An SLS Launched Cargo and Crew Lunar Transportation System Utilizing an ETLV Architecture

SLS launched ETLV-2 at EML1 liquid hydrogen and oxygen  fuel depot (ETLV derived) while the MPCV waits to dock with the now fully fueled lunar landing vehicle

by Marcel F. Williams

Before the end of the decade, the heavy lift capability that America once had during the Apollo  era-- will return in the form of the SLS.  Some, however, have argued that because of the former Space Shuttle's ability to deploy a 94 tonne aerospace plane plus up to 25 tonnes of useful cargo to LEO that , technically,  the Shuttle was also a  heavy lift vehicle. But even the earliest versions of the Space Launch System will be  far more capable than the Space Shuttle in their ability to lift huge payloads into orbit. Unmanned versions of the  SLS should be capable of deploying at least  70 tonnes of payload to LEO.  And with an SLS derived upperstage, as much as 105 tonnes of cargo could be lifted to orbit. Even when deploying the 22 tonne MPCV (Multipurpose Crew Vehicle), the SLS should still be capable of simultaneously  lifting an additional 45 to 80 tonnes of cargo to orbital space.

SLS crew launch and cargo launch vehicles; with an upper stage, the SLS would be capable of deploying nearly 39 tonnes of payload to Trans-Lunar Injection

Still there are those who argue that the SLS could  be deficient in its ability to deploy large crew landers and heavy cargo to the lunar surface-- relative to the now cancelled Ares V configurations. However, any deficiency in the lifting capability of the SLS could be easily compensated for by  deploying-- fuel depots-- at the Earth-Moon Lagrange Points, or in low Lunar orbit, or both. This might suggest to some NASA critics that the space agency would have to spend substantially more of its limited funds in order to finance still another expensive component for  its beyond LEO architecture-- in addition to funding the development of  lunar crew and cargo vehicles. 

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 Delta-V budgets & Destination Travel Times

LEO to TLI - 3.2 km/s dv

LEO to LLO (~2 days) - 4.5 km/s dv

LEO to LLO (~4 days) - 3.97 km/s dv

LEO to EML1 (~2 days) - 4.41 km/s dv

LEO to EML1 (~4 days) - 3.77 km/s dv

EML1 to or from LLO (~2 days) - 0.75 km/s dv

EML1 to or from  LLO (~3 days) - 0.64 km/s dv

LLO to or from the Lunar surface - 1.87 to 2.1 km/s dv

LEO: Low Earth Orbit; TLI: Trans-Lunar Injection; LLO: Low Lunar Orbit; 

EML1: Earth Moon Lagrange Point 1

(Credit John Connolly: NASA-JSC - 2012)

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However, if the next lunar landing vehicle developed for NASA is a-- single stage reusable spacecraft-- then a Lagrange point  fuel depot and a lunar surface fuel  depot  could both be derived from the reusable lunar lander.  Such a reusable single staged lunar vehicle-- would already be inherently designed to refuel and store cryogenic fuels with zero boil-off. So deriving the fuel depot directly from the tanks utilized for the lunar landing vehicle could significantly reduce development cost. Additionally,  the landing vehicle's reusability should also substantially  reduce its annual recurring cost for transporting humans to the lunar surface. 

In an earlier post, I described a reusable single staged lunar landing vehicle concept that  I called the ETLV-2 (Extraterrestrial Landing Vehicle 2). The vehicle would be designed to take  full advantage of a large  8.4 meter to 10 meter SLS payload fairing.  

The ETLV-2 would utilize four CECE engines but just two common bulkhead tanks; each tank would be capable of storing up to 14 tonnes of liquid oxygen and hydrogen fuel. The tanks would utilize a ULA type of Integrated Vehicle Fluid (IVF) technology plus NASA's breakthrough  cryocooler technology to eliminate fuel boil-off and the waste of ullage gases. Such technologies could substantially reduce tank insulation and the overall weight of the space vehicle. 

Basic components of the ETLV-2 lunar landing vehicle

The four RL-10 derived CECE (Common Extensible Cryogenic Engine) engines should enhance vehicle safety with engine out capability and reusability with up to 50 restarts capability. 

Vehicle development cost are further reduced in this concept by deriving the crew habitat module and airlocks from the light weight cryotanks. The pressurized crew hab should be tall enough to accommodate a crew of at least seven individuals, pressure suits, and small cargo on three floor levels. Such a large crew capacity would  make the ETLV-2 potentially compatible with Commercial Crew launched vehicles since such privately operated vehicles should be capable of transporting as many as seven individuals  to Earth orbit per flight. The ETLV-2 would, of course,  also be capable accommodating the maximum crew of six aboard the MPCV.    

The twin airlocks of the ETLV-2 would be utilized for giving humans access to the lunar surface through one airlock  while the second airlock will allow small mobile robots and mobile vehicles access to the lunar surface on the opposite side of the vehicle.  As an unmanned vehicle, the ETLV-2 could potentially be utilized for robotic sample retrieval missions to the lunar surface and possibly to the surfaces of the moons of Mars. In both cases, the regolith samples retrieved from deployed mobile robots would be returned to the Earth-Moon Lagrange points where a MPCV would dock with the unmanned ETLV-2 to pick up the samples for their journey to the Earth.  

Fully fueled, the ETLV-2 should still weigh less than 38 tonnes and could, therefore, be deployed to TLI by the SLS upper stage. 

ETLV-2 lunar landing vehicle: front, corners, & top views

While the ETLV-2 lunar lander would use only two long fuel tanks for its crewed missions to the lunar surface, the EML1 fuel depot concept proposed here would utilize five of the  ETLV-2 tanks within a taller cruciform. The EML1 fuel depot could potentially store more than 60 tonnes of cryogenic fuels.  The L1 fuel depot envisioned here would also be capable of perpetually storing up to 100 tonnes of water and be capable of converting the water into liquid hydrogen and oxygen through solar powered electroysis and cryocooler technology. The space fuel depot would also be capable of self deploying itself practically anywhere within cis-lunar space and even into orbit around Mars and Venus.

A single SLS launch would initially be required to deploy the fuel depot  to EML1 with as much as 20 tonnes of cryogenic fuel. Since the ETLV-2 crew lander  would only require a few extra tonnes of additional fuel when it arrived at L1, 20 tonnes should be enough fuel for perhaps three round trips from L1 to the lunar surface-- if new mostly fueled ETLV-2 vehicle arrives at L1 each time from Earth.   However,  MPCV launches by the SLS to EML1 should be capable of carrying several tonnes of additional cargo. So several tonnes of water cargo could be stored aboard the SLS upper stage along with the MPCV. So any extraction of fuel from the EML1 depot for crewed ETLV-2 lunar missions could be replaced  by water deliveries tagging along with the MPCV flights. 
 An  ETLV derived cargo lander (C-ETLV-4) would be used to deliver up to ten tonnes of payload to the lunar surface. The C-ETLV-4 would be primarily used for deploying the heavy machinery, ground vehicles, and crew habitats necessary to establish a permanently peopled  water and fuel producing and exporting Lunar outpost-- similar to that envisioned by Dr. Spudis and Lovoie in their most recent papers. 

C-ETLV-4 Cargo Lunar Lander: front, top, and interior position of fuel tanks

Since I envision NASA having at least two operational SLS launch pads by the early 2020s-- a two launch scenario-- would be utilized for early manned missions to the lunar surface. Such a launch infrastructure could also allow at least four heavy lift launches per year for both cargo and crew missions. 

NASA's first manned lunar mission utilizing the SLS  could send the ETLV-2 to TLI (Trans-Lunar Injection) where the remotely controlled unmanned crew lander will separate from the SLS upper stage and utilize some of its fuel to reach EML1. The ETLV-2 will then dock with the previously SLS deployed  EML1 fuel depot in order to add the additional required fuel for its round trip journey to the lunar surface and back to L1.

A second SLS launch, probably a few days later,  would send the MPCV plus a few tonnes of water  to EML1. The MPCV will dock with the fully fueled ETLV-2 and the crew (up to 6 people) will transfer to the lunar lander for their  journey to the Lunar surface and then, eventually, back to L1 after their lunar mission is over. The EML1 fuel depot will dock with the water tank, stored at the top of  the SLS upper stage, and pump the water into the fuel depot water compartment where it will eventually be converted into liquid hydrogen and oxygen.

On their return trip to EML1, the crew will transfer back to the MPCV for their return to Earth.  Under this scenario, the deployed ETLV-2 would remain at L1  until the EML1 fuel depot is finally being supplied with water from the lunar surface for the manufacture of extraterrestrial fuel. This will allow a small fleet of reusable lunar landers to be deployed at EML1 by the SLS over just a few years for future use for manned lunar missions. Once an ETLV-2 vehicle is reactivated, it will refuel at L1 and then travel-- unmanned back to the lunar surface--  to ensure that the reusable vehicle is fully functional for human use again.  The ETLV-2's CECE engines could be utilized for at least ten round trips before they would be required to be replaced-- or the landing vehicle retired.

I should note that the two launch scenario can also be utilized-- even if their is only one launch pad for the SLS (delaying the next launch from the pad for a few months)-- since the ETLV-2 would be equiped with cryocoolers capable of re-liquifying ullage gasses from is fuel tanks, providing zero boil-off of fuel for several months or even several years. However, limiting the SLS  to just two launches per year would substantially slow down  progress towards establishing  manned outpost on the lunar surface and eventually on the surface of Mars. But there's really no logical reason to limit heavy lift launches to just two a year since NASA was able to launch as many as-- four heavy lift vehicles per year-- during the Apollo era and as many as nine Space Shuttle missions per year during the peak of the Shuttle era! 

Once the fleet of ETLV-2 landing vehicles are utilizing lunar fuel resources for their operation and lunar water is being exported to the EML1 fuel depot from ETLV derived lunar tankers, NASA should then be able to incorporate the use of Commercial Crew vehicles as a cheaper component for sending astronauts to the Lunar surface. Reusable, ETLV-2 derived reusable Orbital Transfer Vehicles (OTVs) equipped  with delta-v reducing aerobrakers should allow NASA to travel between LEO and EML1 a lot more cheaply. NASA astronauts and possibly even space tourist could then travel to the Moon by first taking  a Commercial Crew vehicle to LEO where they would dock with an ETLV-2 derived OTV that utilizes lunar fuel stored at EML1 and possibly also at LEO. Once at EML1, the ETLV-2 would take the passengers down to the lunar surface.

So under this proposed scenario, the SLS and the MPCV could be used to set up a reusable  transportation infrastructure that could eventually give passengers aboard private Commercial Crew launch vehicles affordable and convenient access to the surface of the Moon-- just a few years after the SLS/MPCV/ETLV program begins.  

Further details about the ETLV components that will give Commercial Crew passengers access to the lunar surface will be discussed  in more detail  in future post.

 Marcel F. Williams
© 2013 MuOmega Enterprises

Links and References

1. The SLS and the Case for a Reusable Lunar lander 

2.  Mission and Implementation of an Affordable Lunar Return (Spudis & Lavoie)

 3. Using the resources of the Moon to create a permanent, cislunar space faring system (Spudis & Lavoie)

4. Human Lunar Exploration Architectures
 
5. Conquering Cis-Lunar Space with Shuttle and ULA Derived Technologies

6. Review of Human Spaceflight Plans Committee