Year in Review (Part III) – SLS development, mission possibilities take shape
2012: The year when the Space Launch System rocket began to take shape. For NASA, 2012 saw tremendous progress toward the development of the SLS rocket – the rocket that will see humanity’s return to regions of space beyond Low Earth Orbit and eventually on to our ultimate destination: Mars.
SLS rocket development:
While many initial, generalized descriptions of the SLS rocket were revealed to the general public in 2011, it was not until 2012 that the power-house rocket actually began to take shape from a true design standpoint.
Owing in large part to political dogfights about what the rocket, the successor to the Space Shuttle, would actually be, much of the work on the SLS rocket did not begin until late 2011.
This work continued in earnest in 2012, with the rocket passing the first of its Preliminary Design Reviews this year.
In all, 2012 began with what many had already suspected: the salvaging of the Space Shuttle Main Engine (SSME) family from the Shuttle program for use in the initial launches of the SLS rocket.
In January, the 15 SSMEs that helped close-out the Shuttle Program were shipped to the Stennis Space Center in Mississippi for post Space Shuttle Program safing and decommissioning in preparation for their use on the Space Launch System rocket.
The engines, known in the engineering community as RS-25D engines – were the backbone of the Space Shuttle orbiters’ propulsion systems and will now serve as the initial engines that will power the core stage of the SLS rocket.
As stated by William Gerstemeier, NASA’s Associate Administrator for Human Exploration and Operations Mission Directorate, “The relocation of the RS-25D engine assets represents a significant cost savings to the SLS program by consolidating SLS engine assembly and test operations at a single facility.”
Clustered in pairs – consisting of four engines at the base of the core stage of SLS – the holdover 15 engines from the Shuttle program will be used on the first three to four flights of the SLS rocket – allowing NASA to capitalize off of previously flown and understood hardware while at the same time pushing ahead with the development of an eventual upgrade to the engines – the RS-25E.
The need for the RS-25Es is demonstrated not just by NASA’s commitment to increasing the safety of the work-horse engine family but in the simple fact that, unlike with the engines of the Shuttle Program which were recovered and reused after every flight, the core stage liquid engines of SLS will be lost with the core stage during its destructive impact with the ocean after launch.
How the SLS will launch:
Following this initial activity, by late February, engineers within NASA had completed the first outline of the Concept of Operations presentation, or Con Ops presentation, relating to how the SLS rocket will launchd from the Kennedy Space Center in Florida.
Mirroring as closely as possible the operations that were honed over the 30-year lifetime of the Shuttle program, many of the pre-launch operations for SLS from a Mission Management Team perspective will be identical to that of Shuttle, including the program- and agency-level Flight Readiness Reviews to clear the vehicle, from an agency standpoint, for liftoff.
At the launch pad during countdown operations for crewed SLS operational flights, the Orion capsule and the SLS rocket will be able to “talk” with one another and with the Flight Control Teams in the Firing Room at the Kennedy Space Center, providing vital data on the vehicle’s health during propellant loading and final checks for liftoff in the final few hours and minutes of the countdown.
Like Shuttle, the SLS rocket’s countdown will include several built-in holds to allow processing teams time to catch up on any activities that may require slightly more time than anticipated.
Also like Shuttle, the 21st Century Ground System at the Kennedy Space Center will have primary control over the countdown and vehicle until very late in the count, like the Ground Launch Sequencer did for Shuttle up until the T-31 second mark.
While it is not yet known at what specific time in the countdown the 21st Century Ground System will handoff control of the countdown to the SLS’s onboard computers, once this occurs, Flight Rules and Lunch Commit Criteria will provide the system-specific constraints of acceptable parameters in which the vehicle can launch.
Launch pad abort options will be available for emergencies late in the count both to provide safety for the crew in a crewed launch vehicle situation and for the vehicle itself in a non-crewed situation.
After liftoff, as has been the case since the initial days of Apollo, once the SLS rocket launches, flight control will transfer to Houston and the Mission Control Center.
However, unlike Apollo and Shuttle when flight operations were officially transferred to the Mission Control Center upon clearing of the launch tower, flight control for the SLS rocket will transfer to Houston at the moment of first motion of the integrated stack off of the launch pad.
After lifting off, the SLS rocket will provide automated and autonomous flight operations assets to both the controllers on the ground and astronauts during crewed missions.
Notably, human rating rules for the SLS rocket require it to complete each mission, whether crewed or uncrewed, with automated and autonomous capability to account for a possible loss of communications with the ground.
This will be especially important should a loss of communication with the ground be coupled with a need to abort the mission.
To this end, abort modes will be built into the SLS rocket’s software to account for crew escape operations and termination of the flight hardware via a Range Safety System in the event of a mishap during launch.
Coupled with this capability will be a program called Abort Decision Logic which will monitor, through a Fault Management system, the health of the SLS rocket and vehicle. In the event of a critical issue, the Abort Decision Logic program would be able to issue the necessary commands to activate the Launch Abort System to pull the Orion capsule free from the failing SLS rocket.
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Impressively, the Abort Decision Logic would also be able to react differently to similar situations during crewed v. uncrewed missions. For example, in the event of a single engine out scenario during second stage flight of an uncrewed SLS cargo mission, the Abort Decision Logic would be able to “seek mission accomplishment until propellant is depleted” instead of aborting the mission outright.
The roadmap of development:
Finally, by late February, a developmental roadmap for the SLS rocket had been created, bringing the rocket’s evolution one step closer to its inevitable conclusion: a maiden launch on the Exploration Mission -1(EM-1) in December 2017.
It was from this roadmap that confirmation finally came as to what the initial Block 1 design of the SLS rocket would look like and what its first mission would be.
Flanking the core stage of SLS will be two 5-segment Solid Rocket Boosters produced by ATK in Utah, the same company that produced the SRBs for the Space Shuttle Program.
Joining these two monster power-houses for the initial two minutes of flight will be four SSME, RS-25D, engines burning liquid oxygen and liquid hydrogen from the core stage tanks of the SLS.
Sitting on top of the core stage will be the Orion Crew Module, flying the EM-1 mission in an uncrewed configuration, with an already existing Delta IV rocket Upper Stage (Interim Cryogenic Propulsion) adapter that will use liquid hydrogen and liquid oxygen.
For EM-1, following ascent with the SRBs and core stage engines, the Delta IV’s Upper Stage will be used to propel the Orion capsule out of Earth orbit and onto a circumlunar course.
The second mission of the SLS Block 1 design will feature an identical rocket, only this time with the crew of four aboard the Orion capsule. EM-2 will have the same general objective: the circumnavigation of the moon by the Orion capsule and its safe return to Earth.
Additionally, the development roadmap also provided the first detailed look at what the Block IA and Block 2 configurations of the SLS rocket, both in its crewed and uncrewed configurations, will look like and provided the first performance indicators for the SLS rocket in its twin 5-segment SRB configurations and its twin advanced liquid booster configurations.
Through this roadmap came the understanding that the Liquid Rocket Booster versions of the Block 1A and Block 2 SLS vehicles would – should they be chosen – provide a greater performance margin for payload to orbit considerations than would the Solid Rocket Booster configurations.
Competition for the contract for the Advanced Rocket Boosters for the SLS rocket, either solid propellant or liquid propellant, is not set to end until 2015 – meaning the design teams for SLS must incorporate both designs into the initial overview of the vehicle’s projected performance.
SLS development continues midyear:
By March, specific baseline designs for the three SLS rocket variances had taken shape, including specific power level limits for the liquid fueled engines, propellant mixture ratios for the engines, specific impulses for the engines, the operational constraints for the Solid Rocket Boosters, and the architecture that will be used for the rocket during its stay at the pad.
This included significant progress on the development of the Block 1 design which, as of mid-year, was still targeting a maiden voyage in December 2017.
Moreover, substantial work was made with the launch tower and the Mobile Launcher platform that the SLS rocket will use during its time at the Kennedy Space Center.
Specifically, engineers were able to determine the tower-to-rocket interfaces that will be needed to properly service the SLS in the Vehicle Assembly Building and at the launch pad.
These interfaces were designed based on the preliminary understanding of the Block 1 SLS design and the eventual evolution of the rocket to its Block 1A and Block 2 configurations.
The interfaces themselves will include various swing arms to service the Orion crew module and service module and will provide access to certain areas of the vehicle while it is at the launch pad.
Moreover, additional work was done on just how the propellant feedlines will flow from the rocket to the launch pad and out to the propellant storage tanks at the pad.
After the initial idea to put the liquid oxygen and liquid hydrogen Tail Service Masts and propellant feedlines on opposite sides of the rocket, the design was changed by the end of the year to incorporate the new understanding that both propellant feedlines and Tail Service Masts will be located next to each other on the same side of the rocket.
Additionally, the evolving design of the SLS Block 1 configuration sparked questions as to the exact nature and need of the hold-down systems that will be required for the vehicle on the Mobile Launcher.
Specifically, questions arose as to whether or not the Solid Rocket Boosters will have to be bolted to the Mobile Launcher for the duration of rollout and pad stay operations – as was the case with the Space Shuttle.
Currently, there is evidence to suggest that the mass of the SLS rocket combined with the vehicle stabilizer tower arm will be enough to secure the SLS rocket to the launch pad, thus negating the need to bolt the Solid Rocket Boosters to the mobile launcher in a way that would require them to be detonated prior to lift off – as was the case with Shuttle.
Wind tunnel testing and the move to Preliminary Design Reviews:
By the end of July, wind tunnel testing on the initial design of the SLS Block 1 was underway ahead of the rocket’s Preliminary Design Review.
The fact that SLS reached its Preliminary Design Review less than one year after its conception indicates that the program is maturing on pace to maintain the targeted maiden voyage of the SLS rocket in 2017 – something that is almost unheard of in the world of spaceflight.
Furthermore, from the documents leading into the Preliminary Design Review came the realization that NASA was investigating a new Block 1 version of the SLS rocket, the Block 1B – a vehicle that mitigates against the major and potentially costly changes of key hardware of the Block 1 design.
The addition of a new Block design to the SLS rocket family indicates a commitment to exploring the best options for the evolution of the vehicle, thus ensuring the best possible approach for a still developing exploration roadmap that will rely heavily on the SLS.
A new service module and advancements toward integration:
As the 2012 year entered its final months for the SLS rocket’s development, the Crawler Transporters were put through their paces for testing for SLS, and changes to the SLS engine heatshield design were announced.
The competition for the Advanced Booster contracts also heated up with the announcement that Dynetics and PWR (Pratt and Whitney Rocketdyne) are planning the resurrect the Apollo/Saturn V’s massive F1 engines for use on proposed Liquid Rocket Boosters for SLS, and pad escape options for pad workers and crews of future SLS missions were presented for discussion and fine tuning.
While these were significant advancements toward the eventual debut of the world’s new Heavy Lift Vehicle (HLV), significant news came in late November when the European Space Agency announced that they would offer to build an ATV (Automated Transfer Vehicle) -derived service module for Orion and that it would be ready to launch with the first unmanned Orion capsule for it circumlunar navigation voyage in 2017.
The news, which had been talked about for a several months prior to the official announcement, came only after the United Kingdom offered additional funding for the ATV service module project.
Kennedy Space Center prepares for the SLS:
While work on the development of the actual rocket continued, so to work to accommodate it at the Kennedy Space Center.
Undertaking a massive refurbishment and 21st-century technological upgrade initiative, the Kennedy Space Center saw significant upgrades to its facilities in 2012.
The multi-phased effort at the space center was deemed necessary in order to upgrade all of the equipment into the 21st-century.
This has been especially true at launch pad 39B where substantial work underneath the pad’s structure and at its water tower took place this year to upgrade systems to reduce the amount of effort that will be needed to monitor the SLS’s systems once the vehicle is realized on the launch pad.
According to KSC, “This project provides for extensive repair work for the 40-year-old launch pad infrastructure to prepare it for future lunch activity.
The project focuses on the concrete structures, and includes repairs to the pad’s slope, repairing the pad grating and trench systems, constructing water diversion improvements, repairing the catacombs and high pressure gas area walls and ceilings, repairing the flumes that lead to the north holding ponds, repairing the wildlife grates, and repairing the sound suppression water tower.”
A destination for SLS – Outlining potential missions for the new HLV:
While only two missions have been even remotely outlined for the SLS, the EM-1 and EM-2 circumlunar navigation missions of the Orion capsule, work continued behind-the-scenes to identify other potential uses for America’s new HLV.
In particular, interest in Near Earth Asteroid missions were presented as a logical stepping stones toward humanity’s eventual use of the SLS rocket to go to Mars.
However, several other options were also presented via an Exploration Roadmap conference in late 2011 which could help define both exploration targets and exploration gateway complexes that would make exploration of the inner solar system easier.
While the range of possibilities are vast, most of the Exploration Roadmap suggestions focused on Gateway platforms, complexes built in or around the Lagrangian points of the Earth-Moon system that would enable the stockpiling of supplies and propellant for space-constructed vehicles that would then be used to conduct missions to Near Earth Asteroids, the Moon, and eventually Mars.
The relevance of these propellant depots or Gateway platforms was made clear with the understanding that the stockpiling of supplies at these locations would reduce the weight that the SLS rocket would have to carry with it on every launch out of Earth orbit with the crews for missions to a Near Earth Asteroids or the Moon.
This savings in mass could then be allocated to other supplies or hardware devices that could not be stockpiled at Gateway platforms.
Moreover, the Exploration Roadmap and gateways presentations discussed the use of known technology aboard the International Space Station to assist in the building of these Lagrangian point platforms.
In fact, one of the goals of the gateways Exploration Roadmap presentation was the creation of a Deep Space Habitat vehicle, one that could be parked within one of the Earth-Moon Lagrangian points, flown to by a crew in the Orion capsule, and then used to either go to Near Earth Asteroids or perform long-duration, non-Low Earth Orbit crew stays.
In short, the Exploration Roadmap and gateways presentations advocated using the SLS to build non-Low Earth Orbit stations and vehicles that would utilize habitable module information and lessons learned from the modules comprising the International Space Station to capitalize off already known and understood technology while we continue to investigate the needed technology, systems, infrastructure, and human-related aids for an eventual multi-year mission to Mars.
(Images: Via L2 content from L2’s SLS specific L2 section, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. Other image via NASA)
(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here: https://www.nasaspaceflight.com/l2/)
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