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Exploration of Ocean Worlds is challenging from an electronics perspective, given the combination of extreme radiation (5 Mrad) and low temperatures (-180°C) encountered on the surface. Legacy approaches (e.g., Mars rover) require placing electronics in protective “warm boxes” to ensure their operation, but this is not viable for Ocean Worlds given the constraints on battery life.
From a mission-science perspective, it is desirable to utilize an electronics technology that possesses “environmental-invariance” (operates robustly in whatever environment it finds itself). On Ocean Worlds, on-surface electronics will be required (e.g., for distributed sensor networks and communication links). Ideally, this same electronics technology should also support the friendlier below-surface mission needs associated with ice-drilling and submersibles. The envisioned electronics should be commercially available, highly integrated, low-cost, support digital/analog/RF circuits, and bring compelling SWaP-C advantages.
Our objective is to develop and demonstrate silicon-germanium (SiGe) electronics that can survive the combination of radiation and low temperatures on Ocean Worlds. In 2006, Cressler led a large team on a NASA ETDP project; a 5-year, $12M project for lunar exploration, “Integrated SiGe Electronics for Extreme Environments.” We demonstrated a SiGe subsystem for the Moon (a sensor interface IC) for use outside the warm box (-180°C, 100 krad radiation), exiting at TRL 5. Early-generation SiGe was used, and included infrastructure development (modeling, packaging, circuits, and test).
In COLDTech, we will extend that original approach to the more extreme surface conditions of Ocean Worlds, now utilizing state-of-the-art SiGe. The team has preliminary results demonstrating that SiGe transistors can withstand radiation levels to 5 Mrad and operation down to -180°C temperatures. SiGe technology embodies both SiGe transistors and CMOS on-die (i.e., SiGe BiCMOS). CMOS, however, has known concerns under extreme radiation and low temperatures, and thus SiGe offers unique advantages. For example, since a major objective is to demonstrate digital components, we will develop a library of environmentally-invariant SiGe digital elements capable of multi-GHz speeds at very low power levels (<100 µW). While lower density than CMOS logic, this tradeoff changes if area-hungry techniques are required to enable 5 Mrad capability for CMOS (e.g., annular geometries). In addition, SiGe transistors do not require advanced (costly) lithography, enhancing its affordability. State-of-the-art SiGe uses 90 nm lithography, adequate for Ocean Worlds use. 90 nm is also compatible with Xilinx Virtex-class FGPAs.
The COLDTech team were all part of the original NASA ETDP SiGe team, have worked together many times, and have extensive experience in extreme environment electronics. Georgia Tech and Tennessee will develop analog/digital/RF circuits, and JPL will provide packaging and testing utilizing their Co-60 and Dynamitron facilities (high flux electrons down to -180°C) for verification. As a first step, we will evaluate the two available domestic SiGe foundries for use on Ocean Worlds (GlobalFoundries and TowerJazz) and select the one that best suits our needs. The team’s existing SiGe chips from each foundry will be provided at no cost to NASA and used for initial radiation/temperature studies and final downselect. We will develop enhanced models for circuit design and use these to develop digital, analog, and RF building blocks for surface operation on Ocean Worlds. We will then use our design library to create a large-scale integrated circuit prototype as proof-of-concept, validating it to TRL 5/6. Outputs of this project will be directly infused into the future SMD missions to Ocean Worlds.
Developing Instrument or spacecraft technology to improve measurements for future planetary science missions
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