Utilizing the SLS to Build a Cis-Lunar Highway

The Earth seen rising above the Lunar horizon aboard Apollo 17, the last human mission to the Moon (Credit: NASA)

by Marcel F. Williams

By 2017,  American astronauts should be back in space aboard American made and launched private commercial vehicles. 2017 will also be the year that NASA launches it first true heavy lift vehicle since the days of Apollo.

SLS crew & cargo  vehicles

Some perceive the SLS as the antithesis of Commercial Crew development. But others view the Space Launch System as complimentary to Commercial Crew development. While Commercial Crew vehicles will enable Americans to have access to orbit again, the SLS launched  MPCV (Multipurpose Crew Vehicle) will give NASA the ability to launch humans practically anywhere within cis-lunar space-- and safely back to Earth's surface.

But  the Space Launch System could also be utilized to do a lot more.  

The SLS could be used to deploy a reusable cis-lunar architecture that could give passengers aboard Commercial Crew vehicles easy access to the surface of the Moon and to other commercially viable regions within cis-lunar space.

Below is a possible scenario that could make this happen by using a standard reusable ETLV (Extraterrestrial Landing Vehicle) derived architecture, starting in the year 2021. 

Nomenclature: 

EML (Earth Moon Lagrangian point); 
LEO (Low Earth Orbit); 
SLS (Space Launch System); 
MPCV (Multipurpose Crew Vehicle); 
CM (Command Module)
ETLV-2 (crewed Extraterrestrial Land Vehicle; 
ETLV-2R (Unmanned Automated ETLV-2); 
C-ETLV-4 (cargo lunar lander); 
WFD-OTV-5 (Water- Fuel Depot Orbital Transfer Vehicle); 
WFD-LV-5 (Water- Fuel Depot Lunar Landing Vehicle); 
RWT-LV-5 (Reusable Water Tanker Lunar Landing Vehicle); 
LRH (Lunar Regolith Habitat); 
Water Bug (Robotic Microwave Water Extraction Vehicle);
ATHLETE (All-Terrain Hex-Legged Extra-Terrestrial Explorer) 

Earth-Moon Lagrangian Points (Credit: NASA)

Before manned beyond LEO cis-lunar missions can begin, a new satellite communications system must be deployed at two of the Earth-Moon Lagrange points. Under this scenario, in  2020, a Delta IV heavy or an Atlas 401 will launch two satellites to EML2 (Earth-Moon Lagrange point 2). A second launch of either or the two vehicles will deploy two more communications satellites at EML1 (Earth-Moon Lagrange point 1).  This will allow continuous communications coverage for nearly the entire lunar surface. However, there will be some brief periods at some small mid-latitude regions that will be unable to communicate with the deployed constellation of Lagrange point satellites. But the deployment of satellite pairs at EML1 and EML2 should mostly eliminate the need for Earth-based tracking.

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)

 

2021

Unmanned ETLV-2R docked with the WFD-OTV-5 fuel depot at ELM1

Derived from the Extraterrestrial Landing Vehicle (ETLV), the WFD (Water Fuel Depot) OTV (Orbital Transfer Vehicle) will utilize the same  cryotanks used for the ETLV-2. But these will be five in number instead of two, fixed within a higher cruciform in order to enhance the depot's ability to store the maximum amount of cryofuel. The WFD-OTV-5 would be capable of storing nearly 70 tonnes of LOX/LH2 fuel in addition to more than 100 tonnes of water. However, when the WFD-OTV-5 fuel depot is initially deployed at EML1 by the SLS upper stage, it will contain only 20 tonnes of fuel and no water because the SLS upper stage will only be able to deliver a little more than  30 tonnes to the Lagrange point.

The first ETLV-2 mission to the lunar surface under this scenario will be an unmanned mission to the South Lunar Pole. But first the SLS will launch The ETLV-2R will be launched by the SLS to the fuel depot at  EML1. Although the ETLV-2R would be nearly fully fueled, some additional fuel would be required  in order  for the vehicle's return to the Lagrange point after landing on the lunar surface.

Once on  the lunar surface, a variety of small mobile robots will be deployed to explore the polar region, test water extraction technologies, and return a variety of samples from lunar regolith. After a few days, or a few weeks, the ETLV-2R will return to L1.

A similar mission will occur with the third launch of the SLS in 2021. But the unmanned destination will be the North Lunar Pole. Again, after  a few days, or a few weeks, the ETLV-2R will return to L1.

So the end of both unmanned missions to the lunar surface will not only retrieve lunar samples from the lunar poles but will twice demonstrate the ability of the ETLV-2 vehicle to travel to and from the lunar surface from L1 on a single fueling of it's twin tanks. These two demonstrations of the ETLV-2,  to and from the lunar surface, should enhance the safety of the first crewed mission of the ETLV-2 in 2022.

MPCV (Multipurpose Crew Vehicle) Credit: NASA

The fourth launch of the SLS that same year will be the first manned mission of the MPCV. Astronauts will be sent to EML1 to dock with both  ETLV-2 vehicles in order to retrieve the lunar material for return to Earth. The SLS upper stage will also carry nearly ten tonnes of water destined for the L1 fuel depot. The WFD-OTV-5 will convert this water into liquid hydrogen and oxygen, producing more than enough fuel to replace the extra fuel extracted by a single ETLV-2 on its way towards a round trip to the lunar surface.

Astronauts will return to Earth aboard the CM of the MPCV, demonstrating the vehicle's ability to travel within cis-lunar space while also bringing back precious regolith samples from the north and south lunar poles.

2022

C-ETLV-4 and the ETLV-2 cargo and crew lunar landing vehicles

The first SLS launch of 2022 will send the C-ETLV-4 lunar cargo vehicle directly to the lunar surface. An ATLETE robot will deploy two small mobile excavators, two mobile sintering robots, and a single back hoe for depositing regolith into the walled interior of human habitat structures.

ATLETE robot for offloading cargo from the C-ETLV-4 (Credit: NASA)

The ATLETE robot will be routinely relied upon to unload habitats and machines from future C-ETLV-4 missions to the lunar surface.  

Lunar excavation robots (Credit: Astrobotic Technology and Carnegie Mellon)

The mobile excavators will be used to remove rocks and level the surface area for eventual sintering. Mobile sintering machines will move over the paved area using microwaves to melt the lunar regolith, creating a hard sintered layer approximately 0.5 meters deep and a smooth  solid surface approximately 3 to 5 cm deep.  Two widely separated  areas will be prepared by the excavators and the sintering machines. One area will be for the deployment of the Lunar Regolith Habitats. The other area will be exclusively prepared for landings by the ETLV-2, C-ETLV-2, Reusable Water Tankers, and  lunar fuel depots. Both areas will be connected to each other by a paved and sintered road perhaps a kilometer or more long.

Lunar sintering robot (Credit: Credit: Larry Taylor)

The battery powered or fuel cell powered back hoe won't be utilized until the Lunar Regolith Habitats are deployed.

An electric powered (battery or fuel cell) back hoes would have to be deployed to the lunar surface in order to deposit lunar regolith inside of the regolith walls of a Lunar Regolith Habitat (LRH) (Credit: Volvo)

The second launch of the SLS in 2022 will deploy the Lunar Regolith Habitat. The ATLETE robot will remove the habitat from the top of the C-ETLV-4 and transport it to the sintered area previously prepared for human habitat occupation.

Lunar Regolith Habitat (LRH): Lunar regolith is deposited by the back hoe within the 2 meter cavity between the pressurized SLS hydrogen tank derived habitat area and the automatically deployed exterior wall.  This will  provide micrometeorite and thermal protection in addition to protection against major solar events and a reduction of cosmic radiation exposure to below maximum levels for radiation workers on Earth. Power for the habitat is provided by the solar panel on top. And radiators on top of the habitat help to regulate and dissipate excess heat. A mobile water tanker will periodically pump lunar water into the habitat for washing, cooking, drinking, growing food, and for the production of air.

Once it is in position, the LRH-1 will automatically expand its solar panel to recharge the habitat batteries. An SLS hydrogen tank derived pressurized habitat will automatically expand its wall panels to produce a rigid and continuous wall around the pressurized area, creating a 2 meter wide cavity between the wall and the pressurized habitat. The lunar back hoe will deposit lunar regolith inside of the cavity to the top of the regolith wall which will also extend approximately two meters above the top level of the pressurized habitat. This will provide astronauts, scientist, and other visitors to the habitat with thermal and micrometeorite protection while also protecting them from the radiation of major solar events and while also reducing their annual exposure to cosmic radiation to levels below that required for radiation workers on Earth. This will allow astronauts and scientist to continuously remain at such habitats for more than a decade without coming close to their lifetime NASA limits for radiation exposure.

Within the 8.4 meter in diameter pressurized housing, there would be two levels each with approximately  55 square meters of area. So each habitat level would be about the size of a one bedroom apartment on Earth. In total, these two levels would have more floor area than the average family home in Great Britain.  Airlocks derived from the ETLV tanks would be located below the pressurized habitat area.

The last two SLS launches in 2022 will send the ETLV-2 and the MPCV to EML1. Again, the water will also be delivered to the fuel depot at L1 during the MPCV launch to EML1. After adding additional fuel, the ETLV-2 will deliver six astronauts, four Americans and two foreign guest  to the lunar surface. But they will only spend a few days or a few days on the lunar surface to inspect the lunar habitat and to collect more lunar samples.   The ETLV-2 will return the astronauts back to EML1 where it will dock with the MPCV for the crews return to Earth. The ETLV-2 will remain at L1 for future use once new fuel is being manufactured at L1 from lunar water resources. And it will be part of a fleet of three reusable vehicles starting in 2025.

2023

The solar powered WFD-LV-5 will be able to store Lunar water while also being able to  convert water into liquid hydrogen and oxygen for storage and distribution. Mobile cryotankers will extract cryofuels from the fuel depot for fueling space vehicles like the ETLV-2. Mobile water tankers supply the  fuel depot with Lunar water from the Water Bugs .

The first SLS launch of 2023  will send a solar powered water storage and cryofuel producing depot to the new lunar outpost. This will be followed just a few weeks later by the  C-ETLV-4 deployment of two mobile cryotankers derived from ETLV cryotank technology.  The mobile cryotankers will be used to extract cryofuels from the WFD-LV-5 lunar fuel depots in order to  refuel lunar landing vehicles. The mobile cryotankers will also be capable of scavenging residual fuel from the dormant C-ETLV-4 vehicles.

2023 will end with another pair of SLS launches for the ETLV-2 and MPCV  in order for another temporary human  visit to the lunar outpost . 

2024

Mobile water tanker next to a Water Bug robotic microwave water extraction vehicle. Water Bugs will recharge their batteries in the sunlight before venturing within shadowed craters for water mining. Mobile water tankers will extract the water from the Water Bugs for deposition at the fuel depot or in lunar water bags.

2024 will open with the SLS launch of a C-ETLV-4 to the lunar outpost. The ATHLETE robot will deploy two mobile water tankers plus a twin pair of Water Bug  microwave water extraction vehicles. Each Water Bugs should be able to extract as much as one to two tonnes of water from the lunar ice deposits per day. Excess water that can't be accommodated by the fuel depot, the mobile tankers, and the lunar habitats will be stored in water bags at the outpost.

A second SLS launch in 2024 will use the C-ETLV-4 to deploy a second habitat to the lunar outpost (LRH-2). The second habitat will double the area for human accommodations at the outpost. Each habitat will also serve as backup accommodations for the other in case there is a  serious malfunction at one of the habs.

Two SLS launches will end the year, bringing the first long term inhabitants to the lunar outpost. Some of these individuals will remain on the lunar surface for more than a year simply to determine if there are any deleterious physical or psychological effects for human individuals after living in a low gravity environment for more than a year. Before the first human attempts to venture to the orbit of Mars and to the Martian surface, some astronauts will have to eventually stay on the lunar surface as long as four years.  The results of these simple human test on the lunar surface could have enormous implications for humanity's future in the rest of the  solar system.

 2025

RWT-LV-5 water tanker next to the ETLV-2

A single SLS launch in 2025 will deploy two reusable lunar water tankers to the lunar outpost. Each vehicle will be capable of transporting more than 50 tonnes of lunar water to the EML1 fuel depots per flight while still being able to return to the lunar surface. With their CECE engines, each vehicle should be capable of at least ten round trips between ELM1 and the lunar surface before their engines or the entire vehicle is replaced.  

RWT-LV-5 transferring lunar water to the WFD-OTV-5 at ELM1

A single SLS launch will be used to deploy three partially fueled Orbital Transfer Vehicles (OTV-2) to LEO. Three expandable aerobrakes will accompany the three vehicles into orbit. Each OTV-2 will have enough fuel to reach the fuel depots at EML1. The OTV-2 is simply an ETLV-2 without the landing legs. So there will be minimal development cost for the vehicle. The aerobrake will be required in order to minimize fuel utilization upon returning from the Lagrange points to Earth orbit.

An OTV-2 preparing to dock with an Aerobrake Shield and another OTV-2 docked with an Aerobrake Shield

The deployment of the reusable OTV-2 vehicles will  mean that an SLS launch of the MPCV will no longer be necessary in order to transport astronauts to the Earth-Moon Lagrange points. However, NASA astronauts will still need to be able to get to LEO in order to access the OTV-2. But by 2025, NASA should have a wide variety of  Commercial Crew and foreign vehicles available to give NASA astronauts access to orbit.    

Russian Soyuz

Chinese Shenzhou

Dream Chaser (Credit: Sierra Nevada Co.)

Dragon (Credit: Space X)

CST-100 (Credit: Boeing)

SKYLON (Credit: REACTION ENGINES LTD)

 Commercial Companies could also have private commercial access to the lunar surface by simply purchasing an OTV-2 and an ETLV-2 from the American vendors that produce them. And this could allow private American companies them to provide access to the lunar surface to other nations and for wealthy space tourist and space lotto winners. So as early as 2026, reusable ETLV derived vehicles and fuel depots deployed by the SLS could allow private Commercial Crew companies to expand space tourism and other commercial enterprises all the way to the lunar surface.

OTV-2 docked with an ETLV-2 lunar landing vehicle at EML1

A single SLS launch will deploy two additional fuel depots (WFD-OTV-5) to LEO. One will use its own engines to reach EML1 while the other will remain at LEO to refuel the OTV-2 vehicles. Once a  LEO fuel depot begins to run low on fuel, it will transport itself to EML1 to be refueled with water from the lunar tankers in order to manufacture enough fuel for its redeployment back at LEO.

X-Ray of Skylab II with its SLS derived pressurized habitat at ELM1 (Credit: Griffin)

The final SLS launch in 2025 will be to deploy an SLS hydrogen fuel tank derived habitat with an internal hypergravity centrifuge to EML1. Lunar water exported to L1 will provide enough radiation shielding for the Lagrange point habitat to protect astronauts from a major solar event. The deployment of the lunar water shielded Skylab II will be first test  of a potential interplanetary habitat for possible manned missions to the orbit of Mars.

 Marcel F. Williams
© 2014 MuOmega Enterprises

Links and References

• LOW-COST LUNAR COMMUNICATION AND NAVIGATION
•  Utilizing Space Shuttle Main Engines (SSME) for Early SLS Cargo Launches and Commercial Crew Destinations
• An SLS Launched Cargo and Crew Lunar Transportation System Utilizing an ETLV Architecture
• The SLS and the Case for a Reusable Lunar Lander
• Mission and Implementation of an Affordable Lunar Return (Spudis & Lavoie) 
•  Using the resources of the Moon to create a permanent, cislunar space faring system (Spudis & Lavoie)
•  The Future of NASA and the Commercial Crew Program
• How ATHLETE Robots could Deploy Pressurized Habitats and other Large Payloads to the Lunar Surface 
• Microwave Sintering of Lunar Soil: Properties, Theory, and Practice
• Cooking Up Water From the Moon? NASA Studies Water Extraction With Microwaves 
  
   

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. 

___________________________________________

 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)

_________________________________________

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