Scientific Satellites

Science satellites carry out a range of tasks to observe objects and phenomena in space. They have transformed many scientists’ views of the universe. Science satellites’ instruments often measure radiation in various forms. IRAS (Infrared Astronomical Satellite) was launched in 1983. In its ten-month lifespan, it discov­ered 20,000 galaxies (including a new kind called a starburst galaxy), 130,000 stars, and a comet. In 1999, the Space Shuttle Columbia launched an X-ray observatory named Chandra. It has an unusual elliptical orbit that brings it to

SPACE JUNK

Old satellites and leftover pieces of satellite launch vehicles end up as trash drifting in space. Space junk is heaviest at a height of around 530 miles (850 kilometers), where most satellites orbit. After a half-century of space launches, there is now a lot of space junk. Scientists have recorded at least 11,000 objects larger than 4 inches (10 cen­timeters) in diameter. The junk includes used-up rocket stages, tools lost by astronauts, and lumps of solidified fuel. Space junk is a potential hazard, since a lump of fist-size debris, traveling at more than 21,000 miles per hour (33,800 kilometers per hour), can make a serious hole in an expensive spacecraft.

within 6,000 miles (9,650 kilometers) of Earth and then swings out to 86,000 miles (about 138,400 kilometers)-about a third of the way to the Moon. Each orbit takes 64 hours. Being so far out means Chandra keeps clear of the belts of charged particles that surround Earth and so provides astronomers with longer peri­ods of clear observation time.

SEE ALSO:

• Gravity • Rocket • Space Probe

• Space Race

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