The Space Launch System (SLS), the heavy-lift rocket NASA is building at the behest of Congress to support future deep-space exploration missions, recently cleared two key milestones in its early development process, the space agency said.

The system requirements and system definition reviews set down the cost, schedule, performance and design requirements for the future heavy lifter, NASA said in a July 25 press release. Having passed these reviews, the SLS can proceed toward its preliminary design review, which is scheduled for late 2013, NASA said.

SLS is being built to launch the Lockheed Martin-built Orion Multi-Purpose Crew Vehicle. Both craft are being built according to concepts that originated in the now-canceled Constellation lunar exploration program.

For its first two missions, now scheduled for 2017 and 2021, an initial SLS variant capable of boosting 70 metric tons to orbit will send Orion around the Moon and back. Only the second mission will be crewed.

Boeing Space Exploration of Houston is building the SLS core and upper stages and supplying the rocket’s avionics package. The first stage will be powered by a pair of five-segment solid-rocket boosters from ATK Space Systems of Magna, Utah, and a cluster of four space shuttle main engines from Pratt & Whitney Rocketdyne of Canoga Park, Calif. The rocket’s second stage initially will be powered by a modified Delta 4 upper stage provided by Boeing. Future variants of the SLS will have a second-stage propulsion system based on the Apollo-heritage J-2X being developed by Rocketdyne.



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