Feature | April 1, 2021

On the Path Towards Unprecedented Science

four engineers examining a Europa Clipper instrument

Engineers test a prototype of one of Europa Clipper’s radar antennas in 2018 on a hilltop at NASA’s Jet Propulsion Laboratory. Credit: NASA/J. Thompson

In an unprecedented year, the Europa Clipper project continues on the path toward unprecedented science.

Four hundred years after its discovery by Galileo Galilei, the Jovian moon Europa is arguably the most exciting place to look for present day life in our solar system. Evidence from prior missions through the Jupiter system shows that Europa has over twice the amount of liquid water than Earth. Much of Europa’s water is in the form of a liquid, salty ocean. Europa’s tidal heating warms this ocean, and its rocky interior also likely supplies the ocean with minerals. The Europa Clipper mission will explore Europa to investigate its habitability — whether the icy moon could harbor conditions suitable for present-day life.

Now only a few years from launch, Europa Clipper is taking shape in “shipyard” facilities across the country and overseas. Europa Clipper’s components are complex, custom-built devices. They are designed to withstand extremes in temperature, as well as Jupiter’s insidious radiation belt in which Europa orbits. The fabrication of the spacecraft components and scientific instruments is making good progress toward its future Earth departure. Here is a tour of these elements, along with depictions of the testing and checks required to ensure mission success.

Europa Clipper will have nine science instruments and several engineering subsystems. Shown here is an interactive rendering of the spacecraft. Fully deployed, the spacecraft will be more than 5 meters (15 feet) tall, 17 meters (50 feet) long, and will span about 30 meters (100 feet) in width — longer than a basketball court from tip to tip of its solar arrays. Credit: NASA/JPL-Caltech Download Options

The solar panels and overall physical structure visible in the interactive model are aspects of spacecraft subsystems that comprise the flight system. The science instruments, attached directly to the spacecraft or through a boom, are referred to as the payload. Europa Clipper’s antennas fall into both of these categories; some antennas provide only a spacecraft (telecom) function, other antennas provide only a science function (for the radar), and yet others perform both telecom and science (gravity and radio science) roles.

The Europa Clipper flight system design incorporates lessons learned from prior missions; the scientific instruments are at least partly based on interplanetary mission predecessors. Informed by those experiences, the spacecraft and its components are designed to be appropriately robust to the Europa environment. Europa Clipper’s components also need to be mutually compatible with one another while being operated. Given that, the testing and performance verification is designed to reflect “flying conditions” as well as possible. Let’s look at two subsystems whose fabrication is underway.

two people in clean room attire working on the Europa Clipper propulsion module
NASA’s Goddard Space Flight Center (GSFC) engineers align the upper and lower cylinders of Europa Clipper’s propulsion module for a fit check. Credit: NASA/B. Lambert

The propulsion subsystem is essentially Europa Clipper’s “gas tank.” It will carry fuel and oxidizer sufficient to change Europa Clipper’s velocity by about 3,600 miles per hour (5,800 kilometers per hour). While this is a large amount and a critically important capability, it represents about five percent of the velocity change needed to accomplish this mission. The bulk of the velocity change necessary to adjust trajectories once in Jupiter orbit will come from gravitational flybys of Jovian moons as planned. Given the overall size of the tanks, the propulsion subsystem is designed as part of a “propulsion module” that includes the solar arrays and radiation monitors.

view of the bottom of Europa Clipper's high-gain antenna
Europa Clipper’s bowl-shaped high-gain antenna faces down in this image. This radio dish will allow ground controllers to send and receive commands and data between Earth and the spacecraft in Jupiter orbit — more than one million times farther from Earth than the International Space Station orbits. Credit: NASA

The telecom subsystem is the link between Europa Clipper and Earth. It provides command reception and science and engineering data downlink. It also provides interplanetary navigation data. Through the high gain antenna (HGA), Europa Clipper will downlink on the order of several gigabytes of science data per typical Earth antenna tracking session, enough data to fill a smartphone in about a week. The HGA also serves as a sunshade when Europa Clipper is still relatively close to the Sun, while en route to the Jupiter system. With respect to its gravity science role, scientists will use the radio signals exchanged between the telecom sub-system aboard the spacecraft and NASA's Deep Space Network to detect subtle variations in the gravitational attraction between Europa and Europa Clipper. The variations reflect details of Europa’s internal mass distribution, allowing us to learn about Europa’s interior structure.

The Europa Clipper mission intends to answer the big question: Is Europa habitable? This question encompasses hypotheses about the nature of water, chemistry, and energy exchange at Europa, which in turn leads to these additional major questions to be answered: How deep and salty is the ocean? How thick is the ice shell? How active is the ice shell? Are there plumes, and if so, what is in the plumes? What is in the red/brown Europa surface features? How do these features form?

Europa Clipper’s science instruments work together to answer those questions, with overlapping responsibilities. Each instrument’s observations will be enhanced by observations from other instruments. Science team members, representing the instruments and many science disciplines, steadily collaborate with one another to fully exploit the capabilities of the spacecraft’s powerful payload. By the time Europa Clipper enters Jupiter’s orbit and begins its Europa flybys, the Europa Clipper instruments and science team will be primed and ready to respond to what Europa Clipper reveals.

science team meeting in a conference room
In addition to ongoing remote collaboration, Europa Clipper’s science team members meet in person twice each year (conditions permitting) for more focused planning. Shown here are mission scientists in discussion at Cornell University in 2019. Multiple parallel sessions foster cross-pollination of ideas across the team. Credit: NASA/J. Thompson

Let’s look into the science instruments being built to enable Europa Clipper’s science investigations.

Europa Thermal Emission Imaging System

The Europa Thermal Emission Imaging System, or E-THEMIS, will produce infrared images of Europa to allow scientists to measure the moon’s surface temperatures. The instrument will search for signs of recent resurfacing, such as warm ice at or near the surface. E-THEMIS will also help map surface roughness, identifying relatively hazard-free regions to inform designs and planning for a potential future Europa lander.

  • E-THEMIS Telescope Housing

    E-THEMIS Telescope Housing

    The telescope housing for Europa Clipper’s E-THEMIS infrared instrument, which will measure the temperature and permit interpretation of roughness of Europa’s surface. Credit: NASA/Arizona State University.

    E-THEMIS Focal Plane Module

    An engineering model of the focal plane module for Europa Clipper’s E-THEMIS instrument. Credit: NASA/Arizona State University

Europa Clipper magnetometer

The Europa Clipper Magnetometer (ECM) sensors will measure the direction, strength, and time-varying nature of magnetic fields in the immediate vicinity of Europa and in the Jovian system. Europa’s magnetic field is created by the interaction between Jupiter's strong magnetic field and the suspected liquid ocean of salty water within Europa. ECM should allow scientists to confirm the existence of that ocean, measure its depth and salinity, and determine the thickness of the ice shell above. ECM will be on a boom, which will be deployed after launch.

ECM sensor and harness
The Europa Clipper Magnetometer (ECM) sensor. At left is the interior of the sensor that will measure Europa’s magnetic field, along with the sensor’s pigtail harness. Credit: NASA/JPL-Caltech

Europa Imaging System

Europa Clipper’s visible light camera suite is called the Europa Imaging System, or EIS (pronounced “ice”). EIS consists of a wide-angle camera and a narrow-angle camera, each a digital camera with an eight-megapixel sensor sensitive to visible wavelengths of light, as well as slightly into near-infrared and ultraviolet wavelengths. Both cameras will acquire stereoscopic images, and both will have six filters to acquire color images. EIS will map Europa at resolutions vastly better than previous missions, down to about 20 inches (50 centimeters) per pixel in places. EIS will reveal surface features and how they relate to subsurface structures, and will search for signs of recent geologic activity on Europa’s surface, as well as potential plumes venting material into space.

  • EIS Narrow Angle Camera

    EIS Narrow Angle Camera

    An engineering (non-flight) model of the EIS narrow-angle camera. The camera is mounted on gimbals, which allow the camera to pivot 60 degrees on each of two axes, enabling the camera to target a surface feature and to build mosaics of multiple high-fidelity images of Europa’s surface. Credit: NASA/JHU-APL
  • EIS Wide Angle Camera

    EIS Wide Angle Camera

    Here, mechanical engineers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, set up the engineering model of the Europa Imaging System (EIS) Wide Angle Camera (WAC) telescope and electronics in a thermal-vacuum chamber for environmental testing. EIS will allow groundbreaking measurements and will map most of Europa at resolutions previous missions could only achieve in specific areas. EIS data will offer fresh insights into Europa’s geological structure and processes and will be used to search for evidence of recent or current geologic activity, including potential erupting plumes. Credit: NASA/Johns Hopkins APL/Ed Whitman

Ultraviolet Spectrograph

Europa Clipper’s Ultraviolet Spectrograph, or Europa-UVS, will collect ultraviolet light with a telescope and spread that light onto a detector for analysis. This instrument will help scientists identify atmospheric gases and surface materials at Europa. Europa-UVS will also search around Europa for further evidence that liquid water from within the moon is venting into space in the form of plumes.

UVS Flight Housing
Flight housing for the Europa-UVS (Europa Ultraviolet Spectrograph) instrument in early summer 2020, as it was about to begin assembly and testing. Credit: NASA/SWRI

MAss SPectrometer for Planetary EXploration/Europa

The MAss SPectrometer for Planetary EXploration/Europa, or MASPEX, will collect gases and “bounce” their charged ions back and forth within the instrument. By precisely timing their transit through the instrument, scientists can determine the mass of those charged gases. MASPEX will be used to study gases in Europa’s faint atmosphere for clues about its surface, its suspected subsurface ocean, and how the ocean and surface exchange material. The instrument will also be used to study how Jupiter’s radiation alters chemical compounds on Europa’s surface, and it will analyze any plume material being vented into space from ice-embedded liquid reservoirs.

MASPEX Instrument Assembly, Integration, and Test
The horizontal cylinder of varying diameter running across the top third of this image is an engineering (non-flight) model of Europa Clipper’s MASPEX mass spectrometer instrument in assembly and test. Credit: NASA/SWRI

Mapping Imaging Spectrometer for Europa

The Mapping Imaging Spectrometer for Europa, or MISE (pronounced “mize”), will collect infrared light reflected from Europa and separate it into its various wavelengths. Like a visible light camera, MISE will produce images, but these images depict the composition of surface materials. MISE will be used to map the distribution of ices, salts, organics, and the warmest hotspots on Europa. These maps will help determine if Europa’s suspected ocean is an environment suitable for life, and they will also help to characterize Europa’s geologic history.

  • MISE Dyson CaF2 Lens

    MISE Dyson CaF2 Lens

    As infrared light enters Europa Clipper’s MISE instrument, mirrors bounce the light into its calcium fluoride (CaF2) lens (flight model shown), which directs the light onto a diffraction grating. Credit: NASA/JPL-Caltech
  • MISE Diffraction Grating

    MISE Diffraction Grating

    The flight model for MISE’s diffraction grating, which disperses light, in a manner similar to a prism, before the light strikes the instrument's detector. Credit: NASA/JPL-Caltech

Plasma Instrument for Magnetic Sounding

Europa Clipper’s Plasma Instrument for Magnetic Sounding, or PIMS, will have four sensors called Faraday cups to measure the electrical current produced by charged particles (plasma) as they strike a detector plate inside each sensor. Scientists will use PIMS to study the characteristics of plasma around Europa to better understand the moon’s ice shell thickness, ocean depth, and ocean salinity.

  • PIMS Collector Assembly

    PIMS Collector Assembly

    A collector assembly that will fly aboard Europa Clipper in one the four PIMS Faraday cups, which will help scientists study the charged particle (plasma) environment around Europa. The sensor plate shown has a layer of gold over palladium, with a copper base. Credit: NASA/JHU-APL
  • PIMS Faraday Cup Sensors

    PIMS Faraday Cup Sensors

    Built by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, PIMS is made up of two instruments, each with two identical sensors called Faraday cups that will measure the plasmas, or electrically charged gases, in Europa’s ionosphere and Jupiter’s magnetosphere. Pictured in a clean room at APL are the recently assembled Faraday cup sensors and instrument housings in two configurations. On the left is the final flight hardware, with insulating thermal blankets installed; on the right is a test configuration that protects sensitive hardware for transportation. Plasma measurements made by PIMS will contribute to Europa Clipper’s science investigation to determine the thickness of the ice shell that covers Europa and the depth and makeup of the liquid-water ocean below that shell. Credit: NASA/Johns Hopkins APL/Ed Whitman

SUrface Dust Analyzer

Along with plasma, tiny pieces of Europa’s surface inhabit nearby space, lofted there by micrometeorites. These microscopic dust particles can be sensed by Europa Clipper’s SUrface Dust Analyzer, or SUDA. SUDA will measure the particle composition, as well as the speed and direction dust is traveling, revealing the particles’ region of origin on Europa’s surface. If Europa is found to be venting subsurface water and entrained particles into space, SUDA will measure that material as well.

  • SUDA Assembly and Testing

    SUDA Assembly and Testing

    The SUrface Dust Analyser (SUDA) instrument for Europa Clipper, shown during assembly and testing at the Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder. Credit: NASA/CU Boulder-LASP.
  • SUDA Assembly and Testing

    SUDA Assembly and Testing

    Europa Clipper’s SUDA instrument, pictured in the clean room, will collect and analyze particles lifted from Europa’s surface by micrometeorites. Credit: NASA/CU Boulder-LASP.

Radar for Europa Assessment and Sounding: Ocean to Near-surface

Europa Clipper’s radar instrument is called Radar for Europa Assessment and Sounding: Ocean to Near-surface, or REASON. REASON will use high frequency (HF) and very high frequency (VHF) radio signals to penetrate up to 18 miles (30 kilometers) into Europa’s icy shell. The radio waves will bounce off subsurface water or other features and return to the spacecraft to create pictures of the icy interior. REASON will help scientists to look for Europa’s suspected ocean, measure ice thickness, and better understand the icy shell's interior structure and circulation. The instrument will also study the elevation, composition, and roughness of Europa’s surface, and it can sense Europa’s upper atmosphere for signs of plume activity.

  • REASON VHF Radar Antenna

    REASON VHF Radar Antenna

    A JPL engineer holds one of four VHF radar antennas for Europa Clipper’s REASON instrument in its deployed configuration. In its stowed configuration for launch, the device will be about the size of a small lunchbox. In the weeks after launch, the VHF antenna will deploy to its operational configuration, of 8.5 feet (2.6 meters) long. Credit: NASA/JPL-Caltech.
  • REASON HF Radar Antenna

    REASON HF Radar Antenna

    Engineers test one of two high frequency radar antennas for Europa Clipper’s REASON instrument on a hilltop at NASA’s Jet Propulsion Laboratory. The antenna is the narrow copper tube, held straight by several cables and a cross bar on the tower at right. In space, the copper tube will stick out straight on its own, but in Earth's gravity, the antenna requires supports to keep it straight for testing. Credit: NASA/JPL-Caltech.

As with ECM and the solar arrays, the REASON antennas will be stowed for launch, then deployed into operational configuration in the weeks after launch. Engineering teams are testing the antenna deployment systems here on Earth to ensure that REASON will unfurl smoothly and completely.

Deployment Sequence in 3…2…1

While much work remains, much has been accomplished during the past challenging year. Each step in fabrication and preparation brings us closer to what will be unprecedented science at Europa. We invite you to continue to follow the Europa Clipper mission, in eager anticipation and ultimate excitement of unprecedented discovery.