Aaron Brackett posted on the specifics of NASA’s UARS satellite crashing to earth later this week.
However, a few of you have asked “Why do things ‘burn up’ on re-entry? Is the temperature of the atmosphere that warm?” Actually, more so than the relatively cool temperature of the atmosphere is the frictional properties of re-entry as an object moves into the atmosphere at thousands of miles per hour.
You could set a fragile crystal wine goblet into the vacuum of space and (if set high enough from earth’s gravity) could remain for thousands of years. However meteors and satellites that succumb to the effects of earth’s gravity will fall toward earth. As these objects fall into the upper levels of the atmosphere they are greeted by air. The air in front of the object quickly compresses and heats up rapidly, in some cases to temperatures more than 3,000°F! Most meteors are small enough that they burn up entirely. At night these are observed by most often as “shooting stars.” In some cases a tiny fraction of the meteor’s material will make it through the lower atmosphere and to the earth’s surface.
NASA’s Space Shuttle system had heating tiles that allowed the air to heat the tiles without damaging the materials under them. This system proved successful until a crack caused Space Shuttle Columbia to burn up on re-entry, crashins in East Texas in 2003. The crash killed all astronauts aboard.
The UARS satellite is obviously very big…about the size of a school bus. It’s for this reason scientists are forecasting several pieces to make it to the ground. In fact, the process of this thing falling through the atmosphere may light up the night sky quite brilliantly.
It is not yet known the remaining pieces of UARS will land but NASA says it could happen between Thursday night and Saturday morning, USA time.
The pieces have a 1:3,200 chance of striking a human being. Although debris from Space Shuttle Columbia was strewn over hundreds of square miles without injuring anyone in East Texas.
Side note: Newer satellites are designed to burn up completely on re-entry. NASA has a plan for The International Space Station (the largest man-made structure ever to orbit the planet) to bring it down in about 10 years (or when it’s usefulness is deemed small enough).
Historical re-entries include Russia’s “Mir” station which came down during 2001. Older folks may well remember “Skylab,” a satellite that was hurled harmlessly into Australia and the Indian Ocean in July 1979, not before touching off a firestorm of worried humans all over the globe. -ES
This post was written by Eric Sorensen on September 20, 2011