“We got everything out of the flyby that we dreamed,” said Don Blankenship, NASA’s REASON radar principal investigator, as mission engineers delved into a wealth of new data from the Europa Clipper’s recent Mars flyby. For planetary radar engineers and spaceflight engineers, the successful demonstration of REASON Radar for Europa Assessment and Sounding: Ocean to Near-surface during the March flyby represents a critical milestone toward preparation for one of the most audacious explorations of the outer solar system.
The test, which took place as the Europa Clipper flew by Mars at altitudes of 3,100 miles or more down to a mere 550 miles above the planet, offered the first chance to confirm the performance of the radar in deep space environments simply not possible to simulate on Earth. The probe, which was tasked with looking behind Europa’s mysterious ice cover, transmitted and received radio waves across the Martian equator for approximately 40 minutes, and gathered 60 gigabytes of high-fidelity radar information. This amount, an interplanetary radar test record, became evident to engineers immediately that the instrument was working as designed. As Trina Ray, deputy science manager for the Europa Clipper at JPL, explained, “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!”
‘ Behind REASON’s technical success is its dual-frequency radar design, a first on a planetary mission beyond Mars. The system makes use of two sets of narrow antennas, each running from the solar arrays on the spacecraft to stretch 58 feet (17.6 meters). This will accommodate a high-frequency (HF) band centered at 9 MHz and a very-high-frequency (VHF) band at 60 MHz, allowing the radar to penetrate from the exosphere down to Europa’s suspected subsurface ocean. The 10 MHz VHF channel is also designed for shallow sounding and can provide vertical resolution of 15 meters in ice to depths of 4.5 kilometers, or switch to 150 meters resolution for greater penetration.
The HF channel, at 1 MHz bandwidth, is dedicated for anti-Jovian passes and may look for an ice-ocean interface up to 30 kilometers deep, with a vertical resolution of 150 meters REASON instrument details. The engineering challenge to test such a system was daunting. While development testing included stretching prototype antennas on open-air towers above JPL, the final flight hardware required sterile assembly and could only be tested in the vast High Bay 1 clean room. Simulating the radar’s “echo” in full would have demanded a chamber nearly three-quarters the length of a football field an impractical feat.
So, the flyby by Mars provided the initial real-world test of the combined system, involving signal bounceback calibration and data processing pipelines. In addition to hardware testing, the Mars flyby played a two-for-one role in mission design. The maneuver was staged as a gravity assist, using Mars’ angular momentum to reorient Europa Clipper on its long flight to Jupiter’s moon. These gravity aids, as discussed in planetary mission design texts, are necessary for interplanetary travel because they allow spacecraft to lose or gain speed without burning additional fuel.
Europa Clipper’s flight path will ultimately be 1.8 billion miles (2.9 billion kilometers), and another important Earth gravity assist is planned for 2026. The successful test of the radar has near-term scientific relevance. The 60 GB of Mars data is now being utilized to improve ice shell thickness modeling and exercise data processing methods that will be critical at Europa. The REASON team is drawing experience from Earth and Mars radar sounders, including MARSIS and SHARAD, which have imaged buried craters and layered deposits on Mars, but no ice-penetrating radar has ever been sent to the outer solar system. MARSIS and SHARAD mission findings.
The pipeline of data is being stress-tested so that when Europa Clipper flies as close as 16 miles (25 kilometers) above the surface of Europa, the radar is able to tell surface topography apart from subsurface interfaces and possible pockets of liquid water or brine.
REASON’s science goals are ambitious: to establish the thickness and composition of Europa’s ice crust, examine material transfer between ocean and surface, and define geologic features that could indicate habitability. REASON’s flexibility merging altimetry, reflectometry, sounding, interferometry, and plasma diagnosis makes it poised to answer outstanding questions regarding Europa’s potential as a life-bearing world. REASON science objectives. With its journey progressing, the Mars flyby is testament to the discipline of planetary radar engineering and the promise of revealing the secrets that lie beneath the frozen crust of Europa.
