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NASA’s Europa Clipper gets its wheels for deep space travel – NASA’s Europa Clipper

Engineers install two-foot-wide reaction wheels on the main body of NASA’s Europa Clipper spacecraft at the agency’s Jet Propulsion Laboratory. The orbiter is in the assembly, testing and launch phase in preparation for a launch in 2024. Credits: NASA/JPL-Caltech

Just as NASA’s Mars rovers rely on rugged wheels to roam the Red Planet and do science, some orbiters also rely on wheels — in this case, reaction wheels — to keep pointing in the right direction. Engineers and technicians at NASA’s Jet Propulsion Laboratory in Southern California recently installed four reaction wheels on Europa Clipper, which will rely on them during its journey to Jupiter’s icy moon Europa.

When NASA’s spacecraft goes through deep space, orbits Jupiter and collects scientific observations as it flies dozens of times across Europe, the orbiter’s wheels turn so its antennas can communicate with Earth and its scientific instruments, including cameras, can be aimed. stay .

Shown here are four reaction wheels, one in each of the four corners of the image.  The reaction wheels are black.  In the configuration shown, the wheels are visible from their sides, allowing you to see the wiring and other mechanical equipment attached to the reaction wheels.  In the center of this image you can see a silver triangle, the base of the main body of the spacecraft.  Thick bundles of gold wires extend from the reaction wheels, with green tape holding the bundles in place as the spacecraft continues to assemble.

All four reaction wheels installed on NASA’s Europa Clipper All four reaction wheels installed on NASA’s Europa Clipper are visible in this photo taken from under the spacecraft’s main body as it is being assembled at the NASA’s Jet Propulsion Laboratory desk . Credits: NASA/JPL-Caltech

Two feet wide and made of steel, aluminum and titanium, the wheels spin quickly to create torque that causes the orbiter to spin in the opposite direction. Isaac Newton’s third law of motion also applies in deep space and explains the underlying phenomenon: for every action there is an equal and opposite reaction. The reaction wheels make the spacecraft react to the spinning action of the wheels.

Here’s one way to visualize how reaction wheels work: Imagine you’re sitting in a swivel chair and lift your feet off the floor so you can spin freely. If you pull your torso in one direction, the seat and your legs will rotate in the opposite direction. The reaction wheels work the same way: as the reaction wheel motor accelerates the metal wheel in one direction, the spacecraft experiences acceleration in the opposite direction.

Without those reaction wheels, Europa Clipper would not be able to conduct its scientific surveys when it arrives at the Jupiter system in 2030 after launch in 2024. Scientists believe that Europa is home to a vast internal ocean that may have suitable conditions to support life. The spacecraft will collect data on the moon’s atmosphere, surface and interior — information that will help scientists learn more about the ocean, ice crust and possible plumes that may be propelling subsurface water into space.

During its orbits around Jupiter, Europa Clipper will rely on reaction wheels to help it perform thousands of turns or “slews.” While the spacecraft could perform some of those maneuvers with thrusters, the thrusters require fuel — a finite resource on board the orbiter. The reaction wheels will run on electricity provided by the spacecraft’s massive solar panels.

The main body of the spacecraft standing in a white clean room is the central part of this image.  The tall structure is covered with protective covers to keep sensitive equipment safe during assembly and what appears to be white paper, which is used to make patterns for the spacecraft's protective insulation.  Four engineers can be seen under the base of the spacecraft, installing the reaction wheels, as if they were working on the undercarriage of a car.  Two engineers on the left lie on their stomachs and two engineers on the right lie on their backs.

Engineers and technicians are working together to install reaction wheels on the underside of the main body of NASA’s Europa Clipper spacecraft, which is in the assembly, testing and launch phase at the agency’s Jet Propulsion Laboratory. Credits: NASA/JPL-Caltech

The trade-off is that the reaction wheels work slowly. The Europa Clipper’s reaction wheels take about 90 minutes to turn the craft 180 degrees – a movement so gradual that it would be imperceptible to the human eye from a distance. The spacecraft’s rotation will be three times slower than the minute hand on a clock.

In addition, they can wear out over time. It happened on NASA’s Dawn spacecraft, requiring engineers to figure out how to rotate using thrusters with the available fuel. To address this, engineers installed four wheels on the Europa Clipper, though only three are needed for maneuvering. They alternate which three wheels are in operation to even out the wear. That leaves them with a “spare” wheel if one of the others fails.

Installing the wheels was one of the most recent steps of the phase known as assembly, test and launch operations. Science instruments continue to arrive at JPL to be added to the spacecraft. Several tests will then be conducted as the spacecraft heads towards the October 2024 launch window. Having traveled more than 2.9 billion kilometers, Europa Clipper will be ready to unravel the secrets of this icy world.

More about the mission

Missions such as Europa Clipper contribute in the field of astrobiology, the interdisciplinary field of research that studies the conditions of distant worlds that could host life as we know it. While Europa Clipper is not a life-detection mission, it will conduct a detailed exploration of Europa and investigate whether the icy moon, with its subsurface ocean, has the capacity to support life. Understanding the habitability of Europa will help scientists better understand how life evolved on Earth and the potential to find life beyond our planet.

Operated by Caltech in Pasadena, California, JPL is leading development of the Europa Clipper mission in conjunction with the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, for NASA’s Science Mission Directorate in Washington. APL designed the main spacecraft in collaboration with JPL and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, conducts program management for the Europa Clipper mission.

News Media Contacts

Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, California.

Karen Fox / Alana Johnson
NASA Headquarters, Washington
301-286-6284 / 202-358-1501 /

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