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By NASA
Download PDF: Statistical Analysis Using Random Forest Algorithm Provides Key Insights into Parachute Energy Modulator System
Energy modulators (EM), also known as energy absorbers, are safety-critical components that are used to control shocks and impulses in a load path. EMs are textile devices typically manufactured out of nylon, Kevlar® and other materials, and control loads by breaking rows of stitches that bind a strong base webbing together as shown in Figure 1. A familiar EM application is a fall-protection harness used by workers to prevent injury from shock loads when the harness arrests a fall. EMs are also widely used in parachute systems to control shock loads experienced during the various stages of parachute system deployment.
Random forest is an innovative algorithm for data classification used in statistics and machine learning. It is an easy to use and highly flexible ensemble learning method. The random forest algorithm is capable of modeling both categorical and continuous data and can handle large datasets, making it applicable in many situations. It also makes it easy to evaluate the relative importance of variables and maintains accuracy even when a dataset has missing values.
Random forests model the relationship between a response variable and a set of predictor or independent variables by creating a collection of decision trees. Each decision tree is built from a random sample of the data. The individual trees are then combined through methods such as averaging or voting to determine the final prediction (Figure 2). A decision tree is a non-parametric supervised learning algorithm that partitions the data using a series of branching binary decisions. Decision trees inherently identify key features of the data and provide a ranking of the contribution of each feature based on when it becomes relevant. This capability can be used to determine the relative importance of the input variables (Figure 3). Decision trees are useful for exploring relationships but can have poor accuracy unless they are combined into random forests or other tree-based models.
The performance of a random forest can be evaluated using out-of-bag error and cross-validation techniques. Random forests often use random sampling with replacement from the original dataset to create each decision tree. This is also known as bootstrap sampling and forms a bootstrap forest. The data included in the bootstrap sample are referred to as in-the-bag, while the data not selected are out-of-bag. Since the out-of-bag data were not used to generate the decision tree, they can be used as an internal measure of the accuracy of the model. Cross-validation can be used to assess how well the results of a random forest model will generalize to an independent dataset. In this approach, the data are split into a training dataset used to generate the decision trees and build the model and a validation dataset used to evaluate the model’s performance. Evaluating the model on the independent validation dataset provides an estimate of how accurately the model will perform in practice and helps avoid problems such as overfitting or sampling bias. A good model performs well on
both the training data and the validation data.
The complex nature of the EM system made it difficult for the team to identify how various parameters influenced EM behavior. A bootstrap forest analysis was applied to the test dataset and was able to identify five key variables associated with higher probability of damage and/or anomalous behavior. The identified key variables provided a basis for further testing and redesign of the EM system. These results also provided essential insight to the investigation and aided in development of flight rationale for future use cases.
For information, contact Dr. Sara R. Wilson. sara.r.wilson@nasa.gov
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By NASA
X-rays are radiated by matter hotter than one million Kelvin, and high-resolution X-ray spectroscopy can tell us about the composition of the matter and how fast and in what direction it is moving. Quantum calorimeters are opening this new window on the Universe. First promised four decades ago, the quantum-calorimeter era of X-ray astronomy has finally dawned.
Photo of the XRISM/Resolve quantum-calorimeter array in its storage container prior to integration into the instrument. The 6×6 array, 5 mm on a side, consists of independent detectors – each one a thermally isolated silicon thermistor with a HgTe absorber. The spectrometer consisting of this detector and other essential technologies separates astrophysical X-ray spectra into about 2400 resolution elements, which can be thought of as X-ray colors.NASA GSFC A quantum calorimeter is a device that makes precise measurements of energy quanta by measuring the temperature change that occurs when a quantum of energy is deposited in an absorber with low heat capacity. The absorber is attached to a thermometer that is somewhat decoupled from a heat sink so that the sensor can heat up and then cool back down again. To reduce thermodynamic noise and the heat capacity of the sensor, operation at temperatures less than 0.1 K is required.
The idea for thermal measurement of small amounts of energy occurred in several places in the world independently when scientists observed pulses in the readout of low-temperature thermometers and infrared detectors. They attributed these spurious signals to passing cosmic-ray particles, and considered optimizing detectors for sensitive measurement of the energy of particles and photons.
The idea to develop such sensors for X-ray astronomy was conceived at Goddard Space Flight Center in 1982 when X-ray astronomers were considering instruments to propose for NASA’s planned Advanced X-ray Astrophysics Facility (AXAF). In a fateful conversation, infrared astronomer Harvey Moseley suggested thermal detection could offer substantial improvement over existing solid-state detectors. Using Goddard internal research and development funding, development advanced sufficiently to justify, just two years later, proposing a quantum-calorimeter X-ray Spectrometer (XRS) for inclusion on AXAF. Despite its technical immaturity at the time, the revolutionary potential of the XRS was acknowledged, and the proposal was accepted.
The AXAF design evolved over the subsequent years, however, and the XRS was eliminated from its complement of instruments. After discussions between NASA and the Japanese Institute of Space and Astronautical Science (ISAS), a new XRS was included in the instrument suite of the Japanese Astro-E X-ray observatory. Astro-E launched in 2000 but did not reach orbit due to an anomaly in the first stage of the rocket. Astro-E2, a rebuild of Astro-E, was successfully placed in orbit in 2005 and renamed Suzaku, but the XRS instrument ceased operation before observations started due to loss of the liquid helium, an essential part of the detector cooling system, caused by a faulty storage system.
A redesigned mission, Astro-H, that included a quantum-calorimeter instrument with a redundant cooling system was successfully launched in 2016 and renamed Hitomi. Hitomi’s Soft X-ray Spectrometer (SXS) obtained high resolution spectra of the Perseus cluster of galaxies and a few other sources before a problem with the attitude control system caused the mission to be lost roughly one month after launch. Even so, Hitomi was the first orbiting observatory to obtain a scientific result using X-ray quantum calorimeters. The spectacular Perseus spectrum generated by the SXS motivated yet another attempt to implement a spaceborne quantum-calorimeter spectrometer.
The X-ray Imaging and Spectroscopy Mission (XRISM) was launched in September 2023, with the spectrometer aboard renamed Resolve to represent not only its function but also the resolve of the U.S./Japan collaboration to study the Universe through the window of this new capability. XRISM has been operating well in orbit for over a year.
Development of the Sensor Technology
Development of the sensor technology employed in Resolve began four decades ago. Note that an X-ray quantum-calorimeter spectrometer requires more than the sensor technology. Other technologies, such as the coolers that provide a
The sensors used from XRS through Resolve were all based on silicon-thermistor thermometers and mercury telluride (HgTe) X-ray absorbers. They used arrays consisting of 32 to 36 pixels, each of which was an independent quantum calorimeter. Between Astro-E and Astro-E2, a new method of making the thermistor was developed that significantly reduced its low-frequency noise. Other fabrication advances made it possible to make reproducible connections between absorbers and thermistors and to fit each thermistor and its thermal isolation under its X-ray absorber, making square arrays feasible.
Through a Small Business Innovation Research (SBIR) contract executed after the Astro-E2 mission, EPIR Technologies Inc. reduced the specific heat of the HgTe absorbers. Additional improvements made to the cooler of the detector heat sink allowed operation at a lower temperature, which further reduced the specific heat. Together, these changes enabled the pixel width to be increased from 0.64 mm to 0.83 mm while still achieving a lower heat capacity, and thus improving the energy resolution. From Astro-E through Astro-H, the energy resolution for X-rays of energy around 6000 eV improved from 11 eV, to 5.5 eV, to 4 eV. No changes to the array design were made between Astro-H and XRISM.
Resolve detector scientist Caroline Kilbourne installing the flight Resolve quantum-calorimeter array into the assembly that provides its electrical, thermal, and mechanical interfaces.NASA GSFC Over the same period, other approaches to quantum-calorimeter arrays optimized for the needs of future missions were developed. The use of superconducting transition-edge sensors (TES) instead of silicon (Si) thermistors led to improved energy resolution, more pixels per array, and multiplexing (a technique that allows multiple signals to be carried on a single wire). Quantum-calorimeter arrays with thousands of pixels are now standard, such as in the NASA contribution to the future European New Advanced Telescope for High-ENergy Astrophysics (newAthena) mission. And quantum calorimeters using paramagnetic thermometers — which unlike TES and Si thermistors require no dissipation of heat in the thermometer for it to be read out — combined with high-density wiring are a promising route for realizing even larger arrays. (See Astrophysics Technology Highlight on these latest developments.)
The Resolve instrument aboard XRISM (X-ray Imaging and Spectroscopy Mission) captured data from the center of galaxy NGC 4151, where a supermassive black hole is slowly consuming material from the surrounding accretion disk. The resulting spectrum reveals the presence of iron in the peak around 6.5 keV and the dips around 7 keV, light thousands of times more energetic that what our eyes can see. Background: An image of NGC 4151 constructed from a combination of X-ray, optical, and radio light.Spectrum: JAXA/NASA/XRISM Resolve. Background: X-rays, NASA/CXC/CfA/J.Wang et al.; optical, Isaac Newton Group of Telescopes, La Palma/Jacobus Kapteyn Telescope; radio, NSF/NRAO/VLA Results from Resolve
So, what is Resolve revealing about the Universe? Through spectroscopy alone, Resolve allows us to construct images of complex environments where collections of gas and dust with various attributes exist, emitting and absorbing X-rays at energies characteristic of their various compositions, velocities, and temperatures. For example, in the middle of the galaxy known as NCG 4151 (see figure above), matter spiraling into the central massive black hole forms a circular structure that is flat near the black hole, more donut-shaped further out, and, according to the Resolve data, a bit lumpy. Matter near the black hole is heated up to X-ray-emitting temperatures and irradiates the matter in the circular structure. The Resolve spectrum has a bright narrow emission line (peak) from neutral iron atoms that must be coming from colder matter in the circular structure, because hotter material would be ionized, and would have a different emission signature. Nonetheless, the shape of the iron line needs three components to describe it, each coming from a different lump in the circular structure. The presence of absorption lines (dips) in the spectrum provides further detail about the structure of the infalling matter.
A second example is the detection of X-ray emission by Resolve from the debris of stars that have exploded, such as N132D (see figure below), that will improve our understanding of the explosion mechanism and how the elements produced in stars get distributed, and allow us to infer the type of star each was before ending in a supernova. Elements are identified by their characteristic emission lines, and shifts of those lines via the Doppler effect tell us how fast the material is moving.
XRISM’s Resolve instrument captured data from supernova remnant N132D in the Large Magellanic Cloud to create the most detailed X-ray spectrum of the object ever made. The spectrum reveals peaks associated with silicon, sulfur, argon, calcium, and iron. Inset at right is an image of N132D captured by XRISM’s Xtend instrument.JAXA/NASA/XRISM Resolve and Xtend These results are just the beginning. The rich Resolve data sets are identifying complex velocity structures, rare elements, and multiple temperature components in a diverse ensemble of cosmic objects. Welcome to the quantum calorimeter era! Stay tuned for more revelations!
Project Leads: Dr. Caroline Kilbourne, NASA Goddard Space Flight Center (GSFC), for silicon-thermistor quantum calorimeter development from Astro-E2 through XRISM and early TES development. Foundational and other essential leadership provided by Dr. Harvey Moseley, Dr. John Mather, Dr. Richard Kelley, Dr. Andrew Szymkowiak, Mr. Brent Mott, Dr. F. Scott Porter, Ms. Christine Jhabvala, Dr. James Chervenak (GSFC at the time of the work) and Dr. Dan McCammon (U. Wisconsin).
Sponsoring Organizations and Programs: The NASA Headquarters Astrophysics Division sponsored the projects, missions, and other efforts that culminated in the development of the Resolve instrument.
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By NASA
NASA/CXC/SAO/D. Bogensberger et al; Image Processing: NASA/CXC/SAO/N. Wolk; Even matter ejected by black holes can run into objects in the dark. Using NASA’s Chandra X-ray Observatory, astronomers have found an unusual mark from a giant black hole’s powerful jet striking an unidentified object in its path.
The discovery was made in a galaxy called Centaurus A (Cen A), located about 12 million light-years from Earth. Astronomers have long studied Cen A because it has a supermassive black hole in its center sending out spectacular jets that stretch out across the entire galaxy. The black hole launches this jet of high-energy particles not from inside the black hole, but from intense gravitational and magnetic fields around it.
The image shows low-energy X-rays seen by Chandra represented in pink, medium-energy X-rays in purple, and the highest-energy X-rays in blue.
In this latest study, researchers determined that the jet is — at least in certain spots — moving at close to the speed of light. Using the deepest X-ray image ever made of Cen A, they also found a patch of V-shaped emission connected to a bright source of X-rays, something that had not been seen before in this galaxy.
Called C4, this source is located close to the path of the jet from the supermassive black hole and is highlighted in the inset. The arms of the “V” are at least about 700 light-years long. For context, the nearest star to Earth is about 4 light-years away.
Source C4 in the Centaurus A galaxy.NASA/CXC/SAO/D. Bogensberger et al; Image Processing: NASA/CXC/SAO/N. Wolk; While the researchers have ideas about what is happening, the identity of the object being blasted is a mystery because it is too distant for its details to be seen, even in images from the current most powerful telescopes.
The incognito object being rammed may be a massive star, either by itself or with a companion star. The X-rays from C4 could be caused by the collision between the particles in the jet and the gas in a wind blowing away from the star. This collision can generate turbulence, causing a rise in the density of the gas in the jet. This, in turn, ignites the X-ray emission seen with Chandra.
The shape of the “V,” however, is not completely understood. The stream of X-rays trailing behind the source in the bottom arm of the “V” is roughly parallel to the jet, matching the picture of turbulence causing enhanced X-ray emission behind an obstacle in the path of the jet. The other arm of the “V” is harder to explain because it has a large angle to the jet, and astronomers are unsure what could explain that.
This is not the first time astronomers have seen a black hole jet running into other objects in Cen A. There are several other examples where a jet appears to be striking objects — possibly massive stars or gas clouds. However, C4 stands out from these by having the V-shape in X-rays, while other obstacles in the jet’s path produce elliptical blobs in the X-ray image. Chandra is the only X-ray observatory capable of seeing this feature. Astronomers are trying to determine why C4 has this different post-contact appearance, but it could be related to the type of object that the jet is striking or how directly the jet is striking it.
A paper describing these results appears in a recent issue of The Astrophysical Journal. The authors of the study are David Bogensberger (University of Michigan), Jon M. Miller (University of Michigan), Richard Mushotsky (University of Maryland), Niel Brandt (Penn State University), Elias Kammoun (University of Toulouse, France), Abderahmen Zogbhi (University of Maryland), and Ehud Behar (Israel Institute of Technology).
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory.
Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
This release features a series of images focusing on a collision between a jet of matter blasting out of a distant black hole, and a mysterious, incognito object.
At the center of the primary image is a bright white dot, encircled by a hazy purple blue ring tinged with neon blue. This is the black hole at the heart of the galaxy called Centaurus A. Shooting out of the black hole is a stream of ejected matter. This stream, or jet, shoots in two opposite directions. It shoots toward us, widening as it reaches our upper left, and away from us, growing thinner and more faint as it recedes toward the lower right. In the primary image, the jet resembles a trail of hot pink smoke. Other pockets of granular, hot pink gas can be found throughout the image. Here, pink represents low energy X-rays observed by Chandra, purple represents medium energy X-rays, and blue represents high energy X-rays.
Near our lower right, where the jet is at its thinnest, is a distinct pink “V”, its arms opening toward our lower right. This mark is understood to be the result of the jet striking an unidentified object that lay in its path. A labeled version of the image highlights this region, and names the point of the V-shape, the incognito object, C4. A wide view version of the image is composited with optical data.
At the distance of Cen A, the arms of the V-shape appear rather small. In fact, each arm is at least 700 light-years long. The jet itself is 30,000 light-years long. For context, the nearest star to the Sun is about 4 light-years away.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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By NASA
The Space Technology Payload Challenge invites individuals, teams, and organizations to submit applications for systems that advance technology to address one or more of NASA’s shortfalls. These shortfalls identify technology areas where further technology development is required to meet future exploration, science, and other mission needs. In addition, technologies to address these select shortfalls are also potentially well suited for a suborbital or hosted orbital flight demonstration to help mature the innovation. The expectation is that the technology will be tested at the end of the challenge aboard a suborbital vehicle, rocket-powered lander, high altitude balloon, aircraft following a reduced gravity profile (i.e., parabolic flight), or orbital vehicle that can host payloads. The shortfalls selected for this challenge are divided into two groups. The first group is derived from the Space Technology Mission Directorate (STMD) civil space shortfall list. The second group is in partnership with NASA’s Biological and Physical Sciences (BPS) Division and is derived from the Commercially Enabled Rapid Space Science Initiative (CERISS) program needs.
Award: $4,500,000 in total prizes
Open Date: December 10, 2024
Close Date: March 4, 2025
For more information, visit: https://www.stpc.nasatechleap.org/
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By NASA
This artist’s concept shows interstellar object 1I/2017 U1 (‘Oumuamua) after its discovery in 2017. While itself not a dark comet, ‘Oumuamua’s motion through the solar system has helped researchers better understand the nature of the 14 dark comets discovered so far.European Southern Observatory / M. Kornmesser These celestial objects look like asteroids but act like comets now come in two flavors.
The first dark comet — a celestial object that looks like an asteroid but moves through space like a comet — was reported less than two years ago. Soon after, another six were found. In a new paper, researchers announce the discovery of seven more, doubling the number of known dark comets, and find that they fall into two distinct populations: larger ones that reside in the outer solar system and smaller ones in the inner solar system, with various other traits that set them apart.
The findings were published on Monday, Dec. 9, in the Proceedings of the National Academy of Sciences.
Scientists got their first inkling that dark comets exist when they noted in a March 2016 study that the trajectory of “asteroid” 2003 RM had moved ever so slightly from its expected orbit. That deviation couldn’t be explained by the typical accelerations of asteroids, like the small acceleration known as the Yarkovsky effect.
“When you see that kind of perturbation on a celestial object, it usually means it’s a comet, with volatile material outgassing from its surface giving it a little thrust,” said study coauthor Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Southern California. “But try as we might, we couldn’t find any signs of a comet’s tail. It looked like any other asteroid — just a pinpoint of light. So, for a short while, we had this one weird celestial object that we couldn’t fully figure out.”
Weird Celestial Objects
Farnocchia and the astronomical community didn’t have to wait long for another piece of the puzzle. The next year, in 2017, a NASA-sponsored telescope discovered history’s first documented celestial object that originated outside our solar system. Not only did 1I/2017 U1 (‘Oumuamua) appear as a single point of light, like an asteroid, its trajectory changed as if it were outgassing volatile material from its surface, like a comet.
“‘Oumuamua was surprising in several ways,” said Farnocchia. “The fact that the first object we discovered from interstellar space exhibited similar behaviors to 2003 RM made 2003 RM even more intriguing.”
By 2023, researchers had identified seven solar system objects that looked like asteroids but acted like comets. That was enough for the astronomical community to bestow upon them their own celestial object category: “dark comets.” Now, with the finding of seven more of these objects, researchers could start on a new set of questions.
“We had a big enough number of dark comets that we could begin asking if there was anything that would differentiate them,” said Darryl Seligman, a postdoctoral fellow in the department of Physics at Michigan State University, East Lansing, and lead author of the new paper. “By analyzing the reflectivity,” or albedo, “and the orbits, we found that our solar system contains two different types of dark comets.”
Two Kinds of Dark Comets
The study’s authors found that one kind, which they call outer dark comets, have similar characteristics to Jupiter-family comets: They have highly eccentric (or elliptical) orbits and are on the larger side (hundreds of meters or more across).
The second group, inner dark comets, reside in the inner solar system (which includes Mercury, Venus, Earth, and Mars), travel in nearly circular orbits, and are on the smaller side (tens of meters or less).
Like so many astronomical discoveries, Seligman and Farnocchia’s research not only expands on our knowledge of dark comets, but it also raises several additional questions: Where did dark comets originate? What causes their anomalous acceleration? Could they contain ice?
“Dark comets are a new potential source for having delivered the materials to Earth that were necessary for the development of life,” said Seligman. “The more we can learn about them, the better we can understand their role in our planet’s origin.”
For more information about asteroids and comets, visit:
https://www.jpl.nasa.gov/topics/asteroids/
Small Body Research at JPL NASA Learns More About Interstellar Visitor 'Oumuamua Lesson: Comet on a Stick News Media Contacts
Ian J. O’Neill
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649
ian.j.oneill@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Bethany Mauger
Michigan State University, East Lansing
maugerbe@msu.edu
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Last Updated Dec 09, 2024 Related Terms
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