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By European Space Agency
Image: The development of ESA’s Earth Explorer FLEX mission has recently passed a significant milestone: the mission’s all-important instrument has been joined to its satellite platform. View the full article
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Europa Clipper’s radar instrument received echoes of its very-high-frequency radar signals that bounced off Mars and were processed to develop this radargram. What looks like a skyline is the outline of the topography beneath the spacecraft.NASA/JPL-Caltech/UT-Austin The agency’s largest interplanetary probe tested its radar during a Mars flyby. The results include a detailed image and bode well for the mission at Jupiter’s moon Europa.
As it soared past Mars in March, NASA’s Europa Clipper conducted a critical radar test that had been impossible to accomplish on Earth. Now that mission scientists have studied the full stream of data, they can declare success: The radar performed just as expected, bouncing and receiving signals off the region around Mars’ equator without a hitch.
Called REASON (Radar for Europa Assessment and Sounding: Ocean to Near-surface), the radar instrument will “see” into Europa’s icy shell, which may have pockets of water inside. The radar may even be able to detect the ocean beneath the shell of Jupiter’s fourth-largest moon.
“We got everything out of the flyby that we dreamed,” said Don Blankenship, principal investigator of the radar instrument, of the University of Texas at Austin. “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.”
In this artist’s concept, Europa Clipper’s radar antennas — seen at the lower edge of the solar panels — are fully deployed. The antennas are key components of the spacecraft’s radar instrument, called REASON.NASA/JPL-Caltech The radar will help scientists understand how the ice may capture materials from the ocean and transfer them to the surface of the moon. Above ground, the instrument will help to study elements of Europa’s topography, such as ridges, so scientists can examine how they relate to features that REASON images beneath the surface.
Limits of Earth
Europa Clipper has an unusual radar setup for an interplanetary spacecraft: REASON uses two pairs of slender antennas that jut out from the solar arrays, spanning a distance of about 58 feet (17.6 meters). Those arrays themselves are huge — from tip to tip, the size of a basketball court — so they can catch as much light as possible at Europa, which gets about 1/25th the sunlight as Earth.
The instrument team conducted all the testing that was possible prior to the spacecraft’s launch from NASA’s Kennedy Space Center in Florida on Oct. 14, 2024. During development, engineers at the agency’s Jet Propulsion Laboratory in Southern California even took the work outdoors, using open-air towers on a plateau above JPL to stretch out and test engineering models of the instrument’s spindly high-frequency and more compact very-high-frequency antennas.
But once the actual flight hardware was built, it needed to be kept sterile and could be tested only in an enclosed area. Engineers used the giant High Bay 1 clean room at JPL, where the spacecraft was assembled, to test the instrument piece by piece. To test the “echo,” or the bounceback of REASON’s signals, however, they’d have needed a chamber about 250 feet (76 meters) long — nearly three-quarters the length of a football field.
Enter Mars
The mission’s primary goal in flying by Mars on March 1, less than five months after launch, was to use the planet’s gravitational pull to reshape the spacecraft’s trajectory. But it also presented opportunities to calibrate the spacecraft’s infrared camera and perform a dry run of the radar instrument over terrain NASA scientists have been studying for decades.
As Europa Clipper zipped by the volcanic plains of the Red Planet — starting at 3,100 miles (5,000 kilometers) down to 550 miles (884 kilometers) above the surface — REASON sent and received radio waves for about 40 minutes. In comparison, at Europa the instrument will operate as close as 16 miles (25 kilometers) from the moon’s surface.
All told, engineers were able to collect 60 gigabytes of rich data from the instrument. Almost immediately, they could tell REASON was working well. The flight team scheduled the full dataset to download, starting in mid-May. Scientists relished the opportunity over the next couple of months to examine the information in detail and compare notes.
“The engineers were excited that their test worked so perfectly,” said JPL’s Trina Ray, Europa Clipper deputy science manager. “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.
More About Europa Clipper
Europa Clipper’s three main science objectives are to determine the thickness of the moon’s icy shell and its interactions with the ocean below, to investigate its composition, and to characterize its geology. The mission’s detailed exploration of Europa will help scientists better understand the astrobiological potential for habitable worlds beyond our planet.
Managed by Caltech in Pasadena, California, NASA’s Jet Propulsion Laboratory in Southern California leads the development of the Europa Clipper mission in partnership with the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, for NASA’s Science Mission Directorate in Washington. APL designed the main spacecraft body in collaboration with JPL and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, NASA’s Marshall Space Flight Center in Huntsville, Alabama, and Langley Research Center in Hampton, Virginia. The Planetary Missions Program Office at NASA Marshall executes program management of the Europa Clipper mission. NASA’s Launch Services Program, based at NASA Kennedy, managed the launch service for the Europa Clipper spacecraft. The REASON radar investigation is led by the University of Texas at Austin.
Find more information about Europa Clipper here:
https://science.nasa.gov/mission/europa-clipper/
Check out Europa Clipper's Mars flyby in 3D News Media Contacts
Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, Calif.
818-287-4115
gretchen.p.mccartney@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.govt
2025-097
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Last Updated Aug 01, 2025 Related Terms
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By European Space Agency
The Meteosat Third Generation Sounder (MTG-S1) satellite, which is hosting the instrument for the Copernicus Sentinel-4 mission, has been placed inside the nose cone of the Falcon 9 launch rocket and is ready for the scheduled liftoff at 23:03 CEST on Tuesday, 1 July.
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
NASA Ames research scientist Kristina Pistone monitors instrument data while onboard the Twin Otter aircraft, flying over Monterey Bay during the October 2024 deployment of the AirSHARP campaign. NASA/Samuel Leblanc In autumn 2024, California’s Monterey Bay experienced an outsized phytoplankton bloom that attracted fish, dolphins, whales, seabirds, and – for a few weeks in October – scientists. A team from NASA’s Ames Research Center in Silicon Valley, with partners at the University of California, Santa Cruz (UCSC), and the Naval Postgraduate School, spent two weeks on the California coast gathering data on the atmosphere and the ocean to verify what satellites see from above. In spring 2025, the team returned to gather data under different environmental conditions.
Scientists call this process validation.
Setting up the Campaign
The PACE mission, which stands for Plankton, Aerosol, Cloud, ocean Ecosystem, was launched in February 2024 and designed to transform our understanding of ocean and atmospheric environments. Specifically, the satellite will give scientists a finely detailed look at life near the ocean surface and the composition and abundance of aerosol particles in the atmosphere.
Whenever NASA launches a new satellite, it sends validation science teams around the world to confirm that the data from instruments in space match what traditional instruments can see at the surface. AirSHARP (Airborne aSsessment of Hyperspectral Aerosol optical depth and water-leaving Reflectance Product Performance for PACE) is one of these teams, specifically deployed to validate products from the satellite’s Ocean Color Instrument (OCI).
The OCI spectrometer works by measuring reflected sunlight. As sunlight bounces off of the ocean’s surface, it creates specific shades of color that researchers use to determine what is in the water column below. To validate the OCI data, research teams need to confirm that measurements directly at the surface match those from the satellite. They also need to understand how the atmosphere is changing the color of the ocean as the reflected light is traveling back to the satellite.
In October 2024 and May 2025, the AirSHARP team ran simultaneous airborne and seaborne campaigns. Going into the field during different seasons allows the team to collect data under different environmental conditions, validating as much of the instrument’s range as possible.
Over 13 days of flights on a Twin Otter aircraft, the NASA-led team used instruments called 4STAR-B (Spectrometer for sky-scanning sun Tracking Atmospheric Research B), and the C-AIR (Coastal Airborne In-situ Radiometer) to gather data from the air. At the same time, partners from UCSC used a host of matching instruments onboard the research vessel R/V Shana Rae to gather data from the water’s surface.
Ocean Color and Water Leaving Reflectance
The Ocean Color Instrument measures something called water leaving reflectance, which provides information on the microscopic composition of the water column, including water molecules, phytoplankton, and particulates like sand, inorganic materials, and even bubbles. Ocean color varies based on how these materials absorb and scatter sunlight. This is especially useful for determining the abundance and types of phytoplankton.
Photographs taken out the window of the Twin Otter aircraft during the October 2024 AirSHARP deployment showcase the variation in ocean color, which indicates different molecular composition of the water column beneath. The red color in several of these photos is due to a phytoplankton bloom – in this case a growth of red algae. NASA/Samuel Leblanc
The AirSHARP team used radiometers with matching technology – C-AIR from the air and C-OPS (Compact Optical Profiling System) from the water – to gather water leaving reflectance data.
“The C-AIR instrument is modified from an instrument that goes on research vessels and takes measurements of the water’s surface from very close range,” said NASA Ames research scientist Samuel LeBlanc. “The issue there is that you’re very local to one area at a time. What our team has done successfully is put it on an aircraft, which enables us to span the entire Monterey Bay.”
The larger PACE validation team will compare OCI measurements with observations made by the sensors much closer to the ocean to ensure that they match, and make adjustments when they don’t.
Aerosol Interference
One factor that can impact OCI data is the presence of manmade and natural aerosols, which interact with sunlight as it moves through the atmosphere. An aerosol refers to any solid or liquid suspended in the air, such as smoke from fires, salt from sea spray, particulates from fossil fuel emissions, desert dust, and pollen.
Imagine a 420 mile-long tube, with the PACE satellite at one end and the ocean at the other. Everything inside the tube is what scientists refer to as the atmospheric column, and it is full of tiny particulates that interact with sunlight. Scientists quantify this aerosol interaction with a measurement called aerosol optical depth.
“During AirSHARP, we were essentially measuring, at different wavelengths, how light is changed by the particles present in the atmosphere,” said NASA Ames research scientist Kristina Pistone. “The aerosol optical depth is a measure of light extinction, or how much light is either scattered away or absorbed by aerosol particulates.”
The team measured aerosol optical depth using the 4STAR-B spectrometer, which was engineered at NASA Ames and enables scientists to identify which aerosols are present and how they interact with sunlight.
Twin Otter Aircraft
AirSHARP principal investigator Liane Guild walks towards a Twin Otter aircraft owned and operated by the Naval Postgraduate School. The aircraft’s ability to perform complex, low-altitude flights made it the ideal platform to fly multiple instruments over Monterey Bay during the AirSHARP campaign. NASA/Samuel Leblanc
Flying these instruments required use of a Twin Otter plane, operated by the Naval Postgraduate School (NPS). The Twin Otter is unique for its ability to perform extremely low-altitude flights, making passes down to 100 feet above the water in clear conditions.
“It’s an intense way to fly. At that low height, the pilots continually watch for and avoid birds, tall ships, and even wildlife like breaching whales,” said Anthony Bucholtz, director of the Airborne Research Facility at NPS.
With the phytoplankton bloom attracting so much wildlife in a bay already full of ships, this is no small feat. “The pilots keep a close eye on the radar, and fly by hand,” Bucholtz said, “all while following careful flight plans crisscrossing Monterey Bay and performing tight spirals over the Research Vessel Shana Rae.”
Campaign Data
Data gathered from the 2024 phase of this campaign is available on two data archive systems. Data from the 4STAR instrument is available in the PACE data archive and data from C-AIR is housed in the SeaBASS data archive.
Other data from the NASA PACE Validation Science Team is available through the PACE website: https://pace.oceansciences.org/pvstdoi.htm#
Samuel LeBlanc and Kristina Pistone are funded via the Bay Area Environmental Research Institute (BAERI), which is a scientist-founded nonprofit focused on supporting Earth and space sciences.
About the Author
Milan Loiacono
Science Communication SpecialistMilan Loiacono is a science communication specialist for the Earth Science Division at NASA Ames Research Center.
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Last Updated Jun 26, 2025 Related Terms
Ames Research Center's Science Directorate Ames Research Center Earth Earth Science Earth Science Division PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) Science Mission Directorate Explore More
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By NASA
2 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Electrical engineer Nikolas Gibson performs calibration tests on the MODIS/ASTER Airborne Simulator (MASTER) spectrometer, co-developed by NASA’s Ames Research Center and NASA’s Jet Propulsion Laboratory. Gibson works at the Airborne Sensor Facility at Ames, which builds, maintains, miniaturizes, and calibrates instruments.NASA/Milan Loiacono
NASA’s Ames Research Center in Silicon Valley houses a unique laboratory: the Airborne Sensor Facility (ASF). The engineers at the ASF are responsible for building, maintaining, and operating numerous instruments that get deployed on research aircraft, but one of their most important roles is instrument calibration.
Think of calibration like tuning a piano between performances: A musician uses a tuner to set the standard pitch for each string, ensuring that the piano remains on pitch for every concert.
The “tuners” at ASF include lasers, mirrors, and a light source called an integrating sphere – a hollow sphere about 36 inches in diameter that emits a set amount of light from a hole in the top. By checking an instrument against this baseline between each mission, engineers ensure that the instrument sensors provide accurate, reliable data every time.
In the photo above, electrical engineer Nikolas Gibson performs calibration tests on the MODIS/ASTER Airborne Simulator (MASTER) spectrometer, co-developed by NASA Ames and NASA’s Jet Propulsion Laboratory in Southern California.
A spectrometer separates light into individual wavelengths, providing researchers with information about the properties of whatever is creating or interacting with that light. The MASTER instrument measures about 50 individual spectral channels, providing data on wavelengths from the visible spectrum through the infrared.
When it comes to calibration, each of these channels functions like a specific key on a piano and needs to be individually checked against the “tuner.” By pointing the instrument’s sensor at a known quantity of light coming from the integrating sphere, the team checks the accuracy of MASTER’s data output and repairs or adjusts the sensor as needed.
In this image, MASTER had returned from an April 2025 scientific campaign observing prescribed fires in Alabama and Georgia with NASA’s FireSense project. It was recalibrated before heading back into the field for the Geological Earth Mapping Experiment, or GEMx, mission in late May 2025, which will use the instrument to help map critical minerals across the southwestern United States.
About the Author
Milan Loiacono
Science Communication SpecialistMilan Loiacono is a science communication specialist for the Earth Science Division at NASA Ames Research Center.
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Last Updated Jun 11, 2025 Related Terms
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