SPACE STATIONS



The International Space Station, as envisioned upon completion. Image courtesy NASA.


Space Hotels
Tech Level: 11
Inflatable Space Station Modules
Tech Level: 11
Tank Stations
Tech Level: 11
Zerovilles
Tech Level: 12
Spin Modules
Tech Level: 12
Wheel Stations
Tech Level: 13

Space stations are man-made artificial environments meant to house humans in the deepness of space.

Space stations have been envisioned as far back as the turn of the 20th century, and became reality during the Cold War era with structures such as Salyut, Skylab, and Mir. Today, the International Space Station wheels in orbit above Earth, designed as both a working laboratory for humans living and working in space as well as a stepping stone toward bigger and better outposts in the Great Dark.

POWER

Near-future space outposts will have four major options for generating power: nuclear generators, solar cells, electrodynamic tethers, and solar boilers.

Dozens of different designs have been created for space-borne nuclear reactors, from simple radiative heating with radioactive materials to more advanced direct-power designs such as particle bed reactors. While such generators can provide large amounts of power quickly, nuclear reactors are generally no longer considered for manned space stations due to the added complications and cost of shielding the crew from the radiation.

Solar cells are a long-proven technology, and have steadily improved incrementally over the decades. They are typically deployed on large booms away from the main body of a station, in order to maximize available surface area for energy gathering.

Electrodynamic tethers have so far only been used experimentally on Space Shuttle missions. Basically, the station would deploy a kilometers-long electrically conductive cable. As this cable moves through Earthís electromagnetic field, electrical current is generated along its length, providing power the station can use.

A fourth type of space station power plant was originally proposed by Werner von Braun at the dawn of the space age, and occasionally sees the light of day in science fiction: the closed-system solar boiler.

Basically, this is an advanced, space-going steam engine. Large, gimbaled mirrors concentrate sunlight on a fluid medium (usually water, though mercury was also mentioned as a possibility in von Braunís original proposal) pumped through pipes on the sunward side of the station. This water is turned into high-pressure steam which is used to power electrical turbines. The steam is then pumped into pipes under shadow, where in space it cools very quickly and condenses back into liquid water. The liquid is then pumped back to the mirror focus for reheating to complete the cycle.

The solar boiler scheme has a number of disadvantages, such as its many complicated moving parts and the high-pressure cycling system that would need constant monitoring and maintenance. It would, however, be able to generate more power more quickly than either solar cells or electrodynamic tethers as those technologies currently stand, but without the radiation hazards associated with nuclear plants.

Supplementary power systems are also currently present aboard the ISS and will be available to future stations, such as fuel cells and chemical batteries. As space stations become more advanced, chances are they will use a combination of some or all of the above techniques.

LIFE SUPPORT

The first concern in supporting a human crew is providing them with a breathable, healthy atmosphere. It is of course extremely impractical to constantly haul up fresh air from Earth, so a means of generating and/or recycling it is needed.

Means of removing excess carbon dioxide, cleansing the air of particulates, replenishing the oxygen supply, maintaining proper gas pressure, and more all have to be taken into account in order to provide a comfortable environment for the stationís inhabitants. Currently on the ISS, oxygen primarily comes from splitting water molecules with electrolysis. Water is easier to handle and store than tanks of pressurized oxygen, though those are also present as a redundancy. The leftover hydrogen from the electrolysis is combined with excess carbon dioxide in the air from CO2 scrubbers in a chemical reaction that creates water and methane. The water is then fed back into loop while the methane is released into space as a waste gas. Eventually engineers want to reuse the methane as well, perhaps as fuel for maneuvering jets, so that nothing goes to waste in the system.

On more advanced future stations, large amounts of plants or algae, grown and tended in low-gravity hydroponic modules, may be used aboard to help fully recycle the atmosphere, much as they do in Earthís biosphere. As our understanding of closed ecosystems grows, our ability to recycle atmosphere by completely artificial means will probably also become available.

Water recycling is a bit more straightforward, using an advanced three-step filter process that, respectively, removes particulates, eliminates organic and inorganic impurities, and then kills any microorganisms present. The systems on board the ISS reclaim waste water from fuel cells, from urine, from oral hygiene and hand washing, and by condensing humidity from the air. Every drop counts. Without such careful recycling 20,000 pounds per year of water from Earth would be required to resupply a minimum of two crewmembers for the life of the ISS. At current launch costs that would be about $200 million dollars per annum just for hauling up the stationís water.

Water is still lost in several ways: the water recycling systems produce a small amount of unusable brine; the oxygen-generating system consumes water; air that's lost in the air locks takes humidity with it; and the CO2 removal systems leach some water out of the air. Engineers hope to get water recycling up to 95% efficiency or higher, the point at which the water in the astronautís normal food supply would be sufficient to replace the water lost.

Fire suppression, gas mixture control, pressure management, leak detection, solid waste recovery, food storage, and more are all considerations life support engineers of future stations will have to take into account when building their orbital outposts.

RADIATION SHIELDING

The space around Earth is constantly bombarded by radiation from the sun and more distant cosmic sources, radiation that would fry most life on the planet were it not for the double protection of Earthís atmosphere and magnetic field. One of the main reasons the ISS was built in such a low orbit was so it could remain under the protective blanket of the planetís magnetic fields, greatly reducing the potential hazard to its crew.

However, future stations, depending on their purpose, may not have the luxury of such a location, and much greater attention will have to be paid to radiation shielding as a result.

Radiation shielding is traditionally heavy, composed of metal or composite material plates, and therefore can greatly add to a stationís cost. NASAís Johnson Space Center is currently sponsoring the Space Radiation Health Project, designed to develop means of protecting future astronauts from space-borne radiation hazards. The scientists working at the project have developed polyethylene fiber bricks, which are very effective at scattering and absorbing stray particles but are twice as light as aluminum of the same volume. The same technology is used to provide armor for combat helicopters, and the bricks can double as a micrometeoroid shield.

Another means of providing radiation protection is to design a stationís layout to provide maximum shielding in certain areas just from its configuration. This is one of strategies used aboard the ISS. In the event of intense solar storm activity, astronauts retreat to a portion of the station where the outer modules help to provide additional barriers against exposure. Solar cells, water tanks, fuel tanks, and so on can be placed strategically around a station to provide increased protection for its human crew. In fact, fuel and water tanks can be designed specifically as shielding, and be built in large narrow tanks that could completely encircle modules of the station.

Active magnetic shielding has also been proposed as an alternative means of protection. Since both particles from the solar wind and cosmic radiation are charged, a strong magnetic field could theoretically deflect them. We know this works on a large scale, as Earthís own electromagnetic field diverts most of the incoming radiation from space.

The primary means of creating an active electromagnetic barrier on a station would be to use loops of superconductor coils wrapped around the outer hull of the station. High-temperature ceramic superconductors can be held at their nominal operating temperatures by simple radiative cooling into space. In the short term, active magnetic shielding may force a redesign of some station systems, especially electronic, in order to accommodate the presence of a constant magnetic field. In the long term, the effects of these powerful fields may eventually have some adverse affect on the crewís health.

ARTIFICIAL GRAVITY

One of the most perplexing problems involved with space stations is weightlessness. Prolonged exposure to microgravity can lead to decreased bone density, fluid loss, osteoporosis, and a host of other complications. Dietary supplements and rigorous daily exercise can mitigate many of the effects, but canít arrest them completely.

The solution to this problem has been known for almost a century: artificial gravity through centripetal acceleration. In other words, simulating gravity by rotating a body fast enough to provide a continuous acceleration force along its inner surface. Just like on whirling carnival rides, spinning constructs exert continuous g forces that feel indistinguishable from true gravity.

In the fifties and sixties, extensive studies were carried out bye NASA and the US Air Force on the feasibility and comfort factors of rotating habitats. However, as human experience with in space mounted, it seemed less of an immediate concern and research was halted in favor of other projects. Recently, as the possibility of prolonged exposure to microgravity loomed on the horizon for interplanetary missions, interest in the subject revived.

Creating a comfortable artificial gravity environment can be tricky. Research has shown that the human "comfort zone" for gravity, the range people in which can live and work without adverse effects, is between 0.35 gís and 1.0 gís. A certain minimal rotational velocity is needed to provide this, usually starting around 6 meters per second. But the complication here is that the station cannot complete more than four revolutions per minute or else the inhabitants on board will invariable start feeling very dizzy from motion sickness. Motion sickness from is a very real concern, especially if one is going to spend weeks or months on board.

It works out that with a minimal rotational velocity of six meters per second, the radius of any rotating station has to be a minimum of about 15 meters, with a human crew becoming more and more comfortable the larger the spin radius becomes. In other words, the bigger the station, the easier it is to minimize motion sickness and accommodate a human crew comfortably through spin gravity.

Whether designers will incorporate spin gravity into future stations remains to be seen, and will probably depend greatly on the purpose of the station.


SPACE HOTELS
Tech level: 11

The next stage in space station evolution will most likely be a technological step backward. The success of Burt Rutanís Spaceship One in capturing the X-Prize has opened up the very real possibility of near-future space tourism. While it will at first be nothing more than a ride up and back from the edge of space, no one doubts that the industry will eventually upgrade into orbital flights, and from there to runs to "orbital hotels" where passengers can spend a day or more in weightlessness.

However, in order to make such ventures as profitable and as safe as possible, space tourism companies will most likely at first rely on small, low-cost, well-proven designs. This means building stations that would harken back to the basic "tin can" configurations of the first three decades of spaceflight--Salyut, Skylab, and Mir. While most companies talking about space hotels bandy about plans for luxurious, high-tech orbital facilities, its almost certain they will start the same modest way the national space agencies did. Also, it seems likely that space hotels may come online within twenty years or so, and if so will probably beat into orbit any official NASA successor to the ISS.

Private companies will probably at first need to rely on the heavy boosters of the national space agencies to put their first facilities in orbit. A space hotel will need at least four major components: a power plant; a life support and maintenance module; a section dedicated to crew and passenger accommodations; and a "play" space.

Unlike current space facilities, the individual accommodations aboard a space hotel will need to be partitioned for privacy, and will probably be made modular in order to accommodate singles, couples, and families. Also, where as past and present space stations had a lot of their volume dedicated to either scientific or observational equipment, a space hotel could dedicate that to large, open spaces where passengers can play and experiment with a microgravity environment.


INFLATABLE SPACE STATION MODULES
Tech Level: 11
A concept of a space station built primarily from infatable modules now being developed by Bigelow Aerospace. Image (c)Bigelow Aerospace.

Just because space hotels have simple needs does not mean thereís no room for innovation. Las Vegas entrepreneur Bob Bigelow is working in cooperation with NASA in order to develop inflatable space station modules, ones that would cost a fraction of the ISS modules and be able to sport much more room. NASA had its own such program years ago but it was cancelled in one of many waves of belt-tightening. Bigelow took up where the NASA program ended, and despite a stormy initial relationship, Bigelow Aerospace and NASA are now fully integrating their efforts to create viable inflatable modules, whose first applications may well be to establish space hotels.

As originally envisioned in the Transhab project at NASA, the shell of these inflatable modules will be a foot thick, composed of more than twenty different layers of foam, Nextel, Kevlar, Nomex, and other materials. This complex layering would actually provide superior radiation shielding than the modules currently being used by the crews of the ISS. Inside the shuttleís cargo bay a module would have had a diameter of 4.3 meters. Once inflated, though, it would have expanded to 8.2 meters, giving the crew of the ISS a 340 cubic meter facility which would have included a dispensary, wardroom, and individual crew quarters.

Bigelowís modified versions use different exact measurements, but would essentially be the same type of modules.


TANK STATIONS
Tech Level: 11

An idea almost as old as NASAís Space Shuttle itself, perhaps best detailed in David Brinís short story, "Tank Farm Dynamo."

The huge External Tanks (ETs) used by the Space Shuttle are dumped after use, to burn up in the atmosphere. It is the one major part of the system that isnít re-used. However, it would cost the agency little extra money, and the Space Shuttle no real loss in orbital velocity, to carry the tank with it all the way into orbit. Small thruster modules--either attached before launch or mounted in orbit via the shuttleís manipulator arm or a spacewalking astronaut--could help boost the tank into a higher orbit where it can be "stored" for future use.

Each tank is over ten stories tall and contains over fifty thousand cubic feet of volume. Plus, they are already re-inforced structurally to be launch- and vacuum-proof. Perfect, really, to use as a base for simple space stations. NASA could make the tanks into a profit-making venture, storing them in high orbit against future use, and then either sell or rent them to future space entrepreneurs who want a space hotel but donít have the capital to boost a full one into orbit. The space hotelier would still need to provide the operational equipment for the station, life support, power, and so on, but that should prove a minor compared to the thirty-five ton launch mass of the tank itself.

This late in the shuttle program, it is doubtful that the traditionally conservative NASA will alter its policy on its own regarding its Shuttle ETs. However, private investors willing to pay NASA the extra expense for orbiting and storing the tanks could still see this scheme come to fruition.


ZEROVILLES
Tech Level: 12

As space tourism increases in the coming decades, space hotels will likely become larger and far more elaborate. Even when stations with spin gravity come online, the novelty of living in microgravity conditions will still be a powerful draw for many curiosity seekers and adventurers.

Zerovilles are either large stations or tightly-knit groups of smaller stations designed to hold hundreds if not thousands of people seeking the thrill of weightlessness for a week or more at a time. This of course would be a colossal engineering challenge, especially for environmental systems, as how to regulate a large-scale microgravity environment for such things like air filtration and waste management is a quandary no one has yet tackled.

However, having much larger facilities to play around with will allow designers to go far beyond the small microgravity playrooms of first-generation space hotels. One can imagine large, open spaces in Zerovilles dedicated to a number of different purposes. For example, large-scale microgravity entertainment productions could be staged in the center while the audience floats around the edge. Or the space can be a high-pressure environment with a number of artificially-generated air currents, allowing guests to strap on artificial wings for maneuvering in play or sports. Or such spaces can be made over into enormous "parks" with a number of genetically-engineered plants fillings its volume, creating a three-dimensional forest the likes of which has never been seen on Earth.

Though operational crews will for the most part be rotated on and off, the zeroville stations may nonetheless accumulate a permanent population over time. People who suffer from heart diseases, high blood pressure, and other select ailments fair better in a weightless environment. They may permanently move into space for health reasons, with the Zeroville stations providing them with all the necessities needed for a comfortable living. In fact, if space travel becomes common place, whole Zeroville "retirement" communities, unconnected to the tourist trade, may spring up in orbit.


SPIN MODULES
Tech Level: 12

The first stations to use centripetal acceleration to simulate gravity most likely wonít be huge or elaborate. In fact, they will most likely resemble dumbbells--two or more modules of about equal mass, connected to each other by a central corridor. The arrangement will rotate about its central axis, providing artificial gravity to both end modules. The perceived gravity at the center of the axis would be zero, and would increase incrementally the farther out one went. A person on board would always feel their sense of "down" to be toward the outer sections of the station.

The central axes of spinning stations are the most logical place to for a number of systems because it is the one part of the structure that will always remain in microgravity. Docking rings and cargo transfer facilities are the most obvious, as are primary maintenance hubs; repairing and modifying large mechanical systems is easier when on can just float alongside.

However, a station with a single spin module represents a problem: the spinning of the station invokes the phenomenon of progression, which makes it gyroscopically unstable in the plane of its rotation. To put it simply, it will eventually drift in unwanted directions if left to spin on its own. This same phenomenon also perplexed early pioneers of the helicopter, and can be solved in one of the same ways: add another spin module right next to the first one but spinning in the opposite direction, both attached to the same central axis. If both sets of spin modules are of about the same mass and are spinning at the same rate, the effect cancels out. An example of this can be seen in the movie 2010 aboard the interplanetary craft Leonov, where two counter-rotating spin modules provide living and working quarters for the crew.


WHEEL STATIONS
Tech Level: 13
An artist's impression of a wheel station, a design used in 2001: A Space Odessey. Image courtesy NASA

Wheel stations are as old as the idea of space stations themselves. Early space visionaries like Werner von Braun and Konstantin E. Tsiolkovskiy both promoted the design.

To optimize useful space aboard a spinning station without subjecting its crew to too many significant shifts in gravity, one needs a station with a circular cross section. This has traditionally taken the form of "wheel" stations, with a tubular rim fitted with living quarters and working facilities, and a central microgravity hub connected to the rim by two or more spoke-like causeways. Depending on its size, the wheelís rim may contain several decks, with a slightly different gravity level on each the farther out one goes.

As with spin modules, rotational progression may become an issue with a wheel station, so having two or more wheels attached to the same central hub, but rotating in different directions, would be a logical fix for that. This in fact was the type of space station depicted in the film _2001: A Space Odessey_.

With their greatly expanded interior volume and pseudo-gravity, wheel stations, more than any other station mentioned so far, will allow a true permanent manned presence in space. With the health hazards of microgravity and the psychological hazards of cramped quarters greatly diminished, people would be able to work and live in space for months or even years at a time in relative comfort.

Werner von Braunís vision of a wheel station, a design he updated from earlier work by Herman Noordung, remains for space visionaries the standard to this day. As outlined in articles for Collierís magazine in the 1950s, von Braunís station would measure over 76 meters across, with a ten-meter wide rim with three separate decks, rotating once per minute. The station would hold a crew of up to several hundred personnel. Von Braun foresaw the station as a springboard for solar system exploration, a navigation beacon for ships and airplanes back on Earth, a meteorological observatory, and a military reconnaissance platform.


FURTHER INFORMATION

http://www.space.com/news/beyond_iss_020926-1.html

http://www.howstuffworks.com/space-station.htm

space station life support:

http://flightprojects.msfc.nasa.gov/book/contents.html

http://www.firstscience.com/site/articles/breathe.asp

http://science.nasa.gov/headlines/y2000/ast02nov_1.htm

Space Hotels:

http://www.lasvegasmercury.com/2004/MERC-Jul-08-Thu-2004/24250261.html

http://www.thespacereview.com/article/187/1

http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml

Tank Stations:

http://www.davidbrin.com/tankfarm1.html

http://www.spaceislandgroup.com/geode-stations.html

Wheel Stations:

http://davidszondy.com/future/space/colliersstation.htm



Article added 2006

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