The Mir space station has been sailing through space, circling the Earth for 15 years, but the last chapter of its adventure is about to be written.  This week the Russian Space Agency is maneuvering Mir toward the Earth's atmosphere, dooming the craft to a fiery end in the South Pacific Ocean.

Mir weighs 135-tons, making it the heaviest thing orbiting our planet other than the Moon.  As it falls to Earth on March 23rd most of Mir's many parts will burn like fireworks in the Earth's atmosphere.  It will be moving at more than 15,000 miles an hour as it enters the air and heats up -- but some pieces may survive the dive to make one last splash into the ocean, slowed down to only 100-150 mph when they hit! 

This event will be big news -- and rightly so.  Since being built in orbit starting in 1986, Mir has set endurance and space-excitement records that will be hard to beat.  It survived a fire, collisions with spacecraft, and even attacks on its wiring by microbes that ate metal and glass!  Mankind learned a lot from Mir about how to live and work in space.

Mir doesn't work very well after so much wear and tear, and its orbit is failing.  It has been replaced by the new International Space Station, where the USA, Russia and more than a dozen other countries work together.  So Russia has decided to bring Mir down into the ocean in a controlled re-entry so its pieces won't hit places where people live. 

But among scientists who keep a check on what's flying around near planet Earth, a 135-ton object zooming in from space is not so unusual.  

"Asteroids weighing as much as Mir hit Earth maybe 10 times each year," says Bill Cooke of the Space Environments team at NASA's Marshall Space Flight Center.  "Military satellites record the flashes of their explosions in the upper atmosphere." 

Just last year a 200-ton asteroid startled people in Canada with a loud sonic boom and a brilliant fireball as it blew apart high in the sky.  Scientists later found some small meteorites on the ice of a nearby lake, but none larger than a few hundred grams.

"If a rocky asteroid the same size as Mir actually hit solid ground, it would explode like a few thousand tons of TNT, gouging out a crater about the size of a football field," noted Bill.  But Mir will never make it that close to the ground, he says.  "The atmosphere is very good protection, and it breaks up meteorites and other space objects well before they can hit the Earth." 

In fact, if Mir were an asteroid, it wouldn't even be called a hazard.  Compared to real trouble-makers from space, Mir is simply too small.  Yet scientists do expect the space station to put on a good show when it returns! 

Mir is built like an erector set.  It is a gangly-looking bunch of solar panels, labs and living quarters -- not designed for smooth flight through the air.  The station will fall apart quickly as it dives toward Earth. 

"We expect Mir to break into six or more main pieces when it hits the thicker air," says Nicholas Johnson of NASA's Johnson Space Center, where he is in charge of studying objects in orbit. 

"Each piece will resemble a blazing meteor that spits out smaller fireballs as the parts crumble and burn," Nicholas explains.  "Of Mir's 135 tons, the Russians say about 20 tons might reach the surface -- mostly in small bits." 

Mir's major sections include the large 20-ton Core with the crew's living quarters, plus the 19-ton Spektr science lab and the 19-ton Priroda observatory, which is only five years old.  

Mir is sinking lower by about one mile each day as the air drags on it more and more.  If left alone, the station would naturally plunge to Earth from its 155 mile orbit no later than March 28th.  That could be dangerous.  Instead, Mir will be guided to its final resting place by a Progress spacecraft that is already attached to the station. 

"On March 23rd, Russian ground controllers plan to fire the Progress engines to move Mir down inside the atmosphere above the South Pacific," explained Nicholas.  "That's where any pieces that don't burn up will land.  There will be essentially no risk of harm to people or property." 

No one knows more about dumping spacecraft in the remote Pacific waters than the Russians.  Since 1978 they've brought down 80 Progress spacecraft and five Salyut space stations, all in the same area where Mir will fall. 

Mir's dazzling finale won't be seen by many people, but that's OK -- because nobody would want to be under its path!  But there's still time to see Mir from the safety of your own back yard.  The fast-moving space station reflects sunlight -- and if you're outside at the right moment (usually near local dusk or dawn), Mir might look as bright as some of the brightest stars in the sky. 

This famous Russian space station is easy to see -- but don't wait!  The end of Mir is near.  

Editors: Gil Knier  &  Becky Bray