Re: Spaceplane carrier
"No idea, why don't you ask Richard Branson why the f**k he commissioned White Knights One and Two? It obviously wasn't to launch SpaceShips One and Two"
...And strangely enough they desided to drop the rocket/spaceplane DOWN at launch, rather than carry it on top and hope it will not touch something important before it starts to climb.
PiggyBack spaceplanes are a way to TRANSPORT a spaceplane from one site to another, not for launching (SR 71 /D21 excluded for good reasons).
So WHY do you wish to carry a spaceplane on top of an A380 again?