NASA, ESA Join On Jovian Moons Mission
Feb 18, 2009
Jefferson Morris jeff_morris@AviationWeek.com
NASA and the European Space Agency (ESA) have agreed to jointly pursue a new outer planets mission that would send separate U.S. and European spacecraft to visit the four largest moons of Jupiter circa 2026.
Meanwhile, the agencies also will work together on a less mature mission concept for visiting Saturn's moons Titan and Enceladus, which would include a NASA orbiter and an ESA lander and research balloon that would descend to Titan's cloud-shrouded surface.
The two spacecraft of the Europa Jupiter System Mission would launch on separate rockets from different locations in 2020, arriving at the Jupiter system six years later. NASA's orbiter, currently dubbed Jupiter Europa, would have an estimated wet mass of 5,000 kilograms (11,000 pounds), and would launch on an Atlas V. It would conduct four flybys of the volcanically active Jovian moon Io and several of frozen Callisto before settling into orbit around Europa.
Europa is of particular interest to scientists because its icy crust is thought to conceal a subsurface ocean - the existence of which the mission would finally verify. Some have hypothesized that such an ocean could even harbor life.
The spacecraft will produce global maps of Europa detailing the moon's topography, surface composition and subsurface makeup via ground-penetrating radar, and will mark a significant leap beyond the Galileo mission, which launched in 1989 and spent years studying Jupiter and its moons before finally diving into the gas giant's atmosphere in 2003.
"It will be able to transmit a tremendous amount of data back to Earth - something Galileo could not do because of its antenna problem," says Curt Niebur, NASA's Outer Planets Flagship project scientist.
The information gathered also will help inform the design of a possible future Europa lander. The much-coveted lander originally was part of ESA's plans for a separate Europa mission, but has been dropped from this joint effort.
The total mission cost for NASA's probe is estimated at $2.5 billion to $3 billion, according to James Green, director of the Planetary Science division at NASA headquarters in Washington.
Meanwhile, ESA's spacecraft, initially named Jupiter Ganymede, will enter a "resonance" orbit between Ganymede and Callisto, Niebur says. The cost to ESA is estimated at 850 million euros, or roughly $1 billion. Both spacecraft will spend nearly a year orbiting their respective targets.
Bigger than the planet Mercury, Ganymede is the largest moon in the solar system, and the only moon known to possess an internally generated magnetic field. Like Europa, it also may feature a deep subsurface water ocean.
"Everything we know about Ganymede has been done with six passes by Galileo," Green says, while Callisto got eight passes. "So our understanding of the icy moons - Ganymede, Callisto and Europa - will [receive] a significant advance from this mission alone."
Neither NASA nor ESA have yet given either probe the formal go-ahead, but Green says that even if ESA ultimately opts not to move forward with its Jupiter probe, NASA's spacecraft could still be launched as a standalone mission.
Although equally attractive from a scientific standpoint, the Titan Saturn System Mission mission was prioritized below the Jupiter mission simply because the mission concept is less mature. During the study phase, concerns arose over the detailed engineering of the spacecraft, including its propulsion system, trajectory and mass margins. The margins for the Titan flight are slim enough that engineers still fear the concept could outgrow its launch vehicle without further refinement.
Image: NASA
