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Europa: Catching Up with the Clipper

I get an eerie feeling when I look at spacecraft before they launch (not that I get many opportunities to do that, at least in person). But seeing the Spirit and Opportunity rovers on the ground at JPL just before their shipment to Florida was an experience that has stayed with me, as I pondered how something built by human hands would soon be exploring another world. I suppose the people who do these things at the Johns Hopkins Applied Physics Laboratory and the Jet Propulsion Laboratory itself get used to the feeling. For me, though, the old-fashioned ‘sense of wonder’ kicks in long and hard, as it did when Europa Clipper arrived recently at JPL.

Not that the spacecraft is by any means complete, but its main body has been delivered to the Pasadena site, where it will see final assembly and testing over a two-year period. Here I fall back on the specs to note that this is the largest NASA spacecraft ever designed for exploration of another planet. It’s about the size of an SUV when stowed for launch, but we know from the James Webb Space Telescope how large these things can become when fully deployed. In Europa Clipper’s case, the recently delivered main body is 3 meters tall and 1.5 meters wide. Extending the solar arrays and other deployable equipment takes it up to basketball court size.

Image: The main body of NASA’s Europa Clipper spacecraft has been delivered to the agency’s Jet Propulsion Laboratory in Southern California, where, over the next two years, engineers and technicians will finish assembling the craft by hand before testing it to make sure it can withstand the journey to Jupiter’s icy moon Europa. Here it is being unwrapped in a main clean room at JPL, as engineers and technicians inspect it just after delivery in early June 2022. Credit: NASA.

Eight antennas are involved, powered by a radio frequency subsystem that will service a high-gain antenna measuring three meters wide, and as JPL notes in a recent update, the electrical wires and connectors collectively called the ‘harness’ themselves weigh 68 kilograms. Stretch all that wiring out and you get 640 meters, taking us twice around a football field. The main body will include a fuel tank and an oxidizer tank connecting to an array of 24 engines. Tim Larson is JPL deputy project manager for Europa Clipper:

“Our engines are dual purpose. We use them for big maneuvers, including when we approach Jupiter and need a large burn to be captured in Jupiter’s orbit. But they’re also designed for smaller maneuvers to manage the attitude of the spacecraft and to fine tune the precision flybys of Europa and other solar system bodies along the way.”

So what is arriving, or has arrived at JPL, is a spacecraft in pieces, its main body now joining key instruments like E-THEMIS, a thermal emission imaging system developed at Arizona State, and Europa-UVS, the mission’s ultraviolet spectrograph. E-THEMIS is an infrared camera that should give us insights into temperatures on the Jovian moon, and hence offer information about its geological activity. Given that we’re interested in finding places where liquid water is close to the surface, the data from this instrument should be extremely valuable during the spacecraft’s nearly fifty close passes.

The theory here is that as Europa’s surface cools after local sunset, the areas of the most solid ice will retain heat longer than areas with a looser, more granular texture. E-THEMIS will be able to map cooling rates across the surface. The infrared camera works in three heat-sensitive bands, and the warmer regions it should see may be the result of liquid water close to the surface, or possible impacts or convection activity. Not surprisingly, E-THEMIS lead project engineer Greg Mehall points to the radiation environment in Jupiter space as one of the team’s biggest issues:

“The extreme radiation environment at Europa gave far more design challenges for the ASU engineering team than on any previous instrument we’ve developed. We had to use dense shielding materials, such as copper-tungsten alloys, to provide the necessary protection from the expected radiation. And to ensure that E-THEMIS will survive during the mission, we also carried out radiation tests on the instrument’s electronic components and materials.”

Image: The thermal imager will use infrared light to distinguish warmer regions on Europa’s surface, where liquid water may be near the surface or might have erupted onto the surface. The thermal imager will also characterize surface texture to help scientists understand the small-scale properties of Europa’s surface. In the image above, we’re seeing a diurnal temperature color image from the first light test of Europa Clipper’s thermal imager (called E-THEMIS), taken from the rooftop of the Interdisciplinary Science and Technology Building 4 on the Tempe Campus of Arizona State University (ASU). The top image was acquired at 12:40 PM, the middle at 4:40 PM, and the bottom image at 6:20 PM (after sunset). Temperatures are approximations during this testing phase. Credit: ASU.

As to the Europa-UVS instrument, this ultraviolet spectrograph will search for water vapor plumes and study the composition of both the surface and the tenuous atmosphere as it uses an optical grating to spread and analyze light, identifying basic molecules like hydrogen, oxygen, hydroxide and carbon dioxide.

The spacecraft’s visible light imaging system (EIS) is going to upgrade those well-studied images from the Galileo mission enormously. The plan is to map 90 percent of the moon’s surface at 100 meters per pixel, which is six times more of Europa’s surface than Galileo, and at five times better resolution. And when Europa Clipper swings close to Europa during a flyby, it will produce images with a resolution fully 100 times better than Galileo. The Europa Imaging System includes both wide- and narrow-angle cameras, each with an eight-megapixel sensor. Both of these cameras will produce stereoscopic images and include the needed filters to acquire color images.

All told, the spacecraft’s nine science instruments should be able to extract information about the depth and salinity of the ocean under the ice and, crucially, the thickness of the ice crust (I can imagine wagers on that issue going around in certain quarters). Gathering information about the moon’s surface and interior should further illuminate the issue of plumes from the ocean below that may break through the ice.

Assembly, test and launch is a two year phase that, by the end of this year, should see assembly of most of the flight hardware and the remaining science instruments. Kudos to JHU/APL, which has just delivered a flight system that is the largest ever built by engineers and technicians there. Now we look toward bolting on the radio frequency module, radiation monitors, power converters, the propulsion electronics and those hundreds of meters of wiring. Not to mention the electronics vault that must stand up to hard radiation.

The full instrument package will include an imaging spectrometer, ice-penetrating radar, a magnetometer, a plasma instrument, a mass spectrometer and a dust analyzer. Only two years and four months before launch onto a six-year journey of 2.9 billion kilometers. Europa Clipper isn’t a life-finder, but it does have the capability of detecting whether the moon’s ocean really does allow for the possibility of life to develop. It’s our first reconnaissance of Europa since the 1990s. What surprises will it reveal?

Bear in mind, too, that we still have ESA’s JUICE (JUpiter ICy moons Explorer) in the offing, with launch planned for 2023. I note with interest that on June 19, Europa will occult a distant star, which should be useful in tweaking our knowledge of the moon’s orbit before the arrival of both missions. Destined to end its life as a Ganymede orbiter, JUICE will make only two close passes of Europa, but its period of operations will coincide with part of Europa Clipper’s numerous flybys of the moon.


Comments on this entry are closed.

  • Michael Fidler June 10, 2022, 10:01

    The infrared images remind me of the land fly over sequences at the end of the movie 2001 A Space Odyssey…

  • Alex Tolley June 10, 2022, 11:13

    Some more details of the science packages and science goals:

    NASA: Science with Europa Clipper

    Wikipedia: Europa Clipper

    Nature (2020): NASA’s Europa Clipper—a mission to a potentially habitable ocean world

    Technology moves on. The imager has an 8-megapixel camera, less than my 12-megapixel iPhone – although the sensor is probably a lot better to handle the illumination and radiation conditions. This is the inevitable cost of long development times and freezing the technology during a time when rapid technological change is still happening. The mission was proposed in 1997, recommended in 2013, designed 2017-2019, launch in 2024 and arrive in 2030.

    From the Nature article:

    If mixing between the surface oxidants and the reduced ocean water occurs, there is an opportunity in Europa’s ocean or ice shell to produce a reduction–oxidation (redox) potential. All known life on Earth relies on such redox potentials to extract chemical energy from the environment in exchange for heat energy and entropy, enabling cellular maintenance, metabolism, and reproduction. Europa thus has the ingredients that may allow life to emerge (…)

    It gather that the surface oxidation material may cycle down through the ice crust faster than the prior science suggested. I will be looking with interest when the data is returned and analyzed.

    • charlie June 10, 2022, 13:53

      “The mission is scheduled to launch in October 2024 aboard a Falcon Heavy,[8] during a 21-day launch window.[7] The spacecraft will use gravity assists from Mars in February 2025 and Earth in December 2026, before arriving at Europa in April 2030.[7]”

      6 years, these flights are getting long……

      • Alex Tolley June 10, 2022, 16:31

        Galileo – launched 1989 arrived 1995 (6 years)
        Juno – launched 2011 arrived 2015 (5 years)

        Unless one is doing a flyby like Pioneer or Voyager, it probably makes more sense to fly a low-energy orbit, (aided using gravity assists) that allows easy insertion into Jupiter’s orbit.

        But yes, it would be nice if we had more powerful propulsion allowing short flight times. If the Wind Rider team is right, they can do Jupiter in a fraction of that time, although stopping is a little harder.

        • Michael Fidler June 10, 2022, 20:59

          They need to put ion drives on these things powered by “Orbitrons”.


          • Alex Tolley June 11, 2022, 11:05

            Nah! What we need is the Infinite Improbability Drive. This was built accidentally:

            If he thought to himself, such a machine is a virtual impossibility, it must have finite improbability. So all I have to do in order to make one is to work out how exactly improbable it is, feed that figure into the finite improbability generator, give it a fresh cup of really hot tea…

            Then we can really travel…around the galaxy. Jupiter would then be just around the corner…like the local chemist shop.

            The drive doesn’t seem to have any causality violation issues, but there are other side effects to contend with.

            OT. I read NASA is going to investigate UFOs.

            • Michael Fidler June 11, 2022, 22:56

              Well, they need to read this:

              A new, comprehensive timeline of UFO history is available on the CUFOS website .(http://cufos.org/pdfs/UFOsandIntelligence.pdf ) Check the Document Outline icon on the left to retrieve the index, by year. Compiled by veteran researcher George Eberhart, the chronicle is an up-to-date retrospective of UFO history (from Agobard of Lyon to the newly appointed US investigation agency in 2022), intertwined with events in US and world history concerning military and civilian intelligence agencies and the cult of secrecy. It is now 906 pages and more than 814,000 words (including a substantial “Sources and Further Reading” appendix). Readers will discover or rediscover many events, people, and UFO cases they may not be familiar with. Some will find it useful for current or planned research projects. Military cases, those involving commercial aircraft, close encounters involving physical traces and other evidence, reports involving occupants or entities, and events surrounding military and sensitive nuclear sites are emphasized, but this timeline covers the full spectrum of UFO history, from contactee experiences to misidentifications of mundane phenomena and notorious hoaxes.

              • Paul Gilster June 12, 2022, 10:10

                Let’s stay on topic, please. Europa Clipper, not UFOs.

                • Michael Fidler June 12, 2022, 10:13

                  Ok, but thanks for letting it through!

  • Andrew Palfreyman June 10, 2022, 17:37

    “Europa Clipper isn’t a life-finder”
    And yet for decades NASA advertises itself to the public as “seeking out life”. Look what Steve Squyres’ influence did for all those Mars rovers.

    Personally I’m fed up with it.

    • Mike Serfas June 11, 2022, 12:41

      I see a Squyres quote, “our mission kind of arose from catastrophe…” I don’t really know what influence regarding life you have in mind.

      To paraphrase Star Wars, NASA’s claim to be hunting life is “true … in a manner of speaking”. If you don’t know if Mars had ancient water, you don’t know how live the life you’re looking for would have been. If you put a very fine edge on it, we don’t even have a universally agreed definition of life, so even things like desert pavement on Earth have had some people scratching their heads. If we send a microscope and it sends back a picture of “microbacteria”, well, people will still argue whether they are just mineral formations. If it sends back a picture of weird black stuff growing seasonally on the dunes of Mars, they’ll argue if it is brine. If it sends back pictures of blueberries growing and shrinking — well, that’s just wind blowing sand off of them, and there’s no way I can take that seriously. But you should have the idea by now anyway. If you want to sell the news media a picture of a naked Senator in your bedroom, your picture needs to clearly illustrate the *bedroom*, not just the Senator. Any claim of life on other planets will need a lot of context to be believed.

    • ljk June 14, 2022, 11:20

      NASA is still gunshy after Viking’s ambiguous results at Mars in the 1970s.


      Yet now they say they are hopping into the investigation of UAPs!

      No one wants to be labeled as fringe or worse when it comes to reporting alien life, even in 2022, yet I know the day ET is truly confirmed, everyone and their brother will swear they knew it all along.

  • Enzo June 11, 2022, 10:55

    At long last !

  • Eric September 4, 2022, 21:19

    Thanks for the article, my second novel was about the machine that dives through the ice of Europa.