Building the Roadmap for SLS – Con Ops lays out the LEO/Lunar Options

by Chris Bergin

With evaluations continuing into NASA’s future crewed exploration aspirations, the foundations behind what should be a definitive roadmap – otherwise known as Exploration Systems Development (ESD) Design Reference Missions (DRM) – are starting to come to light, as outlined in the Space Launch System (SLS) Concept Of Operations (Con Ops) document.

SLS Mission Ability – PART ONE:

The Roadmap – when announced – will lay out NASA’s flagship goals for the next 20 plus years. This task is under the stewardship of former Space Shuttle Program (SSP) manager John Shannon, who’s team have not released any information into their effort since it began months ago.

While the team is under no obligation to provide a running commentary to the public or media, the lack of a roadmap for SLS remains one of the main criticisms charged against the vehicle which will cost several billion dollars before it even flies.

However, while the November Human Space Exploration Community Workshop on the Global Exploration Roadmap – which is being serialized by this site – has provided some interesting mission options, the SLS Con Ops document – finalized just a few weeks prior to the workshop – reveals the actual foundation of SLS’ hardware, operations and indeed mission baselines.

Known as Exploration Systems Development (ESD) Design Reference Missions (DRM), the Con Ops document – available to download via L2 – introduces the SLS capability as one which provides multiple mission options, ahead of expanding into the current thought process for utilizing the vehicle’s unrivalled upmass capability.

“The SLS will have the largest payload lifting capacity of any launch vehicle previously manufactured in the United States: 70 metric ton (t) class evolvable to 130+ t class (ESD Requirement R-11),” noted the document in the introductory sections.

“This will allow the SLS to accommodate many mission profiles, starting with Orion missions for lunar fly-by and high lunar orbit and eventually deep space near Earth asteroid (NEA) and Mars missions that extend human presence across the solar system (requiring ~130 t).

“The SLS will also accommodate Orion-MPCV missions to low Earth orbit (LEO) for system test and checkout and as a back-up access to the International Space Station (ISS), including transport of replacement ISS modules. Other mission profiles that can be supported by the SLS include science-based missions for deep space astronomy and solar system exploration.

“The SLS payload capability will enable a new generation of planetary (such as a Europa fly-by to collect samples with return capability), Earth, and heliophysics science missions. SLS will also be capable of supporting commercial-based missions and missions supporting other Government agencies, including sending larger objects into LEO, such as commercial space stations.”

While the introduction provides little by way of additional substance into age-old adage of “Moon, Mars and Beyond” – as used by the now-defunct Constellation Program (CxP), the document goes on to provide an expansive and up-to-date overview of the DRMs, whilst adding the caveat the missions may not occur in any particular order and are not set requirements, but are used as a framework to ensure SLS capability.

“The ESD DRMs are categorized as Tactical, Strategic, Architecture, and Analysis timeframe DRMs. The Tactical Timeframe DRMs are intended to reduce overall design risk and help to preserve operations capabilities by allowing missions to be flown earlier in the design process,” the document notes.

“The Strategic DRMs build on the capabilities demonstrated in the Tactical timeframe to ensure a path to achieve the operational capabilities as laid out in the ESD Requirements. The collection of these DRMs is the architecture framework necessary for multi-destination exploration.

“The Architectural timeframe DRMs address the missions where evolved capabilities will be needed to achieve the long-term exploration objectives. These DRMs are critical in understanding the requisite system functionality, and deriving the Program-specific operations block designs that will enable an effective block delivery evolution path. Analysis DRMs are candidate DRMs that are under formal ESD consideration. Analysis will be performed on these DRMs as part of a cost/benefit assessment.

“Once ESD leadership has determined the status of an analysis DRM, the DRM will either be added to the appropriate timeframe DRMs or will be discarded. While programs will need to perform some level of analysis to support this decision-making process, the analysis that supports the evolvability design assessments is not necessary for Analysis DRMs.”

The wording of the above shows some of the challenges of formulating the definitive exploration plan – and the likely reason that as of today such a plan does not exist. NASA’s future plans continue to be hindered by a budget that lacks stability, as much as lawmakers have shown their hand in wishing to protect SLS and Orion from such budget fluctuations.

Ironically, one area of NASA funding which is being subjected to uncertainty is the commercial handover of Low Earth Orbit (LEO), not least from the commercial crew standpoint. With threats of slips – based on lower-than-expected funding and internal technical challenges – there is potential for the need of a back-up, as SLS was intended to be – per the 2010 Authorization Act – for the International Space Station.

However, with SLS’ opening mission – one which is BEO in design – not set to fly until 2017, such slips would have to be serious in nature for NASA to use a vehicle which is now designed specifically for exploration, as opposed to LEO.

Regardless, the back-up ability to transport four crew members on Orion, launched on a basic SLS, opens the DRM list.

“ISS Back-Up Crew Delivery (Analysis): The International Space Station (ISS) Back-Up Crew Delivery mission (DRM ID: LEO_Util_1A_C11A1) is flown with the SLS and the Orion-MPCV, with SLS providing any necessary ballast and launch stack spacers,” noted the presentation.

“This DRM is a single launch of up to four crew members to and from the ISS and is a back-up to the planned commercial crew capability for transportation to the ISS. This mission is flown using the Block 1 SLS without an iCPS.”

The next DRM is currently in the documented approach for SLS’ opening mission in 2017, one that involves an uncrewed test flight around the Moon, on a mission which – according to Con Ops – will last around eight days.

“BEO Uncrewed Lunar Fly-by (Tactical Timeframe): This mission uses a single Block 1 SLS launch with an iCPS and lunar Block 1 Orion-MPCV. This DRM will go beyond Earth orbit (BEO) and test critical mission events and performance in relevant environments,” the Con Ops document noted.

“It will take 3-4 days of transit time, with the Orion-MPCV trajectory taking it around the Moon performing burns as required, and then 3-4 days to return to Earth. The liftoff mass will be approximately 66 t.”

SLS-2 will carry out a similar mission, this time with a crew. Initially manifested for 2021 on the “worst case” scenario, moves have already been made by the Orion Project office to push this up to 2019, or potentially 2018. This mission will last around 14 days, with four days in Lunar orbit.

“BEO Crewed Lunar Orbit (Tactical Timeframe): This mission requires a single Block 1 SLS launch with an iCPS and Lunar Block 1 Orion-MPCV to LEO. It will take 4-5 days of transit time, 4 days in lunar orbit, and 4-5 days for return to Earth. The liftoff mass will be approximately 66 t.

“The iCPS performs the orbit raise burn and TLI (Trans-Lunar Injection) burn prior to disposal. When approaching high lunar orbit, the Orion-MPCV provides the lunar orbit insertion (LOI) burn to insert the Orion-MPCV into a high lunar orbit. The Orion-MPCV will remain in lunar orbit for several days and then perform a trans-Earth injection (TEI) burn and return to Earth.

“The lunar orbit will be selected to maintain the total delta-V for LOI and TEI maneuvers within the Orion-MPCV design capability.”

Opportunities to collect data on the hardware – most notably on Orion’s performance – will be taken via the Exploration Test Flight (EFT-1), scheduled for early 2014.

While these two missions appear to be the most solid part of the short-term mission plan for SLS and Orion, everything that follows is open for evaluation. However, the DRM content in the Con Ops provides multiple options, along with clues as to how such missions would be conducted.

One such example can be found under the DRM of a mission to Geostationary Orbit (GEO), utilizing two SLS launches, 180 days apart. Such a DRM scenario also dismisses the worst-case scenario which shows a maximum near-term flight rate of one launch per year – which would clearly be uneconomic for the HLV.

“GEO (Analysis): The GEO vicinity mission (DRM ID: CIS_GEO_1B_C11B1) requires two SLS launches, with the first carrying CPS1 and a cargo hauler. The second launch, approximately 180 days later, will contain CPS2 and the Orion-MPCV,” noted the overview.

“The mass-to-orbit for both launches will be approximately 110 t each. This would allow crew to perform servicing or deployment missions in GEO, depending on the payload inside the cargo hauler.”

Reverting back to aspirations involving the Moon, the next DRM has seen a large increase in interest over 2011, namely a mission to return humans back to the surface of the Moon.

Work appears to be making good progress on setting up a preferred flight profile for such a Lunar Surface, with one of three options set for deletion. Two of the options can be carried out prior to the evolved SLS coming on line.

“Lunar (Strategic and Architecture Timeframes): The lunar set of missions ranges in distance from lunar vicinity Lagrange Point 1 (L1), to low lunar orbit, to a lunar surface mission,” noted the ConOps.

“The first two of the three mission set, lunar vicinity and low lunar orbit (DRM IDs: CIS_LP1/LLO_1A1A_C11B1, Concept of Operations), which are in the Strategic timeframe, require one SLS launch with the Orion-MPCV and CPS to L1 or low lunar orbit (LLO). The mass-to-orbit for these two missions are approximately 90 t and 95 t, respectively.

“It should be noted that the low lunar vicinity DRM (CIS_LP1_1A_C11B1) is under ESD review for removal.”

The third option requires two SLS launches, this time around 120 days apart. However, the liftoff mass requires the use of the evolved SLS, pushing such a mission out to at least the late 2020s. See SLS configuration option latest (Block 1, 1A, 2) via L2

“The lunar surface mission (DRM IDs: LUN_SOR_1A1A_C11B1, ESD Concept of Operations), which is in the Architecture timeframe, requires two launches, spaced 120 days (TBR) apart, to insert the lunar lander and CPS1 and Orion-MPCV and CPS2 into LLO for a lunar orbit rendezvous (LOR) and landing on the equatorial or polar regions of the Moon. The liftoff masses will be approximately 130 t and 108 t, respectively.”

No reference is made to the fascinating proposal relating to the Exploration Gateway Platform architecture that not only returns man to the lunar surface – via the use of only one SLS launch to a reusable Lunar Lander – but provides a baseline for pathfinders towards an eventual crewed mission to Mars.

However, internal meeting notes (L2) just this month show this L2 gateway is now under official consideration, with mission options being evaluated at present.

“NASA Human Architecture Team (HAT): L2 based DRMs being developed,” noted the Strategic Analysis and Integration Division (SAID).

Such a plan revolves around a deep space platform, known as a gateway, located at Earth-Moon Lagrange (EML) point 1 or 2, after being built from pre-launched hardware, providing the host station for a reusable Lunar Lander – which would also be launched by the SLS.

The Gateway would first be constructed at the ISS, mainly using the Node 4/DHS (Docking Hub System), an orbiter external airlock, an MPLM (Multi-Purpose Logistics Module) habitat module, and an international module.

Further articles on the Gateway will be forthcoming, along with Part 2 to the ESD DRMs from the ConOps, which cover missions to Near Earth Asteroids, SLS science missions to as far out as Enceladus, and Department Of Defense (DOD) missions.

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