cdr design

SLS passes milestone as Critical Design Review is completed.

Marking a significant milestone in NASA’s human exploration of the solar system, the Space Launch System rocket completed its Critical Design Review in July. The final step of the review was announcing the results to NASA, which occurred earlier this week (October 22, 2015).

This is the first time in nearly 40 years that a human-rated rocket has passed the CDR phase of development, and the only exploration-class vehicle to do so since the Saturn V.

The CDR finalizes the design for the rocket and sets a more reasonable timeline for the vehicle’s manufacture, assembly and integration.

For the CDR, the initial version of the SLS was under review. SLS Block 1 is capable of launching 77 tons of payload into Low Earth Orbit. It will utilize two, five-segment Solid Rocket Boosters, four RS-25 engines in the core stage, and the Interim Cryogenic Propulsion Stage. The ICPS is a modified Delta Cryogenic Second Stage already flying on Delta IV vehicles.

The RS-25 engines are leftover from the Space Shuttle program, and are undergoing modifications and testing for SLS. The five-segment SRB’s have been modified as well, with the QM-1 test earlier this year the first of two flight simulation firings.

SLS Block 1B will see the Interim Cryogenic Propulsion Stage replaced with the Exploration Upper Stage, allowing for a baseline LEO capability of 115 tons. The EUS will consist of four RL-10 engines. Block 1B will be introduced on the vehicle’s second flight, Exploration Mission 2, in 2021.

SLS Block 2 will see newly designed solid or liquid boosters replacing the five-segment SRB’s. It will be capable of lofting 148 short tons into LEO.

The most visible change to the rocket’s appearance that came from the CDR was the removal of white paint on the core stage that was considered since the vehicle’s inception in 2011. Painting the vehicle would add thousands of pounds of extra weight that could be used elsewhere. The natural orange insulation will be left exposed.

Now that the Critical Design Review is complete, the next milestone for the SLS program is the design certification. This is completed once the rocket is manufactured, assembled and integrated at Kennedy Space Center. The design certification compares the completed rocket and its systems with the design schematics. This is expected to occur in the second half of 2017 as program managers prepare for EM-1 in early 2018.

Following the design certification, the road to launch is relatively short. The vehicle, already assembled on a Mobile Launcher at Kennedy Space Center, then undergoes a final review and flight readiness review before the final countdown can begin.