SLS finally announced by NASA – Forward path taking shape

by Chris Bergin

After several years of trade studies and political arguments, NASA administrator Charlie Bolden finally gave the Space Launch System (SLS) its official public unveiling on Wednesday. As has been known for months, the Heavy Lift Launch Vehicle (HLV) is Shuttle Derived (SD) and will use $10 billion of NASA funding through to its debut launch in 2017.

SLS History:

Not unlike most launch vehicles, SLS has suffered from a complicated birth, most of which was not of its own doing – as the political element of NASA decision making process questioned the motives of the design, and even the need for a HLV.

Regardless, the wait is now over, as the in-line SD HLV has finally been revealed in the official arena, after a heavily delayed announcement by General Bolden – flanked by lawmakers – on Wednesday.

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“The next chapter of America’s space exploration story is being written, right here, right now. We’ve selected the design for a new space exploration system that will take humans far beyond Earth. This important decision will create high-quality jobs here at home and provide the cornerstone for America’s future human space exploration efforts,” noted the General in an address to employees.

In fact, the chapter – from an in-line SD HLV standpoint – was technically written years ago, and even earlier if taking into account the often-ridiculed mix of NASA engineers and space enthusiasts which created the Direct (Jupiter) alternative to the Constellation Program (CxP), itself based on an old Marshall Space Flight Center (MSFC) concept.

With the Constellation Program cancelled, the SD HLV launch system started to receive an official groundswell of interest, with General Bolden himself – back in January, 2010 – reviewing one of the subsequent trade studies, which showed the in-line HLV as the winning configuration.

With the President’s FY2011 budget proposal effectively putting the HLV on a five year backburner – in order to “study game-changing propulsion” – the highly unpopular outline for NASA’s future was itself realigned via the Senate’s 2010 Authorization Act, which put its weight behind a Space Launch System (SLS) which utilized both Constellation (Ares) and Shuttle hardware.

Under the guidance of the Human Exploration Framework Team (HEFT), three Requirements Analysis Cycle (RAC) teams undertook what was by far the most in-depth evaluation of all types of HLV.

RAC-1 studied in-line, LH2 core vehicles with Solid Rocket Boosters (SRB). While this vehicle was based around the SD HLV, the teams avoided the use of such a name, given they were allowed to trade Space Shuttle Main Engines (SSMEs) with RS-68s, while also trading SRBs with Liquid Rocket Boosters (LRBs), in order to ensure they have the best configuration to battle with the other HLV candidates.

RAC-2 studied a Saturn V-type vehicle, utilizing an RP-1 first stage and LH2 second stage. Like RAC-1, the team was allowed to trade different engine options, within their designated configuration. RAC2 included SpaceX’s Falcon XX (huge vehicle with six Merlin 2 engines) in the trades. Ironically, the announced SLS was given the fanfare of being more powerful than the Saturn V.

RAC-3 studied vehicle designs based around several options, such as EELVs, with a large amount of latitude to study different tank sizes, including the evaluation of clusters of Atlas-sized tanks similar to how the Saturn IB first stage was built.

While some people associated with losing vehicle options claim the study process was automatically aligned to favor the SD HLV, this configuration officially won, as the records show.

Becoming the Design Reference Vehicle (DRV), the SD HLV had to endure a sustained political attack, as the preliminary version of a final report – demanded by the 2010 Authorization Act – insisted the vehicle could not be affordable under the requirements, prior to listing numerous caveats that such findings were incomplete.

With future evaluations centered at the Marshall Space Flight Center (MSFC) under the RAC process, confidence was high that a compliant outline could be presented, which eventually resulted in a completed overview ahead of STS-135 – a timeline which allowed for the announcement, albeit late, to be made on STS-135’s launch day.

The July 8 announcement, which was even noted by Atlantis’ commander Chris Ferguson, was then cancelled, as a stalling process was put into effect, apparently under the order of the White House. This process was classed as a requirement for an independent costing assessment, to be carried out by Booz Allen. Such a process would delay the final report yet further.

Even after the cost assessment process was complete, no announcement was made, much to the anger of several Senators involved with the Authorization Act, brought to a head when a – somewhat mis-written – cost overview was leaked to the Wall Street Journal, in what is claimed to be an attempt to create large-scale opposition from within the space community.

It backfired, as the leaked report caused several meetings between political and NASA heads, based around revealing the true cost estimate findings, and ultimately leading to a joint agreement between all relevant bodies. This agreement paved the way for Wednesday’s official announcement of the vehicle.

“This launch vehicle decision is the culmination of a months-long, comprehensive review of potential designs to ensure that the nation gets the best possible rocket for the investment – one that is not only powerful but is also evolvable so it can be adapted to different missions as opportunities arise and new technologies are developed,” added General Bolden.

“The selection of the vehicle needed to transport our astronauts beyond low Earth orbit is one of the most important decisions NASA will make this decade, and it requires a major commitment on the part of the American people. That’s why we took the time to get it right.

“The hard work and expertise of you in the NASA Family have brought us to this point and will be critical as we continue to do the big things only NASA can do and challenge ourselves as a people to reach our highest potential. The future is bright for exploration, and we can be proud of the major step forward we are taking today.”

SLS – The Vehicle:

Heavily based on Shuttle heritage hardware, the design of the vehicle has been known for some time – as reported by this site. There will be two major roles for SLS, one is to launch cargo and one to launch the Orion (MPCV).

The core stage is an 8.4m diameter “External Tank” heritage system, with the top converted to host the Upper Stage structure, and the aft restructured to house the Main Propulsion System (MPS) – which will drive what will initially be three Space Shuttle Main Engines (RS-25Ds).

The system is designed to eventually fly with five engines in the core.

This core effort – to be hosted at the Michoud Assembly Facility (MAF) in New Orleans – is said to be one of the biggest challenges for the engineering work on SLS. Some “pathfinder” work, conducted by Boeing, has already been completed.

The role of Pratt & Whitney Rocketdyne (PWR) is now official, with SLS’ path towards its 2017 IOC (Initial Operating Capability) ready to utilize the 12 RS-25Ds available for one-off roles with SLS flights, following their transition from the Space Shuttle Program (SSP).

The Kennedy Space Center’s stock of SSMEs consists of the three orbiter sets, now removed from the vehicles, and three engines which made up the spare set.

It has also been confirmed that there will be a transition to the expendable version of the SSME, known as the RS-25E, either after the four sets of RS-25Ds have been used, or after two additional RS-25D sets have been manufactured – per reserved stock at PWR.

The eventual engine driving the core stage is confirmed as the RS-25E, a cheaper engine due to its expendable nature.

As reported, the three shuttle orbiters are now very likely to see their orbiter MPS plumbing and hardware donated to the SLS program.

Discovery’s MPS is likely to be used on test structures, while Atlantis and Endeavour’s MPS are likely to ride with SLS-1 and SLS-2.

Final evaluations are taking place into this $20m effort, with the next SLS article to overview the latest status presentations (L2).

SLS-1 and potentially SLS-2 will ride with ATK’s five segment boosters, although the competition for the confirmed booster of choice for the remainder of SLS’ lifetime will begin shortly.

With the Core designed to be compliant with several booster options – so as not to prejudice to the competition – working with commonality on the core interfaces, and standard approach of the boosters providing stability for the vehicle when attached to the pad, will be some of the baseline requirements.

While the competition will involve a number of booster options, ATK have already published a statement showing their confidence in continuing with SLS through its lifetime.

“ATK applauds NASA’s decision to move forward with a Space Launch System for human deep space exploration. We are proud that NASA will utilize ATK’s five-segment solid rocket motors as the baseline design for the initial flights,” noted the Utah-based company.

“ATK’s five-segment boosters provide unmatched capability and we will deliver this performance within the current budget. We are confident in the design and look forward to the early test flights to demonstrate our capability.

“We are also well positioned to compete for the final design because of our proven performance and a thrust-to-weight ratio of our solid rocket motors which are ideally suited for first stage propulsion.”

As far as ATK’s approach for the fully evolved SLS vehicle, source notes claim a future static test could be provided as a pathfinder test for an upgraded booster.

Such potential upgrades to the booster may include recently proposed change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” thus allowing higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi. This could become key, with NASA mentioning the competition will be mainly looking into the performance numbers of the booster candidates.

As previously reported, 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.

SLS will launch from a modified version of the Ares Mobile Launcher (ML), which means ATK’s Liberty Launch System – should it survive the commercial crew evaluations – will have to find a new launch platform to host its rollout and launch from Pad 39B.

A second ML, or a major conversion to the Shuttle Mobile Launch Platform (MLP-3), will be the likely options available to the Ares-1 style vehicle.

The SLS vehicle is being designed with an Upper Stage, which will be evaluated up to the Preliminary Design Review (PDR) stage. This Upper Stage will be driven by the Constellation-born J-2X engine, currently undergoing initial testing at the Stennis Space Center.

The vehicle will be able to fly without the Upper Stage, and in some cases would fly with a smaller replacement in the form of a Delta IV “Kick Start” Upper Stage system.

SLS will not be decked out in the Saturn V “White and Black” paint, as seen in graphics of the vehicle, which sources note was only for publicity purposes. The vehicle will sport the orange “spray applicated” Thermal Protection System (TPS) foam, as seen on the Shuttle External Tanks.

SLS – Forward Work:

It now appears – as noted at the time – that the initial schedules and costings (leaked or otherwise) were based on worst case estimations, with only the 2017 opening launch date for the vehicle confirmed during Wednesday’s announcement.

The fear the second SLS mission – which would be the first crewed launch – would have to wait until 2021, a four year gap between flights, is now heavily associated with only a total worst case scenario, “the disaster schedule” as one source claimed.

Instead, an increased flight rate, based mainly on finding additional uses of the large fairing design and upmass capability of SLS, has been intimated. Former Space Shuttle Program (SSP) manager John Shannon has also been tasked with creating a schedule and mission architecture for the vehicle.

Work on a schedule and funding path is being worked internally by NASA and in the political arena, but as of this week, no long-term schedule can be cited until the key driver of the funding profile – which is classed as still under consideration, and not final – is officially created.

A lot will depend on what the Congress is able to provide through the annual appropriations process, with the only “official” targeted flight being SLS-1, in 2017. This date is set, with no allowance for it to slip to the right, even in the event of unexpected funding issues.

Work on later goals – such as the Upper Stage for the 130mt version of SLS, or mission content for SLS flights – would instead be slipped or re-worked to protect the 2017 date, which is likely where the “worst case” 2021 date for SLS-2 – and the low flight rate through to 2032 – was formed, based on a scenario where initially achieving the 2017 IOC date suffered from major issues.

Wednesday’s official announcement is vital to SLS, as it enables NASA to now have an approved, focused program planning effort to initiate work that will lead to the usual Systems Requirements Review and Preliminary Design Reviews.

This will lead to final determination of cost and schedule, as is normally the case with any new major vehicle development.

Next up on this path will be the procurement process, which includes meetings this week, through to next week, ahead of an industry day meeting later this month.

As mentioned, the core stage work will be the main opening challenge for the engineering teams, which in turn will drive the vehicle’s major milestone of the PDR, currently scheduled for early 2013.

Earlier key milestones (L2) cite October 24, 2011, for the SRR (System Requirements Review) Checkpoint, and February 15, 2012 for the combined SRR/SDR (System Design Review) kickoff.

(Images: Via L2 content, driven by L2′s new SLS specific L2 section, which includes, presentations, videos, graphics and internal updates on the SLS and HLV. Other images via NASA, ATK and Philip Metschan)

(L2 is – as it has been for the past several years – providing full exclusive SLS coverage, available no where else on the internet. To join L2, click here:

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