On October 14th, 2024, NASA’s Europa Clipper mission began its long journey to Jupiter’s icy moon Europa. On March 1st, the probe reached Mars, where it conducted a gravity-assist maneuver. While orbiting the Red Planet, mission controllers back on Earth took the opportunity to test the probe’s Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON). Once it reaches Europa, Clipper will use this radar instrument to probe beneath the moon’s icy sheet and search for pockets of water that could lie within.
The instrument could also give scientists a glimpse of Europa’s interior ocean, which could theoretically support life. The radar imagery REASON will provide could help verify this by shedding light on how material is transferred from the interior to the surface. The instrument will also study Europa’s ridges and other surface features so scientists can examine how they are connected to features beneath the surface. The test was a complete success, producing a radargram showing the outline of Mars’ topography and providing a taste of what the probe will see when it arrives at Europa.
REASON relies on two pairs of antennas that extend from the spacecraft’s massive solar arrays, measuring 17.6 meters (58 feet) from tip to tip. The flyby at Mars provided an opportunity to test the radar in ways that weren’t possible on Earth. Prior to launch, engineers at NASA’s Jet Propulsion Laboratory (where the Europa Clipper was assembled) conducted a battery of tests, including a deployment test using engineering models using the open-air towers atop the plateau overlooking the facility. But once the actual hardware was built, it could only be tested in the High Bay 1 clean room at JPL to ensure that it remained sterile until launch.
But testing how the bounceback of the radar’s signals (aka. an “echo” test) of the radar was something that could only be performed in space. “We got everything out of the flyby that we dreamed,” said Don Blankenship, principal investigator of the radar instrument, in a NASA press release. “The goal was to determine the radar’s readiness for the Europa mission, and it worked. Every part of the instrument proved itself to do exactly what we intended.”
The test consisted of REASON sending and receiving radio waves for about 40 minutes while the spacecraft flew 5,000 km (3,100 mi) above Mars’ surface, gradually lowering itself to 884 km (550 mi). Once it arrives around Europa, REASON will operate when the Europa Clipper is as close as 25 km (16 mi) to the moon’s surface. The instrument team collected 60 gigabytes of rich data, which they began transmitting in mid-May. Since then, scientists have pored over the data in detail, which verified that REASON was in good working order. Said Trina Ray, Europa Clipper deputy science manager at NASA JPL:
The engineers were excited that their test worked so perfectly. All of us who had worked so hard to make this test happen — and the scientists seeing the data for the first time — were ecstatic, saying, ‘Oh, look at this! Oh, look at that!’ Now, the science team is getting a head start on learning how to process the data and understand the instrument’s behavior compared to models. They are exercising those muscles just like they will out at Europa.
Europa Clipper’s total journey to reach the icy moon will be about 1.8 billion miles (2.9 billion kilometers) and includes one more gravity assist — using Earth — in 2026. The spacecraft is currently about 280 million miles (450 million kilometers) from Earth.
Further Reading: NASA