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By NASA
Explore Hubble Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Hubble and Artificial Intelligence Explore the Night Sky Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts Multimedia Images Videos Sonifications Podcasts e-Books Online Activities 3D Hubble Models Lithographs Fact Sheets Posters Hubble on the NASA App Glossary News Hubble News Social Media Media Resources More 35th Anniversary Online Activities 2 min read
Hubble Observations Give “Missing” Globular Cluster Time to Shine
This NASA Hubble Space Telescope image features a dense and dazzling array of blazing stars that form globular cluster ESO 591-12. NASA, ESA, and D. Massari (INAF — Osservatorio di Astrofisica e Scienza dello Spazio); Processing: Gladys Kober (NASA/Catholic University of America)
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A previously unexplored globular cluster glitters with multicolored stars in this NASA Hubble Space Telescope image. Globular clusters like this one, called ESO 591-12 or Palomar 8, are spherical collections of tens of thousands to millions of stars tightly bound together by gravity. Globular clusters generally form early in the galaxies’ histories in regions rich in gas and dust. Since the stars form from the same cloud of gas as it collapses, they typically hover around the same age. Strewn across this image of ESO 591-12 are a number of red and blue stars. The colors indicate their temperatures; red stars are cooler, while the blue stars are hotter.
Hubble captured the data used to create this image of ESO 591-12 as part of a study intended to resolve individual stars of the entire globular cluster system of the Milky Way. Hubble revolutionized the study of globular clusters since earthbound telescopes are unable to distinguish individual stars in the compact clusters. The study is part of the Hubble Missing Globular Clusters Survey, which targets 34 confirmed Milky Way globular clusters that Hubble has yet to observe.
The program aims to provide complete observations of ages and distances for all of the Milky Way’s globular clusters and investigate fundamental properties of still-unexplored clusters in the galactic bulge or halo. The observations will provide key information on the early stages of our galaxy, when globular clusters formed.
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Last Updated Jul 03, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The SWOT satellite is helping scientists size up flood waves on waterways like the Yellowstone River, pictured here in October 2024 in Montana. SWOT measures the height of surface waters, including the ocean, and hundreds of thousands of rivers, lakes, and reservoirs in the U.S. alone.NPS In a first, researchers from NASA and Virginia Tech used satellite data to measure the height and speed of potentially hazardous flood waves traveling down U.S. rivers. The three waves they tracked were likely caused by extreme rainfall and by a loosened ice jam. While there is currently no database that compiles satellite data on river flood waves, the new study highlights the potential of space-based observations to aid hydrologists and engineers, especially those working in communities along river networks with limited flood control structures such as levees and flood gates.
Unlike ocean waves, which are ordinarily driven by wind and tides, and roll to shore at a steady clip, river waves (also called flood or flow waves) are temporary surges stretching tens to hundreds of miles. Typically caused by rainfall or seasonal snowmelt, they are essential to shuttling nutrients and organisms down a river. But they can also pose hazards: Extreme river waves triggered by a prolonged downpour or dam break can produce floods.
“Ocean waves are well known from surfing and sailing, but rivers are the arteries of the planet. We want to understand their dynamics,” said Cedric David, a hydrologist at NASA’s Jet Propulsion Laboratory in Southern California and a coauthor of a new study published May 14 in Geophysical Research Letters.
SWOT is depicted in orbit in this artist’s concept, with sunlight glinting off one of its solar panels and both antennas of its key instrument — the Ka-band Radar Interferometer (KaRIn) — extended. The antennas collect data along a swath 30 miles (50 kilometers) wide on either side of the satellite.CNES Measuring Speed and Size
To search for river waves for her doctoral research, lead author Hana Thurman of Virginia Tech turned to a spacecraft launched in 2022. The SWOT (Surface Water and Ocean Topography) satellite is a collaboration between NASA and the French space agency CNES (Centre National d’Études Spatiales). It is surveying the height of nearly all of Earth’s surface waters, both fresh and salty, using its sensitive Ka-band Radar Interferometer (KaRIn). The instrument maps the elevation and width of water bodies by bouncing microwaves off the surface and timing how long the signal takes to return.
“In addition to monitoring total storage of waters in lakes and rivers, we zoom in on dynamics and impacts of water movement and change,” said Nadya Vinogradova Shiffer, SWOT program scientist at NASA Headquarters in Washington.
Thurman knew that SWOT has helped scientists track rising sea levels near the coast, spot tsunami slosh, and map the seafloor, but could she identify river height anomalies in the data indicating a wave on the move?
She found that the mission had caught three clear examples of river waves, including one that arose abruptly on the Yellowstone River in Montana in April 2023. As the satellite passed overhead, it observed a 9.1-foot-tall (2.8-meter-tall) crest flowing toward the Missouri River in North Dakota. It was divided into a dramatic 6.8-mile-long (11-kilometer-long) peak followed by a more drawn‐out tail. These details are exciting to see from orbit and illustrate the KaRIn instrument’s uniquely high spatial resolution, Thurman said.
Sleuthing through optical Sentinel-2 imagery of the area, she determined that the wave likely resulted from an ice jam breaking apart upstream and releasing pent-up water.
The other two river waves that Thurman and the team found were triggered by rainfall runoff. One, spotted by SWOT starting on Jan. 25, 2024, on the Colorado River south of Austin, Texas, was associated with the largest flood of the year on that section of river. Measuring over 30 feet (9 meters) tall and 166 miles (267 kilometers) long, it traveled around 3.5 feet (1.07 meters) per second for over 250 miles (400 kilometers) before discharging into Matagorda Bay.
The other wave originated on the Ocmulgee River near Macon, Georgia, in March 2024. Measuring over 20 feet (6 meters) tall and extending more than 100 miles (165 kilometers), it traveled about a foot (0.33 meters) per second for more than 124 miles (200 kilometers).
“We’re learning more about the shape and speed of flow waves, and how they change along long stretches of river,” Thurman said. “That could help us answer questions like, how fast could a flood get here and is infrastructure at risk?”
Complementary Observations
Engineers and water managers measuring river waves have long relied on stream gauges, which record water height and estimate discharge at fixed points along a river. In the United States, stream gauge networks are maintained by agencies including the U.S. Geological Survey. They are sparser in other parts of the world.
“Satellite data is complementary because it can help fill in the gaps,” said study supervisor George Allen, a hydrologist and remote sensing expert at Virginia Tech.
If stream gauges are like toll booths clocking cars as they pass, SWOT is like a traffic helicopter taking snapshots of the highway.
The wave speeds that SWOT helped determine were similar to those calculated using gauge data alone, Allen said, showing how the satellite could help monitor waves in river basins without gauges. Knowing where and why river waves develop can help scientists tracking changing flood patterns around the world.
Orbiting Earth multiple times each day, SWOT is expected to observe some 55% of large-scale floods at some stage in their life cycle. “If we see something in the data, we can say something,” David said of SWOT’s potential to flag dangerous floods in the making. “For a long time, we’ve stood on the banks of our rivers, but we’ve never seen them like we are now.”
More About SWOT
The SWOT satellite was jointly developed by NASA and CNES, with contributions from the Canadian Space Agency (CSA) and the UK Space Agency. NASA’s Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA provided the Ka-band radar interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. The Doppler Orbitography and Radioposition Integrated by Satellite system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground operations were provided by CNES. The KaRIn high-power transmitter assembly was provided by CSA.
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Written by Sally Younger
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Last Updated May 21, 2025 Related Terms
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The Starling swarm’s extended mission tested advanced autonomous maneuvering capabilities.NASA/Daniel Rutter As missions to low Earth orbit become more frequent, space traffic coordination remains a key element to efficiently operating in space. Different satellite operators using autonomous systems need to operate together and manage increasing workloads. NASA’s Starling spacecraft swarm recently tested a coordination with SpaceX’s Starlink constellation, demonstrating a potential solution to enhance space traffic coordination.
Led by the Small Spacecraft Technology program at NASA’s Ames Research Center in California’s Silicon Valley, Starling originally set out to demonstrate autonomous planning and execution of orbital maneuvers with the mission’s four small spacecraft. After achieving its primary objectives, the Starling mission expanded to become Starling 1.5, an experiment to demonstrate maneuvers between the Starling swarm and SpaceX’s Starlink satellites, which also maneuver autonomously.
Coordination in Low Earth Orbit
Current space traffic coordination systems screen trajectories of spacecraft and objects in space and alert operators on the ground of potential conjunctions, which occur when two objects exceed an operator’s tolerance for a close approach along their orbital paths. Spacecraft operators can request notification at a range of probabilities, often anywhere from a 1 in 10,000 likelihood of a collision to 1 in 1,000,000 or lower.
Conjunction mitigation between satellite operators requires manual coordination through calls or emails on the ground. An operator may receive a notification for a number of reasons including recently maneuvering their satellite, nearby space debris, or if another satellite adjusts its orbit.
Once an operator is aware of a potential conjunction, they must work together with other operators to reduce the probability of a collision. This can result in time-consuming calls or emails between ground operations teams with different approaches to safe operations. It also means maneuvers may require several days to plan and implement. This timeline can be challenging for missions that require quick adjustments to capture important data.
“Occasionally, we’ll do a maneuver that we find out wasn’t necessary if we could have waited before making a decision. Sometimes you can’t wait three days to reposition and observe. Being able to react within a few hours can make new satellite observations possible,” said Nathan Benz, project manager of Starling 1.5 at NASA Ames.
Improving Coordination for Autonomous Maneuvering
The first step in improving coordination was to develop a reliable way to signal maneuver responsibility between operators. “Usually, SpaceX takes the responsibility to move out of the way when another operator shares their predicted trajectory information,” said Benz.
SpaceX and NASA collaborated to design a conjunction screening service, which SpaceX then implemented. Satellite operators can submit trajectories and receive conjunction data quickly, then accept responsibility to maneuver away from a potential conjunction.
“For this experiment, NASA’s Starling accepted responsibility to move using the screening service, successfully tested our system’s performance, then autonomously planned and executed the maneuver for the NASA Starling satellite, resolving a close approach with a Starlink satellite,” said Benz.
Through NASA’s Starling 1.5 experiment, the agency helped validate SpaceX’s Starlink screening service. The Office of Space Commerce within the U.S. Department of Commerce also worked with SpaceX to understand and assess the Starlink screening service.
Quicker Response to Changes on Earth
The time it takes to plan maneuvers in today’s orbital traffic environment limits the number of satellites a human operator can manage and their ability to collect data or serve customers.
“A fully automated system that is flexible and adaptable between satellite constellations is ideal for an environment of multiple satellite operators, all of whom have differing criteria for mitigating collision risks,” said Lauri Newman, program officer for NASA’s Conjunction Assessment Risk Analysis program at the agency’s headquarters in Washington.
Reducing the time necessary to plan maneuvers could open up a new class of missions, where quick responses to changes in space or on Earth’s surface are possible. Satellites capable of making quicker movements could adjust their orbital position to capture a natural disaster from above, or respond to one swarm member’s interesting observations, moving to provide a more thorough look.
“With improved access and use of low Earth orbit and the necessity to provide a more advanced space traffic coordination system, Starling 1.5 is providing critical data. Starling 1.5 is the result of a successful partnership between NASA, the Department of Commerce, and SpaceX, maturing technology to solve such challenges,” said Roger Hunter, program manager of the Small Spacecraft Technology program. “We look forward to the sustained impact of the Starling technologies as they continue demonstrating advancements in spacecraft coordination, cooperation, and autonomy.”
NASA Ames leads the Starling projects. NASA’s Small Spacecraft Technology program within the Space Technology Mission Directorate funds and manages the Starling mission.
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Last Updated Mar 26, 2025 LocationAmes Research Center Related Terms
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