Virgin Galactic's SpaceShipTwo could launch into space 'within weeks'

The VSS Unity is a spacecraft designed to carry two crew members and six passengers. It is launched into space using a carrier aircraft called White Knight 2. Once at a certain altitude, the VSS Unity is released, and its rocket engines are activated to reach a height of 100 kilometers, marking its entry into space.

At what altitude does the VSS Unity's rocket engines fire up?

What is the minimum height the VSS Unity must reach to be considered in space?