Stats: Atlas 5 and Delta 4 histories and backlogs (updated April 20)

Following delivery to the launch pad, the United Launch Alliance Atlas 5 rocket stands poised for the NROL-61 mission for the National Reconnaissance Office from Cape Canaveral on Thursday morning.

Technicians planned to attach two Boeing-built communications satellites to a SpaceX Falcon 9 rocket Monday, a day after launch controllers fueled the rocket and fired its nine Merlin first stage engines in a key preflight test.

NASA managers Thursday cleared the $1.5 billion Parker Solar Probe for launch early Saturday on a daring mission to “touch the sun,” repeatedly flying through its outer atmosphere to find out why the blazing corona is millions of degrees hotter than our star’s visible surface.