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Avionics are the electronic systems used on aircraft, artificial satellites, and spacecraft. Avionic systems include communications, navigation, the display and management of multiple systems, and the hundreds of systems that are fitted to aircraft to perform individual functions. Spacecraft avionics provide the critical command and data handling (CDH), communications (Comm), electrical power system (EPS), and attitude control and determination (ADCS) systems required to enable a diverse set of scientific, commercial, and government mission objectives.
Avionics system plays a core role in the realization of information sharing and comprehensive utilization, function integration, resource reorganization and optimization, and information processing and transmission. It is the foundation for spacecraft to implement autonomous management and control and is also a bridge for communication management from a spacecraft to other spacecraft and ground station .
With the continuous advancement of electronics and computer technology, the functions and performance of spacecraft avionics systems have also continuously improved, covering functions such as spacecraft remote measurement and remote management, energy management, thermal management, health management, payload information processing, and mission task management. As the amount of data generated by satellite electronic equipment continues to increase, a large amount of data processing requirements place higher requirements on satellite information processing capabilities. The avionics system is the information core of the whole satellite, especially for the requirements of intelligent satellite systems.
Avionics System trends
At present, satellite sub-systems mostly adopt independent design schemes, which decentralize satellite attitude control, propulsion control, thermal control, satellite-ground link communication, and power control functions. The onboard computer is responsible for tasks such as remote control, telemetry, program-controlled operation, thermal control, and time management. The attitude and orbit control computer are responsible for attitude and orbit (including propulsion control) control. Each sub-system such as power supply, thermal control, and digital transmission is equipped with corresponding lower-level computers responsible for telemetry acquisition and remote control of the respective sub-system. However, the satellite system designed using this approach is usually resulting in heavyweight, high power consumption, large volume (aka high size, weight, and power (SWAP)), complex interface relationships, weak system reconfiguration capabilities, and low functional density.
In the future, the advanced avionics system integrates most of the platform’s electronic equipment. In order to overcome the abovementioned shortcomings and make the satellite avionics system better meet the SWAP and flexible system configuration requirements of future missions, it is necessary to improve its design technology, that is, from the current independent design of each sub-system to the open and modular design of the entire satellite. Based on the principle of unified application, deployment and operation of hardware resources, and the full use of the various functions of the software, the information sharing of the entire satellite, simple system configuration, and overall performance optimization are realized.
The next generation of intelligent avionics systems for future communication satellites aim for an open architecture of “centralized management, distributed measurement and drive, and software and hardware modular design.” The universal, standardized, and scalable intelligent avionics system is built based on the basic modular elements of open hardware modules, open software components, and industry standardized internal and external busses.
In order to achieve autonomous and healthy operation of the satellite, the intelligent satellite system uses the Failure detection isolation and recovery (FDIR) software to monitor the status of the satellite in real-time and diagnose and predict its working status and performance trends. When a failure occurs, the FDIR software can locate the failure in time and determine which components are not working normally or the performance is degraded.
Design goals are Satellites can survive if any failure occurs; When a failure occurs, try to extend the mission time of the satellite and reduce the loss of mission interruption; The life of the satellite should be guaranteed: optimize fuel consumption and minimize system configuration and component losses.
The “lockstep” technology is a fault-tolerant computing technology. This technology uses the same, redundant hardware components and processes the same instructions at the same time. The core idea is to keep multiple central processing units (CPUs) and memories executing the same instructions accurately and synchronously by running synchronous comparisons in operation to improve the fault-tolerant computing capability of the avionics system.
The two typical scenarios usually encountered by satellite avionics systems during operation are (a) a node fails or requires functional reorganization so that some tasks on this node need to be migrated to other nodes through the network and (b) the resource occupancy rate of a node is too high so that some tasks on this node will be migrated to other relatively idle nodes for execution. The avionics system is designed with networked real-time multitasking distributed system software, which can also implement dynamic reconfiguration of functions and task scheduling.
LADEE Spacecraft Avionics
The LADEE (Lunar Atmosphere and Dust Environment Explorer) spacecraft is based on NASA’s Modular Common Spacecraft Bus (MCSB) that was developed between 2006 and 2008 at NASA’s Ames Research Center. The spacecraft bus was developed to carry a variety of scientifically useful payloads to a number of targets including lunar orbit, Low Earth Orbit, lunar surface, Earth-Moon Lagrange Points and Near Earth Objects. Easy manufacturing, parallelism in development and design, and systems components from existing flight-proven product lines contribute to making MCSB a low-cost, but highly efficient spacecraft architecture that will gain extensive flight heritage in a number of applications.
The four LADEE spacecraft modules consist of a Radiator Assembly that carries avionics, electrical systems, attitude sensors and payload equipment; the Bus Module; the Payload Module that facilitates the two largest payloads; and the Extension Modules that house the Propulsion Module of the spacecraft.
Power from the solar panels is routed to the Solar Array and Charge Interface which distributes power to the individual spacecraft systems and a single Li-Ion battery that is being charged for times of higher power demand and night passes. The Solar Array and Charge Interface distributes power to two Power-switching and Pyro Integration boards (PAPI) and two SATORI Boards.
The PAPI boards route power to the Thermal Control, Guidance, Navigation & Control and the Propulsion Subsystems while the SATORI boards provide power to the Command & Data Handling System, the Telecommunications System and the four Payloads. Interface Power Controllers in the individual systems distribute power to the component level. LADEE uses a 28-Volt power bus and features switchable fuses and SATORI over-current protection.
The LADEE flight avionics package consists of an eight-slot 3U cPCI (Compact Peripheral Component Interface) that hosts the SACI, PAPI & SATORI Boards of the electrical system as well as a Mass Memory Board that supports digital input/output & Low Voltage Differential Signaling for high-data rate transfers; an IO Board for data decoding/encoding; and the Central Processing Board. (The eighth slot is a spare)
The heart of the LADEE Spacecraft is a RAD-750 Central Processing Board that is a single-card computer manufactured by BAE Systems in Manassas, Va. The processor can endure radiation doses that are a million times more extreme than what is considered fatal to humans. The RAD750 CPU itself can tolerate 200,000 to 1,000,000 rads. Also, RAD750 will not suffer more than one event requiring interventions from Earth over a 15-year period.
“The RAD750 card is designed to accommodate all those single event effects and survive them. The ultimate goal is one upset is allowed in 15 years. An upset means an intervention from Earth — one ‘blue screen of death’ in 15 years. We typically have contracts that (specify) that,” said Vic Scuderi BAE Business Manager. The RAD750 processors operate at up to 200 megahertz. It operates at temperatures of -55°C and 70°C with a power consumption of 10 Watts. RAD750 can tolerate 100,000rads. RAD-750 has plenty of flight heritage – currently being in use aboard NASA’s Juno Spacecraft, the Curiosity Rover, the two Van Allen Probes and the IRIS Solar Observatory.
The Data Handling System receives data from the payload and can send commands to the payloads as part of stored operational sequences. Data from the navigation sensors are also processed by the Data Handling Systems that in turn command the attitude control system and propulsion systems of the vehicle. Housekeeping operations such as the commanding of heaters based on temp sensor data and power management is also accomplished by the computer system.
The Mass Memory Board directly interfaces with the Telecom system of the spacecraft for data downlink and command uplink. It is also connected to the Lunar Laser Communications Demonstration Payload via a high-data rate connection to provide data for downlink.
LADEE’s communications system uses a modular design featuring a central Interface/Power Controller that distributes electrical power to the individual components. Three S-Band antennas are mounted on the spacecraft – two of which can serve as both, Transmitter and Receiver while the third antenna is an evolved Omni-directional Medium Gain Antenna that transmits data. Developed at Ames, this antenna achieves omni-directional coverage with a smaller area of medium-gain communications. This antenna is connected to a central Transmitter Module via a coupler and BP Filter. A switch can connect the central transmitter either to the medium-gain antenna or the other two low gain antennas. The central Receiver Module is connected to a Diplexer and a Splitter/Coupler and finally the two S-Band Antennas.
The telecommunications system will be used for command uplink and science data and telemetry downlink. The Laser Communications Terminal can also be used to downlink science data, but its use is strictly experimental and part of the vehicle payload.
The GNC System of the LADEE spacecraft is responsible for navigation data collection and vehicle stabilization. A Star Tracker and Inertial Measurement Unit are installed on the Radiator Assembly to determine the state of the spacecraft and provide attitude data to the Data Handling System which then commands four Reaction Wheels that are the primary attitude control system during the flight. The four Reaction Wheels are arranged in a pyramidal fashion to provide three-axis stabilization. They are used for precise vehicle pointing as well as slew maneuvers. During Reaction Wheel momentum dumps, the RCS thrusters are used to counteract forces and so keep the vehicle stable.
In addition to the IMU and Star Trackers, LADEE uses a suite of 12 coarse sun sensors to provide state of vehicle data.
NASA Awards New Spacecraft Avionics Development Contract
In May, NASA also announced that it had selected Charles Stark Draper Laboratory Inc. of Cambridge, Massachusetts, to provide development and operations support for the avionics software suite that will guide the agency’s next generation of human rated spacecraft on missions beyond low-Earth orbit.
The $49 million Advanced Guidance, Navigation and Control (GN&C) and Avionics Technology Development and Analysis III contract is a single-award indefinite-delivery/indefinite-quantity cost-plus-fixed-fee contract. The five-year performance period begins Tuesday, June 1, and extends through May 31, 2026.
The contract will support the work of the Engineering Directorate’s Aeroscience and Flight Mechanics Division at NASA’s Johnson Space Center in Houston. The contract provides support services that include a full range of guidance, navigation and control tools, integrated avionics, and autonomous flight operations systems. These will be used to develop simulation tools and flight software, perform flight-mode-specific analysis, define system architecture, execute test and verification activities, and provide sustaining engineering for the International Space Station and Orion spacecraft. The contract may support other NASA centers’ needs for advanced guidance products and services in the future.
References and Resources also include:
https://spaceflight101.com/ladee/spacecraft-overview/
