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Space Launch System passes major design milestone

The Space Launch System (SLS) has passed preliminary design review (PDR), a crucial design step for the rocket.

The PDR applies to the initial version of the rocket, dubbed 1A, which will use a Rocketdyne RL-10-powered Delta Cryogenic Upper Stage as an interim and solid rocket boosters adapted from the Space Shuttle. The 1A, which will be capable of lofting 70mt into low Earth orbit (LEO) will make one flight in 2017 before replacement by the 1B. The 1B will include a Rocketdyne J-2X-powered upper stage and as-yet-unselected advanced boosters, and is currently scheduled to fly in 2021.

"This may be the most important review we go through, and I say that because now's the chance to make any changes we'd like to make without significant cost to the programme," says Gary Lyles, SLS chief engineer. "Coming out of this review, we feel good, we're ready to go forward.with the margin to do any of the design reference missions."

Eventually a Block 2 version is planned to enter service, capable of lifting 130mt.

Subsystem and component-level PDRs have been ongoing for some time; the core stage, the main part of the launch vehicle, reached PDR in December 2012, and the interim solid rocket boosters in April 2013. Adapting previously-designed and -built components has allowed the SLS team to move faster through reviews than its predecessor programmes.

SLS is designed specifically to launch the Lockheed Martin Orion capsule on crewed journeys beyond LEO, the first such flights since the Apollo moon landings. Though the 2017 flight will be uncrewed, it will likely launch Orion on a cislunar flight to test its equipment.

Orion is scheduled for a first flight in 2014 atop a United Launch Alliance (ULA) Delta IV. Though incapable of launching the heavy capsule beyond LEO, its reentry from a highly elliptical orbit will allow it to achieve speeds simulating a return from lunar orbit.

The 2017 flight will likely involve entering a retrograde orbit around the moon before returning.

Despite its capabilities - when it flies it will be the most capable operational rocket on the planet - there are no operational missions assigned, leading to criticism that the rocket is being built for political purposes instead of a defined scientific requirement. The rocket is called the Senate Launch System by some, alluding to its fervent supporters in Congress.

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