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Revolutionizing space-based thermal systems: AFRL’s SPIRRAL launch on SPX-31
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By NASA
The NESC Mechanical Systems TDT provides broad support across NASA’s mission directorates. We are a diverse group representing a variety of sub-disciplines including bearings, gears, metrology, lubrication and tribology, mechanism design, analysis and testing, fastening systems, valve engineering, actuator engineering, pyrotechnics, mechatronics, and motor controls. In addition to providing technical support, the
TDT owns and maintains NASA-STD-5017, “Design and Development Requirements for Space Mechanisms.”
Mentoring the Next Generation
The NESC Mechanical Systems TDT actively participates in the Structures, Loads & Dynamics, Materials, and Mechanical Systems (SLAMS) Early Career Forum that mentors early-career engineers. The TDT sent three members to this year’s forum at WSTF, where early-career engineers networked with peers and NESC mentors, gave presentations on tasks they worked on at their home centers, and attended splinter sessions where they collaborated with mentors.
New NASA Valve Standard to Reduce Risk and Improve Design and Reliability
Valve issues have been encountered across NASA’s programs and continue to compromise mission performance and increase risk, in many cases because the valve hardware was not qualified in the environment as specified in NASA-STD-5017. To help address these issues, the Mechanical Systems TDT is developing a NASA standard for valves. The TDT assembled a team of subject matter experts from across the Agency representing several disciplines including mechanisms, propulsion, environmental control and life support systems, spacesuits, active thermal control systems, and materials and processes. The team has started their effort by reviewing lessons learned and best practices for valve design and hope to have a draft standard ready by the end of 2025.
Bearing Life Testing for Reaction Wheel Assemblies
The Mechanical Systems TDT just concluded a multiyear bearing life test on 40 motors, each containing a pair of all steel bearings of two different conformities or a pair of hybrid bearings containing silicon nitride balls. The testing confirmed that hybrid bearings outperformed their steel counterparts, and bearings with higher conformity (54%) outperformed bearings with lower conformity (52%). The team is disassembling and inspecting the bearings, and initial results have been surprising. The TDT was able to “recover” some of the bearings that failed during the life test and get them running as well as they did when testing began. Some bearings survived over five billion revolutions and appeared like new when they were disassembled and inspected. These results will be published once analysis is complete.
X-57 Design Assessment
The Mechanical Systems TDT was asked by the Aeronautics Mission Directorate to assess the design of the electric cruise motors installed on X-57. The team responded quickly to meet the Project’s schedule, making an onsite visit and attending numerous technical interchange meetings. After careful review of the design, the TDT identified areas for higher-level consideration and risk assessment and attended follow-on reviews to provide additional comments and advice.
CLARREO Pathfinder Inner Radial Bearing Anomaly
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder was designed to take highly accurate measurements of reflected solar radiation to better-understand Earth’s climate. During payload functional testing, engineers detected a noise as the HySICS pointing system was rotated from its normal storage orientation. Mechanical Systems TDT members reviewed the design and inspection reports after disassembly of the inner bearing unit, noticing contact marks on the bore of the inner ring and the shaft that confirmed that the inner ring of the bearing was moving on the shaft with respect to the outer ring. Lubricant applied to this interface resolved the noise problem and allowed the project to maintain schedule without any additional costs.
JPL Wheel Drive Actuator Extended Life Test Independent Review Team
A consequence of changes to its mission on Mars will require the Perseverance Rover to travel farther than originally planned. Designed to drive 20 km, the rover will now need to drive ~91 km to rendezvous and support Mars sample tube transfer to the Sample Retrieval Lander. The wheel drive actuators with integral brakes had only been life tested to 40 km, so a review was scheduled to discuss an extended life test. The OCE Science Mission Directorate Chief Engineer assembled an independent review team (IRT) that included NESC Mechanical Systems TDT members. This IRT issued findings and guidance that questioned details of the JPL assumptions and plan. Several important recommendations were made that improved the life test plan and led to the identification of brake software issues that were reducing brake life. The life test has achieved 40 km of its 137 km goal and is ongoing. In addition, software updates were sent to the rover to improve brake life.
Orion Crew Module Hydrazine Valve
When an Orion crew module hydrazine valve failed to close, the production team asked the Mechanical Systems TDT for help. A TDT member attended two meetings and then visited the valve manufacturer, where it was determined this valve was a scaled-down version of the 12-inch SLS prevalve that was the subject of a previous NESC assessment and shared similar issues. The Orion Program requested NESC materials and mechanical systems support. The Mechanical Systems TDT member then worked closely with a Lockheed Martin (LM) Fellow for Mechanisms to review all the valve vendor’s detailed drawings and assembly procedures and document any issues. A follow-on meeting was held to brief both the LM and NASA Technical Fellows for Propulsion that a redesign and requalification was recommended. These recommendations have now been elevated to the LM Vice President for Mission Success and the LM Chief Engineer for Orion.
NASA’s Perseverance Mars rover selfie taken in July 2024.
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By Space Force
The mission successfully achieved a complex effort across multiple Space Force organizations to pull an existing GPS III satellite from storage, accelerate integration and launch vehicle readiness, and rapidly process for launch.
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By NASA
This article is from the 2024 Technical Update.
Multiple human spaceflight programs are underway at NASA including Orion, Space Launch System, Gateway, Human Landing System, and EVA and Lunar Surface Mobility programs. Achieving success in these programs requires NASA to collaborate with a variety of commercial partners, including both new spaceflight companies and robotic spaceflight companies pursuing crewed spaceflight for the first time. It is not always clear to these organizations how to show their systems are safe for human spaceflight. This is particularly true for avionics systems, which are responsible for performing some of a crewed spacecraft’s most critical functions. NASA recently published guidance describing how to show the design of an avionic system meets safety requirements for crewed missions.
Background
The avionics in a crewed spacecraft perform many safety critical functions, including controlling the position and attitude of the spacecraft, activating onboard abort systems, and firing pyrotechnics. The incorrect operation of any of these functions can be catastrophic, causing loss of the crew. NASA’s human rating requirements describe the need for “additional rigor and scrutiny” when designing safety-critical systems beyond that done
for uncrewed spacecraft [2]. Unfortunately, it is not always clear how to interpret this guidance and show an avionics architecture is sufficiently safe. To address this problem, NASA recently published NASA/TM−20240009366 [1]. It outlines best practices for designing safety-critical avionics, as well as describes key artifacts or evidence NASA needs to assess the safety of an avionics architecture.
Failure Hypothesis
One of the most important steps to designing an avionics architecture for crewed spacecraft is specification of the failure hypothesis (FH). In short, the FH summarizes any assumptions the designers make about the type, number, and persistence of component failures (e.g., of onboard computers, network switches). It divides the space of all possible failures into two parts – failures the system is designed to tolerate and failures it is not.
One key part of the FH is a description of failure modes the system can tolerate – i.e., the behavior exhibited by a failed component. Failure modes are categorized using a failure model. A typical failure model for avionics splits failures into two broad categories:
Value failures, where data produced by a component is missing (i.e., an omissive failure) or incorrect (i.e., a transmissive failure). Timing failures, where data is produced by a component at the wrong time.
Timing failures can be further divided into many sub-categories, including:
Inadvertent activation, where data is produced by a component without the necessary preconditions. Out-of-order failures, where data is produced by a component in an incorrect sequence. Marginal timing failures, where data is produced by a component slightly too early or late.
In addition to occurring when data is produced by a component, these failure modes can also occur when data enters a component. (e.g., a faulty component can corrupt a message it receives). Moreover, all failure modes can manifest in one of two ways:
Symmetrically, where all observers see the same faulty behavior. Asymmetrically, where some observers see different faulty behavior.
Importantly, NASA’s human-rating process requires that each of these failure modes be mitigated if it can result in catastrophic effects [2]. Any exceptions must be explicitly documented and strongly justified. In addition to specifying the failure modes a system can tolerate, the FH must specify any limiting assumptions about the relative arrival times of permanent failures and radiation-induced upsets/ errors or the ability for ground operator to intervene to safe the system or take recovery actions. For more information on specifying a FH and other artifacts needed to evaluate the safety of an avionics architecture for human spaceflight, see the full report [1].
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By NASA
This article is from the 2024 Technical Update
Autonomous flight termination systems (AFTS) are being progressively employed onboard launch vehicles to replace ground personnel and infrastructure needed to terminate flight or destruct the vehicle should an anomaly occur. This automation uses on-board real-time data and encoded logic to determine if the flight should be self-terminated. For uncrewed launch vehicles, FTS systems are required to protect the public and governed by the United States Space Force (USSF). For crewed missions, NASA must augment range AFTS requirements for crew safety and certify each flight according to human rating standards, thus adding unique requirements for reuse of software originally intended for uncrewed missions. This bulletin summarizes new information relating to AFTS to raise awareness of key distinctions, summarize considerations and outline best practices for incorporating AFTS into human-rated systems.
Key Distinctions – Crewed v. Uncrewed
There are inherent behavioral differences between uncrewed and crewed AFTS related to design philosophy and fault tolerance. Uncrewed AFTS generally favor fault tolerance against failure-to-destruct over failing silent
in the presence of faults. This tenet permeates the design, even downto the software unit level. Uncrewed AFTS become zero-fault-to-destruct tolerant to many unrecoverable AFTS errors, whereas general single fault
tolerance against vehicle destruct is required for crewed missions. Additionally, unique needs to delay destruction for crew escape, provide abort options and special rules, and assess human-in-the-loop insight, command, and/or override throughout a launch sequence must be considered and introduces additional requirements and integration complexities.
AFTS Software Architecture Components and Best-Practice Use Guidelines
A detailed study of the sole AFTS currently approved by USSF and utilized/planned for several launch vehicles was conducted to understand its characteristics, and any unique risk and mitigation techniques for effective human-rating reuse. While alternate software systems may be designed in the future, this summary focuses on an architecture employing the Core Autonomous Safety Software (CASS). Considerations herein are intended for extrapolation to future systems. Components of the AFTS software architecture are shown, consisting of the CASS, “Wrapper”, and Mission Data Load (MDL) along with key characteristics and use guidelines. A more comprehensive description of each and recommendations for developmental use is found in Ref. 1.
Best Practices Certifying AFTS Software
Below are non-exhaustive guidelines to help achieve a human-rating
certification for an AFTS.
References
NASA/TP-20240009981: Best Practices and Considerations for Using
Autonomous Flight Termination Software In Crewed Launch Vehicles
https://ntrs.nasa.gov/citations/20240009981 “Launch Safety,” 14 C.F.R., § 417 (2024). NPR 8705.2C, Human-Rating Requirements for Space Systems, Jul 2017,
nodis3.gsfc.nasa.gov/ NASA Software Engineering Requirements, NPR 7150.2D, Mar 2022,
nodis3.gsfc.nasa.gov/ RCC 319-19 Flight Termination Systems Commonality Standard, White
Sands, NM, June 2019. “Considerations for Software Fault Prevention and Tolerance”, NESC
Technical Bulletin No. 23-06 https://ntrs.nasa.gov/citations/20230013383 “Safety Considerations when Repurposing Commercially Available Flight
Termination Systems from Uncrewed to Crewed Launch Vehicles”, NESC
Technical Bulletin No. 23-02 https://ntrs.nasa.gov/citations/20230001890 View the full article
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
On Dec. 10, 1974, NASA launched Helios 1, the first of two spacecraft to make close observations of the Sun. In one of the largest international efforts at the time, the Federal Republic of Germany, also known as West Germany, provided the spacecraft, NASA’s Goddard Space Flight Center in Greenbelt, Maryland, had overall responsibility for U.S. participation, and NASA’s Lewis, now Glenn, Research Center in Cleveland provided the launch vehicle. Equipped with 10 instruments, Helios 1 made its first close approach to the Sun on March 15, 1975, passing closer and traveling faster than any previous spacecraft. Helios 2, launched in 1976, passed even closer. Both spacecraft far exceeded their 18-month expected lifetime, returning unprecedented data from their unique vantage points.
The fully assembled Helios 1 spacecraft prepared for launch.Credit: NASA The West German company Messerchmitt-Bölkow-Blohm built the two Helios probes, the first non-Soviet and non-American spacecraft placed in heliocentric orbit, for the West German space agency DFVLR, today’s DLR. Each 815-pound Helios probe carried 10 U.S. and West German instruments, weighing a total of 158 pounds, to study the Sun and its environment. The instruments included high-energy particle detectors to measure the solar wind, magnetometers to study the Sun’s magnetic field and variations in electric and magnetic waves, and micrometeoroid detectors. Once activated and checked out, operators in the German control center near Munich controlled the spacecraft and collected the raw data. To evenly distribute the solar radiation the spacecraft spun on its axis once every second, and optical mirrors on its surface reflected the majority of the heat.
Workers encapsulate a Helios solar probe into its payload fairing. Credit: NASA
Launch of Helios 1 took place at 2:11 a.m. EST Dec. 10, 1974, from Launch Complex 41 at Cape Canaveral Air Force, now Space Force, Station, on a Titan IIIE-Centaur rocket. This marked the first successful flight of this rocket, at the time the most powerful in the world, following the failure of the Centaur upper stage during the rocket’s inaugural launch on Feb. 11, 1974. The successful launch of Helios 1 provided confidence in the Titan IIIE-Centaur, needed to launch the Viking orbiters and landers to Mars in 1976 and the Mariner Jupiter-Saturn, later renamed Voyager, spacecraft in 1977 to begin their journeys through the outer solar system. The Centaur upper stage placed Helios 1 into a solar orbit with a period of 190 days, with its perihelion, or closest point to the Sun, well inside the orbit of Mercury. Engineers activated the spacecraft’s 10 instruments within a few days of launch, with the vehicle declared fully operational on Jan. 16, 1975. On March 15, Helios 1 reached its closest distance to the Sun of 28.9 million miles, closer than any other previous spacecraft – Mariner 10 held the previous record during its three Mercury encounters. Helios 1 also set a spacecraft speed record, traveling at 148,000 miles per hour at perihelion. Parts of the spacecraft reached a temperature of 261 degrees Fahrenheit, but the instruments continued to operate without problems. During its second perihelion on Sept. 21, temperatures reached 270 degrees, affecting the operation of some instruments. Helios 1 continued to operate and return useful data until both its primary and backup receivers failed and its high-gain antenna no longer pointed at Earth. Ground controllers deactivated the spacecraft on Feb. 18, 1985, with the last contact made on Feb. 10, 1986.
Helios 1 sits atop its Titan IIIE-Centaur rocket at Launch Complex 41 at Cape Canaveral Air Force, now Space Force, Station in Florida.Credit: NASA
Helios 2 launched on Jan. 15, 1976, and followed a path similar to its predecessor’s but one that took it even closer to the Sun. On April 17, it approached to within 27 million miles of Sun, traveling at a new record of 150,000 miles per hour. At that distance, the spacecraft experienced 10% more solar heat than its predecessor. Helios 2’s downlink transmitter failed on March 3, 1980, resulting in no further useable data from the spacecraft. Controllers shut it down on Jan. 7, 1981. Scientists correlated data from the Helios instruments with similar data gathered by other spacecraft, such as the Interplanetary Monitoring Platform Explorers 47 and 50 in Earth orbit, the Pioneer solar orbiters, and Pioneer 10 and 11 in the outer solar system. In addition to their solar observations, Helios 1 and 2 studied the dust and ion tails of the comets C/1975V1 West, C/1978H1 Meier, and C/1979Y1 Bradfield. The information from the Helios probes greatly increased our knowledge of the Sun and its environment, and also raised more questions left for later spacecraft from unique vantage points to try to answer.
llustration of a Helios probe in flight, with all its booms deployed. Credit: NASA The joint ESA/NASA Ulysses mission studied the Sun from vantage points above its poles. After launch from space shuttle Discovery during STS-41 on Oct. 6, 1990, Ulysses used Jupiter’s gravity to swing it out of the ecliptic plane and fly first over the Sun’s south polar region from June to November 1994, then over the north polar region from June and September 1995. Ulysses continued its unique studies during several more polar passes until June 30, 2009, nearly 19 years after launch and more than four times its expected lifetime. NASA’s Parker Solar Probe, launched on Aug. 12, 2018, has made ever increasingly close passes to the Sun, including flying through its corona, breaking the distance record set by Helios 2. The Parker Solar Probe reached its first perihelion of 15 million miles on Nov. 5, 2018, with its closest approach of just 3.86 million miles of the Sun’s surface, just 4.5 percent of the Sun-Earth distance, planned for Dec. 24, 2024. The ESA Solar Orbiter launched on Feb. 10, 2020, and began science operations in November 2021. Its 10 instruments include cameras that have returned the highest resolution images of the Sun including its polar regions from as close as 26 million miles away.
Illustration of the Ulysses spacecraft over the Sun’s pole.Credit: NASA Illustration of the Parker Solar Probe during a close approach to the Sun.Credit: NASA The ESA Solar Orbiter observing the Sun.Credit: NASA About the Author
John J. Uri
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