Launching the commercial WorldView 4 Earth-imaging satellite for DigitalGlobe, a United Launch Alliance Atlas 5 rocket thunders away from California’s Vandenberg Air Force Base today at 10:30 a.m. local time (1:30 p.m. EST; 1830 GMT).

The launch of a Boeing-built Mexican communications satellite on a Proton rocket has been postponed after engineers discovered an anomaly on a similar spacecraft.

This is our comprehensive fact sheet previewing the United Launch Alliance Atlas 5 rocket deployment of the classified NROL-42 payload for the National Reconnaissance Office.