How Do Astronauts Reenter Earth's Atmosphere Without Burning Up?

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iStock

Robert Frost:

Currently, astronauts and cosmonauts return to Earth in a Soyuz capsule. The Soyuz capsule has a curved ablative heat shield that is used to prevent heat from building up and penetrating the crew cabin.

As the capsule plummets through the atmosphere it slams into molecules of air. These bounce off of the capsule and in turn slam into the air molecules that were behind them. This creates a shockwave in front of the vehicle. The greatest temperature is at the shockwave, so forming the shockwave farther from the vehicle surface reduces the amount of heating the vehicle experiences. This displacement is related to the shape of the capsule and explains the curvature.

Some heat still makes it to the vehicle surface, and that’s where the ablative heat shield comes into play. As the outer molecules of the heat shield absorb heat, they reach a point where they vaporize and leave the surface of the vehicle. When they do this, they carry away the heat they have absorbed. This phenomenon is called pyrolysis. The next layer then gets hotter and hotter until it vaporizes and takes its heat away. Eventually, the vehicle has slowed to the point where heat is no longer significant and what is left of the outer surface will be relatively cool.

So, the idea is to create a heat shield that has the right curvature, ablative properties, and thickness such that significant heat never makes it to the crew compartment or vital equipment.

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6 Protective Mask Bundles You Can Get On Sale

pinkomelet/iStock via Getty Images Plus
pinkomelet/iStock via Getty Images Plus

Daily life has changed immeasurably since the onset of COVID-19, and one of the ways people have had to adjust is by wearing protective masks out in public places, including in parks and supermarkets. These are an essential part of fighting the spread of the virus, and there are plenty of options for you depending on what you need, whether your situation calls for disposable masks to run quick errands or the more long-lasting KN95 model if you're going to work. Check out some options you can pick up on sale right now.

1. Cotton Face Masks; $20 for 4

Protective Masks with Patterns.
Triple7Deals

This four-pack of washable cotton face masks comes in tie-dye, kids patterns, and even a series of mustache patterns, so you can do your part to mask germs without also covering your personality.

Buy it: $20 for four (50 percent off)

2. CE- and FDA-Approved KN95 Mask; $50 for 10

A woman putting on a protective mask.
BetaFresh

You’ve likely heard about the N95 face mask and its important role in keeping frontline workers safe. Now, you can get a similar model for yourself. The KN95 has a dual particle layer, which can protect you from 99 percent of particles in the air and those around you from 70 percent of the particles you exhale. Nose clips and ear straps provide security and comfort, giving you some much-needed peace of mind.

Buy it: $50 for 10 (50 percent off)

3. Three-Ply Masks; $13 for 10

Woman wearing a three-ply protective mask.
XtremeTime

These three-ply, non-medical, non-woven face masks provide a moisture-proof layer against your face with strong filtering to keep you and everyone around you safe. The middle layer filters non-oily particles in the air and the outer layer works to block visible objects, like droplets.

Buy it: $13 for 10 (50 percent off)

4. Disposable masks; $44 for 50

A batch of disposable masks.
Odash, Inc.

If the thought of reusing the same mask from one outing to the next makes you feel uneasy, there’s a disposable option that doesn’t compromise quality; in fact, it uses the same three-layered and non-woven protection as other masks to keep you safe from airborne particles. Each mask in this pack of 50 can be worn safely for up to 10 hours. Once you're done, safely dispose of it and start your next outing with a new one.

Buy it: $44 for 50 (41 percent off)

5. Polyester Masks; $22 for 5

Polyester protective masks.
Triple7Deals

These masks are a blend of 95 percent polyester and 5 percent spandex, and they work to block particles from spreading in the air. And because they're easily compressed, they can travel with you in your bag or pocket, whether you're going to work or out to the store.

Buy it: $22 for five (56 percent off)

6. Mask Protector Cases; $15 for 3

Protective mask case.
Triple7Deals

You're going to need to have a stash of masks on hand for the foreseeable future, so it's a good idea to protect the ones you’ve got. This face mask protector case is waterproof and dust-proof to preserve your mask as long as possible.

Buy it: $15 for three (50 percent off)

At Mental Floss, we only write about the products we love and want to share with our readers, so all products are chosen independently by our editors. Mental Floss has affiliate relationships with certain retailers and may receive a percentage of any sale made from the links on this page. Prices and availability are accurate as of the time of publication.

What Is the Insurrection Act?

The Insurrection Act gives the president the authority to address domestic disturbances using the military.
The Insurrection Act gives the president the authority to address domestic disturbances using the military.
Tero Vesalainen/iStock via Getty Images

The use of military forces to address volatile situations normally under the purview of law enforcement within the United States is a very rare occurrence, and for good reason. Troops are legally forbidden to be involved in domestic law enforcement affairs without prior congressional authorization.

One loophole does exist. It’s the Insurrection Act, and it empowers the president to dispatch soldiers to combat an insurrection, civil disturbance, natural disaster, or terrorist attack on American soil. But actually invoking the Insurrection Act is no simple matter.

The Act was introduced in 1807 and gives the president the authority to direct American troops to intervene in state-level civil unrest in the event local authorities are unable to control the disturbance. (It was amended in 2006 following Hurricane Katrina to include disasters and terrorism.) It’s used sparingly, particularly as modern police forces have become more militarized. The last time the Act was invoked was in 1992, when riots following the acquittal of four police officers tried in the beating of Rodney King consumed Los Angeles.

At the time, the California governor requested military forces—and normally, the president would activate federal troops at the behest of a governor or state legislature. According to the Los Angeles Times, one exception for dispatching soldiers without state approval is an indication that states are violating civil rights, as was the case for several U.S. presidents (Dwight Eisenhower, John F. Kennedy, and Lyndon B. Johnson) who used military forces to back desegregation in Southern states. Alternately, the president would have to believe such events are interfering with a state’s ability to enforce their laws.

Put simply: Military forces are typically sent at the request of the state, but a request isn’t necessary if the president believes troops are needed to restore order.

When states believe local police are being overwhelmed, their preference is to use the National Guard, which is authorized to act as law enforcement on domestic soil.

If the Act is used, the president would first have to issue a proclamation ordering those involved in any disturbance to disperse. If that fails, the president would issue an executive order to activate the military. States would then likely argue against the intrusion of such forces. It is not clear, however, that they would have the legal justification to prevent such an action if the president calls for it.

[h/t Los Angeles Times]