For a while earlier this summer, it looked like NASA’s flagship mission to explore Jupiter’s icy moon Europa might miss its scheduled launch this year.
In May, engineers expressed concern that transistors throughout the spacecraft might be vulnerable to damage from radiation, a constant threat to any spacecraft orbiting Jupiter. The transistors are built into the spacecraft’s circuits and serve about 200 unique applications, many of which are essential to the ongoing mission as it orbits Jupiter and makes multiple flybys of Europa, studying the icy moon with nine scientific instruments.
The Europa Clipper probe’s transistors are already in place, and removing them for inspection and replacement will delay the mission’s launch until late next year, when the probe will begin its journey beyond the solar system on October 10, after a 21-day launch period.
After four months of testing similar transistors on the ground, engineers determined that Europa Clipper’s transistors could withstand the extreme radiation the spacecraft would encounter around Jupiter, without any changes to the mission’s flight plan or trajectory.
“One of the major challenges was analyzing how the transistors on board the spacecraft would handle Jupiter’s radiation environment,” said Jordan Evans, Europa Clipper project manager at the Jet Propulsion Laboratory (JPL). “After extensive testing and analysis of the transistors, the Europa Clipper project and I personally are confident that we will be able to complete the original Europa exploration mission as planned.”
Senior NASA officials decided Monday to agree with the assessment by the Jet Propulsion Laboratory’s Europa Clipper team.
“I’m happy to be here with some incredibly good news,” said Nicky Fox, associate administrator for NASA’s Science Mission Directorate. “We’re all very happy. As it was just reported, the Europa Clipper mission passed an important milestone review, the last big review before launch fever really kicks up, and I’m very pleased that we passed that review today without a hitch.”
With approval from NASA Headquarters, teams preparing Europa Clipper for launch at the Kennedy Space Center in Florida will begin loading about 3 tons (6,600 pounds) of fuel onto the spacecraft later this week. That’s about half the total weight of the Europa Clipper spacecraft, the largest spacecraft NASA has ever built for a planetary mission. Then NASA and SpaceX engineers will place the probe inside a fairing on the launch pad and hook it up to a Falcon Heavy rocket for liftoff next month.
“I am pleased to have confidence that our incredible spacecraft and talented team are ready for launch, operations and a full science mission on Europa,” said JPL director Laurie Lessin.
This is a great mission
Europa Clipper will depart from Florida’s Space Coast next month, arrive at Mars in February 2025, then perform a gravity-assisted flyby to speed up its journey to Jupiter. A December 2026 flyby to Earth will deflect Europa Clipper’s course, allowing it to crash into Jupiter’s orbit in April 2030. The probe will ignite its engines to slow down and be captured by the giant planet’s enormous gravitational field.
Europa Clipper will then be on an orbit that will take it 49 times around Europa over about four years, coming as close as 16 miles (25 kilometers) to Europa’s icy surface. Instruments onboard Europa Clipper will map much of Europa’s icy crust and look for signs that Europa’s subsurface ocean of liquid water could be habitable for life. If scientists are lucky, the probe may fly through plumes of plumes erupting from Europa’s surface, and these plumes may contain pure material from the ocean beneath Europa’s icy shell. If so, Europa Clipper’s instruments will offer a glimpse into the chemical composition of Europa’s ocean.
“This is an epic mission,” said Kurt Niebuhr, Europa Clipper program scientist at NASA Headquarters, “a chance to explore not just a world that might have been habitable billions of years ago, but a world that might be habitable right now.”
Europa is about 90% the size of Earth’s Moon and orbits on the outer edge of Jupiter’s radiation belt, where charged particles could destroy the electronics of any spacecraft passing through the region.
The Europa Clipper’s most sensitive electronics are housed in an aluminum-zinc alloy-walled safe, protecting the components from Jupiter’s radiation. Many of the spacecraft’s transistors are inside this safe, while others are installed in science instruments on the outer edge of the spacecraft.
Transistors have a self-healing property called annealing, which allows them to regain much of their capability after exposure to intense radiation. For much of Europa Clipper’s orbit around Jupiter, the spacecraft will fly in a relatively benign radiation environment, giving the transistors time to repair themselves between close approaches to Europa, where the radiation is at its worst. The only change Europa Clipper’s mission managers will make is to adjust heater settings around some of the suspect transistors in two instruments outside the vault. The higher the temperature, the more efficiently the parts can repair themselves.
“These are metal oxide field effect transistors, so think of them as electronic switches that allow you to close an electronic switch when you apply a voltage to them,” Evans said.
““In some cases, the switch is basically left on the whole time, and if that switch was turning on a little one-watt decontamination heater, that’s not that big of a problem for the mission,” Evans said. “But if that circuitry is telling the spacecraft that it needs to go into safe mode, that’s a bit of a bigger problem. A much bigger problem. So we analyzed all of those circuits, looked at how robust and tolerant they were to degraded transistors, and determined that all of the circuits had enough headroom to confidently accomplish this flagship mission.”
