THE INTERNATIONAL SPACE STATION (ISS)

In 1984, President Ronald Reagan proposed that the United States, in cooperation with other countries, build a permanently inhabited space station. Reagan envisioned a station that would have government and industry support. The U.S. forged a cooperative effort with 14 other countries (Canada, Japan, Brazil, and the European Space Agency -- United Kingdom, France, Germany, Belgium, Italy, The Netherlands, Denmark, Norway, Spain, Switzerland, Sweden). During the planning of the ISS and after the fall of the Soviet Union, the United States invited Russia to cooperate in the ISS in 1993; this brought the number of participating countries to 16. NASA is taking the lead in coordinating the ISS's construction.

ISS Facts

Length: 290 ft (88m)
Width: 356 ft (109 m)
Height: 143 ft (44 m)
Volume: 46,000 ft3 (1300 m3); living space will be about the cabin size of two 747 jets
Mass: 1,000,000 lb (454 metric tons)
Orbit: 217 to 285 miles (362 to 476 km), inclined 51.6 degrees relative to the equator

The assembly of the ISS in orbit began in 1998. The ISS has more than 100 components and will require 44 spaceflights by at least three space vehicles (space shuttle, Soyuz and Russian Proton rocket) to deliver the components into orbit. One-hundred sixty spacewalks, totaling 1,920 man-hours, will be required to assemble and maintain the ISS, which is scheduled for completion in 2010 and will have an anticipated life of 10 years at a projected total cost of $35 to $37 billion. When completed, the ISS will be able to house up to seven astronauts. It will have the following major components:

• Control Module (Zarya) or Functional Cargo Block - contains propulsion (two rocket engines), command and control systems
• Nodes (three) - connect major portions of the ISS
• Service Module (Zvezda) - contains living quarters and life support for early parts of the ISS, docking ports for Progress resupply ships and rocket engines for attitude control and re-boost
• Scientific Laboratories (six) - contain scientific equipment and a robotic arm to move payload on an outside platform
• Laboratory Module - shirt-sleeve environment facility for research on microgravity, life sciences, Earth sciences and space sciences
• Truss - long, tower-like spine for attaching modules, payloads and systems equipment
• Mobile Servicing System - robotic system that will move along the truss; equipped with remote arm for assembly and maintenance activities
• Transfer Vehicles - a Soyuz capsule and a Crew Return Vehicle (X-38) for emergency evacuation
• Electrical Power System - solar panels and equipment for generating, storing, managing and distributing electrical power

ISS in orbit showing (top to bottom) Node-1, Control Module, Service Module and a Progress supply ship (September 2000).

On October 31, 2000, the first crew of the ISS was launched from Russia. The three-member crew spent almost five months aboard the ISS, activating systems, and conducting experiments.
To sustain a permanent environment in outer space where people can live and work, the ISS must be able to provide the following things:

• Life support
• Atmosphere control, supply and recycling
• Water recycling
• Temperature control
• Food supply
• Waste removal
• Fire protection
• Propulsion - move the station in orbit
• Communications and tracking - talk with ground-based flight controllers
• Navigation - find its way around
• Electrical power
• Computers - coordinate and handle information
• Resupply - methods of getting new supplies and removing waste
• Emergency escape route


LIFE SUPPORT

ATMOSPHERE CONTROL, SUPPLY AND RECYCLING
Astronauts on board the ISS need to have the following:
• Atmosphere similar to Earth's
• Carbon dioxide that they exhale removed
• Contaminating or trace gases removed
• Normal humid environment
Our atmosphere is a mixture of gases -- 78 percent nitrogen, 21 percent oxygen, 1 percent other gases -- at a pressure of 14 lbs/in2 (1 atm). The ISS astronauts will need a similar atmosphere. To achieve this, oxygen and nitrogen will have to be supplied:
1. The Russian Elektron generator will make oxygen by splitting water into hydrogen and oxygen (electrolysis).
2. Solid fuel oxygen generators or oxygen candles will be burned to make additional oxygen, if required.
3. The space shuttle or Progress supply ships will bring nitrogen from Earth, and store it in external tanks on the station.
4. In later phases of construction, external tanks will supply oxygen; these tanks can be refilled by the space shuttle. In the final stage, an additional electrolysis oxygen generator will be added to the station.
5. The pressure control assembly (a system of pumps and valves) will mix the nitrogen and oxygen in the right percentages, monitor the atmospheric pressure and depressurize the station when necessary to prevent overpressure or to extinguish a fire during an emergency.
A carbon dioxide removal assembly (a series of beds of special material) will absorb carbon dioxide and release it into outer space. In addition, backup chemical carbon dioxide canisters can remove carbon dioxide by reacting it with lithium hydroxide.
The trace contaminant control system will filter cabin air to remove trace odors and volatile chemicals from leaks, spills and outgassing. As a backup, the harmful impurities filter will also be used.
The station's heating system will control the humidity and circulate the atmosphere throughout the station.
Finally, the major constituent analyzer will constantly monitor the amount and type of gases in the cabin air, and control the atmosphere supply and recycling systems.
WATER RECYCLING
Besides air, water is the most important element aboard the ISS. Initially, the space shuttle and Progress supply vehicles will bring water from Earth. On the ISS, water will be highly conserved. There will be no long, luxurious showers. In fact, most astronauts get by with sponge baths. The water recovery and management subsystem will collect, recycle and distribute water from various sources including:
• Sink
• Shower
• Urine - from the astronauts and from laboratory animals onboard
• Spacesuit wastewater
• Heating and cooling systems
• Cabin air - moisture exhaled by astronauts and laboratory animals
• The space shuttle's fuel cells
The water recovery and management subsystem consists of various condensers, filters and water purifiers. The water will be used for drinking and cooling electrical systems. This system is not 100 percent efficient, and water will be lost through the Elektron oxygen generator, airlocks and carbon dioxide removal systems. Water will be periodically replenished from Earth. However, this system will greatly reduce the amount of water needed from Earth.
TEMPERATURE CONTROL
Outer space is an extremely cold environment, and temperatures will vary drastically in different parts of the ISS. You might think that heating the ISS would be a problem. However, the electronic equipment generates more than enough heat for the station. The problem is getting rid of the excess heat. So the temperature control system has to carry out two major functions -- distributing heat where it is needed on the station and getting rid of the excess. To do this, the ISS has two methods to handle temperature control:
• Passive methods - generally simple; handle small heat loads and require little maintenance
 insulating materials, surface coatings, paints - reduce heat loss through the walls of the various modules, just like your home insulation
 electrical heaters - use electrically-heated wires like a toaster to heat various areas
 heat pipes - use liquid ammonia in a pipe to transfer heat from a warm area to a cold area over short distances. The ammonia evaporates at the warm end of the pipe, travels to the cold end and condenses, giving up heat; then the liquid travels back to the warm end along the walls of the pipe (capillary action).
• Active methods - more complex; use fluid to handle large heat loads; require maintenance
 cold plates - metal plates that collect heat by direct contact with equipment or conduction
 heat exchangers - collect heat from equipment using fluid. The equipment radiates heat to a fluid (ammonia), which in turn passes heat on to water. Both fluids are pumped and recirculated to remove heat.
 pumps, lines, valves - transport the collected heat from one area to another
 heat rejection units - large, winged structures, similar to solar panels, that radiate the collected heat to outer space
For cabin air, the temperature and humidity control system circulates and filters air, removes water (humidity) and maintains a constant temperature range. Any collected water goes to the water recovery and management system.
FOOD SUPPLY
The space shuttle and Progress supply ships will bring food to the ISS. Food comes in several forms (dehydrated, low moisture, heat-stabilized, irradiated, natural, fresh). The ISS has a galley (kitchen) equipped with the following:
• Food storage compartments
• Food warmers
• A food preparation area
• Table with restraints (straps, footholds) so the astronauts do not float away
• Metal trays that stop the food packages and utensils from floating away
TheUnited States and Russia have each agreed to supply half of the food for the crew.
WASTE REMOVAL
Like any home, the ISS must be kept clean. This is especially important in space, where floating dirt and debris could present a hazard. Wastes are made from cleaning, eating, work and personal hygiene. For general housecleaning, astronauts will use various wipes (wet, dry, fabric, detergent, disinfectant), detergents and wet/dry vacuum cleaners to clean surfaces, filters and themselves. Trash will be collected in bags, stowed in a Progress supply ship and returned to Earth for disposal. Solid waste from the toilet is compacted, dried and stored in bags, where it is returned to Earth for disposal (burning). Water reclaimed from solid waste is processed and purified for drinking purposes.
FIRE PROTECTION
Fire is one of the most dangerous hazards in space. During astronaut Jerry Linenger's stay on Mir, a fire broke out. The Mir crew extinguished the fire, but not before the station was damaged. The ISS has a fire detection and suppression subsystem that consists of the following:
• Area smoke detectors in each module
• Smoke detectors in each rack of electrical equipment
• Alarms and warning lights in each module
• Nontoxic portable fire extinguishers - foam or liquid extinguishers that are either carbon dioxide (from the United States) or nitrogen-compound-based (from Russia)
• Personal breathing apparatus - mask and oxygen bottle for each crew member
After a fire is extinguished, the atmosphere control system will filter the air to remove particulates and toxic substances.

POWER
All of the onboard systems of the ISS will require electrical power. Eight large solar arrays will provide electrical power from the sun. Each array is 109 feet (33 m) long and covers an area of 27,000 ft2 (approximately 2508 m2), or about one acre. On each array are two blankets of solar cells. Each blanket is on one side of a telescoping mast that can extend and retract to fold or form the array. The mast turns on a gimbal, so that it can keep the solar cells facing the sunlight. The Russian modules also have 72- to 97-foot (22- to 30-m) solar arrays that provide power.
Like a power grid on Earth, the arrays will generate primary power -- approximately 160 volts of DC electricity. The primary power will be converted by a secondary transformer to provide a regulated 124-volt DC current to be used by the station's equipment. There are also power converters onboard to meet the different currents required by U.S. and Russian equipment. The primary power will also be used to charge the ISS's three nickel-hydrogen battery stations, which will provide power when the ISS passes through the Earth's shadow in each orbit.

RE-SUPPLY

In the ISS, they have to call for "home-delivery." Progress supply ships will be used to ferry new supplies (food, water, medicines,oxygen, nitrogen, fuel, equipment, clothing, personal items) to the ISS. Progress ships will also remove solid waste from the ISS. The space shuttle can bring new supplies to the ISS as well, along with equipment for construction. In addition to Progress and the space shuttle, two new supply vehicles are being developed by the European Space Agency (ESA) and National Space Development Agency of Japan. The ESA's vehicle will be like Progress, capable of supplying nine tons of cargo, including food, clothing, fuel, water, oxygen and nitrogen; the vehicle will also be able to reboost the ISS. The Japanese craft, called the Hope Transfer Vehicle, will be capable of delivering pressurized cargo (food, water, clothing), but not fuel, oxygen or nitrogen.


Living and Working Aboard the ISS

The first space station crew members will spend a lot of their time setting up the station, building its components and conducting various scientific experiments and Earth observations. The crew will live in the service module at first. This module has spartan living quarters, but provides everything the crew needs -- personal sleeping quarters, a toilet, hygiene facilities, a kitchen with a table, a treadmill and a stationary bicycle. Astronauts will have to exercise frequently to keep from losing bone and muscle mass, which happens with prolonged weightlessness.
Sleeping
Sleeping in space is quite different from sleeping on Earth. Instead of a bed, you have a wall-mounted sleeping bag that you slip into and zip up. The bag is also equipped with arm restraints to prevent your arms from floating above your head while you sleep.
Bathing
While stations such as Skylab and Mir have been equipped with a shower, most astronauts take sponge baths using washcloths or moistened towelettes. This reduces the amount of water consumed. Each astronaut will also have a personal hygiene kit with a toothbrush, toothpaste, shampoo, razor and other basic toiletries.
Eating
The food on the ISS will be mainly frozen, dehydrated or heat-stabilized, and drinks will be dehydrated. Astronauts will collect food trays and utensils, locate their individually-packaged meal from a storage compartment, prepare the items (rehydrate if necessary), heat the items (microwave, forced-air convection oven), place them in the tray and eat. After the meal, they will place the used items in a trash compactor, and clean and stow the utensils and trays. Interestingly, astronauts get to select their menus approximately five months before their flight.
Exercising
In weightless conditions, the body loses bone and muscle mass. To counter these losses, astronauts will have to exercise daily. The service module is equipped with a treadmill and a stationary bicycle. Astronauts must strap themselves onto these devices so that they do not float away while exercising.
Working
Once the ISS is completed, work will involve maintaining the station (fixing broken equipment, repairing structures, etc.) and conducting scientific experiments and observations. The station will have six scientific laboratories. Closet-sized racks along the walls of the laboratory module will hold the equipment, and the astronauts will use footholds and restraints so they won't float away while working. The experiment racks will also have remote video and data links so that scientists on the ground will be able to monitor the experiments on-board the ISS continuously. The Japanese laboratory module will have a platform open to space, for determining the effects of the space environment on materials.
Moving Around on the ISS
Working in weightlessness, or microgravity, is very different from what we are used to. For example, as I write this article at my computer, I do not have to worry about floating off of my chair, or having the papers on my desk float away. This is not the case in the ISS. As we have mentioned above, many places (experiment racks, kitchen area, crew quarters) will have restraints to keep the astronauts and equipment from floating away. And while I can walk the corridor in my office with no trouble, astronauts on the ISS will have to use handholds mounted on the walls of the station to keep themselves stable as they move around.
Spacewalks
The crew will have to perform spacewalks during construction and maintenance of the ISS. Initially, the crew will perform spacewalks from the Russian service module using Russian spacesuits. Because spacesuits operate at lower pressures than the station, the astronauts will have to reduce the air pressure of the entire station prior to the spacewalk, so that the spacewalker's body can adjust; otherwise, the spacewalker might get the bends.
Once the Joint Airlock Module (JAM) arrives at the ISS, the crew will be able to use both Russian and American spacesuits, and the entire station will no longer have to be depressurized prior to a spacewalk. To prepare for a spacewalk, the spacewalkers will have to do the following:

• Enter the JAM with their spacesuits and equipment
• Reduce the pressure in the airlock from 14.7 lb/in2 (1 atm) to 10.2 lbs/in2 (0.7 atm)
• "Camp-out" overnight in order to:
 adjust to the low pressure used in spacesuits -- 4.3 lbs/in2 (0.3 atm)
 eliminate nitrogen from the space walker's body, thereby reducing the chance of decompression sickness
• Put the spacesuit on
• Pre-breathe pure oxygen (spacesuits use pure oxygen) for a few minutes prior to the space walk
• Open the airlock doors
• Conduct the spacewalk
The spacesuits used on the ISS will be enhanced versions of those used on the shuttle. They will have the following modifications:
• Internal parts that are more easily replaced
• Carbon-dioxide absorption cartridges that are reusable and removable
• Metal sizing rings that adjust the fit for individual users
• New gloves with increased flexibility and dexterity
• Enhanced radio with more channels, so more people can talk at once
• New heaters, and a cooling system shut-off (ISS spacewalkers will have to work in shadows, where it is colder; shuttle spacewalkers were able to work in the sun, because the shuttle could be turned easily toward sunlight)
• Helmet-mounted flood lights and spot lights
• Jet-pack that allows an untethered astronaut to fly back to the station in an emergency (if he should slip away from the ISS)
The spacesuits will have to be returned to the ground for maintenance after every 25 spacewalks.
Photo courtesy NASA
Astronauts training for the many space walks that will be involved in ISS construction and maintenance.
The ISS will have robotic arms to assist spacewalkers and move large items such as construction modules and some supply ships.
Leisure Time
All work and no play makes for cranky astronauts. This has been observed on space shuttle, Skylab and Mir missions. Crews do need to have leisure time. What can you do with free time on the ISS? You can read, play games or e-mail your friends. However, most astronauts say that what they like to do most is look out the window at the Earth below.
Habitation Module
The United States will provide an additional habitation module, the trans-hab module, for extra crew quarters.

The proposed U.S. trans-hab module.
This habitation module will be able to sleep four astronauts. Each cabin will have a sleeping bag (note that it is upright on the wall), a desk with a computer, and footholds.

Crew quarters of trans-hab module.
The module will also have a wardroom with a galley, table and storage area. This will be a place for the astronauts to eat and gather for meetings.

The wardroom of the trans-hab module.
The module will also contain a level for crew health care, which includes exercise and medical equipment as well as storage space.

The exercise area of the trans-hab module