The satellite is equipped with the Advanced Topographic Laser Altimeter System (ATLAS), which will send pulses of laser light down to Earth and record how long the laser light's photons take to bounce back to the satellite. That information can then be converted into a measure of height. ATLAS will send 10,000 pulses per second, with each pulse containing around 20 trillion photons. Only a dozen or so will make it back up to ICESat-2, however, a trip that will take around 3.3 milliseconds total. The satellite will make a full orbit around Earth every three months, allowing it to collect measurements every season.

NASA plans to launch ICESat-2 at 5:46 AM Pacific on Saturday, September 15th. It will launch aboard a Delta II rocket from Vandenberg Air Force Base in California. You'll be able to watch it live here.