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By NASA
NASA’s Dawn spacecraft captured this image of Vesta as it left the giant asteroid’s orbit in 2012. The framing camera was looking down at the north pole, which is in the middle of the image.NASA/JPL-Caltech/UCLA/MPS/DLR/IDA Known as flow formations, these channels could be etched on bodies that would seem inhospitable to liquid because they are exposed to the extreme vacuum conditions of space.
Pocked with craters, the surfaces of many celestial bodies in our solar system provide clear evidence of a 4.6-billion-year battering by meteoroids and other space debris. But on some worlds, including the giant asteroid Vesta that NASA’s Dawn mission explored, the surfaces also contain deep channels, or gullies, whose origins are not fully understood.
A prime hypothesis holds that they formed from dry debris flows driven by geophysical processes, such as meteoroid impacts, and changes in temperature due to Sun exposure. A recent NASA-funded study, however, provides some evidence that impacts on Vesta may have triggered a less-obvious geologic process: sudden and brief flows of water that carved gullies and deposited fans of sediment. By using lab equipment to mimic conditions on Vesta, the study, which appeared in Planetary Science Journal, detailed for the first time what the liquid could be made of and how long it would flow before freezing.
Although the existence of frozen brine deposits on Vesta is unconfirmed, scientists have previously hypothesized that meteoroid impacts could have exposed and melted ice that lay under the surface of worlds like Vesta. In that scenario, flows resulting from this process could have etched gullies and other surface features that resemble those on Earth.
To explore potential explanations for deep channels, or gullies, seen on Vesta, scientists used JPL’s Dirty Under-vacuum Simulation Testbed for Icy Environments, or DUSTIE, to simulate conditions on the giant asteroid that would occur after meteoroids strike the surface.NASA/JPL-Caltech But how could airless worlds — celestial bodies without atmospheres and exposed to the intense vacuum of space — host liquids on the surface long enough for them to flow? Such a process would run contrary to the understanding that liquids quickly destabilize in a vacuum, changing to a gas when the pressure drops.
“Not only do impacts trigger a flow of liquid on the surface, the liquids are active long enough to create specific surface features,” said project leader and planetary scientist Jennifer Scully of NASA’s Jet Propulsion Laboratory in Southern California, where the experiments were conducted. “But for how long? Most liquids become unstable quickly on these airless bodies, where the vacuum of space is unyielding.”
The critical component turns out to be sodium chloride — table salt. The experiments found that in conditions like those on Vesta, pure water froze almost instantly, while briny liquids stayed fluid for at least an hour. “That’s long enough to form the flow-associated features identified on Vesta, which were estimated to require up to a half-hour,” said lead author Michael J. Poston of the Southwest Research Institute in San Antonio.
Launched in 2007, the Dawn spacecraft traveled to the main asteroid belt between Mars and Jupiter to orbit Vesta for 14 months and Ceres for almost four years. Before ending in 2018, the mission uncovered evidence that Ceres had been home to a subsurface reservoir of brine and may still be transferring brines from its interior to the surface. The recent research offers insights into processes on Ceres but focuses on Vesta, where ice and salts may produce briny liquid when heated by an impact, scientists said.
Re-creating Vesta
To re-create Vesta-like conditions that would occur after a meteoroid impact, the scientists relied on a test chamber at JPL called the Dirty Under-vacuum Simulation Testbed for Icy Environments, or DUSTIE. By rapidly reducing the air pressure surrounding samples of liquid, they mimicked the environment around fluid that comes to the surface. Exposed to vacuum conditions, pure water froze instantly. But salty fluids hung around longer, continuing to flow before freezing.
The brines they experimented with were a little over an inch (a few centimeters) deep; scientists concluded the flows on Vesta that are yards to tens of yards deep would take even longer to refreeze.
The researchers were also able to re-create the “lids” of frozen material thought to form on brines. Essentially a frozen top layer, the lids stabilize the liquid beneath them, protecting it from being exposed to the vacuum of space — or, in this case the vacuum of the DUSTIE chamber — and helping the liquid flow longer before freezing again.
This phenomenon is similar to how on Earth lava flows farther in lava tubes than when exposed to cool surface temperatures. It also matches up with modeling research conducted around potential mud volcanoes on Mars and volcanoes that may have spewed icy material from volcanoes on Jupiter’s moon Europa.
“Our results contribute to a growing body of work that uses lab experiments to understand how long liquids last on a variety of worlds,” Scully said.
Find more information about NASA’s Dawn mission here:
https://science.nasa.gov/mission/dawn/
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.gov
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Last Updated Dec 20, 2024 Related Terms
Dawn Asteroids Ceres Jet Propulsion Laboratory Vesta Explore More
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By NASA
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The SpaceX Dragon Freedom spacecraft carrying NASA astronaut Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov approaches the International Space Station as it orbited 261 miles above Ontario, Canada, near James Bay. NASA published a new report Thursday highlighting 17 agency mechanisms that have directly and indirectly supported the development and growth of the U.S. commercial space sector for the benefit of humanity.
The report, titled Enabling America on the Space Frontier: The Evolution of NASA’s Commercial Space Development Toolkit, is available on the agency’s website.
“This is the most extensive and comprehensive historical analysis produced by NASA on how it has contributed to commercial space development over the decades,” said Alex MacDonald, NASA chief economist. “These efforts have given NASA regular access to space with companies, such as SpaceX and Rocket Lab, modernizing our communications infrastructure, and even led to the first private lunar lander thanks to Intuitive Machines. With commercial space growth accelerating, this report can help agency leaders and stakeholders assess the numerous mechanisms that the agency uses to support this growth, both now and in the future.”
Throughout its history, NASA has supported the development of the commercial space sector, not only leading the way in areas such as satellite communications, launch, and remote sensing, but also developing new contract and operational models to encourage commercial participation and growth. In the last three decades, NASA has seen the results of these efforts with commercial partners able to contribute more to missions across NASA domains, and increasingly innovative agency-led efforts to engage, nurture, and integrate these capabilities. These capabilities support the agency’s mission needs, and have seen a dramatic rise in importance, according to the report.
NASA has nurtured technology, companies, people, and ideas in the commercial space sector, contributing to the U.S. and global economies, across four distinct periods in the agency’s history:
1915–1960: NASA’s predecessor, the National Advisory Committee on Aeronautics (NACA), and NASA’s pre-Apollo years. 1961–1980: Apollo era. 1981–2010: Space shuttle era. 2011–present: Post-shuttle commercial era. Each of these time periods are defined by dominant technologies, programs, or economic trends further detailed in the report.
Though some of these mechanisms are relatively recent, others have been used throughout the history of NASA and NACA, leading to some overlap. The 17 mechanisms are as follows:
Contracts and Partnership Agreements Research and Technology Development (R&TD) Dissemination of Research and Scientific Data Education and Workforce Development Workforce External Engagement and Mobility Technology Transfer Technical Support Enabling Infrastructure Launch Direct In-Space Support Standards and Regulatory Framework Support Public Engagement Industry Engagement Venture Capital Engagement Market Stimulation Funding Economic Analysis and Due Diligence Capabilities Narrative Encouragement NASA supports commercial space development in everything from spaceflight to supply chains. Small satellite capabilities have inspired a new generation of space start-ups, while new, smaller rockets, as well as new programs are just starting. Examples include CLPS (Commercial Lunar Payload Services), commercial low Earth orbit destinations, human landing systems, commercial development of NASA spacesuits, and lunar terrain vehicles. The report also details many indirect ways the agency has contributed to the vibrance of commercial space, from economic analyses to student engagement.
The agency’s use of commercial capabilities has progressed from being the exception to the default method for many of its missions. The current post-shuttle era of NASA-supported commercial space development has seen a level of technical development comparable to the Apollo era’s Space Race. Deploying the 17 commercial space development mechanisms in the future are part of NASA’s mission to continue encouraging commercial space activities.
To learn more about NASA’s missions, please visit:
https//:www.nasa.gov
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Last Updated Dec 19, 2024 EditorBill Keeter Related Terms
Office of Technology, Policy and Strategy (OTPS) View the full article
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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
This article is from the 2024 Technical Update.
The NESC evaluated material compatibility of some common aerospace metals in monomethylhydrazine (MMH) and nitrogen tetroxide (MON-3). Previous work had identified a lack of quantitative compatibility data for nickel alloy 718, 300 series stainless steel, and titanium Ti-6Al-4V in MMH and MON-3 to support the use of zero-failure-tolerant, thin-walled pressure barriers in these propellants. Static (i.e., not flowing) general corrosion and electrochemistry testing was conducted, evaluating varied processing forms and heat treatment of the metals, water content of propellant, and exposure duration. Corrosion-rate data for all tested product forms, fluids, and durations were on the order of 1 x 10–6 inch per year rather than the previously documented “less than 1 x 10–3 inch per year”. The majority of the corrosion products were seen in the first 20 days of exposure, with an overall corrosion rate decreasing with time due to the increased divisor (time). It is therefore recommended that corrosion testing be performed at multiple short-term durations to inform the need for longer-duration testing.
Background
Nickel alloy 718, 300 series stainless steel, and Ti-6Al-4V are commonly used in storable propulsion systems (i.e., MMH/MON-3), but a concern was raised regarding what quantitative compatibility data were available for proposed zero-failure-tolerant, thin-walled (~0.005 to 0.010 inch thickness) pressure barrier designs. A literature search found that limited and conflicting data were available for commonly used aerospace metals in MMH and MON-3. For example, corrosion behavior was listed qualitatively (e.g., “A” rating), data on materials and fluids tested were imprecise, fluids were identified as contaminated without describing how they were contaminated, no compatibility data were found on relevant geometry specimens (i.e., very thin-walled or convoluted), and limited data were available to quantify differences between tested materials and flight components. When corrosion data were quantified, documented sensitivity was “1 x 10–3 inch per year or less”, which is insufficient for assessing long-duration, thin-walled, flight-weight applications.
Discussion
General corrosion testing was performed with a static/non-flowing configuration based on NASA-STD-6001, Test 15 [1]. Design of experiments methods were used to develop a test matrix varying material, propellant, propellant water content, and tested duration. Materials tested were nickel alloy 718 (solution annealed sheet, aged sheet, aged/welded sheet, and hydroformed bellows), 300 series stainless steel (low carbon sheet, titanium stabilized sheet, and hydroformed bellows), and Ti 6Al-4V sheet. Samples were tested in sealed test tubes in MMH and MON-3 with water content ranging from as-received (“dry”) up to specification allowable limits [2,3]. Tested durations ranged from 20 to 365 days. Measurements included inductively coupled plasma mass spectrometry (ICPMS) to identify corrosion products and their concentrations in test fluid, gravimetric (i.e., scale) measurements pre- and post-exposure, and visual inspection. Bimetallic pairs (titanium stabilized 300 series stainless steel: Ti 6Al-4V and nickel alloy 718: Ti 6Al-4V) were tested for up to 65 days in both MMH and MON-3. The test setup incorporated important features of the test standard (e.g., electrode spacing and finish) and adapted the configuration for MMH/MON-3 operation. Measurements included potential difference and current flow between samples. Figure 1 shows images of the general corrosion and bimetallic pair test setups.
Test Results
For all tested materials and product forms, corrosion rates were on the order of 1 x 10–6 inch per year in MMH or MON-3, three orders of magnitude lower than historically reported. Corrosion products were generated in the first 20 days of exposure, and corrosion rate decreased with time due to the increase in divisor (i.e., time). Corrosion products increased as the water content of the propellants increased but remained in the same order of magnitude between the as-received dry propellant and propellant containing the maximum water content allowed by specification. Figure 2 illustrates test results for corrosion rate, mass loss with duration, and mass loss with water content. It is important to note that water has been demonstrated to contribute to flow decay even when water is within the specification allowable limit, and previous NASA-STD-6001 Test 15 data have demonstrated susceptibility of some nickel alloys to crevice-type corrosion attack [4]. Therefore, these results do not reduce the importance of considering the system impact of water content and evaluating for crevice corrosion behavior. Finally, in the bimetallic pair testing, tested materials did not measurably corrode in MON-3 and MMH within specification-allowable water content, as evidenced by no visual indications of corrosion and very low electrical interaction (i.e., corrosion rates derived to be less than 1 microinch per year from electrical interaction).
Recommendations
It is recommended that corrosion testing be performed at multiple shortterm durations to inform the need for longer-duration testing.
References
NASA-STD-6001 Flammability, Odor, Offgassing, and Compatibility Requirements
and Test Procedures for Materials In Environments that Support Combustion MIL-PRF-27404 Performance Specification: Propellant, Monomethylhydrazine MIL-PRF-26539 Performance Specification: Propellants, Dinitrogen Tetroxide WSTF Test 15 Report 12-45708 and WSTF Test 15 Report 13-46207 View the full article
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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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