Assignment:

Please read the given news and prepare 2 (two pages) about:

1) How we put satellites in orbit and

2) Why satellites should eventually fall back to earth.

http://news.yahoo.com/nasa-gives-1-hour-window-falling-satellite-030650758.html

CAPE CANAVERAL, Florida (AP) — The 6-ton NASA satellite on a collision course with Earth clung to space Friday, apparently flipping position in its ever-lower orbit and stalling its death plunge.

The old research spacecraft was targeted to crash via the atmosphere sometime Friday night or early Saturday, putting Canada and Africa in the potential crosshairs, though most of the satellite should burn up during re-entry. The United States was not entirely out of the woods; the possible strike zone skirted Washington State.

‘It just doesn't want to come down,’ said Jonathan McDowell of the Harvard-Smithsonian Center for the Astrophysics.

McDowell state the satellite's delayed demise describes how unreliable predictions can be. That said, ‘The best guess is that it will still splash in the ocean, just because there is more ocean out there.’

Until Friday, increased solar activity was causing the atmosphere to expand and the 35-foot, bus-size satellite to free fall more rapidly. However late Friday morning, NASA said the sun was no longer the main factor in the rate of descent and that the satellite's position, shape or both had modified by the time it slipped down to a 100-mile orbit.

‘In the last 24 hrs, something has happened to the spacecraft,’ said NASA orbital debris scientist Mark Matney.

On Friday night, NASA said it predicted the satellite to come crashing down between 11:45 p.m. and 12:45 a.m. EDT Saturday. This was going to be passing over the Atlantic, Pacific and Indian oceans at that time, and also Canada and Africa.

‘The risk to public safety is very remote,’ NASA said in a statement.

Any surviving wreckage is expected to be limited to a 500-mile swath.

The Upper Atmosphere Research Satellite, or UARS, will be the biggest NASA spacecraft to crash back to Earth, uncontrolled, as the post-Apollo 75-ton Skylab space station and the more than 10-ton Pegasus 2 satellite, both in 1979.

Russia's 135-ton Mir space station slammed via the atmosphere in 2001; however it was a controlled dive into the Pacific.

Some 26 pieces of the UARS satellite - representing 1,200 pounds of heavy metal - are expected to rain down somewhere. The biggest surviving chunk should be no more than 300 pounds (that is, 136 kilograms).

Earthlings can take comfort in the fact that no one has ever been hurt by falling space junk - to anyone's knowledge - and there has been no serious property damage. NASA put the chances that somebody somewhere on Earth would get hurt at 1-in-3,200. But any one person's odds of being struck were estimated at 1-in-22 trillion; given there are 7 billion people on the planet.

‘Keep in mind that we have bits of debris re-entering the atmosphere every single day,’ Matney said in short remarks broadcast on NASA TV.

In any case, finders definitely are not keepers.

Any surviving wreckage belongs to the NASA, and it is against the law to keep or sell even the smallest piece. There are no toxic chemicals on board, however sharp edges could be dangerous, so the space agency is warning the public to keep hands off and call police.

The $740 million UARS was launched in the year 1991 from space shuttle Discovery to study the atmosphere and the ozone layer. At time, the rules were not as firm for safe satellite disposal; now a spacecraft should be built to burn up upon re-entry or have a motor to propel it into a much higher, long-term orbit.

NASA shut UARS down in 2005 after lowering its orbit to hurry its end. The potential satellite-retrieval mission was ruled out following the 2003 shuttle Columbia disaster, and NASA didn’t want the satellite hanging around orbit posing a debris hazard.

Space junk is a growing problem in the low-Earth orbit. More than 20,000 pieces of debris, at least 4 inches in diameter, are being tracked on a daily basis. Such objects pose a serious threat to the International Space Station.