Richard A Lovett
NASA’s beleaguered Europa Clipper spacecraft passed its final technical review today, and is now ready for launch toward Jupiter as soon as its launch window opens next month.
“We are ready for Jupiter,” Jordan Evans, the mission’s project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said today in a teleconference.
“Now that we’ve completed this key NASA review, we’re focused on heading towards the launch pad, doing the final preparations,” he added.
is NASA’s largest, and with a budget of $US 5 billion, probably most expensive robotic spacecraft of all time. Its 10-year prime mission begins with a six-year, 2.9 billion kilometre trip to Jupiter (with gravity assists from Mars and Earth). Once there, it will spend four years orbiting the giant planet, using gravitational nudges from its many moons to make 49 flybys of Jupiter’s fourth-largest moon, Europa.
Europa has fascinated scientists since the first Voyager flyby in 1979 discovered that it was completely sheathed in ice. Subsequent studies have shown that it appears to have a deep ocean lying beneath the ice—an ocean that scientists increasingly believe might be suitable for life as we know it. More recent images have also shown geyser-like plumes of water jetting through cracks in the ice, allowing Europa Clipper, which will pass as close as 25 kilometers to the icy moon’s surface, to get direct samples of the ocean…from space.
“Our spacecraft has a stunning array of sensors that will help us understand Europa—the icy crust and global ocean that we suspect lies beneath it—as well as determine its chemical composition and geology,” says JPL’s director, Laurie Leshin. “It will help determine whether the moon could support life as we know it.”
The mission hit a major hiccup last May, however, when NASA engineers realized that hundreds of crucial transistors might not be suitable for the intense radiation belts created by Jupiter’s enormous magnetic field.
“The planet’s giant magnetic field acts as a particle accelerator,” says Evans. “It accelerates charged particles to create powerful radiation belts, and Europa sits near the outer edge of the worst part of [a] radiation belt.”
The problem, Evans says, was that while the transistors were made from silicon wafers designed for high-radiation environments, they had degraded during storage, and nobody was sure they were now able to survive the entire mission.
Tests have now shown, however, that these transistors are still robust enough to do the job, with no need to shorten the mission or otherwise make major changes to the original plan. In part, that is because the transistors are only exposed to intense radiation for one day out of each of the spacecraft’s 21-day orbits around Jupiter. The rest of the time, they are outside the radiation belts, where, in a process called self-annealing, they can actually recover from whatever damage the radiation inflicts on them during each passage through the belts.
Four months of round-the clock lab tests showed that 20 days outside the radiation belts is more than enough time for this process to occur, especially if the most vulnerable transistors are warmed to room temperature during that time, rather than being allowed to cool to the spacecraft’s exterior temperature. That uses a bit extra electrical power, Evans admits, but the spacecraft’s giant solar panels are up to the task, even in the dim reaches of the outer solar system near Jupiter, where sunlight is only 4 per cent as intense as at Earth.
Next up is for the spacecraft to be fitted to the launch vehicle, fuelled, and otherwise readied for launch, which could happen any day from 10 October to 30 October.