SLS Program pushing toward Critical Design Review

by Chris Bergin

The Space Launch System (SLS) management have set the milestones and dates for the upcoming Critical Design Review (CDR). This key review will serve as the rocket’s graduation ceremony, confirming the design is ready to enter production ahead of its debut flight during Exploration Mission -1 (EM-1), currently targeting July, 2018.


SLS will mark NASA’s return to crewed deep space exploration, with a Heavy Lift Launch Vehicle (HLV) set to loft the Orion spacecraft and associated payloads on missions to asteroids and eventually Mars.

While the rocket continues to enjoy political support, the majority of its future missions remain notional and unfunded.

2015-03-16 17_30_44-L2 Level_ Space Launch System Update Notes And Discussion - Sept, 2014 onwardsThe opening flight for SLS will be an uncrewed mission, lofting Orion 70,000 km past the Moon on a 25 day flight, validating the launch vehicle and Orion’s capabilities.

Although SLS was finally announced in 2011, EM-1 remains the only mission on the official manifest and schedule.

NASA continues to promote SLS as the rocket that is laying a path towards crewed missions to Mars in the mid-2030s. However, while that is technically true, the vehicle is still waiting for some firm direction through its early lifetime.

Examples of the convoluted schedule for SLS begin with its second proposed mission. Officially, the rocket isn’t scheduled to launch again until the 2020s, this time with a crew onboard Orion for the first time, heading out to a captured asteroid, as part of EM-2.

The initial problem of a large gap between the first two missions for SLS is in part due to the requirement to review the performance of the rocket after its debut.

However, the original launch targets – in the second half of this decade – for EM-1 were set politically, as lawmakers looked to SLS and Orion as a “Plan B” to the commercial crew effort.

2015-03-16 17_28_43-Boeing (CST)-100 HR Updates and ImagesOfficial Concept Of Operations (CON OPS) documentation (L2) still, to this day, cites a Design Reference Mission (DRM) that would call for SLS to launch a crew on Orion to the ISS, classed as a back up plan in the event of a major schedule issue with the Commercial Crew Program.

“LEO_Util_1A_C11A1: International Space Station (ISS) Back-Up Crew Delivery: Per Congressional Mandate, NASA is to provide backup capability to the commercial ISS crew delivery and return options,” noted the CON OPS section on this notional mission.

However, it is clear such a mission isn’t being taken too seriously by NASA, not least because such a scenario would involve the overpowered 70mT capable Block 1 SLS (as such launching with tons of ballast) lofting a Beyond Earth Orbit (BEO) designed Orion (to LEO), with a crew on its debut mission (safety rules call for a uncrewed debut), at a cost that would probably solve any Commercial Crew Program woes.

EM-2 Part 1EM-2’s path is also uncertain, with its schedule at the mercy of the Asteroid Redirect Mission (ARM) plan – involving two missions, opening with a robotic mission to head out and capture an asteroid, dragging it into a Lunar orbit, ahead of the EM-2 crew arriving for a hands on investigation.

The challenges associated with the ARM has resulted in claims  – made to NASA’s Aerospace Safety Advisory Panel (ASAP) – that EM-2 may not occur until 2024.

Such a scenario further convolutes SLS’ launch schedule, with the possibility of EM-2 being redefined into an alternative mission, moving the asteroid mission to EM-3 or EM-4 on Orion’s manifest. SLS may also gain the mission to launch the ARM spacecraft on an uncrewed flight.

Z23As always, the main issue appears to be political, as the SLS teams are working numerous mission plans for the rocket, but are unable to publicly promote them due to the lack of political authorization.

However, some of the plans that are being worked on are now gaining mentions in the public domain, such as the possibility of launching a Europa mission via SLS.

As previously reported by, several studies have been conducted between the launch vehicle and spacecraft stewards, ranging from an exercise in planning between SLS and JPL, through to payload fairing designs.

According to the latest L2 information, the next Europa Technical Interchange Meeting is scheduled for May 7-8, with a planning date of 2025 being used as a notional launch date for the mission.

Path To CDR:

Despite the uncertainties over the specific payloads SLS will be lofting, the vehicle’s development has been going well.

The vehicle passed its Preliminary Design Review (PDR) in 2013 with a relatively good report card, a key difference to the troubles suffered during the Constellation Program (CxP).

2015-03-16 18_42_26-L2 Level_ Space Launch System Update Notes And Discussion - Sept, 2014 onwardsThis allowed SLS to pass through the KDP-C (Key Decision Point -C), setting the path towards the upcoming CDR – arguably the biggest milestone for the rocket’s development and approval to head into production.

Per the latest L2 information, a readiness assessment meeting is scheduled for April 2. All deliveries of documents, drawings – and other review items for the data pack – are due on or before April 24, ahead of the CDR kickoff presentation that is scheduled for May 11-13.

The CDR will confirm the maturity of the design is appropriate to support proceeding with full-scale fabrication, assembly, integration, and testing.

2015-03-16 19_04_02-SLS RS-25 Stennis - Google SearchIt’s been a good start to 2015 for SLS, with the return of RS-25 hot fire testing at the Stennis Space Center. Four RS-25s will help power the rocket uphill throughout its lifetime.

The second test of RS-25 engine E0525 is scheduled for April 8.

Part of the “first stage push team” will be two Orbital ATK Solid Rocket Motors. These five segment boosters are one test away from completing their development cycle, following the successful QM-1 (Qualification Motor -1) static fire test last week in Utah.

The QM-2 test is set to take place early next year.

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Meanwhile, the Booster Element will be undergoing a series of Production Readiness Reviews (PRRs) covering various sub-assemblies on the booster. The PRRs will conducted from March 23 through May 4.

2015-03-16 19_05_04-SLS VAC - Google SearchThe heart of SLS’ first stage is the Core, which completed an out-brief review on March 9.

A review was scheduled to take place today (Monday) for a “Recovery Decision Meeting” relating the massive Vertical Assembly Center (VAC) at the Michoud Assembly Facility (MAF) – where the Cores will be welded – which has been suffering from teething issues, such as alignment problems and even a bearing that came loose and fell to the floor recently.

Once those cores begin to roll out of Michoud, they will be shipped via an upgraded Pegasus Barge, which has transitioned from its role with Shuttle External Tanks, to that of being prepared for transporting the stages of SLS.

Modification work is scheduled for completion on May 15, at which time Pegasus will be delivered to the Stennis Space Center on May 20. Outfitting of the barge will be completed June 26.

Images: NASA, JPL and L2 artist Nathan Koga via L2’s SLS sections, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site.)

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