Living Aloft
The Human Factor

Animation of station in orbit

 "Life is either a daring adventure or nothing."

- Helen Keller

Sustained human exploration begins with the International Space Station. The station begins a new era of permanent operations in space. NASA's experience during the Shuttle-Mir program provided some but not all answers to the question of sustaining a long-term operation in space. Habitable, pressurized volume on the International Space Station will be 43,000 cubic feet. That is about the volume of three average American houses, each one containing about 2,000 square feet with a 7-foot ceiling for a total of around 14,000 cubic feet. The pressurized volume will be roughly equivalent to the interior of a 747 jumbo jet.

In 2000, an international crew of three began living aboard the International Space Station, starting a permanent human presence aboard the outpost. This first crew is scheduled to spend 4 months on the station. When they arrived, the ISS consisted of three modules: the Russian Service Module, which will serve as living quarters and an onboard control center for the early station; the U.S.-funded and Russian-built Zarya, a module that provides supplementary power and propulsion functions; and the U.S. built Node 1, a connecting module that provides the attachment points for future U.S. segments. Click here for streaming video from the ISS.

Animation of station in orbit While the International Space Station will be permanently crewed, the crews will rotate during crew exchange flights. As an incoming crew prepares to replace the outgoing crew there will be a 'handover period'.
The current space station crew will communicate by telecon to the crew on Earth any situations not planned for during training, new techniques, or any topic necessary for life aboard the space station. Once the new crew arrives on board the space station, the outgoing crew will brief them on safety issues, vehicle changes and payload operations. When it is fully assembled, the Space Station will house an international crew of up to 7 for stays of between 3 and 6 months.

Life in Microgravity

Many of the problems that arise from living and working in space have been resolved. However, the physiological effects of weightlessness are still not completely understood. Among these are the leaching of certain minerals from bones; atrophy of muscles when not exercised; and space adaptation syndrome, a form of motion sickness found only in spaceflight.

All of the debilitating effects of living in microgravity disappear after an astronaut returns to Earth. Some can be countered while in orbit by special diet and exercises. But even a vigorous exercise program does not appear to stop bone loss or the decrease in the rate of normal bone formation.
Astronaut in a sleeping experiment
Canadian astronaut Robert Thirsk prepares for a sleep experiment

NASA is engaged in a long-term program to understand the causes underlying these changes, in order to develop ways to prevent them. This will be particularly important for the long tours of duty on the space station, where crewmembers will be in orbit for 3-4 months or more at a time.  Astronauts will be required to exercise several hours each day.


Astronauts who spend long durations outside of the protection of the Earth’s atmosphere are exposed to fairly high levels of radiation. Inclinations of over 45 degrees are sufficiently near the Earth’s magnetic poles that they draw in solar energetic particles and galactic cosmic rays.  At least half of the expected exposures for the ISS will be from galactic cosmic ray exposure.  Astronauts who spend 3 months in the ISS will be subjected to over 3 times the maximum recommend dosage of radiation for one year.  Aluminum hull shielding is used on the ISS modules to help to deflect some of the radiation but the TransHab inflatable habitation module will also use water located around the crew’s personal compartments because hydrogen atoms are the best protection from radioactive particles.

The effects of long-term exposure to large amounts of radiation can include an increased risk of cancer, cell damage, and damage to reproductive systems.  Astronauts who intend to travel to Mars and, perhaps, beyond will be exposed to space for much longer periods of time.  Adequate protection such as the use of water tanks will have to be engineered to support the crews.
Animation of Transhab
Cutaway model of the TransHab

In addition solar flares can direct a large amount of solar particles through space; and crews will be required to “take cover” in the most protected part of the space station, such as inside the TransHab modules during those events.  


Sanitation is even more important within the confines of a spaceship or space station than it is on Earth. Studies have shown that the population of some microbes can increase extraordinarily in microgravity and confined spaces. This means many infectious illnesses could easily spread to everyone aboard. The eating equipment, dining area, toilet and sleeping facilities in an orbiter are regularly cleaned to prevent the growth of microorganisms. Since there is no washing machine aboard, trousers (changed weekly), socks, shirts and underwear (changed every 2 days) are sealed in airtight plastic bags after being worn.  Garbage and trash are also sealed in plastic bags.

Animation of station in orbit The crew on the ISS use a toilet that has a steady flow of air moving through the unit when it is in use, carrying wastes to a special container or into plastic bags. The container can be opened to vacuum, which exhausts the water and dries the solids, and the plastic bags, when used, can be sealed.

Some of the wastes may be returned to Earth for postflight laboratory analysis. In the past, such analyses have helped doctors to understand how the body functions in microgravity, including data on which minerals the body loses in unusual amounts.

Unlike Skylab, which had an enclosed shower, the first space station crews will only take sponge baths in space. Water droplets float about in weightlessness, creating a potential hazard for electrical equipment. Water is obtained from a handgun, where the temperature can be set at any comfortable level from 65 to 95oF. Dirty water from the sponge is squeezed into an airflow system, which conveys the water to the Orbiter's waste collection tank.

Astronaut shaving inside the shuttle
Astronaut Joe H. Engle shaving in space
Whiskers cut in shaving could also become a nuisance if they floated about, creating a potential to damage equipment. Astronauts can avoid this problem by using conventional shaving cream and a safety razor, then washing with a disposable towel.

Engineers have drawn on the experience gained in earlier manned spaceflight programs to plan sleeping and sanitary arrangements for the ISS to make them as close to what crews are used to on Earth.

Recreation and Sleeping

Just as on Earth, recreation and sleep are important to maintaining good health when working in space. Astronauts perform a scientifically planned exercise program, largely to counter the atrophy some muscles experience in a weightless environment. Working out also helps to keep crews mentally healthy.  Cards and other games, books and recorded music are taken on board. CD-ROMs and personal laptop computers are available for recreation and communication with loved ones. Communication with family members is regularly scheduled for astronauts via e-mail and video teleconferences.

The sleeping bags used in space are cocoon-like restraints attached to any location. In microgravity astronauts can sleep comfortable in any position or location.  Once the habitat module is installed crew members will have small private areas for sleeping and working. These areas will have an individual light, a communications station, a fan, a sound-suppression blanket, and sheets with microgravity restraints.
Astronaut reading aboard SpaceLab
Skylab astronaut Alan Bean reading a book


The food that NASA's early astronauts had to eat in space is a testament to their fortitude. John Glenn, America's first man to eat anything in the near-weightless environment of Earth orbit, found the task of eating fairly easy but found the menu to be limited.  Other Mercury astronauts had to endure bite-sized cubes, freeze-dried powders, and semiliquids stuffed in aluminum tubes.  Most agreed the foods were unappetizing and they disliked squeezing the tubes. Moreover, freeze-dried foods were hard to rehydrate and crumbs had to be prevented from getting into equipment. During the Gemini missions, the food improved somewhat. The first things to go were the squeeze tubes. Bite-sized cubes were coated with gelatin to reduce crumbling, and  freeze-dried foods were encased in a special plastic container to make reconstituting them easier. With improved packaging came improved food quality and menus. Gemini astronauts had such food choices as shrimp cocktail, chicken and vegetables, butterscotch pudding, and applesauce, and were able to select meal combinations themselves. Apollo astronauts were first the to have hot water, which made rehydrating foods easier and improved the food's taste. These astronauts were also the first to use the "spoon bowl," a plastic container that could be opened and its contents eaten with a spoon.

isshad.jpg Space Station food and other supplies will be resupplied every 90 days by exchanging the Pressurized Logistics Module (PLM). The food system for ISS will be differ considerably from the Shuttle food system.

Since the electrical power for the station will come from solar panels, there is no extra water generated onboard.

Water will be recycled from the cabin air, but that will not be enough for use in the food system. Most of the food planned for SS will be frozen, refrigerated, or thermostabilized and will not require the addition of water before consumption. Many of the beverages will be in the dehydrated form. Food will be heated to serving temperature in a microwave/forced air convection oven. One oven will be supplied for each group of 3-4 astronauts.

The ISS food system consists of daily menu and Safe Haven. Foods chosen for the Daily Menu are selected based on their commonality to everyday eating, the nutritional content and their applicability to use in space. The Daily Menu food supply is based on the use of frozen, refrigerated, and ambient foods. Frozen food includes most entrees, vegetable, and dessert items. Refrigerated food includes fresh and fresh treated fruits and vegetables, extended shelf-life refrigerated foods, and dairy products. Ambient food, include thermostabilized, aseptic-fill, shelf-stable natural form foods, and rehydratable beverages.


Astronauts will choose 28-day flight menus approximately 120 days prelaunch. Additions, deletions, or substitutions to a standard ISS menu will be made using a space station foodlist.  The packaging system for the daily menu food is based on single service, disposable containers.
Astronaut eating M&M's in space
Commander Loren Shriver eating in space

Food items will be packaged as individual servings to facilitate inflight changes and substitutions to preselected menus. Single service containers also eliminate the need for a dishwasher. A modular concept that maintains a constant width dimension is utilized in the package design. This design permits common interface of food packages with restraint mechanisms (stowage compartments, oven, etc.) and other food system hardware such as the meal tray. Five package sizes were designed to accommodate common serving sizes of entrees, salads, soups, and dessert items. Several fresh fruits, bread, and condiments will be provided in bulk packages.

Daily menu frozen, refrigerated and ambient foods will be stowed in 14 day supply increments. The galley will accommodate a 14-day food supply. Food will be transferred from the PLM to the ISS. Unused food will be returned to the proper stowage environment in the PLM with each 14-day food transfer. Inventory control will be maintained on the unallocated food returned to the PLM for use in case the shuttle is late in delivering the next food set. Meal preparation and consumption will involve a series of steps. A general meal scenario is as follows:

  • Collect meal tray and utensils
  • Display preselected meal on the computer
  • Locate food using location display function
  • Prepare food items for heating
  • Place items to be heated in oven
  • Enter cook control codes and press "start"
  • Rehydrate beverages 
  • Place beverages on meal tray
  • Retrieve refrigerated foods
  • Place refrigerated food in meal tray 
  • Retrieve items from oven
  • Place heated foods in meal tray
  • Eat
  • Place used containers in trash compactor
  • Clean and stow meal tray and utensil
The Safe Haven food system is provided to sustain crewmembers for 22 days under emergency operating conditions resulting from an on-board failure. A goal of the system is to utilize a minimal amount of volume and weight. The Safe Haven food system is independent of the daily menu food and will provide at least 2000 calories daily per person. Astronauts eating aboard the shuttle
Mission Specialist John M. Lounge, Commander Frederick H. Hauck (left) and MS David C. Hilmers (right) eating on the shuttle

The food system will be stored at ambient temperatures ranging from 60 to 85oF. Therefore, the food must be shelf-stable. Thermostabilized entrees and fruits, intermediate moisture foods, and dehydrated food and beverages will be used to meet the shelf-stable requirement. The shelf life of each food item will be a minimum of 2 years.

Psychological Health

Total health of the crews on board the space station includes not only their physical but also their mental well-being.  The first-ever mental health study of crews and controllers in human space missions conducted by University of California-San Francisco researchers, reported that the Russian cosmonauts who served aboard the Mir space station were generally happier and more satisfied than their American counterparts. "In multicultural crews, especially small crews, one has to pay a lot of attention to the culture and language background of the people involved," said Nick Kanas, a UCSF professor of psychiatry, "A single person who is different from the other two can feel isolated." 

ISS Expedition 1 crew during survival training
Astronaut Bill Shepherd, left, commander of the first International Space Station crew, and Cosmonaut Sergei Krikalev, flight engineer for the first station crew in survival training

All of the Expedition Crews of 3 persons on the early ISS will have two Americans and one Russian or two Russians and one American. Kanas' study was conducted under contract to NASA and in conjunction with Russia's Institute for Biomedical Problems in it.  Kanas surveyed 13 crewmembers and 58 mission control personnel during NASA missions to Russia's Mir space station between 1995 and 1998.

He found that the American participants were less satisfied with their group interaction and work environment than were the Russians. Kanas said a major reason for the difference was likely the fact that, on each mission, a solitary U.S. astronaut was teamed with two Russian crewmates.

"Any problems that exist are highlighted when you are confined and further highlighted when you are confined for months," Kanas said.  Three-person crews will remain standard because the planned space station's Soyuz escape pod can hold only three people. The psychological training for astronauts as well as the amount of training crews have together before they fly can help to relieve some of the problems that might arise.  One or all of the crews will have some training in interpersonal relationships and in team problem solving.

Click here to hear interviews with four Mir astronauts about their experiences.

Other things that can help to alleviate loneliness include frequent contact with the ground personnel and family members; recreational activities such as watching movies, reading books, writing and listening to music; and exercising.   Shannon Lucid enjoyed reading books during her 6 months on Mir, while John Blaha enjoyed watching taped football games. 
Astronaut/Cosmonauts aboard Mir
Astronaut Shannon Lucid, Cosmonaut Yuriy-V Usachov and Flight Engineer/Cosmonaut
Yuriy-I Onuufriyenko on the Mir

Jerry Linenger wrote letters to his infant son during his spare time.  The astronauts also say that they really value time spent looking at the Earth and that they enjoy taking lots of pictures.

Allowing crews time to do things that they enjoy is important to balance each work day.  In addition, lots of good training before a mission can really solidify the bonds between crewmates similar to how families work out ways to get through the good and bad days.  Eating together is a good ritual that most astronauts say helps them get some downtime and creates a more relaxed atmosphere within the team.

Click here to look at sample menus from the 90-day advanced life support test at the Johnson Space Center.

Medical Training

All crews are trained in emergency first-aid techniques.  Any serious illnesses would require that the astronaut returns to Earth in the Soyuz or the Crew Return Vehicle (X-38), but minor illnesses will be treated on the ISS.  Routine medical exams and minor treatments (such as for headaches, colds, stomach upset and the like) will be performed by the crew upon themselves and each other.  Blood and urine samples will be taken routinely as part of the human experiments done on board.  Telemedicine techniques such as are now used with remote areas on Earth will support the crews.  Flight surgeons in the control centers monitor crew health 24 hours a days, and they are on call to provide emergency intervention when necessary.

Life Support

Astronauts aboard the station

Animation of the station in orbit
The life support systems that will provide the crew of the International Space Station ISS a comfortable environment in which to live and work are designed by NASA engineers and scientists to provide the space station with systems that are safe, efficient, and cost-effective.

These compact and powerful systems are collectively called the Environmental Control and Life Support Systems (ECLSS).  The ECLSS will:

      • Recycle wastewater (including urine) to produce drinking (potable) water
      • Store and distribute potable water
      • Use recycled water to produce oxygen for the crew
      • Remove carbon dioxide from the cabin air
      • Filter the cabin air for particulates and microorganisms
      • Remove volatile organic trace gases from the cabin air
      • Monitor and control cabin air partial pressures of Nitrogen, Oxygen,
      • Carbon Dioxide, Methane, Hydrogen and Water Vapor
      • Maintain total cabin pressure
      • Detect and suppress fire
      • Maintain cabin temperature and humidity levels
      • Distribute cabin air between ISS modules (ventilation)


Rationing and recycling will be an essential part of daily life on the ISS. In orbit, where Earth's natural life support system is missing, the Space Station itself has to provide abundant power, clean water, and breathable air at the right temperature and humidity 24 hours a day, 7 days a week,  indefinitely. Nothing can go to waste.

The ISS's ECLSS will help astronauts use and reuse their water. It will also control air management, thermal control and fire suppression to make the ISS comfortable and safe. It is expensive to ferry water from Earth. There is a Russian-built water processor that collects humidity from the air. Currently, NASA is building a regenerative system that will be able to recycle almost every drop of water on the station and support a crew of seven.

Astronauts floats through the cargo block
Astronaut Koichi Wakata, mission specialist representing Japan's National Space Development Agency (NASDA), floats through the functional cargo block (FGB) of the International Space Station (ISS), replete now with supplies
The ECLSS Water Recycling System will reclaim waste waters from the shuttle's fuel cells, from urine, from oral hygiene and hand washing, and by condensing humidity from the air (the crew's breath!). Without such careful recycling, 40,000 pounds per year of water from Earth would be required to resupply a minimum of four crewmembers for the life of the station.

Not even the research animals are excused from the program. The crew will eventually include lab rats and other animals, and they'll be breathing, too. All of the denizens of the space station lose water when they exhale or sweat. Such vapors add to the ambient cabin humidity, which is eventually condensed and returned to the general water supply.

Since lab animals on the ISS will breath and urinate and NASA plans to reclaim their waste products along with the crew's.  72 rats would equal about one human in terms of water reclamation.  It might sound gross, but water from the purification machines will be cleaner than the water most of us drink on Earth. It is cleaner than tap water because they have a much more aggressive treatment process than is found in municipal waste water treatment plants. 

Portable water container
Potable water quality is checked on the shuttle by comparing the water color to the color chart on the surrounding board
On Earth, water that passes through animals' bodies is made fresh again by natural processes. Microbes in the soil break down urea and convert it to a form that plants can absorb and use to build new plant tissue. The granular soil also acts as a physical filter. Bits of clay cling to nutrients in urine electrostatically, purifying the water and providing nutrients for plants.

Water excreted by animals also evaporates into the atmosphere and rains back down to Earth as fresh water in a natural distillation process. When water evaporates from the ocean and surface waters, it leaves behind impurities. In the absence of air pollution, nearly pure water falls back to the ground as precipitation. Water purification machines on the ISS partly mimic these processes, but they do not rely on microbes or any other living things.  ECLSS depends on machines not microbes because the system must be 100% reliable.

The water purification machines on the ISS will cleanse wastewater in a three-step process. The first step is a filter that removes particles and debris. The second step is when the water passes through the "multi-filtration beds," which contain substances that remove organic and inorganic impurities. And finally, in the third step, the "catalytic oxidation reactor" removes volatile organic compounds and kills bacteria and viruses.   Once the water is purified, astronauts will do everything possible to use it efficiently. On the ISS, the water pressure will be about half what you have in your house.  There are no faucets on the ISS, and  astronauts use washcloths. It's much more efficient. On the space station, people will wash their hands with less than one-tenth the water that people typically use on Earth. Instead of consuming 50 liters to take a shower, the average on Earth, astronauts will use less than 4 liters!

Even with these intense conservation and recycling efforts, the space station will gradually lose water because of inefficiencies in the life support system.

Water is lost by the Space Station 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, to name a few.
Astronuats on the station
Astronauts Julie Payette (left) and Ellen Ochoa onboard the ISS

Lost water will be replaced by carrying it over from the Shuttle or from the Russian Progress rocket. The Shuttle produces water as its fuel cells combine hydrogen and oxygen to create electricity, and the Progress rocket can be outfitted to carry large containers of water.

The ECLSS will join the space station as part of Node 3, which is scheduled to launch in October 2005. Until then, the environment inside the ISS will be maintained primarily by life support systems on the Russian Zvezda Service Module.

Click here to read more about designing for a human presence in space.

NASA has begun examining growing plants for food and oxygen regeneration, and using physico-chemical and biological methods to process waste into usable resources. To this end, the Agency has begun human tests to validate regenerative life support technologies. Plants are also an emotional support for crews away from Earth for long periods of time. Click here to learn more about hydroponic plant growth experiments.


Animation of station in orbit The Advanced Life Support Program was initiated to develop regenerative life support systems directed at long-duration missions, such as on the ISS, and on trips to the Moon and to Mars.

Such missions, which can last from months to years, make resupply impractical and necessitate self-sufficiency. Thus, subsystems must be developed to fully recycle air and water, recover resources from solid wastes, grow plants for food, process raw plant products into nutritious and palatable foods, control the thermal environment, and control the overall system. 

Advanced life support systems will be a combination of physico-chemical and biological components depending on the specific mission and element of interest.

For example, it is anticipated that advanced life support systems used for a planetary transit vehicle will be primarily physico-chemical. More complex systems, using biological elements, would be used on the planetary surface. 
Regenerative life support experiment

Click here to read more about working with plants for regenerative life support.

Advanced life support systems must provide a safe, habitable environment with high reliability over long periods of time, minimizing mass, volume, power, thermal control, and crew time requirements. New technologies to regenerate air for long-duration space missions are needed that control particulates, remove carbon dioxide from breathable atmospheres, provide oxygen, and control airborne contaminants all within spacecraft maximum allowable concentrations. Further, air revitalization systems must accomplish these functions at mass, volume, power, consumables, thermal control requirements, and crew time requirements below those of currently available technologies. 

Efforts in system modeling, materials development, subsystem operational performance, and control responsiveness will be required to provide advanced systems that minimize support expendables and maximize autonomous operations.  The emphasis is on technologies that are lightweight and low volume so that they may also be used in the EVA system portable life support system.  

Research continues in the following areas:

  • Water recovery technologies 
  • Solid waste 
  • Plant production 
  • Food processing and storage 
  • Thermal control systems 
  • Monitoring and control 
  • Extravehicular Activities (EVA)

Click here to learn more about the Advanced Life Support Program and the new BIOPlex facilities.

Click here to read more about plant experiments on the Mir.


Picture of the shuttle undocking from MIR

Questions to think about:

  • How would you decide when an astronaut has had too much exposure to radiation and should not be allowed to fly anymore?

  • What recreational things would you bring with you if you were to spend 4 months on the ISS? Make a list of items (CD's books, videos, etc.) and weigh them.  If they weigh more than 2 pounds trim your list to the essentials.  Was this hard to do?

  • What fresh foods would you miss most?

In the next chapter you will get to explore the TransHab facility and the Crew Return Vehicle (X-38) some of the most cutting edge engineering being done at the NASA Johnson Space Center to support long-duration spaceflight.

Next... The Cutting Edge