Aspects of Centrifugal Artificial Gravity in Science Fiction

The Best Location for a Rotating Space Station

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

 

Japanese Artificial Gravity Colony on the Moon

Producing Artificial Gravity

Creating Artificial Gravity for the Space X Starship

Inflatable Biospheres and Bio-Tori for Large Outpost and Colonies on the Lunar Surface

Notional regolith bag covered Kevlar biosphere and  bio-torus next to two solar powered cylindrical SLS propellant tank technology derived lunar regolith habitats on top of a microwave sintered lunar outpost floor.

by Marcel F. Williams 

NASA's Space Launch System (SLS) scheduled to go into operation by 2020 or 2021. But large cargo landing vehicles are going to be required  in order to utilize the SLS for the deployment of  lunar outposts habitats.  Large multilevel pressurized habitats derived from SLS propellant tank technology  could be deployed to the lunar surface on top of cargo landing vehicles designed to fit within a 10 meter in diameter SLS payload fairing. Such multilevel habitats for the lunar surface could be 8.4 meters in diameter, with two to four levels available for habitation. The average apartment in the US provides approximately 82 meters of floor area.  With each 8.4 meter in diameter level providing more than 55 square meters of floor area, a single multilevel SLS deployed lunar habitat could provide lunar astronauts with 105 to 210 square meters of habitation floor area. 

X-Ray of notional SLS propellant tank derived Lunar Regolith Habitat

However, substantially larger lunar habitats would require the deployment of inflatable structures.

Various  types of inflatable  habitats have been proposed by NASA personal since the dawn of the space agency. In the 1980's, M. Roberts of  NASA's Johnson Space Center,  proposed deploying inflatable   Kevlar biospheres to the lunar surface.  Since the lower hemisphere  of such biospheres would be underground, the radius of the inflated habitats would be limited by the depth of the regolith. Depending on the region on the lunar surface, lunar regolith can be as deep as eight meters or as shallow as two meters before encountering bedrock.  Such depth constraints on the lunar surface would limit the diameter of a biosphere to just  4 to 16 meters. A 16 meter biodome pressurized with an Earth-like  nitrogen and oxygen atmosphere of 14.7 psi (101.3 kPa) with a safety factor of four would weigh only 1.76 tonnes.

X-Ray of notional regolith bag shielded biosphere on the lunar surface (Credit: NASA)

However, the constraints of regolith depth could be easily alleviated by inflating a biosphere-- on top of the lunar surface-- and surrounding it with an inflatable bio-torus. An inflated Kevlar torus would be an inherently self supporting structure. So regolith could be deposited within the cavity between the bio-torus and the biosphere, providing structural support for the inner biosphere. Since the surround bio-torus would require substantially more Kevlar material than the biosphere, reducing the diameter of the torus to approximately half that of the biosphere could substantially reduce the amount of mass needed to be deployed to the lunar surface.  A spacious cavity between the bottom of the biosphere and the surrounding bio-torus could accommodate  additional living space in the form a smaller bio-torus about one third the diameter of the external bio-torus.

Inflatable torus extraterrestrial habitat (Credit: NASA, 1961)

Lunar Statistics

Diameter relative to the Earth: 27.3%

Surface area relative to the Earth: 7.4% (Land area not covered by water only comprises ~ 29% of the Earth's surface)

Surface gravity: 0.17g

Regolith depth: 2 to 8 meters 

Annual amount  of cosmic radiation on the Lunar surface during the solar minimum - 38 Rem

Annual amount of cosmic radiation on the Lunar surface during the solar maximum - 11 Rem

(Maximum amount of  radiation allowed for radiation workers on Earth per year - 5 Rem)
(Maximum amount of radiation allowed for adult female during nine months of pregnancy -)

The biodome and the upper and outer exterior of the bio-torus could be covered with regolith bags that are either 2.5 meters or 5 meters in thick, depending on what level of radiation protection is desired for the habitat. At least, 10 centimeters of lunar regolith is required to protect humans from the cell killing heavy nuclei component of cosmic radiation. Thermal fluctuations of the lunar surface may also require as little as 10 centimeters of lunar regolith. Assuming an average regolith density of about 1.5 grams per cubic centimeter, at least 60 centimeters of lunar regolith would be required to protect the habitat from micrometeorites.

Its relatively easy to shield habitats and even humans in pressure suits  from the heavy ion component of cosmic radiation.  But most cosmic ray particles are composed of the smallest ionized atoms: protons (85%) and alpha particles (ionized helium atoms) which are much more difficult to shield against. Most protons and alpha particles streak harmlessly though the vacuous space between the atoms of the human body. But the relentless rain of these cosmic ray components  inevitably results in impacts upon our body tissues.

On average, humans receive about 620 mrem per year of radiation due to a combination of sources from both cosmic and terrestrial radiation sources. The maximum recommended radiation exposure for  a pregnant woman is 50 mrem per month which comes very close to the average radiation exposure that humans on Earth experience in a year.

The maximum level of radiation exposure for radiation workers on Earth is 5 Rem per year. And that would require approximately 2.5 meters of regolith shielding. But the maximum level of radiation exposure allowed for a woman during the term of her pregnancy is just 0.5 Rem. So lunar regolith shielding would probably have to be increased to  5 meters (the same level of radiation shielding provided for humans by the depth of the  Earth's atmosphere). Inflated with an Earth-like atmospheric pressure, biospheres and bio-tori could easily support the weight of 5 meters of regolith.

Of course, there would be no shortage of available regolith on the surface of the Moon.  Just one  hectare of regolith on the lunar surface could provide between  20,000 to 80,000 cubic  meters of shielding material (2 million to 8 million cubic meters per square kilometer) for  large pressurized habitats.  And the excavation and deposition of lunar regolith and even the production of regolith bags could be done by robots teleoperated by personal employed on the surface of the Earth. 

During solar minimum conditions, the maximum radiation exposure on the lunar surface can  exceed 3000 mrem per month. A hardened pressure suit designed to protect against the heavy nuclei component of cosmic radiation could  reduce general cosmic radiation exposure by two thirds. But even 1000 mrem (one Rem) per month would exceed annual radiation levels for radiation workers in less than six months. Pregnant lunar colonist would probably have to remain inside the protective confines of their habitat during nine months of pregnancy. But even if lunar colonist spent only 10% of their time  outside of  pressurized habitats (less than 2 Rem of annual exposure within radiation hardened pressure suits ), that would still avail them to more than 16 hours a week of EVA time on the lunar surface. But I seriously doubt if most lunar colonist will spend more than 5% of their time outside of the comfort of their lunar habits.

So it seems likely that Lunar colonist will spend at least 90 to 95% of their time on the Moon within the confines of pressurized  habitats. So living on the Moon will mostly be about living within the protective confines of pressurized habitats that are also designed to protect its inhabitants from the dangers of micrometeorites, extreme thermal fluctuations, and excessive radiation exposure.

So if future Lunarians are going to have to spend the overwhelming majority of their time-- indoors, such pressurized habitats should be as comfortably-- spacious-- as possible. Once large SLS propellant tank technology derived habitats are on the lunar surface, much larger (inflatable) habitats could be deployed by the SLS.

A single SLS Block I launch could deploy a 27.5 tonne biosphere, plus a 38 tonne external  bio-torus and a 2.5 tonne inner bio-torus to LEO. So a total mass of 68 tonnes would be deployed by the SLS to Low Earth Orbit. A pair of reusable ACES-68 orbital transfer vehicles could transport the payload to NRHO. Reusable lunar cargo vehicles could transport the biosphere and the bio-tori separately to the lunar surface.

X-Ray of 40 meter in diameter lunar biosphere surround by two bio-tori

A second SLS Block I launch could deploy five 3 meter in diameter and 3 meter high airlocks: one to be connected to the bottom of the biosphere and two each to be connected the bottoms of the two bio-tori on opposite sides. Six 3 meter in diameter expandable tunnels will also be deployed to linearly connect the airlocks to each other and to allow astronauts to enter and exit the base of the inflatable habitats. Six expandable regolith walls will be included to provide a firm regolith base for the biosphere and the bio-tori. Six 2.4 meter in diameter ECLSS modules will be included: two to be attached to the a biosphere airlock and individual modules to be attached to each of the bio-tori airlocks. Piping  will be provided to connect the ECLSS modules to external radiators. And wiring will be provided to connect the ECLSS to external solar, nuclear, and chemical power units.  Again, these payloads will initially be deployed to LEO before be transported to NRHO and then to the lunar surface by reusable LOX/LH2 vehicles.

 Once deployed to the lunar surface, the inflated Kevlar biosphere would be 40 meters in diameter. An 18 meter in diameter bio-torus would surround the biosphere. And an additional 6 meter in diameter bio-torus would be placed with the lower cavity between the biosphere and the external bio-torus.The pressurized biosphere and bio-tori would sit on top a regolith base. Airlocks beneath the biosphere and bio-torus would be connected to cylindrical metallic tunnels internally pressurized with cylindrical Kevlar bags would provide astronauts with easy access to the other sections of the habitat while also allowing them to exit the habitat or to connect to exterior habitats. 

The atmospheric pressure within the biosphere and within the bio-torus would be the same atmospheric pressure as on Earth. And this will allow people working in the bio-torus to move easily back and fourth between the bio-torus and the biosphere without the need of to deal with differences in pressure.

Notional biodome recreational floor area of a 40 meter in diameter bio-torus

With a floor area of 1257 square meters within a spacious biodome 20 meters high, the upper hemisphere of the 40 meter biosphere could be used for a variety of recreational purposes (tennis, volleyball, basketball, gymnastics, swimming, etc). The biodome could also provide astronauts with  a spacious area for relaxation if landscaped with grass and trees and other aesthetically pleasing foliage. 

The lower hemisphere would be composed of four expansive habitat floors, 2.4 to 3 meters high, providing apartments, laboratories, and gyms and more than 1200 square meters of habitable floor space.  The floors, rooms, and apartments will be composed of prefabricated sections manufactured on Earth and assembled within on the Moon within the pressurized biosphere. Ceiling, floor, and wall panels and beams and other structural components could be transported to the lunar surface by reusable and expendable  commercial lunar transports.  So the lower half of the biosphere should be able to provide at least four expansive levels for  habitation, with the lower hemisphere alone far exceeding that of the floor area for  SLS propellant tank derived habitat modules.

The surrounding 18 meter bio-torus would also consist of multiple levels that are composed of modular components. But, under this scenario, the   bio-torus would be divided into five levels. The top level would be used for orchards (apple, orange, lemon, cherry, and peach trees) and also for raising large fauna: pigs, miniature cows, sheep, and possibly even ostriches. The second level would be used for poultry. The third and fourth level would be used for growing fruits and vegetables: bananas, pineapples, watermelons, tomatoes, carrots, lettuce, potatoes, corn, wheat, sugar beets, etc. The bottom level of the bio-torus would be used for aquaculture: brine shrimp, fish, oysters, etc.

The inner 6 meter in diameter bio-torus would be largely used for storage and for emergency habitation in case something serious should occur inside of the biosphere.

The entire facility would be designed to comfortably accommodate between 50 to 100 individuals.

 Diameter and mass of Kevlar biospheres and bio-tori pressurized at 14.7 psi (101.3 kPa) with a safety factor of  four without regolith shielding and structural support

40 meter in diameter  biosphere: 27.5 tonnes
Surrounding 18 meter in diameter bio-torus: 38 tonnes
Surrounding 6 meter in diameter interior bio-torus: 2.5 tonnes

Mass of an M1-Abrams Tank - 62 tonnes

100 meters in diameter biosphere: - 430 tonnes
Surrounding 50 meter in diameter bio-torus: 759 tonnes
Surrounding 16 meter in diameter interior bio-torus: 44 tonnes  

Mass of a Boeing 747 - 440 tonnes

200 meters in diameter biosphere:  3438 tonnes
Surrounding 100 meter in diameter bio-torus: 6071 tonnes
Surrounding 32 meter in diameter interior bio-torus: 348 tonnes

 Mass of the Eiffel Tower - 7300 tonnes

300 meters in diameter biosphere:  11,600 tonnes
Surrounding 150 meter in diameter bio-torus: 20,512 tonnes
Surrounding 50 meter in diameter interior bio-torus: 1264 tonnes

Mass of an Ohio-Class atomic submarine - 16,764 tonnes


400 meter in diameter biosphere: 27, 500 tonnes
Surrounding 200 meter in diameter bio-torus: 48, 574 tonnes
Surrounding 60 meter in diameter interior bio-torus: 2478 tonnes

Mass of a cruise ship - 100,000 tonnes

1000 meters in diameter biosphere: 430,000 tonnes
Surrounding 500 meter in diameter bio-torus: 759, 000 tonnes
Surrounding 160 meter in diameter interior bio-torus: 44, 000 tonnes

 Mass of the Golden Gate Bridge - 804, 673  tonnes

Much larger inflatable facilities will probably require the Kevlar material to be exported from Earth in small sections to be woven together by machines deployed to the lunar surface. And, eventually,  Kevlar threads will be manufactured on the lunar surface from lunar materials mostly found at the lunar poles.

Biospheres that are 400 meters in diameter could be very attractive for human colonization of the Moon. The 200 meter high bio-domes of such facilities would be able to provide artificial lakes and lagoons at least 200 meters in diameter with surrounding sandy beaches where you could not only swim but also put on a pair of  wings and fly under the low lunar gravity.  The top half of the surrounding 200 meter in diameter bio-torus could also be used for housing familiar to that on Earth plus recreational parks and 100 meter lakes and lagoons. And with a 100 meter high rooftop, there should also be enough room in the bio-torus to strap on a pair of wings and fly at least 50 meters above the ground within the upper half of the bio-torus.



Links and References

Inflatable Biospheres for the New Frontier

Structural Design of a Lunar Habitat

Inflatable space habitat

Inflatable Habitation for the Lunar Base


Living and Reproducing on Low Gravity Worlds

Information for Radiation Workers

Doses in Our Daily Lives 

Ionizing Radiation

 GLOBAL LUNAR REGOLITH DEPTHS REVEALED


 ECLSS

John Bucknell on Mining Lunar Ice for Cis-Lunar Habitat

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

Congress Requires NASA to Develop a Deep Space Habitat

SLS propellant tank derived DSH @ EML1 (credit NASA)

The US Congress passed an omnibus spending bill last December requiring NASA to develop a prototype deep space habitation (DSH) module no later than 2018. It also requires NASA to provide Congress with a report on how the enactment of this bill is being complied with by the first half of 2016.

NASA has viewed a DSH  as a necessary component for safely transporting humans from cis-lunar space to Mars orbit in the 2030's and also as a gateway to the lunar surface and beyond. The Earth-Moon Lagrange points EML1 and EML2 have most often been proposed as the place where a Deep Space Habitat should be deployed.

EML2 (L2) has the advantage of requiring the lowest delta-v from LEO in order to deploy the DSH into a halo orbit around the Lagrange point. But crewed journeys from LEO to L2 also has the disadvantage  of taking as long as 8 days to reach the habitat if the low delta v of 3.43 km/s is to be taken advantage of. Such a long journey would expose astronauts to two to four times as much cosmic radiation as journeying to EML1.  A higher delta-v of 3.95 km/s could transport a crew to EML2 in just four days. But this would be higher than the 3.77 km/s delta-v requirement to transport crews from LEO to EML1. EML1 also has the advantage of  a fast 2 day journey from LEO at  4.41 km/s. Such fast journeys would reduce radiation exposure while also reducing the chance of traveling during a major solar event in half. 

The Earth-Moon Lagrange points (Credit the Artemis Project)

Another, long term, disadvantage of a DSH at EML2 is that radio transmissions between the habitat and Earth could interfere with future radio telescopes deployed on the back side of the Moon in order to avoid radio interference from the Earth's surface, Earth orbit, and space craft traveling to and from the Moon. 


Delta- V budgets between LEO and EML1 or  EML2 

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

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

EML1 to Lunar Surface (~3 days) - 2.52 km/s dv

Lunar Surface to EML1  (~3 days) - 2.52 km/s dv

LEO to EML2 (~ 8 days) - 3.43 km/s dv

LEO to EML2 (~ 4 days) - 3.95 km/s dv
 
EML2 to Lunar Surface (~3 days) - 2.52 km/s dv

Lunar Surface to EML2  (~3 days) - 2.52 km/s dv

 
Aesthetically, a Deep Space Hab positioned at EML1 would probably have the most spectacular views within cis-lunar space.  An astronaut  at  EML2 would view an Earth that is slightly smaller than viewed from the front side of the Moon while the view of Earth at EML1 would be slightly larger than is seen from the lunar surface. Both EML1 and EML2 would view a Moon that is titanic in size relative to its view from the Earth. But EML2 would only be able to view the back side of the Moon while EML1 would only be able to view the front side of the Moon.

Because of the reduced time and radiation exposure to get there, the fact that an EML1  habitat wouldn't interfere with radio telescopes on the back side of the Moon, plus the aesthetic view,  I think NASA should deploy the Deep Space Hab at EML1 rather than at EML2.

The relative visual size of the Moon and Earth: at the top, the view of the Moon from the surface of the Earth or low Earth orbit; second from the top, the view of the Earth from the surface of the Moon; third from the top, the view of the Earth from EML1; at the bottom, the view of the Moon from EML1. 

The primary purposes for an EML1 (L1) Deep Space Habitat (DSH) should be to:

1. Serve as a gateway to the lunar surface. Astronauts traveling from the Earth or from the lunar surface could dock their spacecraft at the EML1 habitat, taking advantage of the larger accommodations at the DSH while transferring from one vehicle to another.  

2. Serve as a storm shelter during the occurrence of major solar events. This will probably require at least 30 cm of water shielding for the areas within the habitat that the astronauts will be occupying. Major solar events can last for several minutes or up to several hours.

3. Serve as a maintenance and repair station for reusable lunar shuttles (ETLV) and orbital transfer vehicles. Flex Craft docked at the DSH could be utilized  for extravehicular repairs to  nearby water/propellant depots and associated solar arrays at EML1.

4. Test the effectiveness of various levels of water shielding required to mitigate cosmic radiation and potentially brain damaging heavy nuclei. In theory, 30 cm of water would be enough shielding to to stop the penetration of the heavy nuclei component of cosmic rays, reduce the annual exposure of cosmic radiation in general to less than 25 Rem per year, while also significantly mitigating the effects of major solar events. While an even thicker shielding of water could reduce cosmic radiation exposure, a minimal amount of shielding will be required to minimize the mass for crewed interplanetary vehicles.

5. Test the integrity and reliability of the pressurized habitat structure which could also be used for habitats on the surface of the Moon and Mars and for rotating interplanetary artificial gravity habitats.

Its probably the intent of Congress  for NASA to design the habitat module that will transport humans safely to Mars.  But because of the inherently deleterious physical and psychological effects of a microgravity environment on human beings, its unlikely that any microgravity habitat will ever be able to accomplish this goal.

 Under microgravity conditions, astronauts can lose between 1 to 1.5% of their bone mass in a single month and without regular exercise, astronauts can lose up to 20% of their muscle mass in just 5 to 11 days. A microgravity environment can reduce  cardiovascular fitness-- possibly increasing the chances of heart attaches. And vision problems of varying degrees of severity can occur-- especially in older men. 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. Unfortunately, blood flow redistribution in a microgravity environment can effect medicines ingested or injected into the human body to treat illnesses.

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.

Added to the serious problems above, there are other annoying problems in a microgravity environment that could enhance discomfort and psychological stress aboard ship such as:

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 sweat and 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. This could cause some to misinterpret another individuals expression, possibly causing tension between two individuals aboard a multiyear mission. 

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.

It might be possible to eliminate all of these deleterious microgravity related problems aboard an interplanetary vehicle by  simply rotating pressurized habitats in counter balancing pairs to produce a  significant level of simulated gravity. The  additional benefit of having two pressurized modules is that it also provides a back up module in case there are serious life threatening malfunctions at the other habitat module. 

Pressurized habitats capable of being used in space and on the surface of the Moon or Mars could also be used as counter balancing habitats for rotating spacecraft and space stations that produce some levels of artificial gravity. And development cost could be greatly reduced if the basic habitat pressurized tank can be used for  microgravity habitats, low gravity surface habitats, and for artificial gravity habitats.

Internal configuration of a  lunar habitat derived from  SLS propellant tank technology. A  regolith wall composed of kevlar sandwiched between eight rigid aluminum panels is deployed around the habitat cylinder and filled with regolith to protect astronauts from cosmic radiation, micrometeorites, and fluctuating temperatures on the lunar surface. The airlocks are derived from ETLV propellant tank technology.

NASA could significantly reduce development cost by utilizing SLS propellant tanks for both a DSH but also for lunar and martian habitats. The lunar and martian regolith habs that I've previously proposed would use an SLS propellant tank as a pressurized habitat. Once the habitat module is properly placed on the lunar surface, a kevlar regolith wall sandwiched between  eight three meter wide aluminum  panels would automatically deploy, allowing a lunar backhoe to deposit regolith shielding  within  the two meter cavity between the outer wall and the inner cylindrical wall.

Since crewed interplanetary voyages to Mars probably won't take place until the 2030's, serious funding by NASA for the development of artificial gravity habitats for interplanetary journeys probably won't have to start until the early 2020's. However, this doesn't mean that a  DSH habitat couldn't be designed to function as a microgravity habitat, as a  low gravity habitat, and as a simulated gravity habitat in order to reduce cost for both the cis-lunar program in the 2020's and for the Mars program in the 2030's.

If such habitats are to be used for long  interplanetary journeys  in the future, they must be as comfortably spacious as possible while also minimizing mass.  NASA is evaluating several types of potential Deep Space Habitats derived from current technology:


Habitat Modules Derived from Current Technologies

SLS full class propellant tank derived:
Dry mass: 22.4 tonnes
Habitable volume - 519 m3

SLS minimum class propellant tank derived:
Dry mass: 17.3 tonnes
Habitable volume: 353 m3 

BA-330:
Dry mass 20 to 23 tonnes
Habitable volume: 330 m3 

ISS node & MPLM:
Dry mass: 35.5 tonnes
Habitable volume: 108 m3

ISS hab & MPLM: 
Dry mass: 32 tonnes
Habitable volume: 90 m3


The ISS derived habitats only provide between 2.8 meters  to  3 meters cubed of habitable volume per tonne. The Bigelow BA-330 would provide significantly more volume, between 14 m3 and 17 meters cubed of habitable volume but within severely confined areas. The SLS propellant tank derived habitats, however,  would provide between 20 m3 and 23 m3 of habitable space per tonne (35% to 64% more habitable volume per tonne). Since SLS propellant tanks will already be in production for SLS launches, manufacturing more tanks for Deep Space Habitats and for surface habitats for the Moon and eventually for Mars should greatly reduce development cost for a Deep Space Hab. 

The  SLS Block B with its upper stage would probably only be able to deploy  about 30 to 32 tonnes of  mass  to EML1, allowing it  to  easily deploy an SLS propellant tank derived DSH to EML1. 

An SLS propellant tank technology derived DSH @ EML1. There are four docking ports for four large vehicles. There are also four docking ports for four personal Flex Craft vehicles. There is also one crew hatch for pressure suit excursions. Twin solar panels provide power for the DSH with a central heat radiator extending between them. A crewed  MPCV and a crewed ETLV-2 are docked at the DSH in preparation for an ETLV visit to an outpost on the lunar surface. A lone floating Flex Craft has been utilized to inspect the exterior of the reusable ETLV-2 before departure (MPCV: Credit: ESA).  

Internally radiation shielding two levels of the DSH habitat area within an SLS derived habitat, above and below,  with 30 centimeters of water within that same area within the 8.4 meter in diameter tank would require approximately 71 tonnes of water. If the DSH is accompanied in its halo orbit at EML1 by  nearby water/propellant depots for missions to the lunar surface then at least 30 tonnes more of water will probably be required to be sent to EML1 on an annual basis.

Internal configuration of a DSH microgravity habitat derived from SLS propellant tank technology. The pressurized interior inhabited by humans is surrounded with 30 centimeters of water to stop heavy nuclei and to mitigate the effects of major solar evens while also reducing radiation exposure for the crew to less than 25 Rem per year during solar minimum conditions. The airlocks are derived from ETLV propellant tank technology.  

Supplying  large amounts of water to EML1 could easily be accommodated by additional SLS launches.  But since NASA currently has only 16 RS-25 engines in stock from the old Space Shuttle program,  the number of SLS launch vehicles will limited to just four until until new  RS-25 engines are in production from Aerojet Rocketdyne in 2022 or 2023. This  means that an aggressive SLS program cannot really begin until 2022 or 2023.

Four of the RS-25  engines will be dedicated to an  SLS launch in 2018 to test the MPCV (Multipurpose Crew Vehicle).  Another four engines will be used by NASA for the first crewed MPCV mission beyond the Earth's magnetosphere. That only leaves enough engines available for two additional SLS launches until  new engines are in production.

One SLS launch would be enough to deploy the DSH to EML1. But a the final engines available for one more SLS launch would not be able to transport enough water to appropriately radiation shield the DSH. This could mean that DSH deployment might have to be delayed until 2022 or 2023.
 
In previous articles, I  have suggested  that NASA needs to commit itself to developing a reusable single staged Extraterrestrial Landing Vehicle (ETLV) for crewed and robotic  missions to the surface of the Moon, the moons of Mars, and to the Martian surface (with an ADEPT or HIAD deceleration shield).  An essential component of a reusable ETLV would be an ETLV derived water/propellant depot (WPD) that would be capable of using solar electricity to produce LOX and LH2 from water. Serious funding from Congress for  the development of the ETLV and the associated landing vehicles and orbiting depots derived from it should start in 2017, in my opinion, at a funding level of at least $1.5 billion per year.

An ETLV derived and SLS deployed water/propellant depot at EML1 near solar power station. The solar powered facility would be capable of storing up to 100 tonnes of water while also producing and storing up to 60 tonnes of LOX/LH2 propellant. 

In 2020 or 2021, a WPD could be deployed to  LEO with at least 50 tonnes of water using no SLS upper stage or 80 tonnes of water with an upper stage.   At LEO, the WPD  would  electrolyze water into hydrogen and oxygen and then  liquefy and store the hydrogen and oxygen within five propellant tanks capable of storing up to 60 tonnes of rocket propellant. The WPD would then self deploy itself into a halo orbit at EML1.

Once a WPD has been deployed to EML1 then private commercial providers could deliver water to EML1. Space X will be testing its new Falcon Heavy in 2016. Such a vehicle might be able to supply 10 to 15  tonnes of water to EML1 per launch. The ULA also has plans to develop a heavy lift version of their future Vulcan rocket  (the Vulcan Heavy) which should also be capable of delivering 10 to 15 tonnes of water to EML1 per launch. So starting in 2020, commercial launches could be used to deliver 10 to 15 tonnes of water per month to EML1 (120 to 180 tonnes per year). Monthly commercial water deliveries will continue to EML1 until  lunar water manufacturing and exporting facilities on the lunar surface are complete in the middle or late 2020's.

Artist rendition of Space X Falcon Heavy (Credit: Wikipedia)

Artist rendition of ULA Vulcan Heavy

Once the water has been delivered to EML1 and fairly close (within a few hundred meters) of the water/propellant depot, the WPD will rendezvous with the water tankers, extracting and depositing the water with WPD's water tank. The WPD will dock at an solar power station where it will use that power to convert some of the water into LOX and LH2 while storing the rest.

After the DSH is deployed to EML1, the WPD will also rendezvous with the DSH,  transferring water to the habitat for radiation shielding, drinking, and air production. Once ETLV spacecraft are ready for robotic and crewed missions to the lunar surface, they will be fueled by the WPD at EML1.

 The last remaining engines from the Shuttle era can then be used to launch the MPCV to EML1, testing the ability of the SLS to deliver astronauts safely to the Earth-Moon Lagrange points while also checking out the integrity and functionality of the Deep Space Habitat.

Since long periods of time under  microgravity conditions  is inherently deleterious to human health,  time aboard the DSH at EML1  should be constrained. For astronauts over the age of 40, the most vulnerable astronauts to microgravity visual damage,  I'd limit missions confined to microgravity environments to only 16 days. For astronauts under the age of 40, I'd limit the stay at EML1 to less than 31 days. Such short stays at EML1 would ensure that the astronauts would not receive enough radiation in the DSH to prevent them from participating in future interplanetary missions where they will be exposed to months and even years of cosmic radiation bombardment.

While thicker water shielding for the DSH could further reduce radiation exposure, it would also add substantial amounts of  mass to an interplanetary vessel. One of the goals of the DSH should be to replicate conditions for astronauts aboard an interplanetary vessel. So the DSH should only provided with enough water shielding similar to that of an interplanetary vehicle. And an interplanetary habitat only has to be shielded to a  level that would enable astronauts to complete a three year round trip to and from Mars and Mars orbit without exposing them to more than 50% of the recommended lifetime radiation exposure recommended by NASA-- which would be about 100 Rem for the least vulnerable passengers (women 25 years of age).


Links and References


Spending Bill To Accelerate NASA Habitation Module Work

Deep Space Habitats

Commonality between Reduced Gravity and Microgravity Habitats for Long Duration Missions

Building an L1 depot in phases

Habitat Concepts for Deep Space Exploration

NASA Mega-Rocket Could Lead to Skylab 2 Deep Space Station

BA-330

Solar Storm and Space Weather

Cosmic Radiation and the New Frontier

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

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

ULA Future Full Spectrum Lift Capability

The SLS and the Case for a Reusable Lunar Lander