Commercial Launch Demand to Private Microgravity Habitats at Low Earth Orbit

Notional 7 meter in diameter Blue Origin space habitat (Credit: NASA & Blue Origin)

By Marcel F. Williams 

A 2018 Pew Research poll suggest that 42% of Americans would be interested in traveling into space. But, so far, only seven super wealthy individuals have been able to do so with their own private funds. Multimillionaire Dennis Tito was the first tourist to travel into space to the ISS. Billionaire Charles Simonyi was the first space tourist to pay for  two trips to the ISS.

The Russian space agency has charged these super wealthy individuals between $20 million to $40 million to travel to the ISS. And because of the extraordinarily high cost of space travel,  space tourism has been exclusively for the super wealthy.

Multimillionaire Dennis Tito (far left) became the first space tourist in April of 2001

Bigelow Aerospace is currently offering tickets to the ISS for $52 million each for a one to two month stay at the International Space Station. 

There are over 2100 billionaires on Earth. 52,000 people in the world who are worth over $100 million with 15,000 of those individuals living in the US alone. So there are at least 52,000 people on Earth who could afford to travel to a space and to a space station at current prices.

Companies like Bigelow Aerospace have also been developing their own private space habitats that they hope to deploy some time during the next decade. And  NASA has recently presented space habitat concepts from several private space companies including Blue Origin and Lockheed Martin. 

$50 million seems close to the current rate for training, transporting, housing, and feeding a space tourist.  Optimally, you want to protect your customers health, so ten days in space should prevent any noticeable anatomical or physiological health effects. The ten days would include the launch days to the private space station and the return to the Earth's surface. That should give a tourist 8 full days inside of a private space station.  The pre-launch experience should also include astronaut training with maybe a few hyperbolic flights aboard a jumbo jet to test the individuals reaction to brief periods of microgravity and dynamic flight situations.

Notional 8.4 meter in diameter SLS derived microgravity habitat (Credit NASA)

Once inside of the orbiting space habitat, a paying tourist should be given spacious-- private quarters-- for sleeping, bathing, communicating with friends and family back on Earth and watching network and cable television programs or videos and movies on a private wide screen monitor. 

A large microgravity recreational area should also be available for guest. And the recreational area should be at least as spacious as the accommodations  experienced by astronauts aboard the old 6.6 meter in diameter Skylab facility. Notional habitats derived from the New Glenn upper stage (7 meters in diameter), Bigelow's Olympus: BA-2100 (12.6 meters in diameter), and SLS propellant tank technology derived habitats (8.4 meters in diameter) should provide spacious environments for microgravity recreational activities. 

A Cupola window viewing area of the Earth should be continuously available for guest.

Samantha Cristoforetti taking photos within the ISS Cupola (Credit: NASA)

At least three FlexCraft EVA tours should be available so that guest can experience moving about in space while experiencing spectacular view of the Earth and external views of the  space habitat where they have been residing. FlexCraft would give tourist the advantage of quick and convenient access to space without the need for several hours of pre-breathing oxygen in order to prevent decompression sickness (the bends).  Flexcraft can be flown in space by the tourist or tele-operated by personal on the ground or authorized personal inside of the space habitat. Manipulation arms could also be removed from FlexCraft vehicles that are utilized for tourist.

Notional FlexCraft single person vehicle (Credit: NASA)

The commercial spacecraft pilots could serve as the onsite guest service agents for the tourist they've taken up to the space habitat. Robots operated by personal on Earth could be used by the space habitat owners to assist the pilots and their guest-- even on FlexCraft EVAs. 

If the polls are correct then their should be at least  6300 super wealthy Americans who desire to travel to a space station-- and can afford to do so. And if there is a similar statistical desire  world wide, then there should be  at least  22,000 super wealthy people who want to travel into space-- and can afford to do so.

Annually, if just 10% of the super wealthy who desired to travel into space (2200 people)-- did so-- that would require 440 to 550 private commercial launches every year. In 2018, there were only 111 successful space launches with only four them being crew launches. So space tourism should create dramatic increase in the launch rate accompanied by substantial reductions in launch cost. But even if it were only 1%, that would require 44 to 55 private commercial launches every year.

But what if there was a national or even an international lotto system that could allow private individuals to risk an American dollar for a chance to travel into space? What if  42% of adult Americans risked $5 a year, on average, for a chance to travel into space through a Space Lotto system?  That would generate approximately $1.2 billion a year for crew launches. And that would be enough money to send 24 average Jane's and Joe's into space every year (5 to 6 additional crew launches).

But you could add even more incentive for Americans to purchase Space Lotto tickets if winners were given a monetary prize of $250,000 (less than 1% of the cost for the round trip ticket to space). Winners could be given $125,000 initially for their time off from work for astronaut training and traveling into space. An additional $125,000 would be given to them once they returned from space.

 If 42% of the world's adult population were willing to participate in Space Lotto system with a similar financial reward but only risked $2 per year, that would still generate $5 billion a year. That could purchase enough tickets for 100 winners per year (20 to 25 additional crew launches).

Optimally, a single private space habitat might be able to accommodate 36 tourist flights per year for a 10 day stay. Ten habitats would be required to accommodate 360 flights per year. So, obviously, there would also be a significant launch demand just to deploy the private habitats needed to accommodate potential tourist. 



Recreational activity within the interior of the 6.6 meter in diameter Skylab space station. 


References and Links

Space tourism? Majority of Americans say they wouldn’t be interested

NASA LEO Commercialization Study Results 

Space Tourism

Space Adventures 

 FlexCraft

Bigelow aims to sell rides to space station on SpaceX Dragon ships for $52M a seat

The World's Billionaires

You're not rich until you have $100 million, says rich people

Ultra high-net-worth individual

Here's where the world's richest 0.00168% live

Walking On Mars

Links and References

Gravity is a Massive Problem

What if you were born in space?

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

Gravity is a Massive Problem

Links and References

What if you were born in space?

Living and Reproducing on Low Gravity Worlds

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

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

Living and Reproducing on Low Gravity Worlds

1972 photograph of Apollo astronaut, Eugene Cernan, walking towards the LRV on the lunar surface (Credit: NASA)

by Marcel F. Williams

Establishing a permanent human presence beyond our planet of evolutionary origin is one of the long term goals of human space travel. The expansion of human settlements throughout the solar system has the potential to dramatically increase the economic wealth of human civilization while also greatly enhancing the survival of our species.

Some space advocates believe that the long term colonization of the solar system will require the manufacture of titanic artificial worlds that rotate to  produce simulated Earth-like gravities within their interior surfaces.  But there are still others  who believe that low gravity worlds such as  the Moon and Mars could be utilized as near term destinations for human colonization.

But can Homo sapiens really live and reproduce on hypogravity worlds?

In his classic 1972 song 'Rocket Man', Elton John says: "Mars ain't the kind of place to raise the kids..."

Well, maybe!


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


Moon

surface gravity relative to the Earth: 0.17g 

diameter relative to the Earth: 27.3%

surface area relative to the Earth: 7.4%


Mars

surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth: 53.1%

surface area relative to the Earth: 28.4%


Mercury

surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth:  38.3%

surface area relative to the Earth:  14.7%


Callisto 

surface gravity relative to the Earth: 0.13g 

diameter relative to the Earth:  37.8%

surface area relative to the Earth:  14.3%

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

Continuous exposure to microgravity conditions over weeks and months is inherently deleterious to human health. And there is growing evidence that long term microgravity exposure can also significantly  lower  fertility in humans and other mammals, possibly leading  to sterility. This suggest that crewed interplanetary missions requiring several months of space travel may require interplanetary vehicles capable of producing artificial gravity during the journey. Obviously, humans can't colonize Mars by sterilizing their passengers before they get there!

But it is currently unknown how much gravity is required to mitigate or eliminate significant infertility in humans. However,  if the lower gravity of the Moon or Mars turns out to seriously effect the long term fertility of humans then daily exposure to-- hypergravity-- through short armed centrifuges may be a possible solution.

Short radius hypergravity centrifuge could help to mitigate the possibility of infertility on lower gravity worlds such as the Moon and Mars.   (Credit NASA)

But the lower gravity on extraterrestrial worlds could have another deleterious effect that may effect human reproduction and even the ability of people to return to the normal gravity of the Earth's surface. Bone mineral loss under microgravity conditions is already known to occur in astronauts living in space for several weeks. And significant bone loss could distort the shape of the female pelvis to a degree that endangers her and a potential infant during attempted childbirth. Unfortunately, while hypergravity centrifuges may mitigate muscle loss in low gravity environments, they appear to have no effect on bone mineral loss.  Rigorous exercise in microgravity, however,  does seem to lower the rate of bone mineral loss-- but does not stop it.


Predicted time limits beyond the Earth  for significant  bone loss in humans that could  risk  skeletal fractures once astronauts return to Earth

Space (microgravity) - 36 weeks (60 weeks with exercise)

Moon (1/6 gravity) - 96 weeks

Mars (2/5 gravity) - 159 weeks


The predicted level of tolerable bone loss for humans in space is about 36 weeks. However, if astronauts exercise rigorously for a few hours every day then their stay in space can be extended to 60 weeks (more than a year). So it seems logical that rigorous exercise should enable humans to mitigate or even eliminate significant bone mineral loss under the hypogravity conditions of the Moon and Mars.

Having some gravity could make it possible for people to use heavily weighted vest or backpacks in order to avoid bone mineral loss while maintaining their Earthling strength-- even without daily strenuous exercise.  While lifting weights can strengthen the arms, weighted vest or backpacks producing an Earth-like weight to be carried by their hindlimbs would strengthen the legs which are normally physiologically weakened under microgravity and low gravity environments.,Within pressurized habitats on the Moon an Mars, heavily weighted vest could be worn throughout the day, providing exercise for the leg muscles when standing, walking, running and jumping.

However, children and infants who are born on the Moon and Mars  may also have to wear weighted vest on a regular basis soon after they are born if their bodies are to grow and develop properly on such low gravity worlds. But  it would appear that humans should be able to live and reproduce on low gravity planets and moons such as the Moon and Mars if they wear the appropriate clothing (weight vest or weight packs) while periodically experiencing hypergravity on a short armed centrifuge.

Of course, Homo sapiens is a species that it use to modifying  its clothing and its habitats in order to survive in more hostile environmental. That's why human ancestors were able to radiate from the tropical regions of Africa into the wintery weather of  Europe, Northern Asia, and eventually North America-- especially during the Earth's glacial periods.



Links and References

Bone Loss and Human Adaptation to Lunar Gravity

 Effects of artificial gravity during bed rest on bone metabolism in humans

 How Much Gravity Is Needed to Establish the Perceptual Upright?

Impacts of Altered Gravity on Male and Female Reproductive Health

 Detrimental Effects of Microgravity on Mouse Preimplantation Development In Vitro

 Morphological and Morphometric Study on the Effect of Simulated Microgravity on Rat Testis

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

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

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