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No matter what mode of transportation you take for a long trip, at some point, you’ll have to refuel. For cars, this could be a simple trip to a gas station, while planes, trains, and ships have more specialized refueling services at their depots or ports. However, for spacecraft, there is currently no refueling infrastructure whatsoever. And since the fuel spacecraft use must be stored cryogenically, and the tanks the fuel is stored in are constantly subjected to the thermal radiation from the Sun, keeping enough fuel in a tank for a trip to Mars with astronauts is currently infeasible. Luckily, NASA is currently working on it and recently released a detailed look at some of that work on a blog on their website.

The problem definition is very clear – cryogenic hydrogen and oxygen are used as fuel on most spacecraft missions. Once in space, the tanks the fuel is stored in heat up due to the constant solar radiation they’re subjected to. Since there’s no air, there’s no way to radiate out that heat, so eventually, it can get through even the most sophisticated passive thermal insulation system. When it does, the fuel starts to boil, and mission planners typically have chosen to eject the vaporous fuel out into space rather than leaving it as a potential medium to heat the rest of the fuel faster.

This resultant fuel lost to this sublimation can cost as much as half of the cryogenic fuel needed for a 3-year mission to Mars – in just a single year. In short, crewed trips to Mars are impossible using the current fuel storage technology in space. However, there are alternatives, known as Zero Boil-Off (ZBO) or Reduced Boil-Off (RBO) systems. These advanced tanks use a combination of “active” processes to maintain tank pressure and not allow too much loss of fuel during long space flights.

Fraser makes an argument for why refueling is so critical.

An “active” process must be actively controlled and typically requires some sort of power input. In particular, ZBO systems rely on two technology ideas – a jet mixing of the propellant and a droplet injection technology. Let’s take a look at the mixing technology first.

In this example, part of the fuel would be forcibly mixed back into the vapor space in a particular way that would allow it to control the phase changes of the vapor/fuel interface. In essence, it would stop the fuel from sublimating into a vapor in the first place. Similarly, a droplet injection system would use a novel type of spray bar to inject fuel droplets into the vapor area, causing it to condense and remove some of the pressure from the system.

To add another layer of complexity to these already complicated fluid dynamics systems, this all must be done in microgravity, where things like droplet formation and liquid mixing don’t always happen the same way as they do on Earth. So, NASA decided to do what it does best and run some experiments – in this case on the ISS.

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Image of the ZBOT-1 experiment being installed on the ISS by astronaut Joseph Acaba.
Credit – NASA

Back in 2017, NASA started the ZBOT-1 Experiment on the ISS. It was intended to quantify how the jet mixing would behave in microgravity, and the result of some 30+ tests was that we still understand very little about how these systems work in microgravity. While how they were is different than what most fluid engineers are used to, they are still acting according to physical laws, so more experiments would help narrow down the models that tank designers can use to understand how these ZBO systems might best be used.

Two other experiments are focused on furthering that understanding – one called the ZBOT-NC Experiment, is due to be launched to the ISS in 2025. It will study the effects of microgravity on “non-condensable gases,” which can be used to control the pressure inside the fuel tank. Data from its observations can also be fed into the CFD models, allowing scientists to understand better how the model differs from reality in microgravity.

The final test in the series will focus on droplet phase changes. Known as the ZBOT-DP test, this is the most ambitious of the three, as it tests a technology that has never been used in microgravity at all before. It will focus on understanding how droplets interact with
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Stellar Winds Coming From Other Stars Measured for the First Time

interstellar jpg

An international research team led by the University of Vienna has made a major breakthrough. In a study recently published in Nature Astronomy, they describe how they conducted the first direct measurements of stellar wind in three Sun-like star systems. Using X-ray emission data obtained by the ESA’s X-ray Multi-Mirror-Newton (XMM-Newton) of these stars’ “astrospheres,” they measured the mass loss rate of these stars via stellar winds. The study of how stars and planets co-evolve could assist in the search for life while also helping astronomers predict the future evolution of our Solar System.

The research was led by Kristina G. Kislyakova, a Senior Scientist with the Department of Astrophysics at the University of Vienna, the deputy head of the Star and Planet Formation group, and the lead coordinator of the ERASMUS+ program. She was joined by other astrophysicists from the University of Vienna, the Laboratoire Atmosphères, Milieux, Observations Spatiales (LAMOS) at the Sorbonne University, the University of Leicester, and the Johns Hopkins University Applied Physics Laboratory (JHUAPL).

Astrospheres are the analogs of our Solar System’s heliosphere, the outermost atmospheric layer of our Sun, composed of hot plasma pushed by solar winds into the interstellar medium (ISM). These winds drive many processes that cause planetary atmospheres to be lost to space (aka. atmospheric mass loss). Assuming a planet’s atmosphere is regularly replenished and/or has a protective magnetosphere, these winds can be the deciding factor between a planet becoming habitable or a lifeless ball of rock.

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Logarithmic scale of the Solar System, Heliosphere, and Interstellar Medium (ISM). Credit: NASA-JPL

While stellar winds mainly comprise protons, electrons, and alpha particles, they also contain trace amounts of heavy ions and atomic nuclei, such as carbon, nitrogen, oxygen, silicon, and even iron. Despite their importance to stellar and planetary evolution, the winds of Sun-like stars are notoriously difficult to constrain. However, these heavier ions are known to capture electrons from neutral hydrogen that permeates the ISM, resulting in X-ray emissions. Using data from the XXM-Newton mission, Kislyakova and her team detected these emissions from other stars.

These were 70 Ophiuchi, Epsilon Eridani, and 61 Cygni, three main sequence Sun-like stars located 16.6, 10.475, and 11.4 light-years from Earth (respectively). Whereas 70 Ophiuchi and 61 Cygni are binary systems of two K-type (orange dwarf) stars, Epsilon Eridani is a single K-type star. By observing the spectral lines of oxygen ions, they could directly quantify the total mass of stellar wind emitted by all three stars. For the three stars surveyed, they estimated the mass loss rates to be 66.5±11.1, 15.6±4.4, and 9.6±4.1 times the solar mass loss rate, respectively.

In short, this means that the winds from these stars are much stronger than our Sun’s, which could result from the stronger magnetic activity of these stars. As Kislyakova related in a University of Vienna news release:

“In the solar system, solar wind charge exchange emission has been observed from planets, comets, and the heliosphere and provides a natural laboratory to study the solar wind’s composition. Observing this emission from distant stars is much more tricky due to the faintness of the signal. In addition to that, the distance to the stars makes it very difficult to disentangle the signal emitted by the astrosphere from the actual X-ray emission of the star itself, part of which is “spread” over the field-of-view of the telescope due to instrumental effects.”

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XMM-Newton X-ray image of the star 70 Ophiuchi (left) and
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How to Know How Hard a Hike Will Be

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By Michael Lanza

“How hard will that hike be?” That’s a question that
all dayhikers and backpackers, from beginners to experts, think about all the
time—and it’s not always easy to answer. But there are ways of evaluating the
difficulty of any hike, using readily available information, that can greatly
help you understand what to expect before you even leave home. Here’s
how.

No matter how relatively easy or arduous the hike you’re considering, or where you fall on the spectrum of hiking experience or personal fitness level, this article will tell you exactly how to answer that question—and which questions to ask and what information to seek to reach that answer. This article shares what I’ve learned over four decades of backpacking and dayhiking, including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog, and this knowledge can help ensure that you and your companions or your family don’t get in over your heads.

Whether you’re new to dayhiking or backpacking, a
parent planning a hike with young kids, or a fit and experienced dayhiker or
backpacker contemplating one of the toughest hikes you’ve ever attempted, it’s
important to have a good sense of what you’ll face on a new and unfamiliar hike
and whether it’s within your abilities.

Tet19 047 Me on Teton Crest Trail copy cropped 17 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 backpacker hiking the Dawson Pass Trail in Glacier National Park.
” data-image-caption=”Pam Solon backpacking the Dawson Pass Trail in Glacier National Park. Click photo to read about backpacking in Glacier.
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park-1024×683.jpg?resize=900%2C600&ssl=1″ alt=”A backpacker hiking the Dawson Pass Trail in Glacier National Park.” class=”wp-image-61235″ srcset=”https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg 1024w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg 300w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg 768w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg 150w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/12/06224534/Gla7-117-Pam-Solon-backpacking-the-Dawson-Pass-Trail-in-Glacier-National-Park.jpg 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Pam Solon backpacking the Dawson Pass Trail in Glacier National Park. Click photo to read about backpacking in Glacier.

Exceeding your limits or those of someone with you can
invite unwanted consequences—and the person with the least stamina,
abilities, or experience often dictates any party’s pace, limits, and outcomes.
Those consequences
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The 12 Best Down Jackets of 2024

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By Michael Lanza

Whatever you need an insulated jacket for, there’s a down or synthetic puffy for your needs, within your budget. And whether you want a puffy jacket for outdoor activities like backpacking, camping, skiing, climbing, and hut treks, or just to keep you warm around town or at outdoor sporting events, this review will help you figure out how to choose the right jacket for your purposes, and it spotlights the best down and synthetic insulated jackets available today.

I selected the jackets covered in this review after extensive testing on backpacking, camping, backcountry ski touring, climbing and other backcountry trips. I’ve field-tested dozens of insulated jackets over nearly three decades of testing and reviewing gear, formerly as the lead gear reviewer for Backpacker magazine for 10 years and even longer running this blog.

Technology has blurred the traditional lines between down and synthetics, with water-resistant down that traps heat even when wet—all but eliminating the weakness that had long been the Achilles heel of down—and synthetic insulation materials that approach the warmth-to-weight ratio and compressibility of down.

If you’d prefer, scroll past my buying tips to dive immediately into the jacket reviews.

If you have a question for me or a comment on this review, please leave it in the comments section at the bottom of this story. I try to respond to all comments.

Tet19 047 Me on Teton Crest Trail copy cropped 15 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-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

The Black Diamond Approach Down Hoody.
” data-image-caption=”The Black Diamond Approach Down Hoody in the Grand Canyon.
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1-1024×683.jpg?resize=900%2C600&ssl=1″ alt=”The Black Diamond Approach Down Hoody.” class=”wp-image-52287″ srcset=”https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg 1024w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg 300w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg 768w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg 150w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2022/04/06225653/Black-Diamond-Approach-Down-Hoody-hood-up-1.jpg 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />The Black Diamond Approach Down Hoody in the Grand Canyon.

How to Choose a Synthetic or Down Jacket

Insulated jackets today differ not only in type and amount of insulation, but also in water resistance, breathability, and as always, design features like the hood and pockets. When choosing between down and synthetic models, consider the usual conditions and temperatures in which you’ll use it—in other words, how wet and cold you expect to get, and your body type (how easily you get cold)—as well as the seasonal and activity versatility you require. Some questions to
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