SCA interior

Even with a stripped-down interior, a Shuttle Carrier Aircraft weighs in excess of 250,000 or even 300,000 pounds, while the shuttle that it's toting can weigh upward of 176,000 pounds. That payload means the SCA can burn 40,000 gallons of fuel per hour, double what it expends when unburdened.

"It's brute force that keeps us flying," Larry LaRose, an SCA flight engineer, said in the 2005 NASA article. "When we're carrying an orbiter, we have to use twice the power and a lot more fuel to maintain flight."