The critical phase of launch is during the first three minutes, where the atmosphere is thick enough to accelerate any falling debris very quickly to dangerous impact speeds. Even the smallest chunk of foam can penetrate the orbiter's heat resistant tiles and cause fatal damage, simply due to the sheer speed the Shuttle is travelling. With a final destination orbital speed of 17,500mph (yes, 17 thousand five hundred) the orbiter needs a flawless shield to prevent superheated plasma from entering the vessel and literally melting its innards.
Yesterday's night launch provided a perfect opportunity to see the orbiter surrounded by glowing plasma as it reached orbit. The sight is similar to an aurora, with flashing colours and green curtains of light dancing around the Shuttle. At its initial orbit insertion, the Shuttle is still inside the atmosphere, but it is literally trace molecules. Even up there there is turbulence, and each time the orbiter passes through a wisp of thin air, its sheer speed ignites the molecules into glowing plasma.
I have often been asked why re-entry is so dangerous. Well, think about it... it took all that fuel and energy to get the Shuttle up into orbit, and now it has to slow down from, yes, 17,500 mph, using only drag from the atmosphere! The Shuttle has a propulsion system that fires to slow it down enough to drop into the thicker air, but that's all. If you have ever put your hand outside the window of a car travelling at 70mph you'll know how much energy there is in fast flowing air. Puting your hand out into the window at slow speeds isn't dangerous, but putting it out 17,500 mph most definately is!
Well, that's it for now... Happy Spacing, Spacers!
Posted by SpaceHead at 5:20 PM