From the August 2003 issue

Galileo’s successor

NASA hopes the proposed Jupiter Icy Moons Orbiter will pick up where the Galileo mission left off.
By | Published: August 5, 2003 | Last updated on May 18, 2023

JIMO
Not expected to launch before 2011, JIMO would orbit Jupiter’s icy moons Ganymede, Callisto, and Europa. The spacecraft would use nuclear fission to generate power for its ion engine. One conceptual mission design would place a large array of heat-shedding radiator panels along a 20-meter boom located between the spacecraft’s power source and ion-propulsion thrusters.
NASA / JPL
JIMO
Not expected to launch before 2011, JIMO would orbit Jupiter’s icy moons Ganymede, Callisto, and Europa. The spacecraft would use nuclear fission to generate power for its ion engine. One conceptual mission design would place a large array of heat-shedding radiator panels along a 20-meter boom located between the spacecraft’s power source and ion-propulsion thrusters.
NASA / JPL
With the Galileo mission nearing its end, NASA is already looking toward the future and the next mission to explore Jupiter and its major moons. During its 8-year jovian residency Galileo revealed how interesting Jupiter’s Galilean moons are, but its inability to explore them thoroughly have left many of their characteristics unknown. For example, Galileo found evidence that Jupiter’s icy moons Europa, Ganymede, and Callisto may harbor subsurface oceans, but it couldn’t determine whether the buried seas truly exist, what these potential oceans include, or how deep they are. NASA hopes the Jupiter Icy Moons Orbiter (JIMO) will be able to probe deeper into these moons and their mysteries.

JIMO would also incorporate a new electric propulsion technology: an ion engine fueled by a nuclear fission reactor. NASA’s Deep Space 1 mission, which flew past Comet Borrelly in September 2001, proved the capabilities of ion propulsion, but that spacecraft used solar energy for its power.

The nuclear fission reactor would allow JIMO to travel much farther from the sun and have access to 100 times more power than any other prior mission of comparable size. According to NASA, the energy produced by this reactor would allow the mission to improve the type of science it conducts, enhance communications, use advanced instruments, and make faster data transmissions.

However, in order to have time to develop and test the technology to make sure it can be used in deep space safely and reliably, the mission will not be launched before the year 2011.

Upon arriving at Jupiter, JIMO would initially orbit the giant planet before repositioning itself around Callisto. After several months, it would fire its ion engine and move itself into position around Ganymede. Finally, it would orbit Europa, which is saved for last because of the especially intense radiation environment around the innermost icy moon.

JIMO currently has three overall science goals for its tour of the jovian system: to evaluate the potential for life, learn about the moons’ origin and evolution, and study the radiation environment. While investigating the moons’ possible subsurface oceans, JIMO would also measure the thickness of their icy crusts and chart where organic compounds and other biologically significant chemicals exist on the surface Meanwhile, it would study the moons’ structures, surface features, and compositions. Finally, JIMO would examine the moons and their surroundings to assess the radiation environment and how the moons are affected by it.

For more about JIMO, visit the mission’s website.

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