Re-entry into Earth’s atmosphere

In the last couple of days, I have been doing a bit of research on re-entry into the Earth’s atmosphere. Meteorites burn up when they fall into the Earth’s atmosphere, this basically has to do with the sheer size of the meteorite and kinetic energy, you know, because the large meteorite is going incredibly fast. So when a meteorite enters the Earth’s atmosphere, most of the heat is due to the air that the meteorite runs into. In a sense, the air does not have time to get out of the way, so the air starts to compress and heat up. We’re talking temperatures exceeding 3,000 degrees. Now if the meteor happens to be small enough, then it will burn up entirely before reaching the lower atmosphere.

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Image from http://managementscience.biz

So that got me to thinking, what about all of the satellites up there? They don’t stay up there forever, right? So do they just completely burn up when eventually falling back to Earth? Well a little more research and I found that the newer satellites are actually designed to burn up completely upon re-entry. And the older ones? Well if they are big enough, most of the satellite will burn up, but some of the remaining pieces will actually land on Earth. Let’s take the NASA satellite UARS (Upper Atmosphere Research Satellite) for example. This 6.5 ton satellite actually plunged to Earth in 2011. Luckily UARS crash-landed into the South Pacific Ocean. UARS was not the first, or the last piece of man-made space hardware to come crashing back to Earth. Take the International Space Station for example, a gigantic structure. After a little more digging, I found out that NASA is planning on deorbiting the Space Station in a “controlled way”. What does that mean? Well just your typical debris shower of course, but the debris will be aimed at the ocean.

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Image from http://en.wikipedia.org

So that now leads me to the main question that had me once again Googling like crazy. How then does a spacecraft re-enter Earth’s atmosphere and the astronauts live to tell about it? The first answer that kept popping up was heat shields. Well, that and the shape and angle of the spacecraft entering the Earth’s atmosphere. So back in the early 1950’s the National Advisory Committee for Aeronautics stated that the shape of the aircraft actually lowered the heat load. One quote on-line said that “The air molecules cannot get out of the way quickly enough and actually serve as a cushion”.

In order to slow down, as the spacecraft leaves orbit, it fires its thrusters and the spacecraft is then flown backward for a period of time. After it is safely out of orbit, the spacecraft turns nose-first again and enters the atmosphere. The leading edges and nose of the spacecraft use something called RCC (Reinforced Carbon-Carbon) material. They say this material can sustain re-entry heat due to its high heat capacity. Boy, I hope so, we’re talking about temperatures in excess of 3,000 degrees. The material also includes high-temperature black surface insulation tiles on the upper fuselage around the windows. The spacecraft must enter the Earth’s atmosphere at 40 degrees attitude.

Author: Claude