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By NASA
3 min read
NASA’s Juno Back to Normal Operations After Entering Safe Mode
NASA’s Juno flies above Jupiter’s Great Red Spot in this artist’s concept. NASA/JPL-Caltech The spacecraft was making its 71st close approach to Jupiter when it unexpectedly entered into a precautionary status.
Data received from NASA’s Juno mission indicates the solar-powered spacecraft went into safe mode twice on April 4 while the spacecraft was flying by Jupiter. Safe mode is a precautionary status that a spacecraft enters when it detects an anomaly. Nonessential functions are suspended, and the spacecraft focuses on essential tasks like communication and power management. Upon entering safe mode, Juno’s science instruments were powered down, as designed, for the remainder of the flyby.
The mission operations team has reestablished high-rate data transmission with Juno, and the spacecraft is currently conducting flight software diagnostics.The team will work in the ensuing days to transmit the engineering and science data collected before and after the safe-mode events to Earth.
Juno first entered safe mode at 5:17 a.m. EDT, about an hour before its 71st close passage of Jupiter — called perijove. It went into safe mode again 45 minutes after perijove. During both safe-mode events, the spacecraft performed exactly as designed, rebooting its computer, turning off nonessential functions, and pointing its antenna toward Earth for communication.
Of all the planets in our solar system, Jupiter is home to the most hostile environment, with the radiation belts closest to the planet being the most intense. Early indications suggest the two Perijove 71 safe-mode events occurred as the spacecraft flew through these belts. To block high-energy particles from impacting sensitive electronics and mitigate the harmful effects of the radiation, Juno features a titanium radiation vault.
Including the Perijove 71 events, Juno has unexpectedly entered spacecraft-induced safe mode four times since arriving at Jupiter in July 2016: first, in 2016 during its second orbit, then in 2022 during its 39th orbit. In all four cases, the spacecraft performed as expected and recovered full capability.
Juno’s next perijove will occur on May 7 and include a flyby of the Jovian moon Io at a distance of about 55,300 miles (89,000 kilometers).
More About Juno
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency (ASI) funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft. Various other institutions around the U.S. provided several of the other scientific instruments on Juno.
More information about Juno is available at:
https://www.nasa.gov/juno
News Media Contacts
DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Deb Schmid
Southwest Research Institute, San Antonio
210-522-2254
dschmid@swri.org
2025-049
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Last Updated Apr 09, 2025 Related Terms
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By NASA
6 Min Read NASA Stennis Flashback: Learning About Rocket Engine Smoke for Safe Space Travel
An image shows engineers at an early version of the test stand at the Diagnostic Testbed Facility. From 1988 to the mid-1990s, NASA Stennis engineers operated the facility to conduct rocket engine plume exhaust diagnostics and learn more about the space shuttle main engine combustion process. Credits: NASA/Stennis NASA’s Stennis Space Center near Bay St. Louis, Mississippi, is widely known as the nation’s largest rocket propulsion test site. More than 35 years ago, it also served as a hands-on classroom for NASA engineers seeking to improve the efficiency of space shuttle main engines.
From 1988 to the mid-1990’s, NASA Stennis engineers operated a Diagnostic Test Facility to conduct rocket engine plume exhaust diagnostics and learn more about the space shuttle main engine combustion process. The effort also laid the groundwork for the frontline research-and-development testing conducted at the center today.
“The Diagnostic Test Facility work is just another example of the can-do, will-do attitude of the NASA Stennis team and of its willingness to support the nation’s space exploration program in all ways needed and possible,” said Joe Schuyler, director of the NASA Stennis Engineering and Test Directorate.
The Diagnostic Test Facility work is just another example of the can-do, will-do attitude of the NASA Stennis team…
joe schuyler
NASA Stennis Engineering and Test Directorate Director
Tests conducted at the Diagnostic Testbed Facility played a critical safety role for engine operations and also provided a real-time opportunity for NASA Stennis engineers to learn about exhaust diagnostics. NASA/Stennis An image shows the Diagnostic Testbed Facility test stand data acquisition trailer. NASA/Stennis The Need
Envision a rocket or space vehicle launching into the sky. A trail of bright exhaust, known as the engine plume, follows. As metals wear down in the engines from the intense heat of the combustion process, the flame glows with colors, some visible, such as orange or yellow, and others undetectable by the human eye.
The colors tell a story – about the health and operation of the engine and its components. For space shuttle main engines, which flew on multiple missions, engineers needed to understand that story, much as a doctor needs to understand the condition of a human body during checkup, to ensure future engine operation.
Where better place to study such details than the nation’s premier propulsion test site? Paging NASA Stennis.
An image shows the rocket motor and thruster at the Diagnostic Testbed Facility. NASA/Stennis An image shows the Diagnostic Testbed Facility blended team of NASA personnel and contractors. Kneeling, left to right, is Brantly Adams (NASA), Felix Bircher (Sverdrup Technology), Dennis Butts (Sverdrup Technology), and Nikki Raines (Sverdrup Technology). Standing, left to right, NASA astronaut John Young, Greg Sakala (Sverdrup Technology), Barney Nokes (Sverdrup Technology), John Laboda (Sverdrup Technology), Glenn Varner (NASA), Stan Gill (NASA), Bud Nail (NASA), Don Sundeen (Sverdrup Technology), NASA astronaut John Blaha.NASA/Stennis The Facility
NASA Stennis has long enabled and supported innovative and collaborative work to benefit both the agency and the commercial space industry. When NASA came calling in the late 1980s, site engineers went to work on a plan to study space shuttle main engine rocket exhaust.
The concept for an enabling structure about the size of a home garage was born in October 1987. Five months later, construction began on a Diagnostic Testbed Facility to provide quality research capabilities for studying rocket engine exhaust and learning more about the metals burned off during hot fire.
The completed facility featured a 1,300-square-foot control and data analysis center, as well as a rooftop observation deck. Small-scale infrastructure was located nearby for testing a 1,000-pound-thrust rocket engine that simulated the larger space shuttle main engine. The 1K engine measured about 2 feet in length and six inches in diameter. Using a small-scale engine allowed for greater flexibility and involved less cost than testing the much-larger space shuttle engine.
An image shows Sverdrup Technology’s Robert Norfleet as he preps the dopant injection system for testing at the Diagnostic Testbed Facility. The goal of the facility was to inject known metals and materials in a chemical form and then look at what emissions were given off. During one test, generally a six or 12 second test, operators would inject three known dopants, or substances, and then run distilled water between each test to clean out the system.NASA/Stennis An image shows engineers Stan Gill, Robert Norfleet, and Elizabeth Valenti in the Diagnostic Testbed Facility test control center. NASA/Stennis The Process
Engineers could quickly conduct multiple short-duration hot fires using the smaller engine. A six-second test provided ample time to collect data from engine exhaust that reached as high as 3,900 degrees Fahrenheit.
Chemical solutions simulating engine materials were injected into the engine combustion chamber for each hot fire. The exhaust plume then was analyzed using a remote camera, spectrometer, and microcomputers to determine what colors certain metals and elements emit when burning.
Each material produced a unique profile. By matching the profiles to the exhaust of space shuttle main engine tests conducted at NASA Stennis, determinations could be made about which engine components were undergoing wear and what maintenance was needed.
We learned about purging, ignition, handling propellants, high-pressure gases, and all the components you had to have to make it work…It was a very good learning experience.
Glenn Varner
NASA Stennis Engineer
The Benefits
The Diagnostic Testbed Facility played a critical safety role for engine operations and also provided a real-time opportunity for NASA Stennis engineers to learn about exhaust diagnostics.
Multiple tests were conducted. The average turnaround time between hot fires was 18 to 20 minutes with the best turnaround from one test to another taking just 12 minutes. By January 1991, the facility had recorded a total of 588 firings for a cumulative 3,452 seconds.
As testing progressed, the facility team evolved into a collection of experts in plume diagnostics. Longtime NASA Stennis engineer Glenn Varner serves as the mechanical operations engineer at the Thad Cochran Test Stand, where he contributed to the successful testing of the first SLS (Space Launch System) core stage onsite.
However, much of Varner’s hands-on experience came at the Diagnostic Test Facility. “We learned about purging, ignition, handling propellants, high-pressure gases, and all the components you had to have to make it work,” he said. “It was a very good learning experience.”
An image shows the Diagnostic Testbed Facility team working in the test control center. Seated, left to right, is Steve Nunez, Glenn Varner, Joey Kirkpatrick. Standing, back row left to right, is Scott Dracon and Fritz Policelli. Vince Pachel is pictured standing wearing the headset. NASA/Stennis The physical remnants of the Diagnostic Testbed Facility are barely recognizable now, but that spirit and approach embodied by that effort and its teams continues in force at the center.
joe schuyler
NASA Stennis Engineering and Test Directorate Director
The Impact
The Diagnostic Testbed Facility impacted more than just those engineers involved in the testing. Following the initial research effort, the facility underwent modifications in January 1993. Two months later, facility operators completed a successful series of tests on a small-scale liquid hydrogen turbopump for a California-based aerospace company.
The project marked an early collaboration between the center and a commercial company and helped pave the way for the continued success of the NASA Stennis E Test Complex. Building on Diagnostic Testbed Facility knowledge and equipment, the NASA Stennis complex now supports multiple commercial aerospace projects with its versatile infrastructure and team of propulsion test experts.
“The physical remnants of the Diagnostic Testbed Facility are barely recognizable now,” Schuyler said. “But that spirit and approach embodied by that effort and its teams continues in force at the center.”
Additional Information
NASA Stennis has leveraged hardware and expertise from the Diagnostic Testbed Facility to provide benefit to NASA and industry for two decades and counting.
The facility’s thruster, run tanks, valves, regulators and instrumentation were used in developing the versatile four-stand E Test Complex at NASA Stennis that includes 12 active test cell positions capable of various component, engine, and stage test activities.
“The Diagnostic Testbed Facility was the precursor to that,” said NASA engineer Glenn Varner. “Everything but the structure still in the grass moved to the E-1 Test Stand, Cell 3. Plume diagnostics was part of the first testing there.”
When plume diagnostic testing concluded at E-1, equipment moved to the E-3 Test Stand, where the same rocket engine used for the Diagnostic Testbed Facility has since performed many test projects.
The Diagnostic Testbed Facility thruster also has been used for various projects at E-3, most recently in a project for the exploration upper stage being built for use on future Artemis missions.
In addition to hardware, engineers who worked at the Diagnostic Testbed Facility also moved on to support E Test Complex projects. There, they helped new NASA engineers learn how to handle gaseous hydrogen and liquid hydrogen propellants. Engineers learned about purging, ignition, and handling propellants and all the components needed for a successful test.
“From an engineering perspective, the more knowledge you have of the processes and procedures to make propulsion work, the better off you are,” Varner said. “It applied then and still applies today. The Diagnostic Testbed Facility contributed to the future development of NASA Stennis infrastructure and expertise.”
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Last Updated Feb 25, 2025 EditorNASA Stennis CommunicationsContactC. Lacy Thompsoncalvin.l.thompson@nasa.gov / (228) 688-3333LocationStennis Space Center Related Terms
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