Partially Radiation-Tolerant OBC Architectures for LEO Missions: A Cost-Optimized Reliability Approach

Fully radiation-hardened on-board computers, typically designed to withstand TID levels in excess of 100 krad and Single Event Effects up to LET ≥ 60 MeV·cm²/mg, provide the highest level of assurance for long-duration and deep-space missions. However, these systems often come at a cost premium of 8–10× compared to OBCs built around COTS or radiation-tolerant components. In addition, lead times for rad-hard devices can exceed 12–24 months, impacting program schedules.

For many LEO missions—typically operating at altitudes of 400–800 km with mission durations of 2–7 years—the expected radiation environment is significantly less severe. As a result, mission operators increasingly seek architectures that improve FM reliability while maintaining cost and schedule constraints.

LEO Radiation Environment and Design Requirements

Typical LEO radiation exposure, assuming aluminum shielding of 4-6 mm, results in:

TID: ~5–20 krad over 5 years depending on inclination and solar activity
Proton-induced SEEs as the dominant risk
Heavy ion flux significantly lower than in GEO or interplanetary missions

Under these conditions, full rad-hard margins are often unnecessary. Instead, compliance with radiation tolerance levels aligned with ECSS-Q-ST-60-15C, ECSS-E-ST-10-04, and NASA EEE-INST-002 guidelines can be achieved through selective hardening and system-level mitigation.

Reliability-Driven Component Selection

Improving OBC reliability without a major cost increase requires a structured system engineering approach. A Failure Modes and Effects Analysis (FMEA) is essential to identify failure paths that lead to loss of mission or loss of spacecraft. The resulting Critical Item List highlights components where radiation-induced failures have the highest impact.

Experience shows that the most critical contributors to unrecoverable radiation events in LEO OBCs are typically:

Volatile memory (SEUs, SEL-induced corruption)
Non-volatile memory (SEFI, stuck bits, wear-out acceleration)
Power management ICs (single-event latch-up, single-event burnout)
High-speed interface PHYs (link loss, permanent degradation)

Targeted Use of Radiation-Tolerant Components

A cost-effective mitigation strategy is to selectively upgrade these high-impact components to radiation-tolerant versions with typical specifications such as:

Radiation-tolerant SRAM / DDR
- TID: ≥ 30–50 krad(Si)
- SEL immunity: LET ≥ 60 MeV·cm²/mg
- SEU rates compatible with ECC-based mitigation
Radiation-tolerant Flash / MRAM
- TID: ≥ 50 krad(Si)
- Reduced SEFI susceptibility
- Improved data retention under proton exposure
Radiation-tolerant power regulators and supervisors
- SEL-free operation up to LET ≥ 60 MeV·cm²/mg
- SEB-hardened MOSFET structures
- Stable output under transient radiation events
Radiation-tolerant interface PHYs (CAN, SpaceWire, Ethernet)
- TID: ≥ 30 krad(Si)
- Reduced risk of permanent link failure or latch-up

These targeted upgrades significantly reduce the probability of unrecoverable faults while adding only a modest cost increment compared to a fully rad-hard OBC.

Case Study: OBC-Polar Architecture

The OBC-Polar platform is based on the Microchip PolarFire FPGA SoC, which provides inherent radiation robustness well suited for LEO missions:

Latch-up immune by design (flash-based FPGA fabric)
Heavy-ion SEE performance demonstrated up to LET ≈ 37 MeV·cm²/mg
TID tolerance typically in the range of 25–50 krad(Si) (device- and mission-dependent)

For many LEO missions, this level of radiation performance already meets or exceeds system requirements. Replacing the PolarFire SoC with a fully rad-hard processor would introduce a substantial cost increase while offering only marginal improvement in mission reliability within the LEO radiation envelope.

A more balanced and cost-effective approach is therefore to retain the PolarFire SoC and selectively upgrade surrounding components—memory devices, power regulation, and interface ICs—to radiation-tolerant versions. This improves overall system reliability, reduces the likelihood of SEL-induced power cycling or permanent memory corruption, and minimizes mission risk without a disproportionate increase in cost.

For many LEO missions on FM, partially radiation-tolerant OBC architectures offer the optimal balance between reliability, cost, and schedule. By applying FMEA- and CIL-driven design decisions and selectively hardening only the most critical subsystems, it is possible to achieve robust flight model performance aligned with ECSS and NASA standards.

This approach delivers a high value-for-money solution, enabling reliable spacecraft operations while avoiding the cost and lead-time penalties associated with fully rad-hard OBC designs. Sensible FM approach for your mission is:

Keep the standard / military-temperature PolarFire SoC (MIL temp slightly increase the cost)
Upgrade all or some of: RAM, Flash, power supplies, and critical interface PHYs to radiation-tolerant variants where beneficial.
Rely on system-level mitigation (watchdogs, resets, power cycle)

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