The launch of NASA’s twin GRAIL spacecraft

The U.S. Air Force on Thursday demolished towers once used to assemble Delta 2 rockets at Cape Canaveral for missions to Mars, four dozen flights to deploy the GPS navigation network, and numerous launches with scientific, commercial and military payloads.

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.

Flying for the 155th and final time, a United Launch Alliance Delta 2 rocket took off from California on Sept. 15 with NASA’s ICESat 2 satellite.