( CNN ) -- It was a strange sight indeed -- one large aircraft carrying another large aircraft strapped on top . But that 's exactly what skyward-looking folks in Washington saw Tuesday as Space Shuttle Discovery , atop a Boeing 747 , made an inspiring pass over the capital in its final flight . It makes you wonder : How can the 747 transport something that big and heavy ? Well , the shuttle-airliner combo is not as heavy as you might first think . In fact , it 's a relatively easy load to hoist . When the shuttle missions started in the 1980s , NASA designated several places as landing strips for the orbiter , including Edwards AFB in California . Discovery taken its final destination , a Smithsonian museum . But all the launches were from Florida , so NASA needed a way to transport to Kennedy Space Center from Edwards . A shuttle ca n't fly itself after it leaves orbit , as it is basically a big glider . So NASA created the designed the Shuttle Carrier Aircraft , which is a Boeing 747 designed to fly with a shuttle on top . All that 's well-known , at least to space buffs . But what may surprise many people is that a Boeing 747 with a space shuttle strapped on its roof weighs less -- that 's right , less -- than a 747 airliner full of passengers . At first that might seem counterintuitive , but Lisa Malone , a spokeswoman for NASA , says the 747 they use is stripped clean of anything in the main cabin . There 's a cockpit and a big empty shell . But the 747s used by airlines have hundreds of seats , galleys , lavatories -- even a bar in some cases . Add 300-plus passengers , their luggage , food , water and assorted other cargo , and the weight adds up . Capturing Discovery 's final flight . The 747 that carried Discovery weighed about 488,000 pounds . Jim Proulx , a spokesman for Boeing , says a commercial 747 airliner can weigh more than 800,000 when carrying passengers . There will be another chance to see the Shuttle Carrier Aircraft in action later this week . That 's when it will carry Space Shuttle Enterprise , which was used for tests but never flew in space , will be flown from Dulles International Airport in Virginia to its new home on board the USS Intrepid , a retired aircraft carrier turned floating museum in New York City .
Shuttle Discovery hitches ride atop a Boeing 747 to Washington . The load is not as taxing on the specially outfitted 747 as you might first think . A regular 747 carrying a full complement of passengers is much heavier .