With the recent announcement the Space Launch System (SLS) has become challenged by her schedule, the NASA rocket may soon find herself in a battle with a commercial “alternative”. SpaceX’s super powerful Exploration Class rocket is targeting crewed missions to Mars up to 10 years ahead of SLS – although both vehicles continue to avoid being classed as competitors.

Monster Rockets:

The requirement of a Heavy Lift Launch Vehicle (or HLV) for lofting large payloads into deep space has been a central element of mission architectures since the Apollo program.

During the Space Race, both the Soviet Union (with the N1 rocket) and the United States (with the Saturn V) were challenged with sending humans to the surface of the Moon, assisted by the power of a HLV.

While the N1 suffered from four launch failures, the Saturn V was a success, allowing the United States to achieve the historic goal of Man on the Moon.

Since NASA returned to the realm of Low Earth Orbit (LEO) via the Space Shuttle Program (SSP), plans for a new HLV have been numerous, such as the National Launch System (NLS) evaluations in the early 1990s.

Although some experts claim a HLV is a luxury budget item – and instead promote the use of a train of Medium Lift Launchers to loft numerous elements of payloads for assembly in orbit – the “need” for an Exploration Class HLV has usually been at the forefront of NASA’s exploration mindset.

The since-defunct Constellation Program (CxP) concurred with this requirement, working via the Exploration Systems Architecture Study (ESAS) recommendations that created a “1.5 architecture” of the Ares I crew vehicle and the Ares V HLV.

Both before and after CxP’s cancellation, alternatives were already being discussed, once again with a HLV at the center of the evaluations.

Alternatives ranged from Agency to independent proposals, such as the DIRECT movement that was created via members of the NASASpaceFlight.com forum, before earning a review by the Augustine Commission’s Review of the USA’s Human Space Flight plans in 2009.

That review also discussed the Flexible Path approach, which recommended a monster 200 metric ton human rated “Exploration Class” launch vehicle as a future proof rocket.

“Exploration-Class Rocket: A human-rated system with LEO throw-mass on the order of 200 mT, designed purposely for extremely high reliability and minimum operations cost, rather than being sized directly by an architecture that may change later,” noted the impressive presentation (available in L2).

“200 mT, sized by ‘knee in the curve’ of launch vehicle economics. Not driven by the architecture de jour.”

In what was a precursor to the eventual selection of the SLS, Shuttle-Derived HLVs were also promoted at the Augustine Commission, with the goal of a smoother transition between the Shuttle Program and the opening exploration missions.

In some cases, this involved a Shuttle extension using two orbiters, flying for several years after their planned retirement date.

In tandem, a SD HLV was to be brought into action, beginning with a side-mounted HLV that would eventually become an in-line HLV, both of which heavily utilized Shuttle hardware.

This plan was created under the leadership of former SSP manager John Shannon, resulting in the creation of an extensive 726 page presentation (available in L2).

However, this proposal fell by the wayside, as political direction called for a much deeper evaluation of NASA’s next big rocket.

Numerous vehicles and concepts were evaluated by three main bodies of engineers and experts at the Marshall Space Flight Center (MSFC), known as the Requirements Analysis Cycle (RAC) teams.

RAC-1 studied in-line, LH2 core vehicles with Solid Rocket Boosters (SRBs). RAC-2 studied a Saturn V-type vehicles, utilizing an RP-1 first stage and LH2 second stages. RAC-3 studied vehicle designs based around several options, such as EELVs, with a large amount of latitude to study different tank sizes.

While the winning RAC-1 vehicle was selected as the rocket to pursue, memos showed RAC-2 team members thought they had won the study, while RAC-3 observers claimed the EELV companies weren’t even consulted on the evaluations based around their vehicles.

On To SLS:

In the end, the RAC-1 SD HLV was confirmed as the winner, not least due to the political language in the 2010 Authorization Act that insisted on utilizing Shuttle and former CxP hardware as key ingredients for the rocket.

That rocket would be named the Space Launch System (SLS) and was formerly announced in 2011.

The rocket was to be evolved over time, opening with the 70mT Block 1, that was set to debut in 2016, prior to a cost review pushing the opening launch to 2017.

This was to be followed by an intermediate Block 1A/B, capable of 105 mT and set to be the workhorse of the 2020s, prior to the Mars-class Block 2 in the 2030s, with a lift capacity of 130 mT.

The SLS rocket has enjoyed a far less dramatic childhood when compared to the Ares woes of the Constellation Program.

Refinement of the vehicle’s specifications have all proceeded to plan, with thousands and thousands of technical drawings created ahead of being fed into the machinery at the Michoud Assembly Facility (MAF) where the rocket will be built.

For all her technological charms, SLS still lacks a viable number of missions.

While the overall plan is to utilize the rocket in the “proving grounds” of visiting asteroids, the ultimate aim remains focused on Mars – as much as no detailed plans exist and remain a distance dream of being realized in the mid-2030s.

Only two missions are currently on the books, the first of which now “slipped” to November, 2018.

While Exploration Mission -1 (EM-1) was classed as likely to slip for some time – specific to schedule issues with the development of the much-much-maligned Orion spacecraft – internal documentation was showing a slip to around the summer of 2018.

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In presenting the new date as not an actual slip this week, NASA managers noted they will try and improve on the November, 2018 date. However, despite the billions of dollars already spent, the new date is only at a 70 percent confidence level, per the milestone of the KDP-C (Key Decision Point -C).

SLS will also have to negotiate the minefield of a change of President in 2016, an event that always risks a dramatic redirection in space policy.

Not The Only American HLV:

SpaceX has made no secret of its intentions to send humans to the Mars, not least when the company’s founder and CEO, Elon Musk, told the BBC’s Jonathan Amos that he wants to be able to go to the Red Planet himself, before he gets “too old”.

That level of personal motivation is likely to hold several advantages when compared to NASA and its constraints of being at the mercy of lawmakers.

Mr. Musk’s aspiration of tasking SpaceX with the goal of driving humanity to become a multi-planetary species is claimed to be an accelerated path, when compared to NASA’s notional roadmap.

While NASA is aiming for humans on Mars in the mid 2030s, SpaceX’s ambition is to achieve that milestone by the mid 2020s.

At the heart of that plan is another HLV, a key driver of the Mars Colonial Transporter (MCT) system.

SpaceX is expected to build a family of Super Heavy Lift Launch Vehicles (SHLVs) driven by nine Raptor “full flow methane-liquid oxygen” rocket engines.

While the plans are still being refined, to the point that only sketchy details have been provided, the Raptor engine is already preparing to test components at NASA’s Stennis Space Center.

“Raptor is a very large LOX/methane engine which we are working on as a follow-on to Falcon Heavy, a Super Heavy if you will, but I don’t think we’re calling it that,” noted Dragon V2 Program Lead Dr. Garrett Reisman to the Future In-Space Operations (FISO) Working Group this week.

“It’s currently undergoing component testing at Stennis. Starting injector testing and other component testing. We’re deep into the design process and component testing.”

Sources note that component design has progressed to the 3D printing stage, ahead of a test regime at the E-2 test stand at Stennis, which has been upgraded to allow for the use of methane.

The SpaceX Super Heavy Lift Launch Vehicle (SHLV) – which does not yet have an official name, but is widely known in the space community as the BFR (Big ‘Frakking’ Rocket) – would be very big and very powerful indeed.

In a rare insight into the vehicle, SpaceX Vice President (VP) of Propulsion Development Tom Mueller – speaking at the “Exploring the Next Frontier: The Commercialization of Space is Lifting Off” event earlier this year in Santa Barbara, California – revealed the Raptor engine had already mutated to a 1Mlbf (4,500kN) gas-gas (full flow) liquid methane and oxygen engine.

Mr. Mueller then later updated his numbers at a follow-on conference to portray 6,900 kN of sea-level thrust, and 8,200 kN of vacuum thrust.

Further refinements to the numbers are expected, as the development cycle – which is still in its infancy – continues through to full engine testing.

However, it is clear SpaceX envisions a rocket far more powerful than even the fully evolved Block 2 SLS – a NASA rocket that isn’t set to be launched until the 2030s.

SpaceX’s monster rocket will utilize nine Raptor engines on a 10 meter diameter core, with the potential to advance the vehicle to a triple core. Other options are understood to include 12.5m and 15m cores, although those focus on the single core HLV.

The eventual goal would be to allow for a rocket capable of lofting the MCT spacecraft, transporting 100 colonists at a time to Mars. The launch system would also be fully reusable.

Such a colonization effort would be be deep into the future. However, the initial launch of the first Raptor-driven BFR could occur before the end of the decade.

While that is a highly ambitious time scale, it would result in the BFR debuting close to the time NASA’s SLS will be conducting test flights.

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It is notable, yet understandable, that SpaceX has never openly portrayed its BFR plans in competition with NASA’s SLS.

The Agency is SpaceX’s biggest customer and Mr. Musk has noted on more than one occasion that his company owes a debt of gratitude for NASA’s support and contracts during this early phase of its existence.

Also, when asked about SLS during a recent interview on “The Space Show”, SpaceX President Gwynne Shotwell diplomatically avoided being drawn on commenting about NASA’s HLV.

However, should SpaceX make solid progress on the development of its BFR over the coming years, it is almost unavoidable that America’s two HLVs will attract comparisons and a healthy debate, potentially at the political level.

(Images: via SpaceX, NASA, SLS L2, SpaceX L2. BFR/MCT graphics via L2, created by L2 members – click here the large range of renderings in L2. These are not official SpaceX graphics).

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