Help does metal burn in the atmosphere?

Question

My mom thinks that no one has ever been to the moon...and no one has ever been to space for that matter. She thinks that if rocks burn in the atmosphere that everything else would too. Can someone help me explain to my mom that rock and metal are two different substances, meaning that one has a higher tolerance towards heat and friction?

Thanks,

K

Answer 1

She needs to learn ablative cooling.  The idea is that the outer layers get hot and fall off, carrying much of the heat with them.  That keeps the lower layers cool.  For Apollo, the heat shield was fairly thin, maybe only 6 inches or so.

It may interest you that the Apollo capsule's descent wasn't just descent.  They could steer it, and in fact were able to bring it into a climb while still quite high up.  The longer rollercoaster ride allowed them to get rid of a considerable amount of speed while still in fairly thin atmosphere. This keeps the peak temperature down.

NASA has a video which describes this in detail.  I've no idea how to get my hands on it.

Answer 2

http://en.wikipedia.org/wiki/Mohs_scale this link will should show the difference between the levels of hardness of the rock and of the metal, now from what i read stuff floats around in orbit at about 17,000 mile per hour so when a piece of metal or rock enters the atmosphere at that speed both are going to get hot now metal has a better chance of surviving an atmospheric reentry because the the density of the metal as opposed to a piece of rock.

Answer 3

Hopefully you and your mother can agree to disagree on this.

It sounds like you're asking whether metal spacecraft would burn up in re-entry, and wondering why rocks do.

The answers are pretty simple.

First, not all rocks burn up as meteors.  What we have on the Earth as meteorites, oddly enough, are those made mostly of iron.  Heavy, dense materials survive heating in air.

Speed is important.  Incoming meteors travel very fast.  The faster something moves through air, the more energy is created by the air's action against the object.  First, the object pushes air ahead of it and compresses it.  As you may have learned in school, when you compress a gas, it heats up.  That's the principle effect, which is why the surfaces of spacecraft that most directly face the oncoming air are the most protected.

Second, air sliding across the surface of the object creates friction, just like rubbing two solid surfaces generates heat between them.

Spacecraft don't generally travel as fast as meteors, and so there's less energy for them to have to deal with as heat.

Now onto materials.  The parts of the spacecraft that deal most with heat aren't metal.  The space shuttle uses an exotic method of heat management -- those silicon tiles you've read so much about.  They accept and store heat, releasing it later very slowly.  It's really a kind of ceramic.  So they accept and store up a lot of the heat of re-entry and release it later.

But they also simply don't transmit heat very well.  Every substance has either a good or a bad ability to transmit heat.  Your cast iron skillet does, which is why its handle is hot.  A wooden stick doesn't, which is why you can hold one end of it and stick the other end in a fire.  It's okay for the outer surface of these materials to get very hot during re-entry, so long as it doesn't transmit heat to the more sensitive interior portions of the ship.

An older method used a phenolic resin (that's engineering talk for "goop") injected into a honeycomb of aluminum.  That's what Apollo heat shields were made of.  That was developed for the heat shields of re-entry vehicles for nuclear warheads.

In this method, the resin (which dries hard like a varnish) heats up and turns to gas in response to aerodynamic heating.  The act of turning from solid to liquid to gas eats up some heat for every unit of mass it happens to.  So you start with ten or twelve inches of the stuff at the start of re-entry and it gets worn down to four inches at the end.  Any design that does this is called an "ablative" heat shield.

But there's a secondary effect too.  The gas that's created has very poor heat transfer properties.  And so a constantly-renewed thin layer of this gas sits between the heat shield and the superheated bow wave of air trying to get out of the way and getting compressed instead.

When you're done you have a charred underside to your spacecraft, so this kind of shield can obviously only be used once.

We create these synthetic materials either by chemical processes or by refining minerals to obtain them in more pure forms so that their desirable properties are amplified by concentration.  This differs substantially from naturally-occurring minerals that don't necessarily have the proper strength or heating properties in their natural forms.

Answer 4

1) Not all meteors burn up.

2) It isn't actually burning itself up, it is heating up due to the friction until its surface vaporizes.

3) An object can't burn up leaving the atmosphere as you have drag and gravity slowing you down... its hard enough just resisting gravity let alone leaving quickly enough to burn up.

4) Reentry craft are designed for the task of resisting the heat of a controlled reentry by taking the perfect trajectory to the Earth so as to produce the least amount of heat while not bouncing off the atmosphere. The bottoms of the craft are also covered in heat shielding. The individual tiles that make up the heat shield can be heated to whiteness and then be picked up within seconds by the uncovered hand... its the wonders of modern material science.

Answer 5

The Van Allen radiation belt is what surrounds the planet and the ozone is what protects us from it. Anything up there has to have a high temperature resistance to avoid being incinerated. Meteors have to be a certain size or they'll just break apart. They are pretty much frozen from being in space and get heated up from friction and the radiation coming through the sky. Where as metal that is sent up there undergoes a bunch of test that will ensure its durability.

Answer 6

The spaceships do not burn up because they have heat shielding materials on the outside, and they enter the atmosphere at a speed low enough to prevent incineration.    Give the scientists some credit for knowing what they are doing.   Anyone who does not believe in the accomplishments of the space program is poorly informed about the facts.    Why don't airplanes burn up in the atmosphere?    Their speed is too low!