 Four, six or nine Castor-2 solid rocket boosters were attached to increase thrust at lift-off.These improvements permitted the Delta 1000 series to lift 1,835 kg (4,045 lbs) to LEO or 635 kg (1,400 lbs) to GTO.The nickname "Straight-Eight" comes from the fact that its second stage variants had the same 8 ft. (2.4 m) diameter as the first stage; previous Delta second stages were smaller in diameter.