Conversation-Stopper - Why Don't the Space Shuttle and Space Station Fall to Earth?,Gravity - the attractive force between two masses (or bodies - the product of their masses divided by the square of the distance between the two centers) - does act continually and everywhere; the answer, therefore, is that the Shuttle, Space Station and Moon are each traveling at high speeds and (corresponding) heights, circling Earth, as does the Earth in its orbit around the Sun - and that all are always ""falling around"" the curvature, e. of the Earth. The same is true throughout the universe, and while attractive forces exist between all bodies in the Universe, each to each other, the factor of distance-squared in the denominator effectively eliminates the significance of all other bodies in comparison to the two involved in satellite orbiting. At the completion of the mission, to return to Earth, the Orbiter is slowed slightly - dropping closer to Earth - smashing into individual air molecules, which are ""vaporized"" by the impact - a tiny pulse of both ""drag"" (causing further slowing and lowering of the Shuttle) and also of ""heat"". The concept of the Space Shuttle is remarkably and functionally (and beautifully) simple and reliable - as a result of reliance upon this function of insulation - in an absolutely hostile, unforgiving space environment of cryogenic iciness plus vacuum. The tiles are individually designed for the anticipated reentry temperatures, 6x6 inches in size and average about 1 inch in depth; Inside, they are comprised of extremely long, fine filaments of quartz, compressed into the vacuumized tile volume, with a covering of thin glass. Tile surfaces are relatively easily damaged, the inside appearance likened to white styrofoam - however, when the outside temperature is 3000 degrees F, the backside (attached to the aluminum structure of the Orbiter by ordinary RTV Room Temperature Vulcanizer) - is only 80 degrees F. However, because of the tremendous insulating capability of the tiles, a greatly simplified and reliable Space Shuttle concept has been achievable: The Orbiter vehicle itself was essentially designed and constructed much as a conventional aircraft - its only flight function, landing after reentry, uses conventional flight controls, tires and brakes (the landing speed is similar to a commercial jet aircraft, about 160 mph). The most powerful and efficient rocketry arrangement is therefore designed for the lift-off sequence: two solid rockets (approximately twelve feet in diameter), plus the three Orbiter engines (fueled by the large center fuel-oxidizer tank); all five are fired simultaneously for maximum thrust at lift-off (approximately seven million pounds thrust required) - along with the giant ground-retention explosive bolts at the base of the solid rockets (only attachment of the entire assemblage to the launch platform). A human-interest worry about mankind's 21st century ""Space adventures"" is space debris - the remains of space-hardware rocketry that have not, as yet, returned to Earth. The larger ones are monitored - just recently, March 5, 2009, warnings about a possible strike of the International Space Station forced the US astronauts to take shelter in the parked Russian Soyuz capsule. The NASA Orbital Debris Program Office is at Johnson Space Center, reporting that about 13,000 such threats are constantly tracked, of about 600,000 total debris items.