ABSTRACT
In 1995, the Galileo spacecraft [1,2] arrived at Jupiter to conduct follow-up experiments on pathfinder Pioneer [3,4] and key Voyager [5–7] discoveries especially at Io, Europa, Ganymede, and Callisto [8]. These new observations helped expand our scientific knowledge of the prominent Galilean satellites; studies revealed diversity with respect to their geology, internal structure, evolution, and degree of past and present activity [2,8,9]. Jupiter’s diverse Galilean satellites, of which three are believed to harbor internal oceans, are central to understanding the habitability of icy worlds. Galileo provided for the first time compelling evidence of a nearsurface global ocean on Europa [10–13]. Furthermore, understanding the Jupiter system and unraveling the history of its evolution from initial formation to the emergence of possible habitats and life give insight into how giant planets and their satellite systems form and evolve [14]. Most importantly, new light is shed on the potential for the emergence and existence of life in icy satellite oceans [15]. In 2009, NASA released a detailed Jupiter Europa Mission Study (EJSM) [16] that proposed an ambitious Flagship Mission to understand more fully the satellites Europa [11] and Ganymede [14] within the context of the Jovian system. The success of EJSM is linked to the success of both the NASA-led Jupiter Europa Orbiter (JEO) [17] and the ESA-led Jupiter Ganymede Orbiter (JGO) [18]. JEO and JGO would execute a choreographed exploration of the Jovian system before settling into orbit around Europa and Ganymede, respectively. The National Academies Planetary Decadal Survey, 2011 [19], has listed the NASA-led JEO as the second highest priority mission for the decade 2013–2022, and, if chosen, it would be launched in 2020 with arrival at Jupiter in 2025. If the JEO mission is not chosen, it is anticipated that there will be opportunities in future decadal cycles. Jupiter Orbit Insertion (JOI) begins a 30 month Jovian system tour followed by 9 months of science mapping after Europa Orbit Insertion (EOI) in July 2028. The orbiter will ultimately impact the surface of Europa after the mission is completed. The current JEO mission concept includes a range of instruments on the payload to monitor dynamic phenomena (such as Ios volcanoes and Jupiter’s atmosphere), map the Jovian magnetosphere and its interactions with the Galilean satellites, and characterize water oceans beneath the ice shells of Europa and Ganymede [15,17]. The payload includes a low-mass (3.7 kg) and low-power (<5 W) thermal instrument (TI) for measuring possible warm thermal anomalies on Europa’s cold surface caused by recent (<10,000 years) eruptive activity [20,21]. Regions of anomalously high heat flow will be identified by thermal mapping using a nadir pointing, push-broom filter radiometer that provides far-IR imagery in two broadband spectral wavelength regions, 8–20 and 20–100 μm, for surface temperature measurements with better than a 2 K accuracy and a spatial resolution of 250 m/pixel obtained from a 100 km orbit. The temperature accuracy permits a search for elevated temperatures when combined with albedo information. The spatial resolution is sufficient to resolve Europa’s larger cracks and ridge axial valleys. In order to accomplish the thermal mapping, the TI uses sensitive thermopile arrays that interface to 850a custom-designed low-noise multichannel digitizer (MCD) ASIC, which resides very close to the thermopile linear array outputs. Both the thermopile array and the MCD ASIC will need to show full functionality within the harsh Jovian radiation environment, operating at cryogenic temperatures, typically 150–170 K. In the following, a radiation mitigation strategy together with a low-risk radiation-hardened-by-design (RHBD) methodology [22] using commercial foundry processes is given for the design and manufacture of an MCD ASIC that will meet this challenge.
