Johns Hopkins APL Europa Clipper Team Marks a Month of Major Milestones

Last month, a team at the Johns Hopkins Applied Physics Laboratory (APL) completed a series of significant milestones as part of its contribution to NASA’s mission to explore Jupiter’s icy moon Europa.

After years of development, assembly and testing, the APL Europa Clipper team in Laurel, Maryland, delivered the spacecraft’s plasma detection instrument, called the Plasma Instrument for Magnetic Sounding (PIMS); the spacecraft’s Europa Imaging System Wide-Angle Camera (EIS WAC); and its radiation monitor (RadMon), which will gauge the wave of electrons bombarding the spacecraft as it performs 40-50 flybys of Europa.

These critical deliveries come on the heels of APL’s delivery of the Europa Clipper core spacecraft, radio frequency and telecommunications module, and propulsion module in May. They join Mapping Imaging Spectrometer for Europa (MISE) components and the second of two of the spacecraft’s thermal pump electronics assemblies, which were delivered earlier this year, in integration and test at the Jet Propulsion Laboratory (JPL) in Pasadena, California.

“Our partners at NASA challenged us, and we learned, grew and ultimately met the moment — a great accomplishment considering numerous global obstacles,” said Bobby Braun, head of the Space Exploration Sector at APL. “Europa Clipper has the potential to uncover incredible secrets of our solar system and place in the universe, and I’m very proud of the hundreds of APL staff members who worked tirelessly for many years to prepare this hardware for delivery and ultimately launch.”

Slated to take off in 2024, NASA’s Europa Clipper will explore Europa, a moon of Jupiter with an ocean that contains twice as much water as all of Earth’s oceans combined and that may have the conditions to support life. The spacecraft will observe Europa’s space environment, surface and interior, helping to determine the thickness of the moon’s icy crust, the depth and salinity of its ocean, and signs of plumes venting from the ocean into space.

The instruments and flight system components APL delivered play a critical role in achieving those objectives. The team’s final instrument delivery — the EIS Narrow-Angle Camera (EIS NAC) — is scheduled for this fall.

At JPL, over the next two years, engineers and technicians will assemble and test the complete spacecraft, ensuring it can withstand its journey to Jupiter and the harsh space environment at Europa.

Untangling Magnetic Distortions

Beyond its massive size, Jupiter takes another solar system superlative: the planet with the harshest radiation environment.

Europa Clipper guards against the radiation with metallic shielding to protect instruments and electronics from damage while the spacecraft’s RadMon keeps constant vigilance of the surrounding environment.

But radiation also has a profound effect on Europa. As Jupiter’s enormous magnetic field washes over the moon, its interactions with the electrically conductive salty ocean induce a magnetic field around the moon, which Europa Clipper’s magnetometer will measure to determine Europa’s ocean depth and conductivity as well as the thickness of its icy shell.

The hot soup of charged particles, or plasma, moving in tow with Jupiter’s magnetic field at 60 miles (100 kilometers) per second, however, creates its own magnetic fields, distorting Europa’s induced field and making it hard to interpret.

That’s where PIMS comes in. Using four metal containers called Faraday cups, PIMS will measure the plasma’s density, temperature and velocity around Europa, which physicists can then use to develop computational models to subtract the plasma’s effect on Europa’s magnetic field.

“It sounds simple, but it’s anything but that, and the interpretation of the data is going to be complex,” said Joseph Westlake, a chief scientist for space physics at APL and principal investigator for PIMS. “But because our instrument is going to be so sensitive to these small currents, we are going to have such a cleaner and clearer picture of Europa’s subsurface ocean than ever before.”

PIMS’s Faraday cups were specially designed to deal with Jupiter’s radiation environment. At about 8 inches (20 centimeters) wide and 3 inches (8 centimeters) deep, each cup was designed like a little stadium, with tiers of progressively smaller metal rings and insulating spacers that lead to a flat detector plate at the bottom.

“It’s a design that is very different from the way it’s ever been done in the past,” said Matthew Grey, an electrical engineer at APL and the former lead instrument engineer for PIMS. It also ensures plasma particles have no direct way to hit materials behind the tiered rings, which would otherwise capture and bleed off the charge to other parts or instruments.

A Wider View

The WAC — one of two cameras in the spacecraft’s Europa Imaging System (EIS) — has one of the largest sensors to be flown in deep space: an 8-megapixel sensor that can capture color and stereoscopic images as good as about 23-feet (7-meter) per-pixel resolution.

A refractive telescope, the WAC captures light directly, passing it through a series of lenses built to withstand Jupiter’s radiation and focusing the light on a metal-oxide semiconductor like those found in cell phones and digital cameras. The camera will capture wide swaths of Europa’s landscape on every flyby, providing new information about materials and geologic features on the surface.

Although multiple missions have already imaged Europa, they’ve captured only about 15% of its surface at even moderate resolution, and very little of it in color or stereo, said APL planetary scientist Zibi Turtle, EIS’s principal investigator.

In combination with its narrow-angle counterpart, the WAC will image roughly 90% of Europa’s surface at better than 330 feet (100 meters) per pixel, providing an unprecedented global data set of Europa’s geology.

Using those images, scientists will determine what geologic processes acting in the ice shell might have created (or continue to create) Europa’s many surface features.

“We can use these images to understand the individual landforms and relationships between different landforms, and the better we understand the landforms, the better we can put constraints on the structure of the interior,” Turtle explained.

In coordination with the mission’s radar team, the camera will help scientists interpret structures beneath the surface and search for fresh deposits from Europa’s purported water vapor plumes, which, if found, would reveal an ongoing exchange between the subsurface water and the icy surface. Finally, the WAC will help identify ideal landing sites for a potential future lander mission.

APL is a partner in the development of NASA’s Europa Clipper, which JPL leads for NASA’s Science Mission Directorate in Washington. The mission is managed by Caltech in Pasadena, California. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, executes program management of the Europa Clipper mission.

Learn more about Europa and Europa Clipper here.