78 “The spacecraft is cozy. It has heaters and an active thermal loop, which keeps it in a much more normal temperature range,” says Taejoo Lee, solar array product delivery manager at APL. “But the solar arrays are exposed to the vacuum of space without any heaters. They’re completely passive, so whatever the environment is, those are the temperatures they get.” About 90 minutes after launch, the arrays will unfurl from their folded position over the course of about 40 minutes. About two weeks later, six antennas affixed to the arrays will also deploy to their full size. The antennas belong to the radar instrument, which will search for water within and beneath Europa’s thick ice shell. These unfold to 17.6 m, perpendicular to the arrays. Radiation risk Another key challenge for the power system is the radiation around Jupiter, the most intense in the solar system. The planet’s enormous magnetic field, 20,000 times stronger than Earth’s, traps charged particles and accelerates them to very high energies. When it circles the Europa moon, the craft will need to go in and out of these radiation bands. NASA has been testing the radiation performance of power MOSFETs from Infineon Technologies. Those from Infineon’s acquisition of International Rectifier are used throughout the craft’s electrical power systems. NASA engineers extensively tested the MOSFETs at the Jet Propulsion Laboratory after learning that some of these parts might not withstand the radiation around Jupiter. Tests are also being conducted in Maryland, at APL in Laurel and NASA’s Goddard Space Flight Centre in Greenbelt. APL designed the main spacecraft body in collaboration with JPL and NASA Goddard. The issue with the MOSFETs came to light in May, when the mission team was advised that similar parts were failing at lower radiation doses than expected. In June, Infineon issued an alert to notify users of this issue, and it worked with the mission team to support ongoing radiation testing and analysis efforts. Test data showed some transistors are likely to fail as the parts are not as radiation-resistant as expected. However, the electronics are enclosed in a vault with walls made of 1/3 in-thick (9.2 mm) aluminium-zinc alloy sheets to protect them. The vault is bolted to the spacecraft’s propulsion module, which houses the 24 engines. The MOSFETs are US DLA QPL products up to MIL-PRF-19500 JANS level and the hermetic packaging is screened to the European ESCC5000 specification. The NASA team worked out how many MOSFETs may be susceptible and how they will perform in flight, and developed options for maximising the transistors’ longevity in the Jupiter system. NASA says the issue that might be having an impact is a phenomenon the industry wasn’t aware of, which represents a newly identified gap in the industry standard radiation qualification of transistor wafer lots. However, launch preparations are progressing with the spacecraft at the Kennedy Space Centre in Florida, where the team recently attached the high-gain antenna. When Clipper arrives at Jupiter in 2030, it will conduct science investigations to understand the potential habitability of the Europa moon as it flies by multiple times. Precision flight A European consortium is developing laser sensors to help satellites navigate with ultra-precision and enable uncrewed vehicles to fly further for longer. The INPHOMIR project is developing two new ultra low-power, compact sensing devices – an optical gyroscope and a mid-infrared FMCW Lidar – with the aim of making space missions more efficient and cost-effective. “As we aim to explore space much deeper while conducting more complex missions, the need for precise, reliable and efficient sensors is now more critical than ever. The advanced sensing technologies we October/November 2024 | Uncrewed Systems Technology The Aethero NxN Edge Computing Module is a space-rated computer for computationally intensive tasks with real-time decision-making capability (Image courtesy of Antmicro)
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