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The Solar System’s moons are intriguing objects for exploration. Especially moons like Europa and Enceladus. Their subsurface oceans make them primary targets in the search for life.

But why not send one spacecraft to visit several moons? NASA’s about to launch its Lucy mission which will visit 8 separate asteroids. Could the same be done for a mission to multiple moons?

For a spacecraft to do that, it would have to do a little dance with the notorious three-body problem, which makes a stubborn partner. A new study presents a possible way to do that.

Missions like Galileo and Cassini were able to gather some data on the moons of Jupiter and Saturn. But they performed distant flybys; they never orbited the moons. It’s tricky sending a spacecraft to visit and orbit different moons around the same planet because of all the gravitational forces involved. A spacecraft with unlimited propellant could use brute force to enter and exit orbits. But that’s not how space travel works. Everything is launched from Earth on rockets, at great expense, and fuel must be carefully husbanded.

A new study looks at a method to move a spacecraft between lunar orbits without using mission-busting quantities of fuel. The title of the paper is “Transfer design between neighbourhoods of planetary moons in the circular restricted three-body problem: The Moon-to-Moon Analytical Transfer Method.” The lead author of the paper is David Canales from the School of Aeronautics and Astronautics, Purdue University.

The “circular restricted three-body problem” is one of those vexing aspects of space travel in need of a stronger solution. In the case of transferring a spacecraft between different moons. the planet, the moons, and the spacecraft create a complicated gravitational situation that’s difficult to navigate. Especially when the moons are travelling at different velocities, and on different orbital planes.

For a better understanding of the three-body problem, watch this video.

Their solution is called the Moon-to-Moon Analytical Transfer (MMAT) Method. MMAT is a general methodology for transferring spacecraft between moons “…within the context of the circular restricted three-body problem..” the authors write.

“A simplified model enables analytical constraints to efficiently determine the feasibility of a transfer between two different moons moving in the vicinity of a common planet. In particular, connections between the periodic orbits of such two different moons are achieved,” they write. In their paper, they present two case studies: one for the Jovian system and one for the Uranian system.

The authors explain that other researchers have come up with solutions to the three-body problem. But they say that these solutions are unsatisfactory for different reasons. For example, some solutions assume that the moons are on coplanar orbits, which may not be true. Some solutions require too much fuel and restrict mission design. And some modelled solutions don’t hold true when modelled at higher resolutions. They write that solutions must be “…sometimes adjusted on a case-by-case basis.”

Their MMAT method is more effective. They describe it as “…an alternative general methodology for transfer design between moons applicable to any given system;”

This figure from the study illustrates the circular rotating three-body problem (CR3BP.) Ls one through five are equilibrium points. Image Credit: Canales et al 2021.
This figure from the study illustrates the circular rotating three-body problem (CR3BP.) Ls one through five are equilibrium points. Image Credit: Canales et al 2021.

The specific math behind the MMAT method is beyond this article’s scope. Interested readers can explore the paper for themselves. For the rest of us, the paper’s conclusion explains it best.

In their conclusion, the authors drive home the point that transfers from moon to moon are extraordinarily complex maneuvers. “Trajectory design for transfers between different moons moving in the vicinity of a common planet is a balance between diverse constraints, priorities and requirements to enable trajectory design for successful missions.” The solution involves the use of libration points in the system. “The analysis supports transfers between libration point
orbits near different moons,” they write.

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Curiosity Rover is Climbing Through Dramatic Striped Terrain on Mars

Mars Curiosity from HiRISE Circled PIA26245 figA 580x460 1 jpg

Just about every day we here on Earth get a breathtaking picture of Mars’s terrain sent back by a rover. But, the view from space can be pretty amazing, too. The Mars Reconnaissance Orbiter (MRO) just sent back a thought-provoking picture of Curiosity as it makes its way up a steep ridge on Mount Sharp.

The rover is a tiny black dot in the center of the image, which gives a good feeling for what MRO’s HiRISE camera accomplished. For scale, the rover is about the size of a dinner table, sitting in a region of alternating dark and light bands of material on the Red Planet.

NASA's Curiosity Mars rover appears as a dark speck in this image captured from directly overhead by the agency's Mars Reconnaissance Orbiter, or MRO. Credit: NASA/JPL-Caltech/University of Arizona
NASA’s Curiosity Mars rover appears as a dark speck in this image captured from directly overhead by the agency’s Mars Reconnaissance Orbiter, or MRO. Credit: NASA/JPL-Caltech/University of Arizona

Where’s Curiosity?

The Curiosity rover is exploring an ancient ridge on the side of Mount Sharp, which is the peak of a crater on Mars. It’s sitting on the side of a feature called Gediz Vallis Ridge, and the terrains and materials preserve a record of what things were like when water last flowed there. That happened about three billion years ago. The force of the flow brought significant amounts of rocks and debris through the region. They piled up to form the ridge. So, much of what you see here is the desiccated remains of that flooding.

Debris flows are pretty common here on Earth, particularly in the aftermath of floods, volcanic eruptions, tsunamis, and other actions. We can see them wherever material floods through a region or down a slope. In a flood-based flow, the speed of the water combines with gravity and the degree of slope to send material rushing across the surface. A debris flow can also be a dry landslide, and those can occur pretty much anywhere on Earth where the conditions are right. Another type of debris flow comes from volcanic activity. That occurs when material erupts from a volcano, or when earthquakes combined with an eruption collapse material into the side of the mountain. That results in what’s called a “lahar”. Folks in North America might recall the Mount St. Helens eruption in 1980; it resulted in several lahars that buried parts of the surrounding terrain.

Now that scientists see similar-seeming regions on Mars, they want to know several things. How did they form? Were they created by the same processes that make them on Earth? And, how long ago did they begin to form? Curiosity and Perseverance and other rovers and landers have been sent to Mars to help answer those questions.

Understanding the Debris Ridge

Did any of these actions happen on Mars? The evidence is pretty strong, which is why Gediz Vallis itself is a major exploration goal for the rover. It’s a canyon that stretches across 9 kilometers of the Martian surface and is carved about 140 meters deep. Gediz was likely carved by so-called “fluvial” activity (meaning flowing action) in the beginning. Later floods deposited a variety of fine-grained sands and rocks. Over time, winds have blown a lot of that material away, leaving behind protected pockets of materials left behind by the flooding. The size of the rocks tells something about the speed of the flows that deposited all the material. Geological studies of those rocks will reveal their mineral compositions, including their exposure to water over time.

The Gediz Vallis ridge resulted from the action of water pushing rocks and dirt around to build it up over time. Planetary scientists now need to figure out the sequence of events that created it. The clues lie in the scattered rocks in the region and the surrounding terrain. Mount Sharp itself (formally known as Aeolis Mons), is about 5 kilometers high and is, essentially, a stack of layered sedimentary rocks. As Curiosity makes its way up the mountain, it explores younger and younger materials.

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A Giant Gamma-Ray Bubble is a Source of Extreme Cosmic Rays

Gamma ray burst illustration article jpg

Gamma-ray bursts (GRBs) are one of the most powerful phenomena in the Universe and something that astronomers have been studying furiously to learn more about their origins. In recent years, astronomers have set new records for the most powerful GRB ever observed – this includes GRB 190114C, observed by the Hubble Space Telescope in 2019, and GRB 221009A, detected by the Gemini South telescope in 2022. The same is true for high-energy cosmic rays that originate from within the Milky Way, whose origins are still not fully understood.

In a recent study, members of China’s Large High Altitude Air Shower Observatory (LHAASO) Collaboration discovered a massive gamma-ray burst (designated GRB 221009A) in the Cygnus star-forming region that was more powerful than 10 peta-electronvolts (PeV, 1PeV=1015eV), over ten times the average. In addition to being the brightest GRB studied to date, the team was able to precisely measure the energy spectrum of the burst, making this the first time astronomers have traced cosmic rays with this energy level back to their source.

The team was led by Prof. Cao Zhen, a professor at the Institute of High Energy Physics of the Chinese Academy of Sciences (CAS-IHEP), and included CAS members Dr. Gao Chuandong, Dr. Li Cong, Prof. Liu Ruoyu, and Prof. Yang Ruizhi. Their results were described in a paper titled “An ultrahigh-energy gamma-ray bubble powered by a super PeVatron,” which appeared on November 15th in Science Bulletin. The LHAASO Collaboration comprises over 280 members representing 32 astrophysics research institutions worldwide.

The Large High-Altitude Air Shower Observatory (LHAASO) is a composite array made up of 5216 electromagnetic particle detectors, 1188 muon detectors, a 78,000-square-meter water Cherenkov detector array, and 18 wide-angle Cherenkov telescopes. The observatory is located at a height of 4,410 meters (14468.5 ft) on Mount Haizi in Sichuan Province, China, and is dedicated to studying cosmic rays. When cosmic rays reach Earth’s atmosphere, they create “showers” of secondary particles, some of which reach the surface.

The origin of cosmic rays is one of the most important issues in astrophysics today. In the past few decades, astronomers have detected three high-energy GRBs at a peak of about one petaelectronvolts (PeVs) – one quadrillion electronvolts (1015eV) – in their energy spectrum. Scientists believe cosmic rays with energy beneath this level come from astrophysical sources within the Milky Way (like supernovae). This peak energy represents a limit for cosmic rays, which generally take the form of protons accelerated to near-light speed.

However, the origins of cosmic rays in the region of a few petaelectronvolts remain one of the more intriguing mysteries in astrophysics today. Based on data acquired by LHAASO, the Collaboration team discovered a giant ultra-high-energy gamma-ray bubble in the Cygnus X cluster (the largest star-forming region in the Solar neighborhood) located roughly 2.4 billion light-years from Earth. Photons detected inside the structure showed a maximum energy reading of 2.5 PeV, while those ejected showed energy values of up to 20 PeV – the highest ever recorded.

From this, the team inferred the presence of a massive cosmic ray accelerator near the center of the Bubble, which they believe to be the massive star cluster Cygnus OB2 within Cygnus X. This cluster is composed of many young massive stars, including blue-white O-type giants and B-type blue giants, with surface temperatures of over 35,000 and 15,000 °C (63,000 and 27,000 °F), respectively. These stars generate radiation pressure hundreds to millions of times that of the Sun that blows stellar surface material away, creating solar winds that move at speeds of up to thousands of kilometers per second.

GRB
GRB 221009A: looking back through time. Credit: ESA

Collisions between this wind and the ISM create high-energy gamma rays and the ideal environment for efficient particle acceleration. These findings represent the highest-energy cosmic rays detected to date and the first cosmic ray accelerator ever observed. The team’s observations also indicated that the
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Hiking Half Dome: How to Do It Right and Get a Permit

Tet19 047 Me on Teton Crest Trail copy cropped 4 jpg

By Michael Lanza

No hike in the country really compares with Yosemite’s Half Dome. The long, very strenuous, challenging, and incredibly scenic day trip to one of the most iconic and sought-after summits in America begins with ascending the Mist Trail through the shower constantly raining down from 317-foot Vernal Fall and below thunderous, 594-foot Nevada Fall. Climbing the cable route up several hundred feet of steep granite slab delivers a thrill that partly explains the hike’s enormous popularity.

The 8,800-foot summit of Half Dome—where many hikers complete the experience by standing on The Visor, a granite brim jutting out over Half Dome’s sheer, 2,000-foot Northwest Face—delivers an incomparable view of Yosemite Valley and a 360-degree panorama of a big swath of the park’s mountains.

Half Dome validates every step of effort you put into it.

Having been up and down those cables a handful of times over more than 30 years of dayhiking and backpacking all over the country—including many years running this blog and previously as the Northwest Editor of Backpacker magazine for 10 years—I consider Half Dome one of the very best dayhikes in the entire National Park System and certainly one of America’s hardest dayhikes.

Tet19 047 Me on Teton Crest Trail copy cropped 5 jpg
Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-books to classic backpacking trips. Click here to learn how I can help you plan your next trip.

A hiker atop Half Dome in Yosemite National Park.
” data-image-caption=”Mark Fenton on The Visor of Half Dome, high above Yosemite Valley, in Yosemite National Park.
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?fit=300%2C199&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?fit=900%2C598&ssl=1″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?resize=900%2C598&ssl=1″ alt=”A hiker atop Half Dome in Yosemite National Park.” class=”wp-image-35446″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?resize=1024%2C680&ssl=1 1024w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?resize=300%2C199&ssl=1 300w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?resize=768%2C510&ssl=1 768w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?resize=1080%2C717&ssl=1 1080w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2018/07/Yos11-041-Mark-summit-of-Half-Dome-Yosemite-N.P.-CA-2.jpg?w=1200&ssl=1 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Mark Fenton on The Visor or Half Dome, high above Yosemite Valley, in Yosemite National Park. Click photo to read about this backpacking trip.

The cables are up for hiking Half Dome from late May through mid-October. A permit is required for this popular dayhike and a permit lottery takes place throughout March. Yosemite requires a reservation to drive into or through the park on some days from April 13 through Oct. 27; nps.gov/yose/planyourvisit/reservations.htm.

This story shares what I’ve learned about navigating the competitive permit system and embarking on such a demanding day of hiking that’s roughly 16 miles round-trip with almost 5,000 feet of elevation gain and loss. Please share your thoughts or questions about hiking Half Dome in the comments section at the bottom of this story. I try to respond to all comments
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