Therefore, there are still certain technical difficulties and risks in using PXI bus technology to build high-precision large and medium-sized data acquisition systems that meet the requirements of spacecraft dynamics environment tests.

Combining the above-mentioned characteristics of VXI bus technology and PXI bus technology, through the analysis and research on the bus technology currently used in the establishment of spacecraft dynamics environmental test systems at home and abroad, VXI bus technology is used in this system as the basis for establishing the hardware platform of the dynamics integrated comprehensive test system, so as to reduce the difficulty and risk of system establishment. At the same time, during the design of the application software system, the design principle of software independence from the hardware platform is adopted as much as possible, and the development of PXI bus technology is kept track of. When PXI technology becomes more mature and conditions are met, the dynamics comprehensive test system can be easily transplanted to the hardware platform.

4 Hardware platform design of integrated test system for spacecraft dynamics environmental test

The hardware platform is the most basic component of the test system structure. The test system must be standardized, modularized, and serialized. Only by building the hardware platform on a highly standardized and modular structure can the development cost be reduced, the system development time be shortened, and the long-term availability of the system be ensured. The hardware platform of the spacecraft dynamics environment test integrated test system adopts a test unit structure composed of a main control computer with dual processors and a VXI chassis. Among them, a zero-slot controller is built into the VXI test bus chassis to manage the coordination and synchronization between VXI test modules; the main control computer is connected to various modules of the VXI test chassis through the PCI-1394 conversion card built into the computer, the IEEE1394 communication cable, and the zero-slot controller to achieve fast data transmission and communication management with the VXI test chassis. During the test, the VXI bus chassis completes the acquisition of dynamic response data through the A/D converter. All the collected data is transmitted to the main control computer in real time through the VXI bus and the IEEE1394 connection line. The main control computer completes tasks such as data processing and analysis, data storage, and real-time display. [page]

In order to meet the needs of comprehensive dynamics testing, a 32-channel high-speed synchronous data acquisition module AMC2322 was developed in the system, which can realize synchronous data acquisition of 128 channels in 4 modules, with a synchronous acquisition speed of 51.2KSa/s, and the number of channels can be expanded to more than 300 when the synchronous acquisition speed does not drop much. Another module designed is a 4-channel arbitrary wave D/A module, which realizes arbitrary wave excitation output, can be synchronized with A/D acquisition, and can be expanded. These two modules meet the performance requirements of the comprehensive test system of spacecraft dynamics environment test, and also leave room for system expansion.

During the development of the system, the following key technical issues were mainly addressed: First, how to save continuous high-speed sampled data. The method was to integrate a 64KWORD space FIFO memory on the data acquisition board to store 32 channels of parallel acquisition data. The module has the function of setting the host computer reading trigger condition, that is, pre-specifying the size of the AD acquisition storage space. Once the condition is met, an interrupt is immediately generated, and the host computer quickly completes the batch data reading. Due to the use of FIFO technology, the host computer reading does not affect data acquisition [5].

Another problem to be solved is the data transmission problem, which requires ensuring that the collected data is transmitted to the computer at the required speed. Because the actual data transmission rate of 1394 is 7-8MB/s, which is not high, we use 1394 FireWire technology to bridge the test system bus and computer, solving the bottleneck of data transmission. In the future, we can use optical fiber technology to bridge the system bus and computer, thereby obtaining greater system data transmission capacity.

Figure 1 Schematic diagram of the hardware platform of the dynamics comprehensive test system

The third problem to be solved is the data storage problem. A large amount of collected data flows into the computer and needs to be stored quickly, otherwise the system will not respond quickly enough. At present, general computer hard disks cannot meet the requirements of data storage. Therefore, we use SCSI technology disks to quickly store a large amount of collected data in the computer. We also optimize the software design to perform post-analysis and playback of data that does not need to be processed, which improves the overall collection speed of the system.

5 Conclusion

The design of the integrated test system for spacecraft dynamics environmental tests fully meets the technical indicators required for data collection and analysis in spacecraft dynamics environmental tests in all aspects, which lays a good foundation for us to develop large and medium-sized integrated test systems.