SLS configuration nears decision point – Two-phase approach rejected

by Chris Bergin

A decision on the configuration of the Space Launch System (SLS) Heavy Lift Launch Vehicle (HLV) is just weeks away, as final evaluations take place into a “staged evolution of a single heavy launcher”, after NASA’s leadership rejected the two-phase approach, which would have resulted in an open competition for the Beyond Earth Orbit (BEO) derivative of the SLS.

The HLV Centrepiece:

The process to finalize the new path for NASA – following the cancellation of the Constellation Program (CxP) – remains under evaluation. The lack of a clear direction continues to burden the Agency, something which will continue to be the case even after the centerpiece rocket is revealed.

Although the ultimate goal for the Agency’s exploration plan is manned missions to Mars, no definitive roadmap has risen from the ashes of the Ares-based architecture, resulting in a path where a Heavy Lift vehicle is being designed before the missions it is set to cater for have been set in stone – something which often is pointed out as the wrong way around.

However, with the knowledge that very large payloads will need to be lofted uphill for the future goals, NASA teams are steadfast in their opinion that an HLV is required, a sentiment SpaceX – often championed as the exciting alternative and cheaper path for the United States to once again carry out manned BEO missions – agree with, as much as they embedded the caveat their agreement is specific to trips to Mars.

“Falcon Heavy should not be confused with the super heavy lift rocket program being debated by the U.S. Congress,” SpaceX officially cited when revealing their Falcon Heavy launch vehicle. “That vehicle is authorized to carry between 70-130 metric tons to orbit. SpaceX agrees with the need to develop a vehicle of that class as the best way to conduct a large number of human missions to Mars.”

Top level NASA meetings late last week (notes on L2’s SLS section) once again emphasized their agreement with the HLV requirement in the Authorization Act – which was based on NASA input during its drafting – noting that all findings concur there are no real savings in multiple smaller launches, which they claim also increase risk.

Such claims are often questioned, when citing alternatives such as EELVs and other commercial medium lift vehicles.

The main question for SLS at present relates to the configuration of the HLV, with the bulk of the RAC (Requirements Analysis Cycle) studies now concluded at the Marshall Space Flight Center (MSFC).

SLS Approach (all notes via L2’s SLS Section):

As previously reported by this site – and later by other media – a plan was created to fly a Block 0 SD (Shuttle Derived) HLV for four flights, starting in 2016, prior to an open competition to study the options for the evolved SLS which will carry out the BEO missions.

This approach was sent to NASA HQ late in May, only for it to be rejected by NASA administrator Charlie Bolden, who returned the plan to Marshall, tasking the teams to draw up baseline 70 MT vehicle which must fly by 2016 and must be able to evolve to 130 MT.

The order also noted the vehicle must be powered by LH2 (Liquid Hydrogen), powered by RS-25s (SSMEs) or RS-68s, while the Upper Stage must work under the assumption of using the J-2X hardware. However, the teams were allowed to trade on the boosters, between Solids and Liquids. Marshall were asked to send back their findings by June 1.

The result of what was sent back to NASA HQ was revealing, with high level meetings late this week noting the approach is now working with the clear requirement for a “staged evolution of a single large vehicle” – evolved to 130 MT. In other words, the initial 70 MT SLS will be the baseline/template for the 130 MT version.

This vehicle, which continues to be tagged as the Design Reference Vehicle (DRV) for the purpose of the final report to lawmakers, will enable use of core elements, “initially” – the notes claim – utilizing Solid Rocket Boosters to allow the SLS to provide back-up in the 2016-early 2017 time-frame for the ISS support assurance – as requested in the Authorization Act.

As such, the SD HLV RAC-1 option is still leading as the Design Reference Vehicle and is now undergoing a refinement on two areas, the core structure and the core engines, resulting in what would be more fairly described as a hybrid SD HLV, one which will grow within its own skin to evolve into a 130MT vehicle.

The meetings also noted the often-favored Kerolox (RP-1) option is not classed as a viable option, although it was claimed the RAC-2 option proved to be a worthy opponent of the SD HLV, by causing the re-examination of many of the key issues which challenged the leading DRV option.

The biggest challenge noted is the structuring of the procurement approach, along with the program management/oversight path, cited as where they expect to achieve the maximum savings, cost and sustainability, to a point NASA expect SLS to be “viable” under the rules of the Authorization Act – a key change to the preliminary report presented by NASA to lawmakers.

A definitive design and basic systems decision is expected before the end of June, even though these findings may lack the procurement and management strategy at that point. There is understood to be a hard deadline of July 8 – when Atlantis is scheduled to launch on the final Shuttle mission, STS-135.

SLS Hardware – SRBs:

With the allowances to examine Solid versus Liquid boosters on the SLS, the latest meetings would only commit to Solids being used “initially”, as much as sources expect they will win out as the long term solution for the evolved SLS.

A “non official” proposal of using liquid boosters on the HLV was created by a NSF forum member Nate Downes, which cites the liquid option as advantageous due to the simplicity of handling, superior impulse and the logistical advantages of pad fueling simplicity, which enables a wider range of missions for the same cost.

ATK appear to be fully aware their long-term role in SLS is not set in stone and have been busy providing costings and options to both the Marshall teams and “people in power” in Washington, DC.

While information on the latter is unlikely to see the light of day, L2’s SLS section acquired information on one example of a proposal to “boost” the capability of the SRBs over time, evolving the noisy duo which would aid the vehicle’s first stage flight, in tandem with the SLS’ evolution.

This example, provided to the RAC Team 1 at Marshall, proposes the change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” to allow higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi.

There are also proposals to use lighter weight nozzles with expansion ratios up to 12:1, although such a large scale change would require study at least at a Ground Support Equipment (GSE) level, given its relation to Launch Platform design.

Such challenges can be seen in a similar – yet not entirely related – change which was proposed for boosting Ares I’s capability three years ago.

“Extended Nozzle – Ares First Stage: Increase Ares I nozzle expansion ratio from 7.2 to 9.3,” noted a Constellation presentation acquired by L2 in 2008. “Justification: Provide 1200-1300 lb increase in overall vehicle payload capability.

According to that presentation, a larger 10.25 expansion ratio was preferred as “optimum” – though impacts to shipping, manufacturing, the TVC (Thrust Vector Control) hardware and the Mobile Launcher had to be considered in the approved ratio change.

“9.3 expansion ratio provides optimum performance with TVC attach constraints and manufacturing limitations,” cited the document.

ATK are continuing to make preparations for the DM-3 test of their five segment booster at their test facility in Utah.

SLS Hardware – Core Engines:

As has been proposed for some time now, the opening flights of the SLS are highly likely to utilize the existing four sets of Space Shuttle Main Engines (SSMEs) from the Shuttle Program – consisting of three sets from the last three flights of the shuttle and one spare set, all located at the Kennedy Space Center (KSC).

Click here for HLV/SLS- related news articles:

These RS-25Ds were also the centerpoint of the Block 0 SLS under the now-cancelled two-phased approach, which was to fly four times in support of the International Space Station and for opening Orion (MPCV) flights.

The current plan would result in a transition to RS-25Es, a cheaper and expendable version of the SSME, for the next evolution of the SLS.

As noted in a Program Requirements Control Board (PRCB) presentation last year, Pratt & Whitney Rocketdyne (PWR) were placed under an order to “delay the disposal and retain the capability” to manufacture new SSME-based engines.

“SSME New Production Strategic Capabilities (SCA) supports the manufacture of all current configuration major Block II engine components. New production line items consist of manufacturing tooling / equipment, raw materials, hardware details and sub-assemblies,” noted the PRCB presentation.

“Previously approved for retirement at NASA boards (2007/2008) – (overturned). Supports future launch vehicle architecture pending Agency decision.”

Although this is the leading option, the top-level meetings late last week confirmed some trades are continuing on the core structure and core engines, in order to ensure the best configuration for the “staged evolution of a single heavy launcher”.

SLS Hardware – Core Structure/Tank:

The core of the SLS first stage is where a large amount of refinement is taking place.

Firstly, the remaining ET specific workforce at the Michoud Assembly Facility (MAF), who – from managers and engineers – have spent most of their “remaining days” clearing out work stands and equipment from the 420 building to make room for the filming of a Hollywood movie, were expecting to get their 60 day WARN notices on May 26.

Lockheed Martin management informed these workers this was no longer the case, and will instead continue under a temporary funding request, due to what they cite as changes for the end date/funding for the ET program through to the start of a SLS program, which they project will be known this month.

Over at the Boeing side of MAF, managers have hired back previously released ET welders – badging them to Boeing from Lockheed – for the fabrication of what is known as the Pathfinder Tank – a scaled “strong back” tank.

Tooling is already in place to start this work and hardware is being moved into position.

Officially this is not an HLV/SLS project because this is being run as an “unsolicited” Boeing project, with a view for it to become part of the SLS program. However, the work is known to relate to the structural strength of the ET core on the first stage when stretched to a taller SLS configuration, along with modifications to the LH2 tank to support the SLS engine package.

This work on the Pathfinder Tank is being staged in the RWT (Robotic Weld Tool) area. The tooling/form/jig to hold the components together for the weld is being set up, as training for the operators is conducted ahead of the actual prototype being fabricated.

The key information about the Pathfinder relates to the domes being worked, which are classed as spun aluminum – single piece dome – versus the paneled dome used to produce the Shuttle ET.

Eventually, the fabrication will lead to a small scale LH2 tank, using the single piece (spun) dome, which will be used to show it is able to cope with SLS’ load requirements.

The Lockheed MAF planning group have also been told to start writing procedures to bring the MAF VAB (Vehicle Assembly Building) back on line in the event of starting production again – showing a major move to a running start at the time of a SLS decision point.

Currently, the LWT ET-94 remains vertical in the MAF VAB. ET-139 is in situ after the Stringer investigation work, while parts for ET-140 and ET-141 remain in storage.

MAF source information notes they have enough material for two new tanks already on site, but they will have to start up the smelter if they want to make more components.


With the painful job losses continuing to be suffered at the Florida Spaceport, Director Bob Cabana addressed his workforce last week, announcing a Center Director forum in the summer, as he aims to transition the center into the focal point for hosting government and commercial launch service providers.

Mr. Cabana also noted that NASA’s future architecture is emerging, and that he expects a decision “this summer” on the configuration of the SLS, citing KSC has a lot of important work over the coming months and years.

Ironically, KSC has already made a decision relating to hosting a HLV at the spaceport, after the entire Crawler Transporter group – which was already under layoff notice – was told they are keeping their jobs via KSC allocating funding for them to work man hour/material/project estimates for upgrading the famous Crawlers for SLS.

The group was told that NASA Ames had finished design on new Jacking, Equalization and Leveling System Cylinders (16/CT) and bearings, as well as work on new Rollers (88/CT, over 2000lbs/roller, heavy duty, mombo rollers and bearings/bushings) for the belts/shoes.

New GenSets for more AC Power to support the increased demands are in the pipeline too. These upgrade modifications will begin in about four to six month’s time.

Initial testing was completed last year on one area of crawlerway just outside of Pad 39B, via a strange looking contraption which aimed to test the impact of over 25 million pounds on the rock surface of the track.

The findings of the testing, which was conducted by NASA, the United Space Alliance (USA), Architect and Engineering firm Jones Edmunds and Associates (JEA) and a couple of additional contractors, was classed as positive.

No references have been made into the use of the Ares I Mobile Launcher (ML), which remains sat next to the VAB, with a launch mount which is highly specific to the Ares I vehicle.

All This Has Happened Before – Will It Happen Again?:

The saga revolving around NASA’s next Heavy Lift Launch Vehicle has been ongoing for years. Winning trade studies and being a leading option does not provide any certainty such a vehicle will ever see “hammers on aluminum”, as seen just prior to the FY2011 Budget Proposal announcement.

In the weeks leading up to the FY2011 announcement, General Bolden himself tasked a special team to conduct a study into the HLV options, which resulted in the Sidemount HLV and RP-1 (Kerolox) vehicles losing out to the in-line SD HLV.

“HLV study summary from (Mr. Jeff) Hanley – Sidemount doesn’t buy anything and takes hit on safety. A couple of (winning) versions of In-line going to (Mr.) Bolden,” noted one memo surrounding the study at the time. MAF also noted they were all set to implement the plan.

However, the end result was a complete omission from the FY2011 announcement, which focused on a five year study into “game-changing” propulsion, effectively mothballing the HLV bar a small team, before the lawmakers reversed the decision via their Authorization Act.

The coming weeks will prove to be critical for this latest approach to providing NASA with the blueprints for a new HLV.

(The progress on the SLS status will continue to be followed up over the coming weeks. L2 members, follow our exclusive SLS update coverage via the SLS and HLV tags. Images used:  Via L2 content and

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