Thursday, July 10, 2014

Landing Large Cargos and Crews on the Surface of Mars

Tethered beneath a hydrogen inflated ballute, a crewed  Ares 2 (Ares ETLV-2) reusable landing shuttle slowly descends towards the martian surface.

Launching human crews from the surface of the Earth to low Earth orbit (LEO) requires a delta-v of more than 9.3 kilometers per second (km/s). But on the Moon and Mars, the delta-v requirements are significantly lower. Launching humans from the surface of the Moon to lunar orbit can require as little delta-v as 1.87 km/s. And launching human crews from the surface of Mars to low Mars orbit requires a delta-v of only 4.4 km/s.

Landing humans on the surface of the Earth and on the Moon is relatively easy. Only minuscule amounts of delta-v are required to for crews to  leave Earth orbit and glide or parachute through the Earth's thick atmosphere to the terrestrial surface. The delta-v required to land a crew on the surface of the Moon from lunar orbit is equivalent to the delta-v required to leave the lunar surface to low lunar orbit.

Unfortunately,  landing crews and large payloads on the surface of Mars  is much more problematical. The largest spacecraft that NASA has managed to safely  deploy to the Martian surface are all below 600 kilograms in mass. The weight of a lunar derived crewed vehicle to the Martian surface is likely to weigh as much as 10 tonnes, not including the substantial amounts of fuel  needed to return to orbit around the Red Planet. And NASA eventually wants the ability to  deploy as much as 100 tonnes of payload onto the martian surface by a single spacecraft. 

Notional ballutes designed to aerobrake into a planetary orbit or to land on the surface of Mars (Credit: NASA)

 The problem with landing large masses on the surface of Mars is that even though the martian atmosphere is approximately 1% as dense as the Earth's atmosphere, it's still thick enough to produce substantial amounts of frictional heating as a vehicle plunges at hypersonic speeds through its atmosphere  but still not enough friction to sufficiently lower the terminal velocity as it approaches the planet's surface. Small vehicles (less than 600 kg) attempting to land on Mars have, therefore, been designed to have a high  drag coefficients. Designing a spacecraft with a high drag coefficient for vehicles weighing several tonnes or more, however, is much more difficult.

This has pushed NASA towards the idea of utilizing large inflatable ballutes to assist heavy payloads and spacecraft entering the martian atmosphere. The large drag coefficient of a toroidal ballute could allow a spacecraft to decelerate at very low densities high in the martian atmosphere with relatively low rates of frictional heating.  The low frictional heat experienced by the ballute could allow for light-weight construction techniques that could enhance the ability to deploy more mass to the martian surface. Ballutes inflated with gases that are lighter than the carbon dioxide could also increases static lift. Recent studies  suggest that a toroidal ballute with a tube radius of 80 meters could be used to deliver masses the martian surface of approximately 100 tonnes.

Top: ETLV-2 vehicle designed for landing on the surfaces of the Moon and  the moons of Mars; Bottom: An ETLV-2 derived Ares 2 vehicle designed to dock with a disposable heat shield  and compacted ballute in order to land on the surface of Mars.
Placed on the surface of Mars, a single staged reusable vehicle with an inert weight of approximately 10 tonnes (including payload and crew) designed to travel to and from the lunar surface would require at least 18 tonnes of fuel to transport a crew from the martian surface to low Mars orbit;  22 tonnes of fuel  would be required to reach the surface of Phobos and  24 tonnes of fuel would be needed to reach the surface of Deimos from the martian surface. So with a delta-v requirement of less than 5.3 km/s, a fueled  single staged crew vehicle weighing nearly 40 tonnes placed on the surface of Mars should be capable of  traveling all the way from the martian surface to the surface of Deimos or to high Mars orbit.

Left: Ares 2 docked with a compacted (pre-deployed) ballute, configured to  inject the spacecraft towards an aerobraking encounter with the martian atmosphere.  Right: After the rocket burn towards Mars, the Ares 2 would reconfigure itself in order to protect the spacecraft and to inflate the ballute in order to aerobrake and to descend through the martian atmosphere.

A liquid hydrogen and oxygen producing water and fuel depot derived from a reusable orbital transfer vehicle. The Ares 2 landing vehicle would fuel up up at the orbital depot before docking with the compacted ballute/heat shield unit.  Water would be transferred to the fuel depot from water factories on  the martian moons, Deimos and Phobos.

Water factory would utilize mobile microwave water bugs to extract water from the regolith of the martian moons, Deimos and Phobos; WFD-LV would convert water into fuel to launch water to fuel manufacturing depot in high Mars orbit.

A  ballute capable of deploying nearly 40 tonnes to the martian surface could also easily deploy habitats and cargo larger than those contemplated for the Altair vehicle  to the lunar surface. Cargo missions to the martian surface could utilize ballutes to deploy mobile robots  for excavating and sintering the surface of Mars to create landing and launch pads for crewed shuttle vehicles and for regolith shielded outpost similar to those that could be utilized on the lunar surface.

Hydrogen inflated ballute would enable the crewed Ares 2 vehicle to aerobrake and land on the martian surface.
Small nuclear reactors would also need to  be deployed to power the martian outpost at night or during periods when sandstorms block out significant amounts of sunlight.  Methanol/oxygen fuel cell electric power plants could also be deployed as back up power, utilizing methanol produced from the pyrolysis of human biowaste and oxygen extracted from atmospheric carbon dioxide or from the electrolysis of water.

Water factories than mine water from the martian regolith would also need to be deployed. Mobile microwave robots  could be used to melt the ice contained in the martian regolith. Water, of course, is essential for drinking, washing, and growing food but is also essential for the production of oxygen for air. Hydrogen and oxygen can also be used to produce hydrogen and oxygen to fuel the reusable shuttle craft.

Ares 2 hovers near the sintered landing area of a martian outpost.
Under the scenario presented here, fuel depots and rotational human outpost would already be placed in high Mars orbit a few years before the first crewed missions to the martian surface along with water and fuel producing facilities on the surface of the martian moons, Deimos and Phobos. Human interplanetary missions to Mars orbit would utilize an orbital transfer vehicle operating between the Earth-Moon Lagrange points and high Mars orbit.
Rotating regolith shielded (enriched with iron ore) SLS fuel tank derived artificial gravity habitat in high Mars orbit capable of housing as many as 16 astronauts.

Such an interplanetary orbital transfer  vehicle would utilize fuel manufactured from water exported from the lunar poles  when going to high Mars orbit and fuel manufactured from water from the martian moons when returning to cis-lunar space. Such crewed missions would already transport  reusable Ares ETLV-2 vehicles to Mars orbit for docking with orbiting space habitats or transferring crews to the surface of the moons of Mars. A single SLS launch could deploy one or two compacted ballutes plus heat shields to high Mars orbit  for one or two human missions to the martian surface.

Three solar powered regolith shielded habitat modules joined together by two inflated corridors. Additional power for the outpost would be provided by a couple of small nuclear reactors buried beneath the regolith, a few hundred meters away.
The Ares ETLV-2 (Ares 2)  would fuel up in high Mars orbit at a OTV derived fuel depot before docking with a ballute/heat shield unit. The Ares ETLV- 2 would thin boost the Mars landing vehicle towards Mars. During the short journey from high Mars orbit towards Mars, the Ares 2 would reconfigure itself while also deploying the ballute. The ballute would allow the Ares 2 to aerobrake into orbit around Mars and then descend into the martian atmosphere. The final vertical descent to the martian surface would first drop off the protective heat shield, allowing Ares 2 rockets to slow down the final descent to the sintered surface of a martian outpost.

Ares 2 (Ares ETLV-2) about to be fueled for take-off by a mobile LH2/LOX cryotanker.

Links and References

The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet


Summary of Ultralightweight Ballute Technology Advances

A Survey of Ballute Technology for Aerocapture


An Evaluation of Ballute Entry Systems for Lunar Return Missions


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

Pioneering and Commercial Advantages of Permanent Outpost on the Moon and Mars 

Utilizing the SLS to Build a Cis-Lunar Highway

Tuesday, June 24, 2014

Pioneering and Commercial Advantages of Permanent Outpost on the Moon and Mars

Twin Regolith shielded habitats on a sintered  lunar surface area. Each habitat module is connected to each other by an inflatable pressurized  walkway. 
Permanent outposts on the surfaces of the Moon and Mars  could be the first major steps towards the expansion of human civilization into the rest  of the solar system.  Unaided traction for human walking requires a gravity that is at least 10% of the gravity at the  Earth's surface. The Moon, Mars, Mercury, and the Jovian moon, Callisto, are all worlds that have surface gravities higher than 0.1 g. So these are extraterrestrial worlds  that will probably be accessible for continuous human occupation before the end of the century. However, whether such  low gravity environments would  have significant deleterious effects on  human health and reproduction is currently unknown. But long before the permanent settlement of extraterrestrial worlds,  human outpost on the Moon and Mars, could have beneficial scientific, commercial, and even strategic benefits for those nations and businesses that dare to venture there.

Planets and Moons within the solar system that are potentially suitable for human colonization:


surface area relative to the Earth: 7.4%     

surface gravity relative to the Earth: 0.17g 

diameter relative to the Earth: 27.3%


surface area relative to the Earth: 28.4%
surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth: 53.1%

surface area relative to the Earth:  14.7%
surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth:  38.3%


surface area relative to the Earth:  14.3%
surface gravity relative to the Earth: 0.13g 

 diameter relative to the Earth:  37.8%

Note: Land area comprises 29% of the Earth's surface with 71% covered by water

Regolith shielded habitat designed for the Moon and Mars. Mobile water tanker provides water to the habitat for drinking, washing, growing food, and for the production of air.
Internal view of a regolith shielded habitat with regolith placed within the two meter cavity within the automatically deployed walls surrounding  the 8.4 meter in diameter pressurized habitat.

Permanent outpost on the surface of the Moon could immediately exploit lunar regolith to protect humans from significant exposure to harmful levels of radiation.  Just two meters of lunar regolith dumped within the walls of a lunar regolith habitat could reduce annual cosmic radiation exposure below the maximum legal limit for radiation workers on Earth (5 Rem per year)  during the solar minimum while also protecting astronauts from radiation exposure from major solar events. Protection from micrometeorites and extreme temperature fluctuations would be an added benefit of  insulating a lunar habitat with regolith.

A single lunar habitat derived from the technology used to make the light weight 8.4 meter in diameter hydrogen fuel tanks for the SLS could provide two levels of floor space  approximately 111 square meters in area. That would be more floor space than the average home in Germany, Japan, Sweden, Italy, Spain, Russia, and in the UK. The deployment of such  habitats for the private commercial community could also be used  as lunar hotels for space tourist or to house workers for private companies involved in the export of lunar water or regolith for government and private entities.

Creating solid pavement for the deployment of  habitats and other lunar outpost components upon dust free surfaces could be created by using mobile robots to pave and sinter lunar regolith.  This could eliminate tracking in deleterious lunar dust into pressurized habitats when astronauts are working in the paved  lunar outpost area. 

Mobile water tanker for storing and transporting water and a mobile water extracting  robot that uses microwaves to extract water from regolith from the shadowed areas of the lunar poles.
In the lunar polar regions, roving microwave water extraction robots could mine ice particles from the  permanently shadowed areas for the production of water. Water, of course, can be used for drinking, washing, food preparation, and for growing food. Water can also be electrolyzed for the production of oxygen for air and for the production of hydrogen and oxygen for rocket fuel needed to return to Earth.

Human biowaste could be converted into methanol through pyrolysis. Methanol and oxygen can be used with fuel cells to produce electricity for back up energy during periods of lunar darkness. The water produced from the combustion of methanol and oxygen can be recycled. The CO2 produced from the manufacture of methanol and from the combustion of methanol in fuel cells can be used to enhance the growth of indoor lunar crops. Small portable methanol fuel cells could also be used to provide power for pressure suits during lunar excursions.

Nitrogenous biowaste, such as urine, could be used as fertilizer for lunar crops.

However,  there is some  evidence that substantial quantities of carbon and nitrogenous material may also  be a significant component of the permanently shadowed areas at the lunar poles. Astronauts stationed at  lunar outpost at the lunar poles could used to explore and to quantify the amount of volatiles located within the shadowed regions.

Buried nuclear power plant on the lunar surface (Credit: NASA)
While solar panels attached to the habitats would provide the initial power for a lunar habitat, small nuclear reactors   buried beneath the lunar regolith only a few hundred meters away could provide substantial amounts of electricity for the lunar facility, 24 hours a day.

Outposts originally designed for the lunar surface could also be utilized  on the surfaces of Mars, Mercury, and Callisto and even on the meager surfaces of large asteroids and on the moons of Mars.
Three regolith shielded habitat modules on a sintered  Martian surface area. Each habitat module is  connected to each other by two inflatable pressurized  walkways.   

Permanent outpost on the Moon and Mars and on other worlds, would allow the continuous exploration of those surfaces by both humans and robots. Unmanned solar or nuclear powered rovers on the lunar surface, operated by humans on Earth, could visit and collect samples from  practically every area on the surface of the Moon. The collected rocks and soil could then be returned to the lunar outpost for immediate study or for eventual export back to Earth.

On Mars, both robotic rovers and hydrogen blimps could be utilized to continuously explore the Martian surface. Such robots could be operated in real time by the astronauts on the Martian surface or in orbit around Mars at a  space station.  Again, the collected samples by the remote controlled robots could be returned to the Martian outpost for immediate study or for eventual export back to Earth.

A permanent US government presences on the surface of the Moon and Mars will also enhance the ability of private American companies to protect their assets from potentially hostile foreign entities that will probably also be on these new worlds by mid century.

Marcel F. Williams

© New Papyrus

Links and References

 D. Bryant Cramer.  "Physiological Considerations of Artificial Gravity."  Applications of Tethers in Space, volume 1, pages 3·95-3·107.  Edited by Alfred C. Cron.  NASA Scientific and Technical Information Branch, 1985.  Conference Publication 2364: proceedings of a workshop held in Williamsburg, Virginia, June 15-17, 1983.

Lunar Station Protection: Lunar Regolith Shielding

Wet vs Dry Moon

Utilizing the SLS to Build a Cis-Lunar Highway

Cosmic Radiation and the New Frontier

NASA Steps Closer to Nuclear Power for Moon Base

How big is a house? Average house size by country
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)

Tuesday, May 13, 2014

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

In 2031, a reusable OTV-400  places a boom contracted artificial gravity habitat (AGH) and two Extraterrestrial Landing Vehicles (ETLV-2) into high Martian orbit  for a  60 day mission of human exploration of the two Martian moons, Deimos and Phobos, before refueling at a pre-deployed orbiting  fuel depot for the return trip to cis-lunar space.

The relatively weightless conditions of orbital and interplanetary space are inherently deleterious to human health. Humans and other terrestrial animals have evolved their physical and physiological attributes under our planet's heavy gravitational environment.

On the surface of the  Earth, the human heart has to counter the downward pull of gravity  in order to pump adequate amounts of blood to the head and torso when people are standing erect, while blood flowing to the lower limbs is aided by the pull of gravity. But under the microgravity conditions of space,  human blood disproportionately flows to the head and torso while blood flow to the lower limbs is reduced. This makes the human face look puffy while their legs become thinner.

Such blood flow redistribution can  sometimes cause nausea and headaches when astronauts first arrive in orbit but usually disappears after a few days in space. But other minor but annoying problems can be experienced under weightless conditions, including:

1.  Weight loss: the less strenuous conditions diminish appetite, resulting in weigh loss which could become excessive if astronauts don't exercise and eat regularly. 

2. A degraded sense of smell and taste: your favorite foods could taste a little different under microgravity

3. Clumping of tears and perspiration: there's no gravity to force trickles of water to run off the human body 

4. Facial and speech distortions: the face becomes  puffy and the voice tone and pitch becomes more nasal

5. Increased flatulence: since digestive gasses no longer rise towards the mouth, their is an increase in gas being expelled through the posterior orifice

The problems listed above could be viewed as only a minor inconvenience on short missions into space. But during long interplanetary journeys  lasting months or years, such problems could be annoying enough to enhance stress and increase tension aboard ship.

But there are other, more serious health problems that the human body may be subject to during months or years in a microgravity environment:

1. Astronauts can lose between 1 to 1.5% of their bone mass in a single month

2. Without regular exercise, astronauts can lose up to 20% of their muscle mass in just 5 to 11 days.

3. A microgravity environment can reduce  cardiovascular fitness

4. Vision problems of varying degrees of severity can occur especially in older men

5. Blood flow redistribution in a microgravity environment can effect medicines ingested or injected into the human body. 

6. Fluid loss and bone demineralization in a microgravity environment can increase the blood's calcium concentration, increasing the risk of an astronaut developing kidney stones.

7. The infected spray from the cough or the sneeze an ill person on board floats in the air instead of falling to the floor, enhancing the spread of infection aboard ship-- especially in a confined environment.

Returning to Earth after  a few months aboard the ISS, the blood pressure of some astronauts drops abnormally low when they move from a lying position to a sitting or standing position. Some astronauts even have problems standing up, walking, and turning and stabilizing their gaze. 

Since conjunction class missions to Mars may take more than seven months, there could be some question as to whether or not astronauts would  have the physical ability to perform a mission to the Martian surface.  Astronauts would have to endure weightless for several more months during their  return trip from Mars to Earth.

One possible solution to the deleterious effects of weightlessness would be temporary periods of high simulated gravity (hypergravity).   On Earth, sustained bed rest on a flat surface that is tilted  a few degrees backwards can simulate the deleterious effects of a microgravity environment, causing more blood to rush towards the head and less blood to flow into the hind limbs. But if such beds are attached to a short radius centrifuge, high levels of G forces can be experienced at the human foot level.

Short radius hypergravity centrifuge could help to mitigate the deleterious effects of a microgravity environment on the human body (Credit NASA).
Hypergravity studies have shown that protein synthesis in the leg muscles can be sustained if 2.5 G is experienced for just one hour a day at the foot level during a 21 day period. This suggest that daily exposure to a brief period of  hypergravity in space may be an effective counter measure, mitigating the loss of muscle mass in a microgravity environment. 

Production of the 8.4 meter section of the  SLS hydrogen fuel tank. Such components could be used for reusable common bulkhead interplanetary vehicles or for pressurized human space habitats (Credit Boeing Aerospace).
Short radius hypergravity centrifuges require a radius of more than 3 meters to accommodate the human body. So space habitats utilizing such  centrifuges would have to have unobstructed  internal diameters of more than six meters. Habitats derived from the SLS hydrogen fuel tanks could have an internal diameter as large as 8.4 meters. Even surrounded by 50 centimeters of water for radiation mass shielding would still give a habitat 7.4 meters in diameter of space to accommodate such machines. 
SLS  hydrogen fuel tank derived Skylab II concept (Credit Griffin).

So an SLS hydrogen fuel tank derived habitat such as the Skylab II concept could easily accommodate a short radius hypergravity centrifuge to keep astronauts and possibly even space tourist healthier while in orbit or on an interplanetary journy.

However, it has yet to be determined whether short centrifuge hypergravity machines can also alleviate some of the other serious physical and physiological problems associated with a weightless.  And temporary hypergravity would have no effect on the enhanced spread of infectious diseases and some of the minor but annoying problems associated with weightlessness.

To eliminate all of the problems associated with a microgravity environment during long periods of space travel, a continuous artificial gravity environment would be required.

In order to mitigate the physiological effects of Coriolis, a habitat capable of producing at least 0.5g of simulated gravity (higher than the gravity on the Moon and Mars) would require a rotation of  approximately 2rpm (rotations per minute) and a radius of at least 112 meters. That  would require a rotating habitat approximately  224 meters in diameter if twin counterbalancing pressurized habitats were utilized.

Artificial Gravity Habitat (AGH) located at EML4 or EML5 and radiation shielded with iron enriched lunar regolith to reduce annual radiation levels for inhabitants to below those allowed for radiation workers on Earth.
A rotating habitat derived from SLS hydrogen fuel tank technology under this scenario would  require two SLS launches to deploy and assemble the structure at one of the Earth-Moon Lagrange points. A core module would contain a pressurized docking section, solar panels,  plus extendable cables, boom, and twin  cable elevators on each side. Two external air locks derived from the SLS upper stage oxygen tank technology would also be deployed during this launch.

AGH core module featuring elevators and cable attachment rings for the habitat modules.
A second SLS launch to the Lagrange points would deploy two twin pressurized habitat modules that would connect to each side of the previously launched the core module. The total structural mass of the AGH (Artificial Gravity Habitat) is assumed to be less than 60 tonnes before the habitat modules are internally mass shielded by water for interplanetary journeys or with iron enriched regolith for permanent space stations.

Each AGH pressurized habitat module would provide shielded living area equivalent to a small two story homes, providing a spaciously comfortable environment for scientist and astronauts who may have to live in the confined simulated gravity habitats for several months or even a few years. 

AGH habitat module that can be internally shielded with 50 cm of water for interplanetary journeys or 50 cm of iron enriched regolith for permanent space stations.
A crewed or automated OTV-2 vehicle (derived from the ETLV-2) would be utilized to help assemble the AGH structure: docking the external airlocks to the sides of the core module and docking the habitat modules to both ends of the core module.
OTV-2 orbital transfer vehicle positioning the second habitat module to be docked with the core module of an Artificial Gravity Habitat (AGH) at EML4 or EML5.

The expandable boom would be rigid enough to allow thruster pods located at the ends of the habitat modules to increase or decrease its rate of the AGH rotation while the boom and internal cables are fully extended. Steel cables within the external boom would connect the AGH habitat modules to the core module. The cables would pull in the habitat modules before rocket burn maneuvers were conducted, expanding them again once the delta-v maneuvers are over. The hollow boom would also enhance the visibility of the AGH when crewed vehicles are approaching the central axis to dock.

For interplanetary journeys, the twin habitat modules would be shielded with water 50 cm thick. This would reduce astronaut's exposure to cosmic radiation to approximately 20 Rem per year during the solar minimum while also protecting astronauts from major solar events. Internally water shielding two levels of inhabited area within a pressurized habitat would add approximately 118 tonnes of weight to each habitat. Twin habitats, therefore, would add an additional 236 tonnes of mass to an interplanetary vehicle. So an AGH shielded for interplanetary travel would weigh nearly 300 tonnes, not including the additional mass for food, water, and air for the crew. Over the course of 1000 days, a crew of ten would add at least 50 tonnes of additional  mass to the vessel unless their was significant recycling of both air and water.
Reusable SLS hydrogen tank derived  OTV-400 utilizes a common bulkhead tank architecture for storing up to 400 tonnes of cryogenic fuel for interplanetary journeys. IVF technology would utilize ullage gases for tank pressurization and attitude control. Solar powered cryocoolers would eliminate fuel boil-off during long interplanetary journeys. 
At 5.2 km/s to 7 km/s, the delta-v requirements for transporting such a massive vehicle  from LEO to  Mars orbit could be prohibitive.  However, if the interplanetary vehicle was  fueled and  launched from the Earth-Moon Lagrange points to high Mars orbit, the delta-v requirements could be less than 2 km/s.

Delta- V Budget from Cis-Lunar Space to  Mars Orbit

EML1 or EML2 to Mars Capture Orbit -- 1.64 km/s

EML4 or EML5  to Mars Capture Orbit - 1.93 km/s

EML1 or EML2 to Low Mars Orbit ------ 3.04 km/s

EML4 or EML5 to Low  Mars Orbit ----- 3.33 km/s

LEO to Mars Capture Orbit ---------------- 5.2 km/s

LEO to Low Mars Orbit -------------------- 7 km/s

Liquid hydrogen and oxygen fueled cryogenic propulsion stages have been proposed by SpaceWorks with a fuel capacity of over 450 tonnes but with n inert weight of less than 30 tonnes. The ULA has proposed a cluster of six ACES boosters with a LOX/LH2 fuel capacity of approximately 700 tonnes.

Under this scenario, a common bulkhead LOX/LH2 fuel tank derived from the SLS hydrogen tank technology is utilized for a reusable interplanetary booster in order to minimize development cost. The OTV-400 would be capable of storing up to 400 tonnes of fuel for crewed interplanetary journeys to Mars, Venus, and the near Earth asteroids. The standard 400 tonne fuel tank is also utilized for large fuel depots under this scenario in order to minimize cost. Integrated Vehicle Fluid (IVF) technology would utilize ullage gases for tank pressurization and attitude control. Cryofuel boil-off would be eliminated during interplanetary journeys by using  solar powered cryocoolers.

A single SLS launch would be required to deploy the OTV-400 to LEO with enough fuel to travel to an Earth-Moon Lagrange point for refueling. Less than 350  tonnes of fuel would probably be required for a crewed interplanetary journey to high Mars orbit,  including two fully fueled Extraterrestrial Landing Vehicles.

Launching human interplanetary missions from the Earth-Moon Lagrange points to high Mars orbit rather than from LEO has several advantages.

1. To travel from an Earth-Moon Lagrange point to high Mars orbit requires less than 2 km/s of delta-v. But traveling from LEO to high Mars orbit would require more than 5 km/s of delta-v.

2. The delta-v requirement to transport water for shielding and fuel to an Earth-Moon Lagrange point is less than 2.6 km/s. The delta-v requirement to transport water to LEO is more than 9 km/s

3. The vehicles required to transport water to from the Moon to the Earth-Moon Lagrange points could be used for at least ten round trips before their CECE engines would have to be replaced or a new vehicle would be required. The vehicles required to transport water from Earth to LEO, however, would be expendable and could only be used once.

Reusable OTV-400 attached to a contracted AGH during propulsive delta-v maneuvers and a reusable  OTV-400 attached to an expanded rotating AGH after the completion of a propulsive delta-v maneuver.

The interplanetary vehicles return trip from Mars to cis-lunar space would require the OTV-400 to refuel at a previously deployed depot in high Mars orbit.  Fuel depots in orbit around Mars would initially use water exported from the lunar surface to manufacture fuel. But eventually, lunar derived water producing and exporting machines and vehicles would be placed on the surfaces of Deimos and Phobos for water production and export to the Mars orbiting fuel manufacturing depots. 

An OTV-400 derived fuel depot  (WFD-400) capable of producing cryogenic hydrogen and oxygen from stored water. The WFD-400 would be capable of transporting itself  anywhere within cis-lunar space or into orbit around Mars or Venus.
For permanent space stations at the Earth-Moon Lagrange points or in orbit around Mars, the twin habitat modules would require a radiation shield of  iron enriched regolith about 50 cm thick to reduce cosmic radiation exposure to less than 5 Rem annually (maximum allowed for radiation workers on Earth) during the solar minimum. That would require nearly 1865 tonnes of mass shielding (932 tonnes of iron enriched regolith for each habitat module). This would require one or two SLS launches of twin reusable regolith shuttles to the lunar surface-- depending on whether or not the CECE engines on the regolith shuttles are replaced after ten round trips.

Delta-V requirements to transport water for fuel, air, drinking, and mass shielding to LEO or to the Earth-Moon Lagrange Points

Lunar surface to EML1 --------------------- 2.52 km/s

Lunar surface to EML2---------------------- 2.53 km/s

Lunar surface to EML4 or EML5 ---------- 2.58 km/s

Lunar surface to LEO (with aerobraking) - 2.74 km/s

Earth's surface to LEO ----------------------- 9.3 km/s

Earth's surface to EML2 -------------------  12.73 km/s

Earth's surface to EML1 -------------------  13.07 km/s

Earth's surface to EML4 or  EML5 -------  13.27 km/s

Reusable lunar tankers capable of delivering more than 50 tonnes of water or regolith to the Earth-Moon Lagrange points. Their CECE engines should be capable of at least ten round trips from the lunar surface to the Lagrange points before the engines, or the entire vehicle, needs to be replaced. So after ten round trips, each vehicle would be capable of delivering more than 500 tonnes of fuel or regoltih  to the Earth-Moon Lagrange points.

Transporting an iron enriched regolith shielded  space station to high Mars orbit  would obviously require a much larger vehicle than the OTV-400. A light sail with a surface area of at least 100 square kilometers should be able to transport a few thousand tonnes to Mars within a years time. But if light sail technology is still not available,  vehicles capable of transporting a few thousand tonnes to Mars orbit  could easily be assembled by clustering four or more OTV-400 tanks around a core tank. A cluster of five OTV-400 vehicles would create an OTV-2000 interplanetary booster. A cluster of seven OTV-400 boosters would create an OTV-2800 interplanetary booster. Large clustered LOX/LH2 fuel tanks have also been proposed by the ULA for their human interplanetary vehicle concepts.

 The fuel requirements for such large interplanetary vehicles under this scenario would require one or two SLS launches of reusable water shuttles to the lunar surface. The lunar tankers would then transport water manufactured on the Moon to  fuel manufacturing depots at L4 or L5. Again, such lunar tankers should be capable of at least ten round trips before their CECE engines would need to be replaced. 

OTV-2000 is comprised of a cluster of five OTV-400 boosters.
The  OTV-400 would give NASA and possibly private space companies the delta-v capability to conduct  human missions from the Earth-Moon Lagrange points to the orbits of Mars and Venus, and to the NEO asteroids, and to Sun-Earth L4 and L5 as long as fuel depots for the return trip to cis-lunar space  are pre-deployed at those destinations.

 OTV-2000 and OTV-2800 class of interplanetary boosters could  enable human journeys from the Earth-Moon Lagrange points to the asteroid belt to places like Ceres and Vesta, again with WFD-OTV- 2000 or 2800 fuel depots pre-deployed in orbit around such large asteroids.

 Marcel F. Williams
© 2013 Mu Omega Enterprises

Links and References

What if you were born in space

Weightlessness and Its Effect on Astronauts

Effect of spaceflight on the human body (Wikipedia)

Artificial gravity maintains skeletal muscle protein synthesis during 21 days of simulated microgravity

 NASA Gives Artificial Gravity a Spin

Skylab II

Artificial Gravity (Wikipedia)

Artificial Gravity Visualization, Empathy, and Design

Space Launch System's Liquid Hydrogen Tank Under Construction

Cosmic Radiation and the New Frontier

Utilizing the SLS to Build a Cis-Lunar Highway

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

A Study of CPS Stages for Missions beyond LEO

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

Evolving to a Depot-Based Space Transportation Architecture

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