First Human Voyages to the Martian Moons Using SLS and IVF Derived Technologies

Originally utilized for human operations withing cis-lunar space in the 2020s, the reusable LOX/LH2 fueled ETLV-2 now heads towards its first crewed rendezvous and landing on the surface of the martian moon, Phobos, in 2031.

by Marcel F. Williams

NASA suggest that the first human missions to Mars will occur sometime in the 2030s. While the Obama administration has merely suggested a  Mars flyby  for the first crewed interplanetary voyage,  others have proposed much more ambitious early human missions near the vicinity of the Red Planet. One frequent proposal is for a crewed journey  to the orbit of  Mars. Such an orbital mission could also include landings on at least one or both of the martian moons: Phobos and Deimos.

However,  any serious efforts to transport humans on multi-year interplanetary voyages has to resolve the inherent problems of enhanced exposure to cosmic radiation  and major solar events.  Also, the deleterious effects of long term exposure to a microgravity environment over the course of several months and even years has to be resolved.

Mass shielding habitat areas with at least 30 centimeters of water could protect astronauts from the dangers of major solar storms while also enabling multiyear round trip missions to Mars and Venus without excessive exposure to cosmic radiation-- even during solar minimum conditions.  The deleterious effects of microgravity on the human body could also be eliminated or, at least, substantially reduced  by transporting astronauts aboard  rotating interplanetary vessels with twin counterbalancing habitat modules.

However, a water shielded spacecraft with rotating habitat modules  would substantially increase the mass of a crewed interplanetary vessel. One way to compensate for the increase in vehicle mass would be to launch the interplanetary vessel from one of the Earth-Moon Lagrange points-- instead of from LEO. This could shave off at  least 2.8 km/s of delta-v requirement for an interplanetary mission. Dumping the water shielding for the twin habitat modules just a few hours, or a few days,  before  final trajectory burns into  orbit could also substantially reduce the propellant requirements for an interplanetary vehicle.  Finally, utilizing pre-deployed propellant producing water depots supplied with water from the Moon's low gravity well  could also substantially  reduce the propellant requirement for a reusable  interplanetary vehicle.

The crewed interplanetary mission to Mars orbit presented in this article, combines Boeing's SLS propellant tank technology with the ULA's (United Launch Alliance)  emerging IVF (Integrated Vehicle Fluid) technology to create reusable interplanetary spacecraft and  propellant producing water depots for human interplanetary missions to the orbits of Mars and Venus.

In 2030, under this scenario,  eight American astronauts and four foreign astronauts will depart from Earth-Moon Lagrange point four (EML4) towards a flyby of the planet Venus and then, a few months later,  into high Mars orbit. During the interplanetary mission, astronauts will visit both of the martian moons, Phobos and Deimos, returning to Earth after the 22 month mission with a significant tonnage and variety of regolith samples from the moons of Mars. Water exported from the surface of the Moon from one of the  lunar poles will be used to provide the water and propellant needed for the interplanetary mission.

Propellant producing water depot (WPD-LV-5A) on the lunar surface next to a mobile water tanker, LOX/LH2 cryotanker, and a Water Bug mobile microwave water extraction robot.

Nomenclature:

ETLV-2 (Extraterrestrial Landing Vehicle): Reusable LOX/LH2 vehicle capable of landing crews on the surface of the Moon or on the moons of Mars.

LWS (LEO Way Station): Large pressurized microgravity habitat (8.4 meters in diameter) in low Earth orbit derived from SLS hydrogen propellant tank technology.

CLV-5B: Cargo landing vehicles originally utilized to land large payloads on the lunar surface but  that are later utilized as reusable water tankers by latching a water bag to the top of the spacecraft. 

CLV-5A: Reusable cargo landing vehicle specifically designed to transport water,  regolith, or other heavy cargo from the lunar surface to the Earth-Moon Lagrange points.

OTV-400: Reusable SLS hydrogen tank derived orbital transfer vehicle capable of storing up to 400 tonnes of LOX/LH2 propellant. It uses IVF technology to power thrusters for attitude control.

WPD-OTV-400: OTV-400 derived water storage and propellant manufacturing and storage depot capable of storing up to 1000 tonnes of water and up to 400 tonnes of LOX/LH2 propellant.

AGH (Artificial Gravity Habitat):  rotating  pressurized  artificial gravity habitats derived from   SLS hydrogen propellant tank technology. 

Odyssey: Crewed interplanetary vehicle with OTV-400, AGH, and ETLV-2 components  capable of transporting 8 to 16 astronauts  to the orbits of Mars and Venus.


Mars Mission Scenario:

February 2030: OTV-400 trajectory burns transports Odyssey interplanetary spacecraft from EML4 into a Venus-Mars Transfer Orbit.

July 2030: Odyssey spacecraft flyby of Venus with minor OTV-400 trajectory burn (`80 m/s delta-v)

February 2031: OTV-400 trajectory burn places Odyssey into a high Mars orbit.

February, March, and April of 2031: Two crewed  ETLV-2 missions to the martian moon, Deimos and two crewed missions to the surface  of Phobos

April 2031: OTV-400 trajectory burns transports Odyssey spacecraft from high Mars orbit into an Earth transfer orbit.

December 2031: OTV-400 trajectory burns places the Odyssey spacecraft back into a halo orbit at EML4.

Maximum radiation exposure during the 18 month mission during solar minimum conditions (under 30 cm of water shielding aboard the Odyssey and  including 10 days of temporary full exposure during orbital insertion and ETLV-2 visits to Phobos and Deimos): less than 50 Rem.

CLV-5A water tanker capable of  transporting more than 50 tonnes of lunar water to the Earth-Moon Lagrange points. Mobile water tanker and a mobile LOX/LH2 cryotanker are near the shuttle spacecraft.

Cis-Lunar Space

During the early 2020s, a series of SLS cargo launches will be utilized to deploy a water and propellant producing and exporting infrastructure at one of the lunar poles .  So starting in 2026, this will allow NASA to   to focus its priorities  on  deploying the interplanetary infrastructure that will be necessary to take humans to the orbit of Mars in 2031-- and eventually to the surface of Mars in 2036.  Under this scenario, the interplanetary infrastructure needed to accomplish these goals will mostly be derived from the technology and infrastructure developed for the cis-lunar program.

CLV-5A   rendezvous with WPD-OTV-400 at EML4 to transfer more than 50 tonnes of  lunar water. The orbiting depot will be capable of storing up to 1000 tonnes of water and up to 400 tonnes of LOX/LH2 propellant.

2030

Access to Orbit

In February of 2030, three American Commercial Crew vehicles will launch eight American astronauts plus four foreign astronauts from terrestrial launch facilities to low Earth orbit (LEO).  All three of the Commercial Crew vehicles will dock at LEO  Way Station (LWS) that was originally deployed to LEO back in 2020. Simply derived from SLS hydrogen propellant tank technology and deployed by a single SLS launch,  the LWS will be substantially cheaper than the hyper expensive ISS laboratory.

Rather than outsourcing technological participation from foreign space agencies, NASA will charge foreign  space agencies  $150 million  for each foreign astronaut trained to  participate in NASA's first interplanetary mission.  So the inclusion of four foreign astronauts in the interplanetary mission will shave off $300 million in cost to NASA-- and the tax payers. Foreign space agencies whose astronauts are participating in the Mars orbital mission will  receive up to 10 kilograms of material retrieved by astronauts and robots  from the surfaces of the martian moons, Deimos and Phobos.

An OTV-400 interplanetary booster rendezvous with a WPD-OTV-400 at EML4 to receive up to 400 tonnes of LOX/LH2 propellant. The WPD-OTV-400 produces propellant from lunar water when it is docked to a 1.2 MWe solar array (seen in the background) which is also located at EML4.

EML4

Docked at the LEO Way Station will be two reusable ETLV-2 vehicles.  Originally deployed by the SLS during the lunar outpost  program of the early 2020s, each ETLV-2 vehicle will perform orbital transfer duties, transporting the international crew of 12 from LEO to EML4 ( Earth-Moon Lagrange Point Four) in approximately two days at a slightly higher and more propellant expensive delta-v.

The LOX/LH2 propellant needed to fuel the ETLV-2 vehicles will come from a LEO orbiting   propellant producing water depot (WPD-OTV-400). The LEO orbiting WPD-OTV-400 was  originally deployed by the SLS in the 2020's for cis-lunar operations.

 WPD-OTV-400 depots will be capable of storing up to 400 tonnes of LOX/LH2 propellant and up to 1000 tonnes of water. Some of the water for the orbital  depot  will arrive as additional payload  from Earth aboard SLS and other launch vehicles with some extra payload availability beyond the regular payloads that they will be deploying.  But most of the water for the LEO water/propellant depot will originate from the surface of the Moon.

When running low on water and propellant, the LEO orbiting WPD-OTV-400  uses the remaining 50 tones of stored propellant to transport itself  to EML4.  There  it is supplied with water and propellant from another WPD-OTV-400 that is continuously being supplied with lunar water from the lunar   poles from reusable CLV-5A and CLV-5B water shuttles. Once the WPD-OTV-400 filled with 240 tonnes of water in addition to being fully fueled with 400 tonnes of LOX/LH2 propellant, it will redeploy itself back to LEO where most of the 240 tonnes of water will be converted into LOX/LH2 propellant. Large  solar arrays deployed by previous SLS launched at both LEO and EML4 will provide all of the electricity necessary to power the depot  electrolysis plants and cryocoolers for converting water into liquid hydrogen and oxygen. 



The Odyssey

Once at EML4, the two ETLV-2 vehicles with dock at the twin AGH ports for the Odyssey interplanetary vehicle, transferring the 12 astronauts to the vessel  destined for Mars. The Odyssey interplanetary vehicle consist of an OTV-400 orbital transfer vehicle capable of storing up to 400 tonnes of LOX/LH2 propellant; an AGH artificial gravity habitat shielded with 30 cm of lunar water; and two ETLV-2 crew transport vehicles with only 6 tonnes of propellant within each vehicle. These Odyssey components will be deployed to EML4 by three separate  SLS launches the previous year (2029). 

Inside of the Odyssey, the 12 astronauts will  be greeted by six others astronauts who are permanently stationed at an EML4 AGH (Artificial Gravity Habitat) space station.   The permanent artificial gravity space station is protected from dangerous levels of cosmic radiation and major solar events with a shielding of lunar iron slabs that were manufactured by 3D printers on the surface of the Moon and exported to EML4 by reusable CLV-5A cargo landing vehicles.  The EML4 stationed astronauts will return to their AGH space station after helping to prepare the crew of the Odyssey for their interplanetary launch.

Top: Odyssey trajectory burn configuration. 2nd from top: After the trajectory burn the OTV-400, AGH, and twin ETV-2 shuttles separate in preparation for vehicle reconfiguration. 3rd from top: After AGH shifts 90 degrees and then commences to rotate along an axis between the separated OTV-400 and the ETLV-2 vehicles. 4th from the top: AGH internal cables and external  retractable booms expand to produce 0.5g of simulated gravity. Bottom: The two ETLV-2 vehicles rotate to match the rotation of the AGH before they dock with the structure at the pressurized  central docking module.   

Interplanetary Space
 

Since the Odyssey mission will take a longer route to Mars that will  allow it to also fly past the planet Venus, the OTV-400 will require maximum amount of propellant. But launching from EML4 instead of LEO will still shave off nearly 2.8 km/s of its delta-v requirements. The WPD-OTV-400 will fill the Odyssey's  OTV-400  with nearly 400 tonnes of LOX/LH2 propellant and its twin  AGH habitat modules with more than 200 tonnes of water for radiation shielding (142 tonnes) plus water for  drinking, washing, food preparation, and the production of air.  

Initially, the Odyssey will be in a linear configuration when it departs from cis-lunar space. But after the Mars Transfer Orbit  trajectory burns, the Odyssey components will separate in order to   reconfigure itself so that the AGH can rotate and expand the light weight retractable booms surrounding the cables connecting its twin habitat modules. Extending about 112 meters away from the central axis while rotating at 2 rpm, each of the twin modules will experience a simulated gravity of approximately 0.5g.  The astronauts within each habitat module would, therefore, feel a simulated gravity half that of being on the surface of the Earth but still significantly higher than the gravity experienced on the surface of the Moon or Mars.  In theory, the artificial  gravity environment should  substantially reduce and possibly  even eliminate the deleterious effects associated with   microgravity environments. Artificial gravity should also create a much more  comfortable and familiar physical and psychological  environment during their 22 month mission.

In a trajectory configuration, the Odyssey flies past the plant Venus on its way to Mars.

Venus

 In July of 2030, after nearly five months of interplanetary travel, the Odyssey will reconfigure itself into a linear configuration just a few days before it nears the planet Venus. This will allow the OTV-400  to make some minor trajectory burns as they Odyssey flies past Venus on its way to Mars.  During the flyby,  the astronauts aboard the Odyssey could utilize one of the ETLV-2 vehicles to get a better look at Venus during the flyby,  taking photographs and videos of the veiled planet.  After the trajectory burns, the Odyssey will once again reconfigure itself so that the AGH can once again produce an artificial gravity environment for the astronauts.

After the AGH habitats dump their water shielding, the Odyssey reconfigures to a linear position in order to enter   high Mars orbit.

2031


High Mars Orbit

Before the arrival of the Odyssey, two  WPD-OTV-400 water/propellant depots will already be in high Mars orbit along with a pair of large solar electric arrays, originally launched to high Mars orbit during the previous launch window in 2028.

In February of 2031, several hours to a few days before the Odyssey’s rendezvous with Mars, the rotating AGH modules  will dump their 142 tonnes of water shielding.   This will cut the total inert mass of the Odyssey nearly in half which will substantially reducing the amount of propellant required to place the interplanetary vessel into a high Mars orbit. After the final trajectory burn places the Odyssey into orbit, the AGH will separate from the Odyssey to rendezvous with one of the WPD-OTV-400 water/propellant depots  to replace the water shielding for its habitat modules. 

Once the AGH modules are fully water shielded again, the Odyssey will  reconfigure itself so that the AGH can produce 0.5 g of simulated gravity and so that the crew can begin to conduct their exploration of the two martian moons.

The WPD-OTV-400, in high Mars orbit,  rendezvous with the AGH to replenish the 142 tonnes of water for radiation shielding the habitat modules.

Fully water shielded again, the AGH begins to rotate again at 0.5 Gs, expanding its retractable boom and twin habitat modules.

Deimos

One of the ETLV-2 vehicles will dock with one of the orbiting water/propellant depots in high Mars orbit,   accessing the amount of propellant needed for its crewed mission to the surface of Deimos and back to the Odyssey. Six astronauts will participate in the three day exploration of  the outer martian moon. After the astronauts land on the surface of Deimos, a few  mobile robots will be deployed  that will be teleoperated by astronauts still remaining at the  AGH. For over a month, these robots will explore various regions on the surface of Deimos, taking videos and photographs and collecting samples.  These samples will be retrieved a month later by the second six person crew from the Odyssey to land on the surface of Deimos.

 ETLV-2 on its way towards the first crewed landing on Deimos.

Phobos

After the first crewed mission to Deimos, Phobos will be the next destination for a crewed ETLV-2.
Again,  six astronauts will participate in   three days of  exploration. After the astronauts land on Phobos,  mobile robots will be deployed  to explore various regions on the surface of of the inner moon, taking videos and photographs and collecting samples.  These samples will also be retrieved, a month later, by the second six person crew from the Odyssey sent to  the surface of Phobos


Preparations for Departure

After two months in orbit around Mars, the OTV-400 will   fill its tanks up with more than 300 tonnes of LOX/LH2  propellant from one of the WPD-OTV-400 water/propellant depots. 

Reconfigured into a linear configuration, the Odyssey will depart from Mars in April of 2031. After the trajectory burns that launches the Odyssey into an Earth Transfer Orbit, the Odyssey will, once again,  transform into  an artificial gravity producing configuration.

One of the nearly depleted WPD-OTV-400 water/ propellant depots will also leave Mars for cis-lunar space in order to resupply itself with lunar water and propellant for a return to Mars orbit in 2033. 

With the  solar power plant for the WPD-OTV-400 in the background, the OTV-400 rendezvous with the propellant depot to add LOX/LH2 for the Odyssey's return journey to cis-lunar space. 

The Return to  Cis-Lunar Space


In December of 2031, the AGH will once again dump its water shielding as it nears its rendezvous with cis-lunar space.   Once it is linearly reconfigured, the final trajectory burns will place the Odyssey and its crew back in halo orbit at EML4.

The crew will then be transferred by two ETLV-2 shuttles to the EML4 AGH space station for a few days before being transferred again  by two ETLV-2 shuttles to LEO. Commercial Crew vehicles will then transport the astronauts to the Earth's surface, pioneers and heroes  to be welcomed back by the cheering crowds on  Earth. 

The Odyssey interplanetary spacecraft returns to  EML4. Two ETLV-2 shuttles docked at a permanent AGH space station at the Earth-Moon Lagrange point will transport the crew back to the EML4 space station for a few days before the 12 person crew is eventually transported to LEO and then back to the surface of the Earth aboard  Commercial Crew vehicles. 

The Next Interplanetary Mission

NASA, on the other hand, will be preparing for the next crewed mission to Mars orbit which will be launched from EML4 in 2033. The 2033 mission will deploy the first permanent iron shielded AGH space station into high Mars orbit.   The 2033 mission will also deploy the first unmanned ADEPT protected ETLV-2 vehicles to the surface of Mars to test ETLV-2 s ability to land large masses on the surface of Mars while testing the ability of the ETLV-2 to return to orbit from the surface of Mars.   Tele-operated robots will also be deployed by the ETLV-2 vehicles to retrieve regolith samples to be transported to Mars orbit and eventually back to Earth.


Links and References


Comparison of Deimos and Phobos as Destinations for Human Exploration and Identification of Preferred Landing Sites

Deimos and Phobos as Destinations for Human Exploration

Phobos and Deimos: The Moons of Mars

Mining the Moons of Mars

Cosmic Radiation and the New Frontier

A Cryogenic Propellant Production Depot for Low Earth Orbit

Evolving to a Depot-Based Space Transportation Architecture

A Study of CPS Stages for Missions beyond LEO

A Study of Cryogenic Propulsive Stages for Human Exploration Beyond Low Earth Orbit

Ames Research Center Mission Design Center Trajectory Browser 

Delta-v budget

Establishing a Permanent Human Presence on Mars with a Lunar Architecture

Utilizing Lunar Water Resources for Human Voyages to Mars

Utilizing the SLS to Build a Cis-Lunar Highway

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

SLS Fuel Tank Derived Artificial Gravity Habitats, Interplanetary Vehicles, & Fuel Depots

The SLS and the Case for a Reusable Lunar Lander



© Marcel F. Williams
New Papyrus Magazine
11/25/15

NASA Contracts Production of New RS-25 Engines for the Space Launch System

Links and References

NASA and Aerojet Rocketdyne Sign Contract to Restart Production of the RS-25 Engine for the Space Launch System

Aerojet Rocketdyne wins propulsion contracts worth nearly $1.4 billion

RS-25 Engine

White House Summit Video on Nuclear Energy

Landing on Mars with ADEPT Technology

Links and References


Trajectory Optimization for Adaptive Deployable Entry and Placement Technology (ADEPT)

Hypersonic Deployable Decelerators

Reusable Hoppers and Orbiters for Rapid Lunar Transportation and Exploration

by Marcel F. Williams

For NASA and its future SLS program,  developing  a reusable single staged extraterrestrial  landing vehicle (ETLV) could allow America to send astronauts  to the surface of the Moon, Mars, and even to the surfaces of the moons of Mars. Such an ETLV could be used to conveniently transport astronauts from EML1 (Earth-Moon Lagrange point 1) to the surface of the Moon and back to EML1 on a single fueling of LOX/LH2 propellant. NASA astronauts could reach EML1 and return to the Earth via an SLS launched Orion spacecraft.

Eventually, by deploying ETLV derived orbital propellant depots at points of departure and destination, such a reusable spacecraft could also be used as an orbital transfer vehicle, transporting astronauts between LEO and the Earth-Moon Lagrange points. This would allow Commercial Crew vehicles to shuttle NASA astronauts to LEO to dock with an ETLV destined for EML1 or to return astronauts from an ETLV returning from EML1. 


ETLV-2 (Extraterrestrial Landing Vehicle)

Inert weight with cargo and  crew (8 passengers): 10 tonnes

Maximum amount of propellant:  24 tonnes of  LOX/LH2

Maximum fueled weight: 34 tonnes

Specific Impulse of LOX/LH2 engines: ~ 450 seconds 

Top: ETLV-2 reusable lunar crew lander and lunar hopper; Bottom: CTLV-5B reusable LOX/LH2 cryotanker.

CTLV-5B (Cryotanker Landing Vehicle)

Inert weight: 8 tonnes

Maximum amount of propellant: 30 tonnes

Maximum fueled weight: 40 tonnes

Specific Impulse of LOX/LH2 engines: ~ 450 seconds


By utilizing  ADEPT  deceleration shields, such an ETLV could also be used to transport humans from low Mars orbit to the surface of Mars and back into  Mars orbit  on a single fueling.  With an ADEPT decelerator, the delta-v requirement to land on the lunar surface from orbit is only 0.51 km/s. The delta-v to travel from the surface of Mars back to Mars orbit is 4.4 km/s. Propellant depot located in Low Mars Orbit would allow the vehicle to refuel in order to travel to orbital habitats or interplanetary vehicles located in High Mars Orbits. Traveling between High Mars Orbit and the Earth-Moon Lagrange points has the lowest delta-v requirements between Mars orbit and cis-lunar space.

A reusable  ETLV located at propellant producing  lunar outpost that utilizes a reusable CTLV (Cryotanker Landing Vehicle) could also allow humans to continuously explore practically every region on the lunar surface without the need of any additional SLS launches from Earth-- dramatically reducing the cost of the human exploration of the Moon

Once a permanent outpost is established on the surface of the   Moon, the entire lunar surface, including its craters, could be continuously explored by robotic lunar rovers tele-operated from Earth. Such solar and nuclear powered mobile robots could also retrieve regolith samples  for return to the outpost for study and, eventually, transported back to Earth. Such mobile robots could also be used to  locate interesting sites for future human exploration.

Because annual levels of cosmic  radiation on the lunar surface can range from 11 Rem during solar maximum conditions to as high as 38 Rem during solar minimum conditions, astronauts living on the Moon for several months or several years will have to minimize their radiation exposure by mostly living inside regolith shielded habitats to reduce annual radiation exposure to less than 5 Rem (the maximum level of radiation exposure for radiation workers on Earth) during solar maximum and minimum conditions. This can easily be done by landing  habitats on the lunar surface that can automatically deploy regolith walls that can be easily filled with approximately 2 meters of lunar regolith.

If astronauts spend about 10% of their time outside of their shielded habitats  (2.4 hours per day or 16.8 hours per week), their additional exposure after a year would only range from 1.1 Rem to 3.8 Rem. A 25 year old female could live and work on the Moon for a decade and still not exceed her maximum lifetime limit of 100 Rem. Astronauts minimizing their radiation exposure by  exploring the lunar surface for just  four to eight hours per week could, therefore,  explore various regions on the Moon on a weekly basis-- if they could have easy access to such regions.

Since ground vehicles transporting crews across the lunar surface are not likely to exceed 20 km per hour in average speed, the maximum area that could be explored by pressure suited astronauts is not likely to exceed a distance of more than 80 kilometers away from a shielded lunar  outpost.

However, rocket powered sub-orbital Lunar Hoppers hurtling along parabolic arcs have long been advocated as a way for humans to explore more distant regions on the Moon-- far beyond a permanent lunar outpost. But such missions would require the reusable vehicle to have-- enough propellant-- to:

1. take off from the outpost on a suborbital trajectory,

2. land at the site intended to be explored,

3. take off again on a suborbital trajectory,

and,

4. land back at the lunar outpost.

The delta-v and travel times for possible crewed suborbital hops on the lunar surface.

David Hop, on his popular space blog, has done some interesting calculations, suggesting  that lunar hoppers could transport humans anywhere on the lunar surface in less than an hour with a maximum delta-v of only 1.68 km/s. So  transportation between lunar outpost and lunar cities could be conveniently fast and easy-- as long as every lunar outpost or  lunar city can refuel the Hopper for its next suborbital destination.  

An ETLV fueled with a maximum of 24 tonnes of LOX/LH2 propellant (originally designed for round trips between EML1 and the lunar surface) could transport astronauts within a 1300 kilometer radius from a lunar outpost and back.  Beyond 1300 kilometers (45 degrees), however, such an ETLV  would not have enough propellant for its return trip to the lunar outpost.

Since the distance from the poles to the lunar equator would be 2700 kilometers away and to  the opposite pole, more than 5400 kilometers away,  a single polar outpost would pretty much  confine  human exploration via Hoppers mostly to it's polar region.

One way to overcome such geographical limitations would be to launch crewed ETLVs to EML1.  There it would add additional rocket fuel  from a  propellant depot (WPD-OTV-5A) located at EML1 for a round trip mission from the Lagrange point to the lunar site chosen to be explored. After the completion of the exploratory mission, the ETLV would return to EML1 to add propellant for its return trip to its original lunar outpost.


Lunar Exploration via lunar outpost and EML1 propellant depot

1. Crewed ETLV-2 launched from lunar outpost to EML1 (less than 12 hours at high delta-v or two days at a lower delta-v))

2. ETLV-2 rendezvous with WPD-OTV-5A adding enough propellant for a round trip from the lunar surface and back to EML1

3. ETLV-2 travels to lunar orbit and lands at lunar site (~2 days of travel) for a few hours or a few days of exploration

4. ETLV-2 launches itself back to EML1 (~2 days of travel) and rendezvous with WPD-OTV-5A to refuel for trip back to lunar outpost

5. ETLV-2 departs from EML1 to return to lunar outpost (less than 12 hours or up to two days)

This scenario requires only one vehicle (ETLV-2). In theory, it would  allow sorties to be conducted practically anyplace on the lunar surface on a weekly basis.  This method, however,  would require at least five to eight days of travel time-- excluding the time spent exploring the region on the lunar surface. So each lunar sortie would expose astronauts to five to eight continuous  days cosmic radiation outside of a regolith shielded outpost-- for perhaps just a few hours or a few of days of exploration at a particular lunar site.

Alternatively, pre-deploying a mobile propellant depot (MCT) at the site intended to be explored could minimize astronauts radiation exposure during a lunar sortie.

 ETLV-2 lands near a pre-deployed mobile cryotanker (MCT) after it's suborbital flight to a predetermined lunar exploratory site. The MCT will provide the ETLV-2 with additional LOX/LH2 for its return flight to a polar outpost.

 Lunar exploration utilizing mobile cryotankers

1. A solar and fuel cell powered mobile cryotanker (MCT) with up to 12 tonnes of propellant is sent to a lunar exploratory site (distance traveled: 300 km/day) in less than a month

2.  Crewed ETLV-2 launched from lunar outpost to lunar exploratory site (less than an hour)  with a few tonnes of extra fuel for the return trip to the outpost. 

3. MCT adds enough additional  fuel to the ETLV-2 for it to return to the lunar outpost

4. With added fuel, the ETLV-2 launches itself back to lunar outpost in less than an hour of travel time

5. The mobile MCT returns to the lunar outpost after a few weeks of travel time.

This scenario dramatically reduces  astronaut's travel time  to less than two hours of continuous radiation exposure. Preparing for such lunar sorties, however, would require a mobile cryotanker to be deployed to the exploratory site a few weeks before the crewed mission. And then a few weeks would have to be allowed for the cryotanker's return to the lunar outpost.


However, there is another way that lunar sorties from a lunar outpost could be conducted on a daily basis while also minimizing cosmic radiation exposure. This scenario would require an ETLV to be launched in an orbital plane above the intended site to be explored  along with a reusable  CTLV (Cryotanker Landing Vehicle).

Crewed ETLV-2 rendezvous with an unmanned CTLV-5B cryotanker in the same orbital plane as the intended  lunar exploratory site and the lunar outpost. After the lunar exploratory mission is completed, both the ETLV-2 and the CTLV-5B will return to the lunar outpost to be used again for future lunar exploratory missions.

 Lunar exploration utilizing an ETLV-2 and CTLV-5B in lunar orbit

1. CTLV-5B launched from lunar outpost into an orbital plane directly above the intended landing site

2. Crewed ETLV-2 launched from lunar outpost  into the same orbital plane

3. ETLV-2 rendezvous with CTLV-5B adding enough propellant for a round trip from the lunar surface and back into orbit

4. ETLV-2 lands at lunar exploratory site for a few hours or a few days of exploration

5. ETLV-2 launches itself back into orbit along the same orbital plane

6. ETLV-2 rendezvous with CTLV-5B adding enough propellant to return to the lunar outpost

7. CTLV-5B uses the its remaining amount of propellant to land back at the lunar outpost to be eventually refueled to assist in the next sortie mission on the lunar surface

ETLV-2 at an exploratory site on the lunar surface. Distances exceeding  1300 kilometers away from a propellant producing lunar outpost will require the ETLV-2 to use its remaining fuel to launch itself back into the same orbital plane as an orbiting CTLV-5B cryotanker, in order to add the needed fuel necessary for it to return to the lunar outpost.

The CTLV is simply the CLV (Cargo Landing Vehicle) without the cargo. So no new extraterrestrial vehicle would have to be developed in order to utilize the CLV as a reusable propellant vehicle (CTLV).

While this scenario requires two reusable launch vehicles (ETLV-2 and the CTLV-5B), it has the advantage of being able to  deploy astronauts quickly to an exploration site in just a few hours. Most of the few hours of travel time for astronauts would be spent in lunar orbit while rendezvousing with the CTLV-5B propellant  depot to add more propellant.

In the early 2030s, I imagine that most of the water produced at a lunar outpost  would probably be exported to one of the Earth-Moon Lagrange points to provide water for future interplanetary missions to Mars, Venus, ESL4, ESL5, and the NEO asteroids: water for drinking, washing, the production of air, radiation shielding, and LH2/LOX propellant.

But some of the water derived from the lunar poles could also be used for the production of lunar propellant intended for the domestic human exploration of the lunar surface.  This could allow reusable Extraterrestrial Landing Vehicles to  cheaply and conveniently transport astronauts to practically every region on the lunar surface for a few hours or even a few days of exploration. So the production and export of lunar water could not only greatly enhance NASA's ability to send humans to Mars but it could also usher in a new renaissance of human exploration-- on the lunar surface.

Links and References


Trajectory Optimization for Adaptive Deployable Entry and Placement Technology (ADEPT)

Lunar Hopper

Travel on airless worlds 

Lunar pogo hopper

Drones on the Moon
Is it possible to explore the Moon with low-altitude flying spacecraft?

Lunar Lander Designs for Crewed Surface Sortie Missions in a Cost Constrained Environment

The SLS and the Case for a Reusable Lunar Lander

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

Utilizing the SLS to Build a Cis-Lunar Highway

Cosmic Radiation and the New Frontier

Uranium: Twisting the Dragon's Tail

NASA's Lunar Resource Prospector

Resource Prospector