Total Mass, Payload Fraction.
obv. Big Brother 'cause surveillence,
"Virgin Galactic's not saying what LauncherOne weighs"
Fortunately you can read that important detail in the online article
"Virgin Galactic Reveals Boeing 747 For LauncherOne" from Aviationweek
They claim
"55,000-lb. rocket", "400-kg satellites into high-altitude, sun-synchronous orbits"
880lbs gives a 1.6% payload fraction.
Not bad considering they are not using a 'high energy' upper stage, just kerolox.
Biting the hand that feeds IT
