SLS Derived Artificial Gravity Habitats for Orbital Havens and Interplanetary Space Travel

Notional spinning artificial gravity producing AGH 1500 orbiting 600 km above the Earth's surface. Rectractable solar arrays and radiators produce power and regulate temperatures for the twin habitats.    

by Marcel F. Williams

Microgravity environments are inherently deleterious to human health in space. 

Weight loss, the clumping of perspiration and tears, facial and speech distortions, a degraded sense of  taste and smell,  and even an increased frequency of  flatulence are minor problems associated with short term exposure to a microgravity environment. 

 

But months or years under microgravity conditions can cause much more serious problems for  human health in space. Without regular exercise, 20% of muscle mass can be lost in just 12 days. 1.5% of bone mass is lost in a single month. And this bone demineralization can increase the calcium concentration in the blood stream, increasing the risk of developing kidney stones.  Significant reductions in cardiovascular fitness can also result from long periods of microgravity conditions. Vision problems of varying degrees of severity can occur in men in their 40s or older.  And the use of medicine can be hampered due to the changes in blood flow redistribution under microgravity conditions. 

 

After  a few months aboard the ISS, the blood pressure of some astronauts drops to abnormally low levels 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.

 

 The deployment of small habitats that are capable of spinning to produce artificial gravity could alleviate the health problems associated with a microgravity environment. Artificial gravity habitats could allow humans to:

1. Remain in orbit perpetually without the need to return to the Earth’s surface reducing the number of launches necessary to maintain a human presence in space 

2.  Remain physically healthy during long interplanetary journeys 

3. Receive quality medical care while in orbit including major surgical procedures. 

4. Have a  permanent human presence in orbit practically anywhere in the solar system 

5. Test  variable levels of gravity on the health of humans and other animal species

Notional 10 meter in diameter AGH 1500 in launch configuration on top of the SLS compared an SLS vehicle with an EUS and 10 meter in diameter payload faring.

 

An SLS Block I configuration would easily be capable of deploying a 60 tonne artificial gravity habitat to LEO. Reusable EUS derived ROTV 100 orbital transfer vehicles cold to deploy the habitat to the appropriate orbit where thrusters could rotate the structure, expanding its  twin counter balancing pressurized habitats at the ends of a 224 meter in diameter  boom. 

 

Directly derived from the SLS oxygen tank architecture, each habitat would be 8.4 meters wide and 16.8 meters tall. This would allow at least five 8.4 meter in diameter habitat levels that are  at least 2.5 meters high, ten human habitat levels in total for the habitat.    This should be enough room to easily accommodate 12 to 32  astronauts and their guest within the twin counter balancing pressurized modules. Because the combined pressurized  area of the twin habitat modules exceeds 1500 cubic meters in volume, the notional artificial gravity habitat is here referred to   as the: AGH 1500 (Artificial Gravity Habitat 1500).

 

AGH 1500 both contracted for trajectory burns and expanded to rotate producing 0.5g of simulated gravity

 

In order to mitigate the physiological effects of Coriolis, the habitat would be approximately 224 meters in diameter, rotating at approximately 2rpm (two rotations per minute) to produce 0.5g of simulated gravity (higher than the gravity on the Moon and Mars).  Slower rotations could be used to simulate the gravity on the Moon, Mars, Mercury, and Callisto, low gravity worlds that could potentially be colonized by humans someday. 

 

 

X-Ray of AGH 1500 showing floors levels on one of the counter balancing pressurized habitat modules

X-Ray of the top or bottom of the microgravity habitat area of the AGH 1500

 

Housed within a ten meter external cylinder would create a 80 centimeter gap between the pressurized habitat. Less than 20 centimeters of water within an external  polyethylene bag or pipes  could provide astronauts on interplanetary journeys with protection against the heavy nuclei component of cosmic radiation and from major solar storm events while also reducing cosmic radiation exposure in general during multi-month interplanetary journeys. 

Permanent artificial gravity habitats located beyond the magnetosphere within cis-lunar space and in orbit around other planets, moons, and asteroids will have to be provided with much more shielding to protect against excessive radiation exposure and potential micrometeorite damage. About 2 meters of lunar regolith would be required to shield the the pressurized habitat. But less than 80 centimeters of space would be available. However, lunar regolith is rich in much denser iron particles   that could be mined and deployed for external shielding.  So only 40 centimeters of lunar iron could be used to permanently shield artificial gravity habitats. Thorium is an even denser lunar material could also be utilized since there appears to be substantial thorium deposits in certain regions on the Moon. 

 

SLS EUS (Exploration Upper Stage) next to a notional EUS derived ROTV 100 (Reusable Orbital Transfer Vehicle +100 tonnes of propellant)

The telescopic boom cylinders are approximately 5 millimeters thick (much thicker that the fuselage for an airplane).  Five cylindrical booms would be  housed within the ten meter in diameter cylinder that accommodates radiation and micrometeorites shielding before the booms are expanded. One centimeter would be added to the top of each cylinder in order for each segment of the boom to securely attach to each other. So 1.5 centimeters would be required for each cylinder. Plus you have to add a centimeter for the boom cable that allows the boom to expand and contract. So ten centimeters would have to be utilized for the telescopic boom. That would allow nearly 70 meters to be used for radiation and micrometeorite shielding. But, as previously stated, only 40 meters or less would be required to permanently shield the twin habitat modules. 

 

AGH 1500 being deployed to a low Earth orbit 600 km above the Earth's surface by an EUS derivied reusable ROTV-100

Reusable EUS derived ROTV 100 vehicles could deploy the AGH 1500 600 kilometers to mitigate frictional drag from the Earth's atmosphere. After refueling at LOX/LH2 propellant depots, two ROTV 100 orbital transfer vehicles could deploy the AGH 1500 to various locations within cis-lunar space: NRHO, DRO, L3, L4, and L5. And twin ROTV orbital transfer vehicles could also deploy the AGH 1500 from cis-lunar space to the orbits of Mars and Venus-- allowing a permanent human presence in orbit above the surface of Mars and the clouds of Venus.

Twin ROTV 100 orbital transfer vehicles deploy an AGH 1500 from lunar orbit to a high Mars orbit beyond the orbit of the martian moon, Deimos

Links and References 

SLS Derived Artificial Gravity Habitats for Space Stations and Interplanetary Vehicles

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

Cosmic Radiation and the New Frontier

Protecting Spacefarers from Heavy Nuclei

The Logistical Viability of an SLS EUS Derived Reusable Lunar Crew Lander

 

Creating Artificial Gravity for the Space X Starship

SLS Derived Artificial Gravity Habitats for Space Stations and Interplanetary Vehicles

Commercial space plane approaching a rotating AGH space station @ LEO;
a reusable Orion/ACES-41 OTV is docked at one of the  central ports.

by Marcel F. Williams

The inherently deleterious effects of a microgravity environment severely limit the human ability to remain healthy during several months or years in space.

Minor problems associated with long periods of time in a microgravity environment include: weight loss, a degraded sense of  taste and smell, the clumping of perspiration and tears, facial and speech distortions, and an increased frequency of  flatulence.

However, far more serious problems related to months or years in a microgravity environment include:

1. The loss of 1 to 1.5% of bone mass in a single month

2. The loss of up to 20% of muscle mass in just 12 days without regular exercise.

3.  Significant reduction in cardiovascular fitness

4. Fluid loss and bone demineralization,  increasing the blood's calcium concentration while increasing the risk of  developing kidney stones.

5. Increased frequency of common cold due to the fact that the infected spray from the cough or the sneeze from a person  floats in the air instead of falling to the floor, enhancing the spread of viral infections aboard ship, conditions already enhanced by the extremely confined environment. 

6. The hampered effect of medicines due to the changes in blood flow redistribution

7. Vision problems of varying degrees of severity can occur in men in their 40s or older. 


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.

But practically all of the problems associated with a microgravity environment could be eliminated if permanent space stations and crewed interplanetary vehicles  were configured to produced significant levels of simulated gravity.

Rotating a spacecraft in order to produce artificial gravity has long been proposed as a technological  solution to the health problems associated with a  microgravity environment. However, research has shown that rotations exceeding 2 rpm (rotations per minute) require several hours to several days for the human body to adjust. During those hours or days of  adjustment, a significant number of astronauts would experience nausea associated with the Coriolis effect.

Research suggest that rotations that are 2 rpm or less require no training or time to adjust to the simulated gravity environment. A slow rotation also makes it easier for spacecraft to dock at the central axis while allowing astronauts to enter and exit the rotating habitat without the need for several hours or days of physiological adjustment. So rotating a habitat at 2rpm or less, would appear to be the simplest way to avoid the nausea associated  with the Coriolis effect.

However, at 2 rpm, producing a simulated gravity similar to that experienced on Earth  would require habitat modules extending at least 224 meters from the central axis, a spacecraft 448 meters in diameter if  twin counterbalancing habitats were utilized.

But a 112 meter  rotational radius would only be required to produce an artificial gravity of 0.5 g at 2 rpm,  a simulated gravitational level higher than on the lunar surface (0.17g) or on Mars (0.38g). The rate of rotation could even be decreased to simulate levels of gravity on the surfaces of the Moon and Mars.

Rotating AGH with a standard 112 meter radius

2.0 rpm - 0.5g (50% Earth simulated gravity)

1.7 rpm - 0.38g (Mars simulated gravity)

1.17 rpm - 0.17 (Lunar simulated gravity) 

Notional SLS launch of a three module artificial gravity habitat (AGH).

But even  launch vehicles the size of the SLS wouldn't be able to deploy habitats with lengths longer than 40 or 50 meters (radii less than 20 to 25 meters from the central axis).  Attaching long cables or tethers has frequently been proposed as a convenient way of greatly extending the radius of a rotating habitats.   Even in its earliest incarnation, the SLS should be able to deploy large payloads up to 70 tonnes in mass. So, with a single launch,  it would  be relatively easy for the SLS to deploy three pressurized habitats that were attached to each other by cables that could be extended once the habitat begins to rotate in space.   

SLS derived pressurized habitats

Credit: NASA

SLS minimum class propellant tank derived:
Dry mass: 17.3 tonnes
Habitable volume: 353 m3
Habitat length:13.5 meters
Habitat diameter: 8.4 meters

Credit: NASA

SLS full class propellant tank derived:
Dry mass: 22.4 tonnes
Habitable volume: 519 m3
Habitat length: 16.5 meters
Habitat diameter: 8.4 meters 

OTV-400 prepares to be fueled with LOX/LH2 propellant at a WPD-OTV-400 propellant depot @LEO

Once the AGH (Artificial Gravity Habitat) is in low Earth orbit, a large reusable orbital transfer vehicle,  fueled with LOX/LH2 propellant at a LEO orbiting propellant depot,  could be used to transport  the AGH practically anywhere within cis-lunar space or even to the orbits of Venus or Mars.

OTV-400 transports an AGH to an EML1 halo orbit.

The notional AGH habitats described here would be derived from SLS propellant tank technology. The rotating habitat  would consist of two twin habitat modules connected by cables to a central habitat module.  Gaseous hydrogen and oxygen thrusters would be used to rotate or to maneuver the AGH in space.  The hydrogen and oxygen used for space  maneuvers could be directly supplied to the thrusters through the electrolysis of water normally used for the production of air (oxygen) for the crew.

Interior of an Artificial Gravity Habitat (AGH) configured for launch aboard the SLS

Once the AGH is rotating between 1.7 to  2 rpm, the rings connecting the two habitat modules will detach, allow the four sheaves on each side to extend their 100 meter long cables.  Light weight expandable and retractable booms composed of large aluminum cylinders only a few millimeters thick would conceal the connecting habitat cables from view. The twin light weight metallic booms would serve as levers, increasing or decreasing the AGH rotation provided by the hydrogen and oxygen thrusters.

Rotating AGH at EML1 as it begins to expand its interior cables and exterior booms.

Within the interior of each boom, a pressurized module, three meters in diameter,  would serve as an elevator  to transport astronauts from the peripheral habitat module to the central habitat module. The elevator system will consist of two electric drives and two sheaves with two deflector sheaves to provide a gap between the elevator module and the counterweight.

The top and at the bottom of the elevator modules will be equipped with active CBMs (Common Berthing Mechanisms) allow astronauts to enter and exit the elevator modules from the central habitat or the peripheral habitats. Large solar panel recharged lithium batteries will provide power for the elevator and boom cables. 

Once astronauts exit the elevator into the-- central habitat-- they would have access to the elevator module that could transport them to the counter balancing habitat or access to a spacecraft docked at the central axis.

An OTV-400 deployed AGH: Top: OTV-400 transports AGH; second from top: OTV-400 separates from AGH; Third: AGH begins to rotate at 2rpm; bottom: AGH expands its booms and its retractable solar panels.

Cosmic radiation exposure at the peripheral habitats would be mitigated by 30 centimeters of water surround the walls, the ceiling, and the floor. 30 centimeters should be enough shielding to reduce radiation exposure  to less than 25 Rem per year during solar minimum conditions. 30 centimeters of water could also protect the astronauts from the dangers of   major solar events. Circulating the water shield outside of the inhabited areas could also  serve as a heat radiator, transporting warm water from the habitat to a water loops  below the pressurized module where excessive heat generated inside of the habitat could be radiated into space.

During the last leg of an interplanetary journey, the water shielding can also be dumped into space just a few hours or a few days before the last trajectory burns into orbit around a planet. Since water shielding can add more than 100 tonnes of mass to an interplanetary vehicle, dumping it before the final trajectory burns to achieve orbit could substantially reduce the amount of propellant required for an interplanetary mission. Once in orbit,  the water shielding can be quickly restored from pre-deployed orbiting water/propellant depots.

Because of the Earth's magnetosphere and the Earth's mass, an AGH at LEO could reduce radiation exposure to less than 15 Rem a year for astronauts on board. But permanent habitats beyond the Earth's magnetosphere will require substantially more shielding. Forty centimeters of iron shielding derived from lunar regolith or imported asteroids combined with a few centimeters of temperature regulating water shielding  could reduce cosmic radiation levels within inhabited areas below  the maximum levels of radiation allowed for radiation workers on Earth.

AGH @EML1 with an Orion/ACES docked at one of its central ports while a crew carrying ETLV-2 moves away from the AGH, beginning its journey to a lunar outpost at one of the lunar poles.

Average Annual Station Keeping Delta-V Requirements

LEO --------------------------- less than 5 m/s

EML1 and EML2 ----------- less than 10 m/s

EML3, EML4, and EML5 - less than 1 m/s


In order for permanent space stations to  maintain their proper orbits, propellant for station keeping will still be required. Fortunately, within cis-lunar space, station keeping only requires a delta-v of less than 1 meter per second (Earth-Moon Lagrange points 3, 4, and 5) up to  10 meters per second (EML 1 and EML2). So even the heaviest iron shielded AGH (~2000 tonnes) would  require less than 5 tonnes of LOX/LH2 propellant annually for station keeping at EML1 and EML2.

An interplanetary crewed AGH is deployed to high Mars orbit for ETLV-2 exploration of the martian moons: Deimos and Phobos.

The extraterrestrial colonization of low gravity worlds with at least 0.1 of gravity, could restrict humans to the surfaces of the Moon, Mars, Mercury, and Callisto. But SLS propellant tank derived artificial gravity habitats could lead the way towards much larger artificial gravity habitats which could eventually allow humans to colonize and exploit extraterrestrial resources in practically every orbital region of the solar system. 

© Marcel F. Williams

New Papyrus Magazine

Links and References


If We're Serious About Going to Mars, We Need Artificial Gravity

 Gravity is a Massive Problem

 What if you were born in space?

What's the minimum spin hab?

THE ARCHITECTURE OF ARTIFICIAL GRAVITY: ARCHETYPES AND TRANSFORMATIONS OF TERRESTRIAL DESIGN

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

Deep Space Habitats

Habitat Concepts for Deep Space Exploration

Maintaining a Safe, Stable, and Human Accessible Parking Orbit 

Living and Reproducing on Low Gravity Worlds

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

 Short Radius Centrifuge (SRC)

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