NASA's Space Launch System rocket uses components from Apollo, the Space Shuttle, and newly developed spacecraft hardware and is built to go farther than ever before. Its first mission is planned to explore a near-Earth asteroid in the mid-2020s. The Orion Multi-Purpose Crew Vehicle can transport four crew members beyond low-Earth orbit and provide a safe habitat from launch through landing and recovery. The solid rocket boosters stand 17 stories tall, burn approximately six tons of fuel every second, and each generates more thrust than 14 four-engine jumbo commercial airliners. Propulsion for the SLS core stage will come from four RS-25 engines upgraded from the space shuttle program. Exploration Mission-1, then targeted for 2018, was to be the first flight atop the Space Launch System, during which an unscrewed Orion would travel to a stable orbit around the moon. It was to be followed by the Ascent Abort-2 test flight and then the first crewed flight with Orion and SLS for Exploration Mission-2, then scheduled for 2021. The Space Launch System rocket carrying Orion will measure 200 feet by 27.5 feet and will contain liquid hydrogen and liquid oxygen to feed the rocket's RS-25 engines.