Photos: Atlas 5 rolls out for launch

Liftoff of an Ariane 5 rocket from a tropical launch pad in South America was halted moments after its main engine ignited Tuesday in a rare last-second abort for the heavy-lift launcher.

The satellite awaiting launch early Saturday from California aboard the final flight of the venerable Delta 2 rocket should allow scientists to more precisely track changes in our planet’s ice sheets, using six green laser beams to chart the height and slope of polar ice and glaciers, providing a key input into climate change research.

A Boeing-built communications satellite for the Mexican government is set for liftoff Saturday from the Baikonur Cosmodrome in Kazakhstan aboard a Russian Proton rocket.