At 28 feet (8.5 meters) in length, 8.8 feet (2.7 meters) in height, and 27 feet (8.2 meters) in width, which is the distance between the tips of SpaceShipOne’s horizontal stabilizers, the spacecraft is only slightly smaller than the Bell X-l. Table 4.1 shows a size comparison between SpaceShipOne, the X-l, the X-l5, and the Space Shuttle. Although the width of SpaceShipOne is slightly wider than the wingspan of the North American X-l5, it is about half the length of the X-l5. Every time SpaceShipOne flew, it had a different weight. The final spaceflight was
the heaviest, with an empty weight of 2,646 pounds (1,200 kilograms) and maximum weight of 7,937 pounds (3,600 kilograms).The weight advantage of SpaceShipOne was clear when compared to the gross weights of 12,250 pounds (5,557 kilograms) and 38,000 pounds (17,237 kilograms) for the X-l and X-l5, respectively.