Onboard Computers (OBCs) are the central processing units of satellites, responsible for controlling key functions, managing payloads, and ensuring mission success. While many OBCs are advertised as radiation-tolerant and suitable for Low Earth Orbit (LEO), it is critical to look beyond the processor and consider the entire system when evaluating an OBC for space missions. Here are some essential factors to consider:
When evaluating the processing capabilities of an OBC, it’s essential to consider not just the processor architecture (e.g., ARM, RISC-V), but also how the system can be tailored to meet your mission's unique demands. The incorporation of Field Programmable Gate Arrays (FPGAs) in some OBCs provides a significant advantage, enabling custom hardware acceleration for specific tasks.
There are Flash-based and SRAM-based FPGAs available on the market. Flash-based FPGAs have an inherent immunity to Single Event Upsets (SEUs) and do not require additional memory to store their bitstream. They also consume less power compared to SRAM-based FPGAs. However, there is a trade-off: Flash-based FPGAs may be slower for tasks requiring heavy processing loads, while SRAM-based FPGAs can handle such tasks more efficiently. The choice of FPGA should align with the specific performance and power consumption requirements of your mission.
Satellites are exposed to intense space environments where radiation poses a constant threat. An OBC must be radiation-tolerant not only at the processor level but also across the entire system, including the memory that stores and processes critical data. Radiation effects like Single Event Upsets (SEUs) or latch-ups can lead to data corruption or complete system failure if not mitigated properly.
Choose OBCs with comprehensive radiation-hardening measures that include SEU protection, Total Ionizing Dose (TID) resistance, and single-event latch-up immunity. Importantly, assess whether the system includes latch-up protection for its memory components, as this is often an overlooked yet vital aspect of ensuring the OBC’s resilience in space. Redundancy features such as dual or triple redundancy, hot-swappable components, and self-recovery mechanisms also enhance fault tolerance and mission reliability.
The OBC’s interface capabilities determine how effectively it can interact with other satellite subsystems, including sensors, actuators, and communication systems. The more flexible the OBC’s interface configuration, the easier it will be to integrate into your satellite’s architecture. Ensure the OBC supports a wide range of communication protocols such as CAN bus, RS-422, I2C, and SPI, and offers sufficient input/output (I/O) channels to accommodate your mission’s requirements.
Consider OBCs that provide customizable interface configurations, allowing you to scale or modify the system as mission needs evolve—without significantly increasing costs.
Spacecraft typically operate under stringent power constraints, making power efficiency a critical factor when selecting an OBC. An OBC with low power consumption, particularly during non-essential operations or in power-saving modes, can significantly extend a satellite’s operational life. Look for systems that offer advanced power management features, allowing you to optimize energy usage while maintaining performance.
Additionally, ensure that the OBC fits within the satellite's physical and power budgets. Compact form factors and low weight are essential to minimizing the spacecraft’s overall mass, while efficient power consumption ensures compatibility with the satellite's power generation and storage systems.
An OBC must endure the harsh conditions of space, including extreme temperatures, vacuum, radiation, and mechanical stress during launch. It’s important to select OBCs that have undergone rigorous environmental testing, including thermal vacuum tests, shock and vibration testing, and electromagnetic compatibility (EMC) evaluations. These tests ensure the OBC can survive the mechanical stresses of launch and operate effectively throughout the mission’s life cycle.
Mission profiles vary greatly, and OBCs should offer the flexibility to meet these specific demands without incurring steep additional costs. Modular designs, customizable firmware, and configurable memory options can provide the necessary adaptability for different mission architectures. Some OBCs allow for the selective addition of features like real-time clocks, watchdog timers, and additional storage based on the mission requirements, ensuring that you only pay for the features you need.
By leveraging FPGAs and other customizable components, some OBCs offer cost-effective solutions that allow for mission-specific configurations without requiring a complete redesign. This modularity and scalability are particularly advantageous for missions that may need to adapt quickly to changing parameters or budget constraints.
Conclusion
Selecting the right OBC is a complex but crucial task for any satellite mission. Beyond processing power, it's important to consider the system's overall radiation tolerance, latch-up protection, interface flexibility, and environmental resilience. OBCs with customizable options, especially those employing FPGA co-processing, can offer a significant performance boost without excessive costs, making them ideal for a wide range of mission profiles. By thoroughly evaluating these factors, mission planners can ensure their OBC will provide the necessary reliability and performance to achieve mission success in the demanding environment of space.
