Tier 1b is the suborbital commercial human spaceflight platform being developed by The Spaceship Company (TSC), a joint venture of Scaled Composites and Virgin Galactic. It is an evolutionary development of Tier One, the Ansari X-Prize-winning entry in the 2004 spaceflight demonstration contest held by the X-Prize Foundation. Tier 1b's primary components are the White Knight Two carrier aircraft and the SpaceShipTwo suborbital spaceplane, which is expected to begin flying space tourists to suborbital altitudes in 2014.
Read more about Tier 1b: SpaceShipTwo, White Knight Two, See Also