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April 2021 : The Sun in 4K - Viewed By NASA's Solar Dynamics Observatory
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By NASA
Download PDF: Contact Dynamics Predictions Utilizing theNESC Parameterless Contact Model
Modeling the capture of the Mars Sample Return (MSR) Orbiting Sample (OS) involves understanding complex dynamic behavior, which includes the OS making contact against the interior of the capture enclosure. The MSR Program required numerical verification of the contact dynamics’ predictions produced using their commercial software tools. This commercial software used “free” parameters to set up the contact modeling. Free parameters (also known as free variables) are not based on contact physics. The commercial contact model used by MSR
required seven free parameters including a Hertzian contact stiffness, surface penetration, stiffening exponent, penetration velocity, contact damping, maximum penetration depth for the contact damping value, and a smoothing function. An example of a parameter that is not free is coefficient of friction, which is a physics-based parameter. Consider the free parameter, contact stiffness. Contact stiffness is already present in the finite element model’s (FEM) stiffness matrix where the bodies come into contact, and surface penetration is disallowed in a physically realizable contact model, as FEM meshes should not penetrate one another during contact (i.e., the zero-contact limit penetration constraint condition).
As such, with each set of selected free parameters generating a different contact force signature, additional numerical verification is required to guide setting these parameters. Contact modeling is nonlinear. This means that the stiffness matrices of contacting bodies are continuously updated as the bodies come into contact, potentially recontact (due to vibrations), and disengage. The modal properties of contacting bodies continuously change with state transitions (e.g., stick-to-slip). Some contact models have been proposed and incorporated in commercial finite element analysis solvers, and most involve static loading. A relatively smaller number involve dynamics, which has historically proven challenging.
In 2005, NASA conducted a study testing several commercial contact solvers in predicting contact forces in transient dynamic environments. This was necessitated by the Space Shuttle Program (SSP)—after the February 2003 Columbia accident— deciding to include contact dynamics in the Space Shuttle transient coupled loads analysis (CLA) to capture the impact of contact nonlinearities. This rendered the entire CLA nonlinear. The study found major difficulties executing nonlinear CLAs in commercial software. A nonlinear solver developed by the NESC and Applied Structural Dynamics (ASD) that was able to produce physically realizable results was numerically verified by NASA and later experimentally validated as well. This nonlinear solver was subsequently utilized to execute all NASA SSP CLAs (i.e., crewed space flights) from 2005 to the final flight in 2011, as well as currently supporting the SLS Program.
The objective of the MSR contact verification work was to provide data that could be used by the MSR team to help define the free parameters listed above for the commercial tool contact model. The NESC/ASD solver was used to model contact between simple cantilever and free beams, deriving contact forces and relative displacements. These resulting data can be used to determine parameter values for more complex structures. Two of the modeled configurations, one for axial contact (Figure 1) and the other for stick/friction (Figure 2), and sample results from the NESC nonlinear dynamic analyses are presented in Figures 1 and 2.
For information, contact:
Dr. Dexter Johnson dexter.johnson@nasa.gov
Dr. Arya Majed arya.majed@nasa.gov
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By NASA
This article is for students grades 5-8.
The Sun is the star of our solar system. Its gravity holds Earth and our planetary neighbors in its orbit. At 865,000 miles (1.4 million km) in diameter, it’s the largest object in our solar system. On Earth, its influence is felt in our weather, seasons, climate, and more. Let’s learn about our dynamic star and its connections to life on Earth.
What is the Sun, and what is it made of?
The Sun is a yellow dwarf star. It is approximately 4.5 billion years old and is in its “main sequence” phase. This means it is partway through its lifecycle with a few billion more years ahead of it.
The Sun is made of hydrogen and helium gases. At its core, hydrogen is fused to form helium. This nuclear reaction creates the Sun’s heat and light. That energy moves outward through the Sun’s radiative zone and convective zone. It then reaches the Sun’s visible surface and lower atmosphere, called the photosphere. Above the photosphere lies the chromosphere, which forms the Sun’s middle atmosphere, and beyond that is the corona, the Sun’s outermost atmosphere.
The Sun is a yellow dwarf star with a complex series of layers and features.NASA What is the solar cycle?
The Sun goes through a pattern of magnetic activity known as the solar cycle. During each cycle, the Sun experiences a very active period called “solar maximum” and a less active period called “solar minimum.”
During solar maximum, increased magnetic activity creates sunspots. These appear as darker, cooler spots on the Sun’s surface. The more sunspots we can see, the more active the Sun is.
The solar cycle begins at solar minimum, peaks at solar maximum, and then returns to solar minimum. This cycle is driven by the Sun’s magnetic polarity, which flips – north becomes south, and vice versa – every 11 years. It takes two cycles – or 22 years – to complete the full magnetic cycle where the poles return to their original positions.
The Sun’s level of magnetic activity changes throughout its 11-year solar cycle. During each cycle, the Sun experiences a less-active period called “solar minimum” (left) and a very active period called “solar maximum” (right).NASA Wait. The Sun’s magnetic poles can flip??
Yes! Like Earth, the Sun has north and south magnetic poles. But unlike Earth, the Sun’s poles flip regularly. Each 11-year solar cycle is marked by the flipping of the Sun’s poles. The increased magnetic activity during solar maximum makes the north and south poles less defined. As the cycle moves back to solar minimum, the polarization of the poles returns – with flipped polarity.
Unlike Earth, the Sun’s poles regularly flip with each 11-year solar cycle.NASA What is space weather?
Space weather includes phenomena such as solar wind, solar storms, and solar flares. When space weather conditions are calm, there may be little noticeable effect on Earth. But when the Sun is more active, space weather has real impacts on Earth and in space.
Let’s explore these phenomena and how they affect our planet.
Periods of increased solar activity can cause noticeable effects on Earth and in space.NASA What is solar wind?
Solar wind is a stream of charged particles that flow outward from the Sun’s corona. It extends far beyond the orbit of the planets in our solar system. When solar wind reaches Earth, its charged particles interact with Earth’s magnetic field. This causes colorful streams of moving light at Earth’s north and south poles called aurora.
Earth’s magnetic field protects our planet from the charged solar particles of the solar wind.NASA What are solar storms, solar flares, and coronal mass ejections?
The Sun’s magnetic fields are a tangle of constant motion. These fields twist and stretch to the point that they snap and reconnect. When this magnetic reconnection occurs, it releases a burst of energy that can cause a solar storm.
Solar storms can include phenomena such as solar flares or coronal mass ejections. They happen more frequently around the solar maximum of the Sun’s cycle. A solar flare is an intense burst of light and energy from the Sun’s surface. Solar flares tend to happen near sunspots where the Sun’s magnetic fields are strongest. A coronal mass ejection is a massive cloud of material flowing outward from the Sun. These can occur on their own or along with solar flares.
The Sun’s magnetic field is strongest near sunspots. These active regions of the Sun’s surface release energy in the form of solar flares and coronal mass ejections like these.NASA How do these phenomena affect Earth?
When a solar storm erupts towards Earth, our atmosphere and magnetic field protect us from significant harm. However, some impacts are possible, both on Earth and in space. For example, strong solar storms can cause power outages and radio blackouts. GPS signals can be disrupted. Satellite electronics can be affected. And astronauts working outside of the International Space Station could be exposed to dangerous radiation. NASA monitors and forecasts space weather to protect the safety and health of astronauts and spacecraft.
When charged particles from intense solar storms interact with Earth’s magnetic fields, colorful auroras like this one captured in Saskatchewan, Canada, can occur.NASA Learn more about the Sun
NASA’s Parker Solar Probe launched in 2018 on the first-ever mission to fly into the Sun’s corona. Since its first pass through the corona in 2021, every orbit has brought it closer to the Sun. On Dec. 24, 2024, it makes the first of its three final, closest solar approaches of its primary mission. Test your knowledge with NASA’s new quiz, Kahoot! Parker Solar Probe trivia.
Visit these resources for more details about the Sun:
https://science.nasa.gov/sun/facts/ https://spaceplace.nasa.gov/all-about-the-sun/en/ https://science.nasa.gov/exoplanets/stars/ Explore More For Students Grades 5-8 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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Last Updated Dec 10, 2024 Related Terms
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By NASA
5 Min Read Scientists Share Early Results from NASA’s Solar Eclipse Experiments
On April 8, 2024, a total solar eclipse swept across a narrow portion of the North American continent from Mexico’s Pacific coast to the Atlantic coast of Newfoundland, Canada. This photo was taken from Dallas, Texas. Credits:
NASA/Keegan Barber On April 8, 2024, a total solar eclipse swept across North America, from the western shores of Mexico, through the United States, and into northeastern Canada. For the eclipse, NASA helped fund numerous research projects and called upon citizen scientists in support of NASA’s goal to understand how our home planet is affected by the Sun – including, for example, how our star interacts with Earth’s atmosphere and affects radio communications.
At a press briefing on Tuesday, Dec. 10, scientists attending the annual meeting of the American Geophysical Union in Washington, D.C., reported some early results from a few of these eclipse experiments.
“Scientists and tens of thousands of volunteer observers were stationed throughout the Moon’s shadow,” said Kelly Korreck, eclipse program manager at NASA Headquarters in Washington. “Their efforts were a crucial part of the Heliophysics Big Year – helping us to learn more about the Sun and how it affects Earth’s atmosphere when our star’s light temporarily disappears from view.”
Changes in the Corona
On April 8, the Citizen CATE 2024 (Continental-America Telescopic Eclipse) project stationed 35 observing teams from local communities from Texas to Maine to capture images of the Sun’s outer atmosphere, or corona, during totality. Their goal is to see how the corona changed as totality swept across the continent.
On Dec. 10, Sarah Kovac, the CATE project manager at the Southwest Research Institute in Boulder, Colorado, reported that, while a few teams were stymied by clouds, most observed totality successfully — collecting over 47,000 images in all.
These images were taken in polarized light, or light oriented in different directions, to help scientists better understand the processes that shape the corona.
This preliminary movie from the Citizen CATE 2024 project stitches together polarized images of the solar corona taken from different sites during the total solar eclipse on April 8, 2024. SwRI/Citizen CATE 2024/Dan Seaton/Derek Lamb Kovac shared the first cut of a movie created from these images. The project is still stitching together all the images into the final, hour-long movie, for release at a later time.
“The beauty of CATE 2024 is that we blend cutting-edge professional science with community participants from all walks of life,” Kovac said. “The dedication of every participant made this project possible.”
Meanwhile, 50,000 feet above the ground, two NASA WB-57 aircraft chased the eclipse shadow as it raced across the continent, observing above the clouds and extending their time in totality to approximately 6 minutes and 20 seconds.
On board were cameras and spectrometers (instruments that analyze different wavelengths of light) built by multiple research teams to study the corona.
This image of the total solar eclipse is a combination of 30 50-millisecond exposures taken with a camera mounted on one of NASA’s WB-57 aircraft on April 8, 2024. It was captured in a wavelength of light emitted by ionized iron atoms called Fe XIV. This emission highlights electrified gas, called plasma, at a specific temperature (around 3.2 million degrees Fahrenheit) that often reveals arch-like structures in the corona. B. Justen, O. Mayer, M. Justen, S. Habbal, and M. Druckmuller On Dec. 10, Shadia Habbal of the University of Hawaii, who led one of the teams, reported that their instruments collected valuable data, despite one challenge. Cameras they had mounted on the aircraft’s wings experienced unexpected vibrations, which caused some of the images to be slightly blurred.
However, all the cameras captured detailed images of the corona, and the spectrometers, which were located in the nose of the aircraft, were not affected. The results were so successful, scientists are already planning to fly similar experiments on the aircraft again.
“The WB-57 is a remarkable platform for eclipse observations that we will try to capitalize on for future eclipses,” Habbal said.
Affecting the Atmosphere
On April 8, amateur or “ham” radio operators sent and received signals to one another before, during, and after the eclipse as part of the Ham Radio Science Citizen Investigation (HamSCI) Festivals of Eclipse Ionospheric Science. More than 6,350 amateur radio operators generated over 52 million data points to observe how the sudden loss of sunlight during totality affects their radio signals and the ionosphere, an electrified region of Earth’s upper atmosphere.
Students from Case Western Reserve University operate radios during the 2024 total solar eclipse. HamSCI/Case Western Reserve University Radio communications inside and outside the path of totality improved at some frequencies (from 1-7 MHz), showing there was a reduction in ionospheric absorption. At higher frequencies (10 MHz and above), communications worsened.
Results using another technique, which bounced high-frequency radio waves (3-30 MHz) off the ionosphere, suggests that the ionosphere ascended in altitude during the eclipse and then descended to its normal height afterward.
“The project brings ham radio operators into the science community,” said Nathaniel Frissell, a professor at the University of Scranton in Pennsylvania and lead of HamSCI. “Their dedication to their craft made this research possible.”
Also looking at the atmosphere, the Nationwide Eclipse Ballooning Project organized student groups across the U.S. to launch balloons into the shadow of the Moon as it crossed the country in April 2024 and during a solar eclipse in October 2023. Teams flew weather sensors and other instruments to study the atmospheric response to the cold, dark shadow.
The eclipse’s shadow was captured from a camera aboard Virginia Tech’s balloon as part of the Nationwide Eclipse Ballooning Project on April 8, 2024. Nationwide Eclipse Ballooning Project/Virginia Tech This research, conducted by over 800 students, confirmed that eclipses can generate ripples in Earth’s atmosphere called atmospheric gravity waves. Just as waves form in a lake when water is disturbed, these waves also form in the atmosphere when air is disturbed. This project, led by Angela Des Jardins of Montana State University in Bozeman, also confirmed the presence of these waves during previous solar eclipses. Scientists think the trigger for these waves is a “hiccup” in the tropopause, a layer in Earth’s atmosphere, similar to an atmospheric effect that is observed during sunset.
“Half of the teams had little to no experience ballooning before the project,” said Jie Gong, a team science expert and atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But their hard work and research was vital in this finding.”
By Abbey Interrante and Vanessa Thomas
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Dec 10, 2024 Related Terms
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