Cassini Swarm
Damage from Cosmic Rays
Cosmic rays consist of approximately 85% protons, 14% alpha particles, and 1% heavy ions. X-rays and gamma radiation are an additional concern for space ready electronic systems. Lattice displacement can occur in the semiconductor device when a high energy particle impacts the semiconductor. Foreign particles in the semiconductor increase recombination thereby reducing device performance. Even when a lower energy event occurs which does not result in immediate physical device damage, electronic system reliability can be compromised by ionization effects that cause glitches, flipped bits, and latch-up conditions. Shielding of electronics is necessary to reduce the incidence of damage from cosmic rays and space radiation, however additional hardware and software design methods must be leveraged to achieve the robustness required for successful completion of a multi-year space mission.
Radiation Hardened Semiconductor Technologies
Choice of semiconductor device technology important to space ready electronic design. The integrated circuits used in space rated electronics are fabricated using processes with an insulating substrate such as silicon-on-insulator (SOI) and sapphire (SOS). SOI and SOS have superior radiation tolerance to conventional CMOS processes. While a commercially available IC can withstand radiation between 50 and 100 gray (5k and 10k rad), radiation hardened ICs can withstand a total dose of 2k to 10k gray (200k and 1M rad) and higher.
Space Qualified System Design
Redundant hardware in combination with both hardware and software voting schemes, parity checking, and memory scrubbing routines are employed to increase the robustness of the digital systems that control the satellite and process mission critical data. Systems such as the RAD750 computer from BAE Systems are scalable, proven technologies for computing in space. Additionally, Xilinx, Inc. offers space hardened FPGAs which facilitate remote updates of firmware and software and enable reconfigurability during the mission.
Resiliency of Electronics
The electronic systems in the satellite are ruggedized to withstand cosmic radiation and climate controlled to combat extreme temperature variations. Cosmic rays and solar particle events are mitigated in packaging, hardware, and software.
Advantage of RTG use in CubeSats
Waste heat from the unit is circulated throughout the satellite system to keep instruments, computers, mechanical devices and communications systems within their operating temperature ranges. This system-wide thermal control does not draw on the satellite's electrical power, and precludes the need for radioisotope heater units for spot heating.
