The baseline mission configuration for EJSM-Laplace includes two spacecraft: the Jupiter Ganymede Orbiter (JGO) and the Jupiter Europa Orbiter (JEO).
EJSM-Laplace will use these two orbiters to conduct unprecedented detailed studies of the giant gaseous planet Jupiter and its moons Europa, Ganymede, Callisto and Io. ESA's responsibility will be to build, launch and operate the Jupiter Ganymede Orbiter; NASA's responsibility will be to build, launch and operate the Jupiter Europa Orbiter.
The following features of the EJSM-Laplace mission define the JGO spacecraft design.
JGO and JEO will be operated independently in the Jovian system but the mission is designed to execute an extended choreographed exploration of the Jupiter system, after which the two spacecraft settle into orbit around Ganymede and Europa, respectively.
Since JGO focuses on Ganymede and Callisto, it can stay outside of Jupiter's main radiation belts. JEO, however, will be exposed to a greater radiation dose as it explores the inner Galilean satellites Europa and Io. This translates into differences between the spacecraft in terms of protection of the electronics, the power systems, and the payloads. JGO can use shielding as the primary protection for its electronics, however, the JEO design levels are much higher than is practical for standard parts and shielding. Therefore, all electronics on JEO will be designed with high radiation-tolerant electronics to minimize the required shielding, with some electronics and detectors utilizing spot shielding to reduce the radiation exposure. Due to the lower radiation exposure, JGO is able to use solar arrays to provide electrical power, with GaAs solar cells optimized for 'Low-Intensity/Low-Temperature' conditions. JEO will use radioisotope power sources instead.
Both JGO and JEO must meet their respective planetary protection requirements. The requirements for JEO are more stringent than those for JGO since Europa is classified as a COSPAR category 3 object while Ganymede is a category 2+ object. This has implications for the design and integration activities. (See the COSPAR report on Planetary Protection for further details.).