Space Habitat Alpha - Concept Document


Version D002 - 28 August 2013

Author:  Randolph Shelly

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Space Habitat Alpha will consist of a Factory/Facilities Module, a Cupola/Docking Module and a Propulsion Module. It will be self-sufficient and habitable and it will be capable of manufacturing materials for its own use or for other structures, such as Space Habitat Beta.  Artificial gravity will be created by spinning the module.  It will be able to accommodate up to 50 occupants, which means that it could be considered to be a "space village."

The habitat will initially be assembled in low earth orbit (LEO) and when completed, may be moved to a position in space with a low escape energy relative to the Earth-Moon system; however, the habitat could remain in Earth orbit for an extended period, since it will have a number of uses.

The habitat, could be considered to be a second major space station, replacing or complementing the present ISS (International Space Station).  It will be capable of producing artificial gravity, but will also have microgravity conditions.  In addition to manufacturing capabilities, it will have facilities for conducting scientific experiments.

The habitat is an essential step to interplanetary exploration and colonization because:

1.  It will provide a means of testing the effect of long-term reduced gravity conditions on human physiology, before committing to the colonization of the Moon or Mars.

2.  It will establish the technology for maintaining a closed, self-sufficient environment, using only off-earth materials.

3.  It will provide a safe, comfortable environment for a large and diverse crew.

4.  It will be capable of using asteroid materials to produce propellants, atmospheric gases, construction materials, high value elements and minerals, and other, specialized materials.

5.  It will serve as a mother ship for activities on the surface of the Moon, Mars or other destinations in our solar system.




The purpose of this document is to describe the design approach for Space Habitat Alpha, identify top level requirements, identify the initial work required to further refine these areas, and programmatic concerns.

The document covers the entire Space Habitat system, including:

  • The Space Segment (Factory/Facilities Module, Cupola/Docking Module, Propulsion Module)

  • The Ground Segment

  • The Launch Segment

  • The Transportation Segment

  • Interfaces

In addition, the following cover programmatic subjects are covered:

  • Expected uses

  • Ergonomics

  • Crew Considerations

  • Sources of Revenue

  • Funding Sources

  • Risks


Expected Uses

Understanding the potential uses for the Space Habitat Alpha is essential to its success.  It is intended to be a stand-alone space station that will fill a number of needs that we foresee for the near future.  Following are some of its expected uses.





The Factory/Facilities Module will be capable of producing various materials from small asteroids or lunar soil and rocks.  Following are some examples:

-  Propellants for chemical, nuclear or ion drive thrusters and controllers.

-  Atmospheric gases (oxygen, nitrogen) for itself and the habitation module.

-  Water.

-  Pressure vessel materials (fabrics).

-  Structural elements from iron or aluminum.

-  Silicon and carbon based materials for various uses.

-  Nutrients for agriculture.

-  High value elements, such as gold, platinum and rare-earths from asteroid materials.




Space Tourism

It has been shown that a number of individuals are willing to pay upwards of $20M to experience a trip to the International Space station.  This could be a significant source of revenue for the project.  The habitat will be able to accommodate up to 50 occupants, and it would not be unusual to be able to host six or more tourists at one time.




Science Experiments

The Facilities Module will be able to provide microgravity and enclosed vacuum environments to perform science experiments similar to the International Space Station.  Lab facilities will be provided in the habitat to perform analyses, design experiments, etc.





In addition to manufacturing elements of the larger habitation module, this module will provide the means for its assembly.  With its enclosed area and artificial gravity, it will also be suitable for assembling and launching types of spacecraft that would not be able to survive launch from the Earth.




Technology Demonstrations

Habitation Module

One purpose of the factory/facilities module will be to establish the design parameters for the Habitation Module.  For example, in order to find the minimum module diameter and maximum spin rate, this module can be spun at different rates to determine how well occupants can adapt to various conditions.


One funding approach will be to offer usage of the module in exchange for subsystem providers who might be able to get sponsored funding or who might wish to invest their own money to test new concepts and technologies for Space applications.






Space Segment



Pressure Vessel

The pressure vessel will contain the atmosphere within the factory module.  It should be able to withstand an internal pressure of one atmosphere, with a safety factor of at least 2.0, although reduced pressure might be used in practice.  The preferred base material for its construction is a fabric, such as Vectran, which has a high strength-to-weight ratio (about five times that of steel).  In addition, a fabric is expected to be able to limit and contain a rupture better than a metal, providing a safer environment for the crew. 

The volume of the module is expected to be about 15,000 cubic meters and its mass is expected to be 600,000 kg (compared with 419, 000 kg for the ISS).  This would present a problem for launching an assembled unit, since the highest capacity launch vehicle is expected to be the SpaceX Heavy , capable of launching 53,000 kg to low earth orbit (SLS would have higher capacity, but its future is less certain).  On this basis, it could require as much as 12 launches for the entire module.  The module would then have to be assembled in orbit. 


a.    Bigelow Aerospace is experienced in designing and assembling similar, but smaller units.  Contact Bigelow to discuss the feasibility of assembling the module on orbit.

b.    Check with Bigelow if the mass estimate for the module makes sense, and what items the mass might comprise.

c.    Thin Red Line Aerospace constructed pressure vessels for Bigelow's modules.  Contact them to assist in determining the mass of the pressure vessel, alone (without the other subsystems, which could be launched and assembled separately).

d.    Determine the mass breakdown of BEAM and BA300 and determine the scale-up factor for each one.

e.    Determine if this size of pressure vessel is practical within cost constraints.



Gravity Control

The target gravity will be equivalent to that of the Moon.  The rotation rate that should not result in disorientation of the crew is 3 RPM.  With lunar-equivalent gravity, this results in a module diameter of 34 meters.  The choice of Moon-equivalent gravity results in a diameter that is reasonable for the module.  It is likely that the module will be near the Moon for support of lunar missions and for possible colonization, so having gravity close to that of the Moon will be convenient. 

Another advantage of lunar gravity equivalence is that the module could be used to assess the long-term physiological effects of low-G on humans.  This will have to be known before giving any consideration to setting up colonies on the Moon or Mars.

The module may also be spun up to achieve a higher gravitational force, in order to re-acclimatize occupants to the Earth's gravity.


a.    Research any disorientation effects for this spin rate and diameter.

b.    Investigate artificial gravity options if the module has to be made smaller.




The module will require an internal structure (frame), which will have to attach to the pressure vessel.  It will also require an external structure to attach the propulsion module, cupola/docking module, solar arrays, etc.  The internal frame will support flooring and will provide attachment points for equipment and facilities.

As pressure changes in the pressure vessel, it will expand or contract relative to the internal structure (frame, floor, etc.).  There will have to be a means of allowing relative movement, without compromising the symmetry and stability of the factory/facilities module.  This will be one of the major challenges for the structural design.


a.    Determine how the pressure vessel will expand with increasing pressure.

b.    Produce a design concept for the structure.



Environmental Control

Creating and maintaining the atmosphere will be quite challenging, due to the volume within the module; however, experience with the ISS (International Space Station) can be drawn upon.  The factory/facilities module is intended to eventually provide the materials and systems to construct the habitation module, it will also serve as a prototype for the habitation module.  With this in mind, terraforming and agriculture may be developed, adding to the value and environmental appeal of the module.


a.    Investigate how environments are maintained on the ISS.

b.    Investigate new technologies for off-Earth environments.

c.    Investigate closed environment experiments performed on Earth.




Power will be derived from two primary sources, solar and nuclear.  Solar power would be adequate for routine operations within the factory module; however, this module will have to provide power for the main habitat and for the propulsion system, and it will need to provide power throughout the solar system.  This will require a nuclear reactor as a power source.  The main mode of propulsion will be ion drives, which will require significant amounts of electrical power.  In addition, the habitation module will require power for lighting and daily operations, especially for agriculture.

Compact reactors are in development, such as the G4M system being developed by Gen4 Energy that will weigh less than 10,000 kg.  This is within the capability of a number of launchers, such as SpaceX's Falcon 9 rocket.  A nuclear power system meant for ground applications will likely require modifications to survive launch, which might add to the weight


a.    Estimate how much power the module will require.

b.    Estimate the amount of power needed from solar arrays, and from the nuclear reactor.

c.    Research currently available compact nuclear power generators and determine their suitability for the habitat.



Radiation Shielding

Shielding is an important health and safety concern.  Alpha Habitat will be assembled in low earth orbit (LEO), where shielding is not as much an issue as it will be outside the Earth's atmosphere.  During its time in LEO, light shielding plus a safe haven from solar storms will be adequate.  Above LEO, it will be necessary to have heavier shielding.  Options include a magnetic deflection system, electrostatic deflection, bulk shielding from asteroid or lunar soil, consumable materials made by the module, such as water, or some newly developed light-weight material launched from Earth.


a.    Estimate mass of shielding using "soil" method.

b.    Investigate existing or emerging terrestrial materials.




Chemical rockets, and possibly nuclear rockets will be required for high-thrust applications, but the main mode of propulsion will be ion drives, which make much more efficient use of propellants.  Scaling up ion drives to be effective and cost-efficient as a main propulsion system would be a significant challenge.  One of the capabilities of the factory/facilities module will be the extraction of water from asteroid material and converting it to hydrogen and oxygen through electrolysis.  These elements can then be used as fuel for chemical rockets; however, some oxygen will be needed to maintain the habitat's atmosphere and to serve as a reserve for emergencies.  This will leave some excess hydrogen, which is a suitable fuel for ion drives.


a.    Estimate thrust required to navigate out of Earth orbit.

b.    Estimate thrust required to embark on a Mars mission.

c.    Estimate the amount of energy required to escape Earth gravity.

d.    Perform a preliminary selection of thrusters.



Attitude and Orbit Control

The key concern with spinning the habitat is minimizing wobble.  An inflatable pressure vessel will be more flexible that a rigid one, and movement within the module can change the center of gravity and other mechanical parameters, so instabilities are likely to occur.  Experience with satellite attitude control systems should be adaptable to control wobble, spin up or spin down the module and recover from a tumble situation, should one occur.


a.    Determine spin-up times and thrust required.



Thermal Control

Insulation will be provided by the shell of the module.  Maintaining the internal temperature of the module within a comfortable range can be accomplished by selecting appropriate finishes for the pressure vessel and structure and by using sunshades and radiators.  If the habitat travels into interplanetary space, in particular to the outer planets, it will be necessary to provide heat via the nuclear reactors.


a.    Estimate the amount of internal heat produced by the module.

b.    Estimate mean absorptivity and emissivity requirements.

c.    Investigate thermal control methods.




Communication technology between the Earth and spacecraft is quite mature, so little new development will be expected for this subsystem.


a.    None for now.




The factory module will provide the tools, utilities and materials to construct the habitation module and other subsystems of the space habitat.


a.    Define the minimum manufacturing capabilities to sustain the Factory/Facilities Module.

b.    Define the manufacturing capabilities needed to construct the Habitation Module.

c.    Define other manufacturing requirements, related to research, experimentation, etc.



Guidance and Navigation

Guidance and navigation of spacecraft is quite well developed, so there should be no issues with implementing it for the factory module.


None for now.




In general, docking mechanisms can be similar to the ISS; however, given the intended use of the factory module, it may be necessary to have a docking system that is larger, in in order to accommodate potentially larger payloads.  A dual (large and small) system may be required.

For the factory/facilities module, the docking system will be part of the Cupola/Docking Module, which can be launched as an assembled unit.


a.    Investigate current airlock and docking systems that might be adapted to the habitat.

b.    Investigate interface needs.



Control and Data Handling

Control and data handling systems for spacecraft are well-developed.  Due to the crew capacity of up to 50 people, and the types of activities that will be performed, more IT equipment will have to be added to the typical satellite complement, but this will be normal computer systems and networks, similar to an Earth-based office or small business.


None for now.



Safety and Security

Safety and security will be highly important, due to the large crew capability of the module and the long duration of its missions.  This subsystem will consist of hardware, software and procedural elements.  In addition to protection from orbital debris, it will be necessary to have procedures and training to secure the crew in the event of a rupture of the pressure module.

The Cupola/Docking Module will be set up to sustain the crew for a period of time long enough to affect rescue operations.


a.    Draft preliminary safety plan.






Producing enough food, in particular when the habitat is beyond low earth orbit, will be crucial.  Deciding how much food can be produced, and how much space per person will be required to produce it will ultimately determine the number of occupants the habitat can accommodate.

Agriculture can be combined with environmental control and sanitation/recycling in a number of ways.  In addition to interior space used to produce food and to condition the atmosphere, modules may be added on, dedicated to producing food and scrubbing CO2 from the air.


a.    Research what work has been done to date on producing food in a closed system.

b.    Estimate the amount of space per person required to produce the food.





Sanitation and Recycling

In a closed system such as the habitat, all waste will have to be recycled and reused in some manner.


a.    Research studies and demonstrations of this process for closed systems.

b.    Determine what processes are currently in use, e.g., on the ISS.



Transportation Segment

This segment is concerned with transportation of personnel to and from the habitat, and shuttling of material and supplies from the lunar surface or from an asteroid.  For transportation while in Earth orbit, existing vehicles or new ones currently in development can be used.  After assembly and check out, the habitat will be operated in LEO for an extended period of time.  Following this period, the module may be moved to a lunar orbit or to one of the Earth-Moon system Lagrange points.  If lunar materials are used for the module, or if the module is used as a mother ship for lunar or Mars exploration and development, one or more transporters will be required, capable of descending to the lunar or Martian surface and returning to the module.


a.    Assess current or planned shuttles and landers that might be used with Alpha Habitat.


  4.3 Ground Segment

The ground segment will consist of a control and communications function, habitation management function and one or more ground stations.  These systems and processes are fairly well developed and there should be little new development associated with them.  Habitation management will be mostly software and personnel and will be most active after commissioning of the habitat.


None for now.



Launch Segment

The launch segment will consist of the launch operations to place all elements of the space segment in orbit and provide supplies as required.  It is expected that one launch each will be required for the pressure vessel, cupola/docking module and propulsion module.  Several launches will be required for the structural elements.  Other subsystems will likely require several launches.  Launching is expected to be the dominant cost for the habitat.


a.    Determine which launch vehicles may be available when required.




This aspect of the habitat design deals with the accommodation and comfort of the occupants of the habitat.  The objective is to be able to accommodate up to 50 occupants.



Personal Space

Personal space is the amount of space required to provide some level of privacy for an occupant, including private sleeping accommodations.  As an initial allotment, this will be set at 9 m2 (~ 100 square feet) per occupant.  For 50 occupants, this results in a total of 450 square meters.


None for now.



Common Space

Common space will include recreation space, exercise facilities, dining areas, control rooms and meeting areas.  As the habitat evolves, this should include 'green space.'  As an initial allotment, this will also be set to 9 m2 per occupant, for a total of 450 square meters.


None for now.



Manufacturing, Laboratory and Facilities Space

For a module diameter of 35 meters and a cylinder length of 20 meters, the total floor space would be about 2000 m2.  Personal space and common space total 900 m2, leaving 100 m2 for manufacturing, lab and facilities.  Additional space will also be available in the end caps of the facilities/factory module, for the installation of equipment and systems that are required to manage the environment of the habitat, and to provide other services.


None for now.



Other Factors

Since manufacturing will carried out in the factory/facilities module, hazardous or irritating particulate and gaseous substances may be produced.  The air processing system will have to assure that the atmosphere remains clean.

Noise from equipment and processes will need to be controlled, which will require some degree of isolation and insulation.


a.    Investigate air quality maintenance systems used of the ISS, submarines and other closed systems.



Crew Considerations

The goal should be to to have a mix of people for the following functions, for example:

-  Manufacturing

-  Assembly

-  Maintenance

-  Control

-  Research

-  Health care

-  Space tourism

In addition to crew members, it will be important to be able to accommodate space tourists, since this will be an important source of revenue, as a return on the original investment, and as a source of funding to carry out the ongoing operations of the habitat.


None for now.



Sources of Revenue

Once the habitat is operational, there are a number of possible sources of revenue, including:

-  Space tourism.

-  Rental of research facilities.

-  Production of water and rocket propellants for other missions.

-  Production of precious and rare-earth metals and minerals.

Depending on the value of these sources of revenue, the habitat could be a viable investment.


1.  Estimate the amount of income that can be derived from space tourism.

2.  Estimate the amount of income that can be derived from research facilities rental.

3.  Determine the projected cost of delivering water to orbit from Earth and set as value for water produced on-orbit.

4.  Determine the cost of delivering visitors to the habitat.


Funding Sources

There are a number of possible sources for funding the development of the habitat:

-  Government agencies wishing to incorporate the space habitat into their overall space plans.

-  Private corporations wishing to invest in the entire enterprise or in specific features of the habitat, such as resource extraction.

-  Individuals wishing to have a share in the enterprise, which would convey certain privileges and possible financial returns.


None for now.




At present, the key risks are in the cost of the habitat, and the ability to secure partners to develop the habitat.  Risks will be elaborated later in the feasibility study phase.


None for now.