Acronyms to Ascent – SLS managers create development milestone roadmap
This year will mark several major milestones for the development of the Space Launch System (SLS), with teams already pushing through a systems review process. The roadmap – which may include a “battleship” pathfinder core test at the Kennedy Space Center (KSC) in 2015 – runs through the opening mission in 2017, which has been named as Exploration Mission -1 (EM-1).
The Development Roadmap:
Although the early SLS effort suffered from numerous reviews and alleged delaying tactics at the political level, 2012 has seen a noticeable increase in work on the SLS, especially via the construction of the development roadmap towards the maiden flight of the Heavy Lift Launch Vehicle (HLV) in 2017.
It has been a long road to get to this point, where NASA’s next flagship launch vehicle is now enjoying its the first full year of focused development, a path which started with the Review of Human Space Flight (HSF) Plans Committee (Augustine Panel) back in 2009, prior to no less than 11 reviews over two years being conducted, prior to NASA administrator Charlie Bolden’s announcement of the SLS last year.
Thankfully, engineering and management teams had already begun a level of preparation on the SLS and hit the ground running by entering the System Requirements Review (SRR) checkpoint kickoff meetings the month after the official SLS announcement.
With the Key Decision Point A (KDP-A) “memo” already approved, SLS finds itself into the Cross-Program SRR stage, along with a number of key hardware milestones and tests already under its belt.
These include the five-segment Solid Rocket Booster Development Motor 3 firing success, J-2X upper stage engine full-duration testing, and RS-25 Ground Support Equipment, which is in the process of being positioned for future integration activities at the Stennis Space Center.
The current meetings are working towards the joint System Requirements Review (SRR) and System Definition Review (SDR), which kicked off at the program level meeting stage this month, prior to its concluding meeting which is scheduled for March 29 – a milestone which will feed into the major effort of the Preliminary Design Review (PDR), scheduled for June 28, 2013.
These meetings are discussing the SLS DAC-1 (Design Analysis Cycle) vehicle configurations, which are designated by their Vehicle Configuration Reference (VCR) numbers – as outlined via L2’s SLS Section (L2 Link).
Under the DAC-1 effort, engineering teams identified nine possible configurations, based around the evolvability of the HLV. As previously reported, SLS will initially launch as a 70mt vehicle (2017), prior to evolving to a 105 mt vehicle (2020s), before finally growing to a 130mt vehicle (2030s).
Known as SLS Block 1, the VCR 10000 vehicle consists of two five segment Solid Rocket Boosters (SRBs) boosters, and a core stage which initially was intended to fly with 3, 4, or 5 RS-25D engines. However, this vehicle has since been baselined to fly only in the four engine configuration. The vehicle will also include an ICPS (Interim Cryo Propulsion Stage), with the Orion (MPCV) spacecraft completing the stack.
This configuration is only set – at present – to fly two missions, namely SLS-1 and SLS-2, which are now being reclassified as Exploration Mission -1 (EM-1) and Exploration Mission -2 (EM-2). Both missions will send Orion on laps around the Moon, the first of which will be uncrewed, the second with a crew of four. (An article will be forthcoming on overview the EM-1 mission – L2 Link to the SLS Master Presentation E.5 outlining the mission).
NASA’s leadership continue to use the “worst case” manifest scenario of flying EM-2 in 2021, a full four years after EM-1, although internally managers are working towards a more-desirable 2019 launch date for the second SLS flight.
At present, SLS-3 is set to fly as the Block 1A configuration. No missions have yet been allocated past EM-2, although teams continued to work towards an exploration roadmap, which is now likely to feature an Exploration Platform “Gateway” at Earth-Moon Lagrange (EML) point 2 – based on what are an increasing number of international meetings on the proposal (L2 Link to SLS Exploration Roadmap Updates).
There are four SLS Block 1A configurations on the table, all based around the 105mt requirement, with a crew version and a cargo version of the vehicle, each with either a solid or liquid booster option.
SLS VCR 11000 sports two solid-propellant Advanced Composite Boosters (ACBs), the same core stage as the 10000 vehicle, with a cargo adapter and fairing on top.
SLS VCR 12000 is the same vehicle as the 11000, except this version would use Liquid Rocket Boosters (LRBs) instead of the ACBs. Only one version – be it the 11000 or the 12000 – will fly, based on the advanced booster competition which is likely to be fought out by the two main companies in both the solid and liquid booster arena – ATK and Aerojet. (An article will be forthcoming on this competition).
Because this competition isn’t set to end until 2015, SLS teams have had to analyze both versions of the Block 1A, given the differences in their performance characteristics and environments – such as aerodynamic factors like Max Q, as well as vibration, acceleration, acoustics – thus the engineers need to ensure the core stage design is compatible with both options.
SLS VCR 13000 is the same vehicle as 11000, except this version sports a cargo fairing, with the Orion spacecraft on top of the fairing. Per the Design Reference Mission (DRM) documentation (L2 Link to Presentation), the “cargo” under the Orion will simply be the CPS, as opposed to an actual cargo. SLS VCR 14000 is the same vehicle as 13000, except this version uses LRBs.
Once again, only two of the four Block 1A configurations will ever fly, either 11000 and 13000 or 12000 and 14000. SLS engineers are looking at all of the configurations in order to avoid a core stage design that would preclude potential bidders from proposing either ACBs or LRBs in the 2015 competition.
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During these initial flights, SLS will use up the stock of 15 Pratt & Whitney Rocketdyne RS-2Ds – otherwise know as the Space Shuttle Main Engines (SSMEs) donated by Discovery, Atlantis and Endeavour. There are 15 RS-25D engines – including the nine which helped power the three orbiters uphill during their final missions – along with enough parts to make a 16th engine.
The current plan is to use the RS-25Ds on the first two Block 1A flights, prior to switching to the expendable version of the engine, known as the RS-25E.
Finally, there are four Block 2 (or Block II) configurations for the SLS, versions which are naturally evolved from each of the Block 1A configurations, adding a second stage with two J-2X engines, and making provision for a fifth RS-25E in the core stage.
As such, the Block 2 version of the SLS VCR 11000 vehicle is the 21000 vehicle, the Block 2 version of the 12000 vehicle is the 22000 vehicle, the 13000 becomes the 23000 and the 14000 becomes the 24000.
And as with Block 1A, if the advanced booster winner provides ACBs, only the 21000 and 23000 configurations will fly. If they provide LRBs, only the 22000 and 24000 configurations will fly.
These vehicles will continue through the upcoming major milestones from the review standpoint, with the recent SLS Master Presentation E.5 (L2 Link to Presentation) outlining a full schedule through to the EM-1 mission, as much as the timeline is subject to change.
For FY2012, the SRR and SDR meetings are adjoined to Key Decision Points (KDPs), with the Cross Program SDR and KDP-B highlighted. FY2013 includes KDP-C and the major PDR milestone, prior to a Program Checkpoint meeting at the start of FY2014.
With a Delta IV-Heavy launching the first Orion on the Exploration Flight Test -1 (EFT-1) early in 2014, the following 12 months will be critical for Orion, as the results of the flight will be fed into the spacecraft’s Critical Design Review (CDR), which is currently set for April, 2015.
Another Program Checkpoint will open FY2015, prior to the KDP-C and the Critical Design Review (CDR) in the second quarter of that year. Program Checkpoints continue to be held at the start of each year, surrounding the huge milestone of the Design Certification Review (DCR) at the end of FY2015.
By this time, engineers will have put hammer to metal on SLS hardware, with source notes on the L2 SLS Development Update Section (L2 Link) noting preliminary discussions relating to a 2015 test with a non-flight “battleship” core consisting of four engines.
The pathfinder core would be built at the Michoud Assembly Facility (MAF) in New Orleans, shipped to the Kennedy Space Center and attached to inert/empty SRBs inside the Vehicle Assembly Building (VAB). Studies are looking into whether this would be a “wet-test” or a firing test out at Pad 39A.
Technically, the “battleship” will be a Main Propulsion Test Article (MPTA), and while there is always risk to the entire pad upon a destructive failure, the risk is low do to the experience with the SSMEs via the Shuttle program. There are also cost savings involved by conducting all the MPTA tests at KSC – as opposed to Stennis, and as such, sources note they expect more than one MPTA test firing at KSC.
Notably, the schedule and language of the entire SLS program’s development schedule does point to lesson’s learned from the schedule slips suffered by the Constellation Program (CxP). A large amount of mitigation and flexibility has been built into the SLS schedule, so as to avoid what was almost yearly slips during funding and technical challenges for Ares and Orion.
With over five years to go until the first launch of the SLS, how the schedule actually plays out will be of great interest.
Numerous SLS articles will follow over the next few weeks.
(Images: Via NASA and L2 content. L2’s SLS specific L2 section, which includes, presentations, videos, graphics and internal updates on the SLS and HLV, available on no other site.)
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