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The science behind splashdown − an aerospace engineer explains how NASA and SpaceX get spacecraft safely back on Earth

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theconversation.com – Marcos Fernandez Tous, Assistant Professor of Studies, of North Dakota – 2024-06-27 07:23:16
The Orion capsule from NASA's Artemis I mission splashes down.
NASA via AP

Marcos Fernandez Tous, University of North Dakota

For about 15 minutes on July 21, 1961, American astronaut Gus Grissom felt at the top of the world – and indeed he was.

Grissom crewed the Liberty Bell 7 mission, a ballistic test flight that launched him through the atmosphere from a rocket. During the test, he sat inside a small capsule and reached a peak of over 100 miles up before splashing down in the Atlantic Ocean.

A Navy ship, the USS Randolph, watched the successful end of the mission from a safe distance. Everything had gone according to plan, the controllers at Cape Canaveral were exultant, and Grissom knew he had just entered a VIP club as the second American astronaut in history.

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Grissom remained inside his capsule and swayed on the gentle ocean waves. While he waited for a helicopter to take him onto the USS Randolph's dry deck, he finished recording some flight data. But then, things took an unexpected turn.

An incorrect command in the capsule's explosives system caused the hatch to pop out, which let flow into the tiny space. Grissom had also forgotten to close a valve in his spacesuit, so water began to seep into his suit as he fought to stay afloat.

After a dramatic escape from the capsule, he struggled to keep his head above the surface while giving to the helicopter pilot that something had gone wrong. The helicopter managed to save him at the last instant.

Grissom's near- escape remains one of the most dramatic splashdowns in history. But splashing down into water remains one of the most common ways astronauts return to Earth. I am a professor of aerospace engineering who studies the mechanisms involved in these phenomena. Fortunately, most splashdowns are not quite that nerve-racking, at least on paper.

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Two small rafts, one full of crew members, float next to a metal capsule.
Navy personnel retrieve the crew from the Apollo 11 return capsule after splashdown on July 24, 1969.
AP Photo/Barry Sweet

Splashdown explained

Before it can perform a safe landing, a spacecraft returning to Earth needs to slow down. While it is careening back to Earth, a spacecraft has a lot of kinetic energy. Friction with the atmosphere introduces drag, which slows down the spacecraft. The friction converts the spacecraft's kinetic energy to thermal energy, or heat.

All this heat radiates out into the surrounding , which gets really, really hot. Since reentry velocities can be several times the speed of sound, the force of the air pushing back against the vehicle turns the vehicle's surroundings into a scorching flow that's about 2,700 degrees Fahrenheit (1,500 degrees Celsius). In the case of SpaceX's massive Starship rocket, this temperature even reaches 3,000 degrees Fahrenheit (nearly 1,700 degrees Celsius).

Unfortunately, no matter how quickly this transfer happens, there's still not enough time during reentry for the vehicle to slow down to a safe enough velocity not to crash. So, the engineers resort to other methods that can slow down a spacecraft during splashdown.

Parachutes are the first option. NASA typically uses designs with bright colors, such as orange, which make them easy to spot. They're also huge, with diameters of over 100 feet, and each reentry vehicle usually uses more than one for the best stability.

The first parachutes deployed, called drag parachutes, eject when the vehicle's velocity falls below about 2,300 feet per second (700 meters per second).

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Even then, the rocket can't crash against a hard surface. It needs to land somewhere that will cushion the impact. Researchers figured out early on that water makes an excellent shock absorber. Thus, splashdown was born.

The Apollo 15 command module splashes down into the Pacific Ocean on Aug. 7, 1971.

Why water?

Water has a relatively low viscosity – that is, it deforms fast under stress – and it has a density much lower than hard rock. These two qualities make it ideal for landing spacecraft. But the other main reason water works so well is because it covers 70% of the planet's surface, so the chances of hitting it are high when you're falling from space.

The science behind splashdown is complex, as a long history proves.

In 1961, the U.S. conducted the first crewed splashdowns in history. These used Mercury reentry capsules.

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These capsules had a roughly conical shape and fell with the base toward the water. The astronaut inside sat facing upward. The base absorbed most of the heat, so researchers designed a heat shield that boiled away as the capsule shot through the atmosphere.

As the capsule slowed and the friction reduced, the air got cooler, which made it able to absorb the excess heat on the vehicle, thereby cooling it down as well. At a sufficiently low speed, the parachutes would deploy.

Splashdown occurs at a velocity of about 80 feet per second (24 meters per second). It's not exactly a smooth impact, but that's slow enough for the capsule to thwack into the ocean and absorb shock from the impact without damaging its structure, its payload or any astronauts inside.

the Challenger loss in 1986, when the space shuttle Challenger broke apart shortly after liftoff, engineers started focusing their vehicle designs on what's called the crashworthiness phenomena – or the degree of a craft takes after it hits a surface.

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Now, all vehicles need to prove that they can offer a of survival on water after returning from space. Researchers build complex models, then test them with laboratory experiments to prove that the structure is sturdy enough to meet this requirement.

Onto the future

Between 2021 and June 2024, seven of SpaceX's Dragon capsules performed flawless splashdowns on their return from the International Space Station.

On June 6, the most powerful rocket to date, SpaceX's Starship, made a phenomenal vertical splashdown into the Indian Ocean. Its rocket boosters kept firing while approaching the surface, creating an extraordinary cloud of hissing steam surrounding the nozzles.

SpaceX has been using splashdowns to recover the Dragon capsules after launch, with no significant damage to their critical parts, so that it can recycle them for future missions. Unlocking this reusability will allow private companies to save millions of dollars in infrastructure and reduce mission costs.

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SpaceX's Starship splashes down in a cloud of steam on June 6, 2024.

Splashdown continues to be the most common spacecraft reentry tactic, and with more space agencies and private companies shooting for the stars, we're likely to see plenty more take place in the future.

This article has been updated to correct that SpaceX has been recovering their Dragon capsules during splashdown.The Conversation

Marcos Fernandez Tous, Assistant Professor of Space Studies, University of North Dakota

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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The Conversation

Supreme Court kicks cases about tech companies’ First Amendment rights back to lower courts − but appears poised to block states from hampering online content moderation

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theconversation.com – Lynn Greenky, Professor Emeritus of Communication and Rhetorical Studies, Syracuse University – 2024-07-01 15:26:42
How much power do social companies have over what users post?
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Lynn Greenky, Syracuse University

The U.S. Supreme Court has sent back to lower courts the about whether states can block social media companies such as Facebook and X, formerly Twitter, from regulating and controlling what users can post on their platforms.

Laws in Florida and Texas sought to impose restrictions on the internal policies and algorithms of social media platforms in ways that influence which posts will be promoted and spread widely and which will be made less visible or even .

In the unanimous decision, issued on July 1, 2024, the high court remanded the two cases, Moody v. NetChoice and NetChoice v. Paxton, to the 11th and 5th U.S. Circuit Courts of Appeals, respectively. The court admonished the lower courts for their failure to consider the full force of the laws' applications. It also warned the lower courts to consider the boundaries imposed by the Constitution against interference with private speech.

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Contrasting views of social media sites

In their arguments before the court in February 2024, the two sides described competing visions of how social media fits into the often overwhelming flood of information that defines modern digital society.

The states said the platforms were mere conduits of communication, or “speech hosts,” similar to legacy telephone companies that were required to carry all calls and prohibited from discriminating against users. The states said that the platforms should have to carry all posts from users without discrimination among them based on what they were saying.

The states argued that the content moderation rules the social media companies imposed were not examples of the platforms themselves speaking – or choosing not to speak. Rather, the states said, the rules affected the platforms' behavior and caused them to censor certain views by allowing them to determine whom to allow to speak on which topics, which is outside First Amendment protections.

By contrast, the social media platforms, represented by NetChoice, a tech industry trade group, argued that the platforms' guidelines about what is acceptable on their sites are protected by the First Amendment's guarantee of speech free from government interference. The companies say their platforms are not public forums that may be subject to government regulation but rather private services that can exercise their own editorial judgment about what does or does not appear on their sites.

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They argued that their policies were aspects of their own speech and that they should be to develop and implement guidelines about what is acceptable speech on their platforms based on their own First Amendment rights.

Here's what the First Amendment says and what it means.

A reframe by the Supreme Court

All the litigants – NetChoice, Texas and Florida – framed the issue around the effect of the laws on the content moderation policies of the platforms, specifically whether the platforms were engaged in protected speech. The 11th U.S. Circuit Court of Appeals upheld a lower court preliminary injunction against the Florida , holding the content moderation policies of the platforms were speech and the law was unconstitutional.

The 5th U.S. Circuit Court of Appeals came to the opposite conclusion and held that the platforms were not engaged in speech, but rather the platform's algorithms controlled platform behavior unprotected by the First Amendment. The 5th Circuit determined the behavior was censorship and reversed a lower court injunction against the Texas law.

The Supreme Court, however, reframed the inquiry. The court noted that the lower courts failed to consider the full range of activities the laws covered. Thus, while a First Amendment inquiry was in order, the decisions of the lower courts and the arguments by the parties were incomplete. The court added that neither the parties nor the lower courts engaged in a thorough analysis of whether and how the states' laws affected other elements of the platforms' products, such as Facebook's direct messaging applications, or even whether the laws have any impact on email providers or online marketplaces.

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The Supreme Court directed the lower courts to engage in a much more exacting analysis of the laws and their implications and provided some guidelines.

First Amendment principles

The court held that content moderation policies reflect the constitutionally protected editorial choices of the platforms, at least regarding what the court as “heartland applications” of the laws – such as Facebook's News Feed and YouTube's homepage.

The Supreme Court required the lower courts to consider two core constitutional principles of the First Amendment. One is that the amendment protects speakers from being compelled to communicate messages they would prefer to exclude. Editorial discretion by entities, including social media companies, that compile and curate the speech of others is a protected First Amendment activity.

The other principle that the amendment precludes the government from controlling private speech, even for the purpose of balancing the marketplace of ideas. Neither state nor federal government may manipulate that marketplace for the purposes of presenting a more balanced array of viewpoints.

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The court also affirmed that these principles apply to digital media in the same way they apply to traditional or legacy media.

In the 96-page opinion, Justice Elena Kagan wrote: “The First Amendment … does not go on when social media are involved.” For now, it appears the social media platforms will continue to control their content.The Conversation

Lynn Greenky, Professor Emeritus of Communication and Rhetorical Studies, Syracuse University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Disability community has long wrestled with ‘helpful’ technologies – lessons for everyone in dealing with AI

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theconversation.com – Elaine Short, Assistant Professor of Computer Science, Tufts University – 2024-07-01 07:19:34

A robotic arm helps a disabled person paint a picture.

Jenna Schad /Tufts University

Elaine Short, Tufts University

You might have heard that artificial intelligence is going to revolutionize everything, save the world and give everyone superhuman powers. Alternatively, you might have heard that it will take your job, make you lazy and stupid, and make the world a cyberpunk dystopia.

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Consider another way to look at AI: as an assistive technology – something that helps you function.

With that view, also consider a community of experts in giving and receiving assistance: the disability community. Many disabled people use technology extensively, both dedicated assistive technologies such as wheelchairs and general-use technologies such as smart home devices.

Equally, many disabled people professional and casual assistance from other people. And, despite stereotypes to the contrary, many disabled people regularly give assistance to the disabled and nondisabled people around them.

Disabled people are well experienced in receiving and giving social and technical assistance, which makes them a valuable source of insight into how everyone might relate to AI in the future. This potential is a key driver for my work as a disabled person and researcher in AI and robotics.

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Actively learning to live with help

While virtually everyone values independence, no one is fully independent. Each of us depends on others to grow our food, care for us when we are ill, give us advice and emotional , and us in thousands of interconnected ways. Being disabled means support needs that are outside what is typical and therefore those needs are much more visible. Because of this, the disability community has reckoned more explicitly with what it means to need help to than most nondisabled people.

This disability community perspective can be invaluable in approaching new technologies that can assist both disabled and nondisabled people. You can't substitute pretending to be disabled for the experience of actually being disabled, but accessibility can benefit everyone.

The curb-cut effect – how technologies built for disabled people help everyone – has become a principle of good design.

This is sometimes called the curb-cut effect after the ways that putting a ramp in a curb to help a wheelchair user access the sidewalk also people with strollers, rolling suitcases and bicycles.

Partnering in assistance

You have probably had the experience of someone to help you without listening to what you actually need. For example, a parent or friend might “help” you clean and instead end up hiding everything you need.

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Disability advocates have long battled this type of well-meaning but intrusive assistance – for example, by putting spikes on wheelchair handles to keep people from pushing a person in a wheelchair without being asked to or advocating for services that keep the disabled person in control.

The disabled community instead offers a model of assistance as a collaborative effort. Applying this to AI can help to ensure that new AI tools support human autonomy rather than taking over.

A key goal of my lab's work is to develop AI-powered assistive robotics that treat the user as an equal partner. We have shown that this model is not just valuable, but inevitable. For example, most people find it difficult to use a joystick to move a robot arm: The joystick can only move from front to back and side to side, but the arm can move in almost as many ways as a human arm.

The author discusses her work on robots that are designed to help people.

To help, AI can predict what someone is planning to do with the robot and then move the robot accordingly. Previous research assumed that people would ignore this help, but we found that people quickly figured out that the system is doing something, actively worked to understand what it was doing and tried to work with the system to get it to do what they wanted.

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Most AI systems don't make this easy, but my lab's new approaches to AI empower people to influence robot behavior. We have shown that this results in better interactions in tasks that are creative, like painting. We also have begun to investigate how people can use this control to solve problems outside the ones the robots were designed for. For example, people can use a robot that is trained to carry a cup of to instead pour the water out to water their plants.

Training AI on human variability

The disability-centered perspective also raises concerns about the huge datasets that power AI. The very nature of data-driven AI is to look for common patterns. In general, the better-represented something is in the data, the better the model works.

If disability means having a body or mind outside what is typical, then disability means not being well-represented in the data. Whether it's AI systems designed to detect cheating on exams instead detecting students' disabilities or robots that fail to account for wheelchair users, disabled people's interactions with AI reveal how those systems are brittle.

One of my goals as an AI researcher is to make AI more responsive and adaptable to real human variation, especially in AI systems that learn directly from interacting with people. We have developed frameworks for testing how robust those AI systems are to real human teaching and explored how robots can learn better from human teachers even when those teachers change over time.

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Thinking of AI as an assistive technology, and learning from the disability community, can help to ensure that the AI systems of the future serve people's needs – with people in the driver's seat.The Conversation

Elaine Short, Assistant Professor of Computer Science, Tufts University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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How was popcorn discovered? An archaeologist on its likely appeal for people in the Americas millennia ago

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theconversation.com – Sean Rafferty, Professor of Anthropology, University at Albany, University of New York – 2024-07-01 07:19:19

Could a spill by the cook fire have been popcorn's eureka moment?

Paul Taylor/Stone via Getty Images

Sean Rafferty, University at Albany, State University of New York

Curious Kids is a for of all ages. If you have a question you'd like an expert to answer, send it to curiouskidsus@theconversation.com.

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How was popcorn discovered? – Kendra, age 11, Penn Yan, New York


You have to wonder how people originally figured out how to eat some foods that are beloved . The cassava plant is toxic if not carefully processed through multiple steps. Yogurt is basically old milk that's been around for a while and contaminated with bacteria. And who discovered that popcorn could be a toasty, tasty treat?

These kinds of food mysteries are pretty hard to solve. Archaeology depends on solid remains to figure out what happened in the past, especially for people who didn't use any sort of writing. Unfortunately, most stuff people traditionally used made from wood, animal materials or cloth decays pretty quickly, and archaeologists like me never find it.

We have lots of evidence of hard stuff, such as pottery and stone tools, but softer things – such as leftovers from a meal – are much harder to find. Sometimes we get lucky, if softer stuff is found in very dry places that preserve it. Also, if stuff gets burned, it can last a very long time.

Corn's ancestors

Luckily, corn – also called maize – has some hard parts, such as the kernel shell. They're the bits at the bottom of the popcorn bowl that get caught in your teeth. And since you have to heat maize to make it edible, sometimes it got burned, and archaeologists find evidence that way. Most interesting of all, some plants, maize, contain tiny, rock-like fragments called phytoliths that can last for thousands of years.

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green plant stalks with reddish tendrils

The ancestor of maize was a grass called teosinte.

vainillaychile/iStock via Getty Images Plus

Scientists are pretty sure they know how old maize is. We know maize was probably first farmed by Native Americans in what is now Mexico. Early farmers there domesticated maize from a kind of grass called teosinte.

Before farming, people would gather wild teosinte and eat the seeds, which contained a lot of starch, a carbohydrate like you'd find in bread or pasta. They would pick teosinte with the largest seeds and eventually started weeding and planting it. Over time, the wild plant developed into something like what we call maize today. You can tell maize from teosinte by its larger kernels.

There's evidence of maize farming from dry caves in Mexico as early as 9,000 years ago. From there, maize farming spread throughout North and South America.

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Popped corn, preserved food

Figuring out when people started making popcorn is harder. There are several types of maize, most of which will pop if heated, but one variety, actually called “popcorn,” makes the best popcorn. Scientists have discovered phytoliths from Peru, as well as burned kernels, of this type of “poppable” maize from as early as 6,700 years ago.

cobs of popcorn over popped kernels, one showing popping on the cob

Each popcorn kernel is a seed, ready to burst when heated.

Rick Madonik/Toronto Star via Getty Images

You can imagine that popping maize kernels was first discovered by . Some maize probably fell into a cooking fire, and whoever was nearby figured out that this was a handy new way of preparing the food. Popped maize would last a long time and was easy to make.

Ancient popcorn was probably not much like the snack you might munch at the theater today. There was probably no salt and definitely no butter, since there were no cows to milk in the Americas yet. It probably wasn't served hot and was likely pretty chewy with the version you're used to today.

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It's impossible to know exactly why or how popcorn was invented, but I would guess it was a clever way to preserve the edible starch in corn by getting rid of the little bit of water inside each kernel that would make it more susceptible to spoiling. It's the heated water in the kernel escaping as steam that makes popcorn pop. The popped corn could then last a long time. What you may consider a tasty snack today probably started as a useful way of preserving and storing food.


Hello, curious kids! Do you have a question you'd like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the where you live.

And since curiosity has no age limit – adults, let us know what you're wondering, too. We won't be able to answer every question, but we will do our best.The Conversation

Sean Rafferty, Professor of Anthropology, University at Albany, State University of New York

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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