Payload refers to the direct realization ofspacecraftInstruments, equipment, personnel, test organisms and test pieces for specific tasks to be completed during on orbit operation.Spacecraft payloadIt is the most important subsystem for spacecraft to perform its final space mission in orbit.[1]
Payload is an important part of spacecraft. It is important because the quality of the final function and performance of payload selection and design will directly affect the quality of the realization of the final specific space mission.When the spacecraft platform is loaded with payload, it becomes a complete spacecraft capable of completing specific space tasks.Therefore, if the spacecraft is regarded as a primary system, the platform and payload are two secondary systems subordinate to it, and they are two subsystems at the same level.[2]
The payloads of spacecraft vary with different tasks, so there are many kinds of payloads and different classifications.According to the use of spacecraft and payloads, they can be roughly divided into remote sensing (or information acquisition), communication (or information transmission), navigation (or information benchmark), science, confrontation and others, as shown in the overview diagram.[2]
The payload of a satellite is the instrument, equipment or subsystem that directly performs a specific satellite mission.There are many kinds of payloads, and even the same type of payloads, their performance varies greatly.Payload capacity refers to the performance and detection capability of these instruments, equipment or subsystems.
Remote sensing payloads refer to various remote sensors for earth observation, including visible light remote sensors (using film and photoelectric)Multispectral scanner, infrared remote sensorMicrowave radiometer(passive), radar or scatterometer, etc.These remote sensors can obtain various military or civilian information on the ground (water surface), atmosphere, space, etc.
Communication payload is a typical payload, which is mainly composed of repeater and antenna.Such payloads can be used for military or civil satellite communications, as well as remote sensing spacecraft information transmission to the ground, and occupy a dominant position in commercial and military aerospace activities.[2]
Navigation payloads refer to various instruments and equipment that provide information about space and time benchmarks.Such payloads can be used for satellite navigation.
Scientific payloads include X-ray telescope spectrometerSolar optical telescopeIon mass spectrometer, X-ray spectrometer and various space environment measurement and monitoring devices.Such payloads can be used for space environment detection, astronomical observation and space science experiments.
Countermeasures payloads include laser, microwave, particle beam, kinetic energy, electronic interference, robot capture or adsorption, computer virus, pollution and other tools or equipment.Such payloads can be used for space attack defense confrontation.[2]
Other payloads mainly include new technology test payloads and special payloads.New technology test payloads refer to some new spacecraft, subsystems, instruments, equipment, even components and other technologies that have not been tested in orbit. They are launched into a certain orbit through special new technology test satellites for testing to verify their principles, schemes, feasibility, compatibility and reliability.Special payloads refer to non-technical payloads, such as space tourism (payloads are tourists), space souvenirs (payloads are envelopes, flags, etc.).[2]
A single purpose satellite is usually equipped with one or two payloads.Multi purpose satellite, usually equipped with several payloads.With the continuous development of aerospace technology, payloads are gradually developing towards the direction of low power consumption, small mass and small volume.aboutEarth observation satelliteIn terms ofRemote sensorInstalling on a satellite to complete different tasks is the main development trend to improve the efficiency cost ratio.Installing satellites with different payloads results in multi-purpose satellites, such as resource reconnaissance satellites and environmentmeteorological satellite, navigation and positioning satellites, etc.
Status and role
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Payload is the core of spacecraftspacecraft design Play a leading role in.
1. From the perspective of application functions
The nature and function of spacecraft are mainly determined by the payload.Space and space missions are completed by spacecraft, and the symbol for spacecraft to complete tasks and realize functions in space is to produce outputs that meet mission requirements.The effective output of spacecraft is mainly the output of payload.The subsystems in the spacecraft platform generally provide services and support for generating direct output payloads or other subsystems in the platform from different perspectives and aspects.For example, transponders and antennas on communication and broadcasting satellites providing communication and broadcasting services;Various radiometers on meteorological satellites that obtain atmospheric cloud imagessynthetic aperture radar ；CCD camera and infrared camera on earth resource satellite;The ocean water colorimeter, radar altimeter and imaging spectrometer on the ocean satellite.[2]
2. Judging from the difficulty of development
Due to the variety of payloads and the complexity of instruments, payloads have become the bottleneck in spacecraft development.After decades of development, the space technology has moved towards the application stage. Today, the platform has become more mature. However, due to the diversity of space missions, the payloads on the platform need to meet the needs of a variety of application tasks and develop more new instruments and equipment.The development of each new type of remote sensing instrument, observation instrument and scientific instrument, starting from the needs of users, through the preliminary scheme demonstration and feasibility study, to determine the overall scheme, carry out key technology research, develop the appearance, prototype, prototype stage, and finally launch into space, will take about ten years or even decades.[2]
3. From the perspective of research and development funds
The proportion of payload and platform development funds is about 3:1, and the payload has obvious advantages.For both remote sensing satellites and communication satellites, the ratio of platform to payload mass and the ratio of development funds are similar.The payload development funds account for about 75% of the total funds of the whole satellite, which means that the payload development funds are about three times of the platform.This also shows the weight and importance of payloads in the development of the whole satellite.
Therefore, in order to enable the payload to perform the space mission normally on orbit, it is necessary to require each support subsystem of the spacecraft to work normally during the whole life cycle of the spacecraft on orbit, and provide necessary support and support for the payload, otherwise, no matter how good the payload is, it cannot play its final role.This requires the spacecraft power subsystem to provide sufficient power to the payload;The thermal control subsystem shall ensure that the payload has an appropriate working temperature;The structural subsystem shall ensure that the payload has sufficient strength and stiffness;The control subsystem shall provide the payload with track keeping and high-precision pointing;The measurement and control, data management subsystem shall provide enough telemetry parameters and remote control commands to the payload.Here, it should be added that the above support subsystems should not only provide necessary support and guarantee for the payload, but also provide necessary support and guarantee for each other among the support subsystems.Therefore, in the system design, the subsystems constituting the spacecraft platform should not only take the need for payloads as their most basic design requirements, but also the design requirements of payloads on the platform subsystems should be determined under the auspices of the chief designer of spacecraft systems and after full consultation between payloads and platform subsystems,It shall comply with the principle of spacecraft function realization and overall optimization.[2]
Similarly, due toSpacecraft payloadIt is also an integral part of the spacecraft application system, so the design of spacecraft payload must also meet the requirements of the spacecraft application system, coordinate with other components in the application system, and strive to achieve the overall optimization of the spacecraft application system.For example, transponder saturation flux density W of communication satellite payloadsEffective omnidirectional radiation power EIRPs。、Receiving system performance quality (G/T)s。Such indicators must be consistent with the effective omnidirectional radiation power EIRP of ground application systems (various ground communication stations or terminals)EReceiving system performance quality (G/T)E。Such indicators can only be coordinated through communication link analysis, so that satellites can complete in orbit space missions and achieve satellite communication.[2]
work environment
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Figure 1 Composition of Payload Working Environment
As the core of spacecraft system, the design requirements of payload are different from those of general engineering system projects.One of the biggest reasons for the difference is that it will encounter some special environments that are not available in general engineering system projects.These special environments mainly include various external space environments (such as atmospheric environment, plasma environment, space debris, etc.) encountered when the payload is exposed to space operation, and various internal platform environments (such as mechanical environment, thermal environment, electromagnetic environment, etc.) encountered by the payload inside the spacecraft, as shown in Figure 1.In the analysis and design of payloads, these special environments need to be taken as constraints so that the developed payloads can adapt to these special environments.Due to the influence of special environment, the development process and products of spacecraft payloads are very different from general projects, such as space cameras andHome cameraThere are great differences in structure, shape, material, performance, price, etc.Therefore, the study of the environmental factors of the payload and their impact on the payload plays a particularly important role in the whole process of the development and application of the payload, and is also an important link and basis for the design of the payload system.[2]
System development program
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The development of the payload subsystem generally goes through the steps of constraint analysis, technical index determination, technical scheme formulation, technical index distribution, detailed design, test verification, manufacturing, assembly and application (see Figure 2), and it often needs several cycles to make the development scheme more reasonable and optimized.
Fig. 2 General procedure of spacecraft payload system development
1. Constraint analysis This is the first step in the development of the payload system.On the basis of the overall analysis and design of spacecraft, it is necessary to consider multiple constraints such as spacecraft system requirements, environmental conditions, technical level, time period, funding and so on, analyze the constraints of the payload system, and clarify the goals and technical approaches of payload system development.[2]
2. Determination of technical indicators
The main characteristics and performance parameters of spacecraft, such as overall dimensions, mass, power consumption, attitude control accuracy, etc., are mainly determined according to the requirements of payloads.Therefore, when designing the overall technical indicators of the payload, the bearing capacity of the spacecraft platform must be considered, and the advancement and realizability of the technical indicators must be taken into account. The overall technical indicators of the payload must be determined through comprehensive analysis and demonstration.The overall technical indicators of the payload should be comprehensive and quantitative, with precise definitions and measurability.[2]
3. Preparation of technical scheme
The scheme formulation shall be based on the premise of meeting the overall technical indicators, study and analyze various restrictions, formulate a variety of technical schemes, and select the best scheme from them.The determined scheme shall give consideration to innovation and inheritance: the adoption of new technologies, new materials, new processes and advanced design methods and means shall be encouraged, but ready-made and mature technologies shall be used as far as possible, and simple schemes with overall performance and functions meeting the requirements shall be used as far as possible, which can save money, shorten the development cycle and improve reliability.[2]
4. Allocation of technical indicators
The distribution of the overall technical indicators of the payload generally goes through the iterative process of analysis, prediction, adjustment, verification, etc.After the overall scheme and technical indicators of the payload are determined, the indicators shall be allocated to each subsystem within the payload.Through analysis and comparison, each subsystem scheme is finally determined to analyze and predict the index value that each subsystem can reach.Synthesize the contribution that each subsystem can make to the overall technical indicators to obtain the overall technical indicator prediction value of the payload.If the predicted value reaches or exceeds the overall design index, it can be distributed based on the predicted value;If the predicted value does not meet the requirements of the overall design index, another cycle of allocation and prediction will be carried out. If necessary, the key subsystems that affect the overall design index should be further improved and optimized from the scheme to the technical approach.This iterative process of indicator allocation makes the indicator allocation result achieve the best effect.[2]
5. Detailed design and verification
In the detailed design stage of the payload, the technical scheme, technical indicators and technical approaches have been defined. The subsystems and components of the payload should be designed in detail to provide all technical data for the payload manufacturing and system software manufacturing.The products manufactured and assembled according to the detailed design of the payload shall be subject to inspection, test and environmental simulation test to verify the performance, function and environmental adaptability of the payload.If problems are found in the inspection and test, it is necessary to improve the design, or even re analyze the constraint conditions, and manufacture and assemble new products according to the improved design, and then conduct inspection and test until all inspections and tests can be passed.[2]
The detailed design can be divided into two stages: the first sample and the first sample.All pass the inspection, test andEnvironmental simulation testThe detailed design of is called the exact detailed design of the payload;The detailed design that needs to be modified and improved is called the prototype detailed design of the payload.
6. Manufacturing, assembly and application
The subsequent development procedure of the detailed design and verification of the payload is the manufacturing, assembly and application of the payload prototype. Attention should be paid to making the designed products have better processability, assembly and reliability, and the economy of manufacturing, assembly and application.
Development requirements
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The specific development requirements of different types of payloads are different, even quite different. However, there are some common problems that must be considered in the development.Spacecraft payloadThe development of shall comply with the following basic requirements:
1. Carefully understand user needs and correctly determine overall technical indicators
This work is very important.User requirements are often put forward for spacecraft or the entire spacecraft application system, rather than directly for payloads. Payload designers need to work with spacecraft application systems and overall spacecraft designers to conduct comprehensive analysis according to user requirements and determine the overall indicators of payloads, which should be as comprehensive and quantitative as possible.For example, for optical imaging remote sensing satellites, users often put forward requirements such as ground resolution, observation band width, repeated observation period, etc., which are not completely aimed at payloads, but are closely related to satellite orbit type (including inclination, height, etc.), optical system focal length, pixel size, scanning mode, pointing control ability, etc.[2]
2. Carefully study various constraints and scientifically select the payload scheme
Generally, there are several schemes available for the design of payloads. On the premise of meeting the overall indicators, various constraints must be carefully studied and compared from various aspects to optimize the selected scheme as far as possible.The comparison of schemes should be quantified as far as possible, and different factors should be given different weights.It is incorrect to overemphasize that the higher the technical indicators of the scheme, the better. It should be based on the principle of meeting user needs;Of course, technical feasibility and economic considerations are also important.[2]
3. Reasonably allocate technical indicators based on the system
After the overall technical indicators of the payload are determined, the indicators shall be reasonably allocated to the equipment level and the component level.This allocation should regard the payload as a system, conduct a comprehensive analysis of the system performance, and the index allocation result should make the system optimal.For example, the satellite optical remote sensing systemmodulation transfer function After the (MTF) has been allocated to the payload optical remote sensor, the optical remote sensor shall be used as the system for MTF index allocation.The MTF of an optical remote sensor is the product of the MTF of the optical system, the MTF of the detector and the MTF of the imaging circuit. The scientific and reasonable allocation of MTF indicators must start from the system.[2]
4. Verify the optimized design through simulation and experiment
The determination of overall indicators, selection of schemes and decomposition of indicators mentioned above is not a one-way process, and it often requires multiple iterations to make the design more reasonable and scientific;At the same time, the establishment and application of appropriate models for simulation analysis in the design can make the design more optimized.The parameters of the system, equipment and components are determined through simulation analysis, and the system performance is estimated, which can reduce the development cost and shorten the development cycle, but the correctness of the model must be verified.Even so, it is generally necessary to carry out the cycle of "design test verification design modification" to make the design meet the requirements as far as possible.This is the task of each development stage, and each stage must pass the review.[2]
In general,Spacecraft payloadThe following principles shall be considered in the development of
(1) The determination of technical indicators shall meet the user's requirements and take into account the advancement and realizability.
(2) Mature technology shall be used as far as possible to ensure reliability and economy.
(3) The formulation of the technical proposal shall fully consider various constraints, as well as the feasibility of processing, assembly and testing.
