Fri Apr 27, 2012, 02:50 PM
steve2470 (25,123 posts)
When the Space Shuttle Buzzed New York City: How Did They Do That?
What was needed was another, even bigger flying machine to carry it around, and the obvious choice was the 747 — sturdy enough for the job, powerful enough for the job and, best of all, a vehicle NASA wouldn't have to build from scratch. The first challenge designers faced when figuring out how a passenger jet could shuttle a shuttle was the unforgiving arithmetic of weight. A fully fueled 747 loaded with seats, passengers, crew, luggage, bathrooms, galleys and overhead bins tips the scales at about 800,000 lbs. (363,000 kg). Pop a shuttle on the top and you come perilously close to a full million pounds. That's bad news since a 747 can't leave the ground if it weights more than 833,000 lbs. (379,000 kg).
Some of that problem solves itself, since you're hardly carrying a load of people on a shuttle ferry flight. But more weight has to be shed still, and the interior of NASA's 747s are thus stripped back to little but cockpit and raw fuselage. That gets the plane down to a nimble 490,000 lbs. (222,000 kg). Even with the shuttle attached, it can still make weight.
Actually hoisting an orbiter onto the back of the aircraft is no small job either. For this, NASA uses what it unpoetically calls a mate-demate device, essentially an erector set of scaffolds and three cranes, each of which can lift about 100,000 lbs. (45,000 kg). Two of the cranes are attached to the shuttle's tail and one to its nose; it's then lifted off the ground and the 747 rolls in under it. The positioning has to be precise, because the hoists can do little more than, well, hoist.
"The lift is actually the biggest challenge," said Casey Wood, an engineer who helps oversee the mating and demating. "With our lift we can only go directly up or directly down. It's strictly vertical; there's no lateral movement."
Interesting stuff indeed.
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