The structural system of a satellite can be compared to a skeleton. Its core task is to carry and transmit force, provide a stable and reliable installation platform for all instruments and equipment, and withstand various mechanical environments (vibration, impact, acceleration, noise, etc.) and space environments (high and low temperature, vacuum, irradiation, etc.) experienced throughout the life cycle from launch to on-orbit operation. Generally speaking, for most satellite structures, the more severe load conditions are during the launch phase, including launch vehicle overload, aerodynamic pressure, interstage separation, wind gusts, engine jets, etc. At present, the mainstream small satellite structural forms include load-bearing cylinder type, truss type, plate frame type, and plate and tube type. Plate structure is the most common structural component in satellites and is divided into homogeneous single-layer panels, reinforced panels and sandwich panels. Currently, the most commonly used honeycomb sandwich structure panel is composed of panels, structural adhesives, inserts and sandwich peak cores, that is, it is composed of two high-strength, thin-thickness surfaces. The panel is on the outside, with a lightweight honeycomb core material in the middle, and is a sandwich structure made of adhesive. The panel is generally a film material with greater strength and stiffness, and the honeycomb core material is a very thin honeycomb lightweight material, usually an aluminum alloy honeycomb core material. Compared with other types of plate structures, honeycomb sandwich structure panels have higher strength-to-mass ratio and stiffness-to-mass ratio, and have better fatigue resistance, vibration damping, sound insulation and noise reduction, heat insulation and other functional characteristics.
The satellite’s mechanical system can be compared to joints and muscles, and its core task is to achieve purposeful and controlled movement. The satellite mechanism system consists of at least one moving part and a power source. The moving part is used to achieve specific actions, and its form needs to be determined according to the function of the mechanism. The power source is used to drive the moving parts, which can take different forms such as motors, pyrotechnics devices, pressure gas sources, springs, strain energy stored in materials, and deformation caused by metal phase changes (such as shape memory alloys). In addition, most mechanisms have a feedback device (such as a potentiometer, travel switch, angular velocity sensor, strain gauge, etc.) to provide information such as position, speed, force, or torque to the mechanism’s control system. Depending on the function of the mechanism, the main types of mechanisms on satellites currently include connection and separation mechanisms (for example, the connection and separation mechanism between the satellite and the launch vehicle or between the satellite sections, usually using a connection device in the form of a strap or a clamp block. After the pyrotechnic device is detonated to release the connection, it relies on the power of the spring or movement. Separation is achieved by the thrust of the launch vehicle separation engine), compression release mechanism (such as the compression release mechanism of an unfolded solar array or antenna, which uses a compression rod or compression belt to compress the solar array or antenna in a retracted state during satellite launch, and detonates a pyrotechnic device in orbit to release the compression rod or compression belt) , deployment mechanism (such as the deployment mechanism required for deployable solar arrays, antennas or other components on the satellite, which relies on some form of power source to extend the components from the retracted state to the required position or shape, and lock it in the required position or shape. Some mechanisms can also be retracted from the locked position to the original retracted position. convergence state), driving mechanisms (such as solar array driving mechanisms for sun orientation and power transmission, antenna orientation mechanisms for one-way or two-way rotation, spin satellite platforms or spin antenna despin components, etc. Motors are generally used as the power source, and relevant components are driven at the specified speed and time according to instructions). Generally speaking, successful deployment is half the success of the mission, while failed deployment is the end of the mission. Therefore, there must be backup for key mechanisms. For example, if a deployment mechanism is stuck, a backup explosive cord or cutter must be used to forcibly cut it off; if a drive motor fails, a backup motor must take over. In addition, there must be space lubrication, which is the “vital gate” of the mechanism. Lubricating oil on the ground will volatilize, solidify, and fail in vacuum. Solid lubrication (such as molybdenum disulfide, polytetrafluoroethylene coating), liquid lubrication (such as special space lubricants such as perfluoropolyether) or special technologies such as rolling bearings must be used to prevent the mechanism from cold welding in vacuum (metal surfaces stick together under vacuum and pressure).
Generally speaking, the materials suitable for satellite structures and mechanisms mainly include metal materials and composite materials. Metal materials mainly refer to aluminum alloys (good processing performance, often used in main structural parts), magnesium alloys (density is lower than aluminum, used in some non-main load-bearing structures that have extreme requirements for weight reduction), titanium alloys (high strength, corrosion resistance, often used in key joints, fasteners and parts that bear extremely high loads). Aluminum alloy is currently the most widely used light metal material on satellites. Its main properties are low density, good process performance, and the lowest cost among all light metal materials. For composite materials, composite materials used as satellite structures are mainly fiber-reinforced composite materials. They are composed of two component materials. One is fiber material (mostly long fiber materials), which plays a reinforcing role. The other is a matrix material, which supports the fiber material, maintains the shape of the material, and transmits loads between fibers. Most of the matrix materials currently use epoxy resin. The biggest advantages of composite materials are high specific strength and high specific modulus (that is, higher strength and greater stiffness under the same weight), and the thermal expansion coefficient can be designed. Through layering design, it can hardly deform under the harsh temperature changes of space, which is the lifeline for high-precision satellites.
From the perspective of industrial development, technological development is mainly driven by the current clearest and largest application demands. The construction of over 10,000 low-orbit constellations represented by StarNet (GW constellation) and Yuanxin (G60 constellation) is currently the core driving force. This has also brought new requirements to the development and production of satellite structures and institutional systems. First, satellite structures and institutions must achieve extreme mass production and low cost (the use of flat-panel and modular designs) (such as Starlink satellites), simplifying the structure and mechanism to facilitate industrialized assembly line production); secondly, as low-Earth orbit becomes increasingly crowded, collision avoidance has become a “rigorous need for survival” of satellites. This requires that future satellite structures may need to consider adding more anti-collision, sensing or propulsion modules. The mechanism needs to have orbital maneuverability, and may spawn new mechanisms such as dedicated robotic arms for on-orbit services (such as refueling, maintenance) and debris cleanup.
