Space Colonies Build a Lunar or Mars City
Transcription
Space Colonies Build a Lunar or Mars City
EXPLORE! A Cooperative Project of the Lunar and Planetary Institute, NASA's Office of Space Science and public libraries Activity: Space Colonies: Build a Lunar or Mars City Level: Grades 5-8 To Take Home: Space Colony Design Background Information Space Colonies A space colony is seen as one of the most important options available to the continuation of mankind in the future. Space colonies on the Moon, Mars, asteroids, other worlds and in orbit around the Earth have been suggested, designed and promoted since the 1950's. Early orbiting space stations were designed like large wheels spinning in space as seen in the film "2001". Many scientists have advocated expanding the human presence to other worlds. There are a great many things we can do on other worlds and in Earth orbit. We can set up mining stations on the Moon, and fund laboratories in space to perform experiments you wouldn't want to do on Earth because of the risks involved to the population. We can also build observatories and factories in space. Isaac Asimov, the famous science writer wrote, " Space settlers … might run mines on the Moon, they would travel in a spaceship that would be very much like the space stations in which they would live (maybe a little smaller but that's all). They would be living inside a world with tight cycling and varying gravitational forces. They would be the natural pioneers. They, not we, would be the Vikings, the Phoenicians, the Polynesians of the future. They would make the long trips to Mars and the asteroids and learn how to mine the asteroids. They could travel out into the solar system and make plans to reach the stars someday. All we can do here on Earth, maybe, is reach the Moon. From worlds in orbit around the Earth, we can reach all the rest." Currently there are three space settlement design contests for young students: the NASA Ames Research Center Annual Space Settlement Contest, the International High School Space Settlement Design Competition, and Spaceset, hosted by the Jet Propulsion Laboratory. The Mars Millennium Project, an official White House Millennium Council Youth Initiative challenges students across the nation to design a community yet to be imagined - for the planet Mars. Lunar Bases By early in the next century, NASA could establish a permanent lunar base for scientific research and mining. Scientists envision an initial outpost for one to two dozen people expanding to a community of thousands as NASA finds ways for commercial interests to move into space. The International Space Station is a prelude to the moon base and that base, in turn, would be a stepping stone to Mars. A lunar outpost could provide valuable information on the long-term physiological and psychological effects on humans living for long periods in space. The information could prove invaluable in the eventual planning for a manned Mars mission that would require years of travel. Also, the moon could serve as a source for the large quantities of oxygen needed to fuel a spacecraft to Mars and back. Living quarters built on a lunar base would probably consist of cylindrical habitation modules made of durable lightweight materials. These modules would be connected together parallel to the ground. By connecting extra modules, the habitable lunar base can be expanded incrementally. Most of each habitation module would be buried underground to ensure its structural stability and to use the lunar soil for protecting humans from exposure to solar cosmic radiation. There would be three types of modules: habitation, laboratory and factory modules. The habitat would have sleeping quarters, a kitchen (or galley) and bathroom facilities. Any windows (if any) would have to be small and made of multiple thick glass sheets to block cosmic radiation. Although the Moon is free from the damaging threats of weather, accidents or fires could occur and meteorites do impact the Moon. If an accident occurs in a large structure, it might be necessary to abandon the entire building. However in a module system, a damaged module could simply be isolated from the rest by closing the hatches shared with other modules, similar to the plan onboard the space station. The modules would be filled with air to enable the crew to breathe, and pressurized like an airplane cabin at a pressure of one Earth atmosphere. Energy, oxygen, food, and water necessary to maintain life in a lunar module would have to be transported from the Earth. Research and experiments would be conducted to find ways of producing or recycling some of these essentials on the Moon. For example, sunlight can be utilized to supply energy, and oxygen could be produced from oxide compounds existing on the Moon. Settlers would grow plants and possibly breed fish on the lunar surface. What kind of people will live on the lunar base? The construction of a lunar base would be a major international project similar to the construction of the International Space Station. Crews sent to the lunar base would most likely be made up of men and women from participating countries around the world. This team would include doctors, researchers, engineers, and scientists. As the colony grew, other personnel such as cooks, and gardeners would to be added to the team. Journalists may also invited to join them. The crews would do research and conduct experiments in the Moon laboratories, work on lunar base construction, maintain the base, mine resources, etc. These crews would be replaced on a regular basis in the same way that teams who work at U.S. and Japanese Antarctic Bases on Earth are. In addition to living quarters, a lunar base would also need a landing/launch pad, a power plant - either solar or nuclear, construction equipment, a spare parts and maintenance garage, a central control and communications center, and life support systems. Mining equipment and a solar oven could be used in building the initial lunar base and then be employed for supplying material for industry in orbital space. Frozen soil at the moon's poles may contain as much as 1-10 billion tons of water locked into deeply shaded craters, according to data from the Lunar Prospector spacecraft. That is an amount equal to what is consumed by U.S. cities in 10 days. More important, it would be enough to supply the population of a lunar base for a long, long time. In addition to sustaining life in a colony, water can be used for rocket fuel by breaking it into its constituent chemicals - hydrogen and oxygen. NASA LUNAR BASE IMAGES Mars Bases If humans are to live on Mars, even for brief periods, they are going to have to be supported by a wide range of infrastructure. They'll need a place to work, rest and live. They will need power, light, food, water, and heat. They'll need robust transportation, equipment able to operate in low temperatures and the hostile environment on Mars. Current NASA exploration plans envision an early prototype of a Mars habitat that could be launched into orbit. The prototype habitat would be joined to the international space station for testing and final training of the Mars exploration crews. Systems to support the crew on Mars would be delivered to the planet nearly 26 months prior to the first crew's arrival. The first elements delivered will include the crew's ascent vehicle, which arrives with empty propellant tanks, propellant production equipment, and various surface habitation and exploration systems. Once the surface payload is unloaded, propellant production begins. The carbon dioxide atmosphere of Mars is reacted with hydrogen imported from Earth to make the nearly 30 metric tons of oxygen and methane required to eventually deliver the crew from the planetary surface back into Mars orbit. The ascent vehicle is fully fueled before the crew leaves Earth to begin their journey to Mars. An international crew of six would spend the 180-day journey to Mars in the habitat they will live in on the planet's surface. This habitat will be a duplicate of one delivered to Mars nearly 26 months earlier. Once on Mars, the crew connects the two habitats together and begins a variety of surface exploration and habitation activities. By using resources available at Mars and emphasizing the development of a robust set of surface systems, the crew's safety and the scientific and economic return of human missions to Mars are dramatically increased, while the cost of such missions decreases substantially. After the habitats are joined, the crew members would have multiple pressurized spaces available for conducting greenhouse experiments, biological research, chemical analysis of samples, and general crew accommodations. The crew would prepare their ascent vehicle in anticipation of returning to Earth. Its job complete, the propellant production plant would be removed from the lander and connected to the outpost, providing future crews with caches of breathing gases and other consumables. After spending nearly 500 days on Mars, the crew would begin their 180day voyage back to Earth by ascending into orbit to rendezvous with their Earth-return vehicle. Subsequent human missions have the option of returning to the site established by the first crew, or placing additional footholds on the surface of Mars. The Earth-return vehicle will have awaited the crew's arrival in Mars orbit for nearly three years. After checking out its systems, the crew would embark on the final leg of their journey in the now familiar Mars habitat. This familiarity will pay off in terms of increased crew safety and reduced program costs. Having spent nearly 900 days away from home, the six crew members would return to Earth landing at the Kennedy Space Center. NASA Mars Mission Images After landing on the Martian surface, the crew uses an unpressurized rover to unload cargo and supplies needed for their stay on the red planet. The crew attaches an inflatable laboratory to their lander to increase the internal pressurized volume of their martian home. The completed outpost on Mars includes the crew's two-story lander habitat, inflatable laboratory and unpressurized rover. The crew's ascent vehicle and propellant production facility can be seen one kilometer away from the completed outpost. In front of a fully-fueled ascent vehicle waiting to return them to Earth, the Mars crew salutes all of the people and nations of the world that made the journey possible. Space Colony Research Programs NASA Advanced Life Support Program When humans establish permanent bases on the lunar surface or travel to Mars for exploration, they will continue to need food, water and air. For long term missions it will not be economically feasible to resupply these life support elements from Earth. Humans will need to develop systems to produce food, purify their water supply and regenerate oxygen from the carbon dioxide they expel. A life support system that would perform these regenerative functions is called a Controlled Ecological Life Support System (CELSS). A CELSS is a tightly controlled system, using crops to perform life support functions, under the restrictions of minimizing volume, mass, energy, and labor. Research on human life support began in the 1950's with oxygen regeneration using algae. The National Aeronautics and Space Administration (NASA) became interested in the CELSS effort in the late 1970's in order to support long-term space missions. Since that time, the Advanced Life Support (ALS) program at NASA has examined growing plants for food and oxygen regeneration, and use of chemical and biological methods to process waste into usable resources, and has begun human testing within ALS at JSC. Between 1995 and 1997, NASA conducted four experiments with humans in sealed CELSS facilities for one, two and four months each. Longer missions are currently planned. These experiments were conducted at the NASA Johnson Space Center in Houston, Texas. Mars Arctic Research Station The privately-funded Mars Society is planning a Mars Arctic Research Station (MARS) for the year 2000, as a practical attempt to solve many of the problems facing those wishing to build habitats that will one day be deployed on Mars. The base will be modeled on a Mars Habitat unit, supported by a garage/workshop used to house allterrain rover vehicles, a solar panel array and a small greenhouse. The Mars Arctic Research Station will be the world's first fully-simulated mars base. It will enable scientists, engineers and even astronauts to test the equipment and technology (habitation, transportation, life support, recycling, etc.), that may be deployed during a manned mission to Mars. Biosphere "Biosphere 2" is a well known experimental complex with a closed ecological system. Funded by Texas multimillionaire Edward P. Bass, Space Biospheres Ventures built an airlock-sealed habitat in Arizona, USA, initially stocked with over 3000 species (since nobody could predict which ones would survive as food chains evolved) - food producing and other plants, fish, trees, etc., and a crew of eight people. It is the largest closed ecological system ever built, at 2.3 acres - about 13,000 square meters. In Mission 1, the facility was closed and sealed, and the crew lived inside for two years from 1991 to 1993. The experiment was designed as a precursor to future self-contained space colonies. It is currently operated in conjunction with NASA Underwater Stations Underwater colonies have been envisioned since the 1960's as testbeds for future space colonies and as research laboratories themselves. Sea colonies were considered one way to expand the human presence on this planet, but could also be used on moons that had oceans like Europa. Terraforming Mars To terraform a planet means to make it like Earth. The best candidate for that project is Mars which already has a thin atmosphere. It is farther from the Sun than Earth, but not too far, and it has polar ice caps, some water, and possibly frozen water ice beneath the surface. To melt the polar ice caps, some scientists advocate mirrors in space, which would catch some of the sunlight racing past Mars and focus it back on the planet. Others advocate spreading black dust or algae on the martian polar caps. The black material would absorb heat, melting the poles. Some believe that we might make breathable air on Mars in only a century or two using tiny self-reproducing robots (called nanotechnology). Others think it might take hundreds of thousands of years. Some believe in a two-part terraforming scheme. In the first part, the planet warms up and a thick carbon dioxide atmosphere is manufactured, suitable for bacteria and possibly plants. It might take only a century. But the second part, in which the plants make carbon dioxide and oxygen, would take much longer. Space Station Colonies In the 1960's and 1970's many designs for rotating space orbiting colonies were made. The images below show some of the concepts. One shows a space-habitat designed for 10,000 people. The inhabitants, members of the workforce of a space manufacturing complex, would return after work to homes on the inner surface of a large sphere, nearly a mile in circumference, rotating to provide them with gravity comparable to that of the Earth. Their habitat would be fully shielded against cosmic rays and solar flares by a non- rotating spherical shell, accumulated from the slag of industrial processes carried out on lunar surface material. Outside the shielded area agricultural crops, far less sensitive to radiation than are humans, would be grown in the intense sunlight of space. Docking areas and zero-gravity industries are shown at each end of the space-community, as are flat surfaces to radiate away the waste heat of the habitat into the cold of outer space. The equator of this rotating habitat is nearly a mile in circumference, and near it wanders a small river whose shores are made of lunar sand. Natural sunshine is brought inside through external mirrors. Rotation of the sphere would produce gravity of Earth-normal intensity at the equator, gradually diminishing to zero at the "poles", where humanpowered flight and other low-gravity sports would become easy. For the short distances within the space-habitat, cars would be unnecessary, and transport would be on foot or bicycle. A corridor at the axis would permit floating in zero-gravity out to the agricultural areas, the observatories, the docking ports, and the industries. Designing Space Colonies Parts of a Space Colony Laboratory Modules - The crew work quarters, where experiments on materials and living things will take place. Habitation Modules - These will have living quarters for the crews and may include a shower, private compartments, and a galley (eating area). Greenhouses - Used for growing food and contributing to the oxygen system, also a way to use excess carbon dioxide. Solar Arrays – To collect and store up electricity to power the various lunar base systems and experimental activities. Antennas - Used for communication back to the Earth and with arriving and departing spacecraft. Surface Rovers - Pressurized rovers can be used for long journeys, simpler open rovers can be used for short trips. Resource Utilization Facilities - Used to mine the resources of the moon or planet for use in the base, or for manufacturing propellant (fuel) for space ships. Telescopes - On the Moon where there is no atmosphere, telescopes would provide scientists and astronomers a great view of deep space beyond Earth's atmosphere. Supply Ships - Spacecraft used to bring crews and supplies to and from the space base. Space Suits - Astronauts will need to wear space suits for construction and repair of the space base, either on the Moon or Mars or on an orbiting space base (although the construct of each may be slightly different due to different conditions). Air Supply Consider that your space colony will need air. The modules will have to be enclosed or the entire living area inside a protective dome. Production facilities could create oxygen from water using electrolysis. Oxygen is also produced by photosynthesis from plants and a greenhouse attached to a living area could help with this process. There is also a process for extracting oxygen from rocks and soil that is being developed for use on the Moon or Mars. Communications Think about how people on the Earth communicate with one another. What methods work best for long distances? For short distances? Consider communicating with colonists who are out of the colony (such as colonists exploring in a rover). How will you communicate with the Earth? How will you communicate with other parts of Mars such as meteorology stations on the other side of the planet? Will you use satellites? Antennas? Food Production What are the basic food requirements for humans? (Consider the four food groups). Space for producing food will be very limited in a space colony. On Mars, or any selfcontained colony, the food must be replenishable, as replacement stock will not be available from Earth. The space available on the ship that transports the colony to Mars will be much more limited than even the colony itself. Even with limited resources, colonists will appreciate a varied diet. Some foods currently under consideration for use in space missions are soybeans and wheat. Soybeans and wheat both take up a small amount of space and are very nutritious. These crops can also be used to purify water and to produce oxygen from carbon dioxide using photosynthesis. A greenhouse will be a necessary addition to any space base. Living Quarters and Laboratories Consider factors such as, will each colonist have private living space? Every square foot of the base will use more resources, but people are happier when they feel they have sufficient space and privacy. What kinds of work spaces will be needed? Laboratories, construction facilities, recycling systems, greenhouses, fuel production facilities, mining stations, etc. Think about the purpose of your colony and what it will need to fulfill that purpose. Recreation Facilities What kinds of recreation facilities would be needed in a space base? Not only the body but the mind needs recreation. How will these facilities be different from those on Earth? Consider for example the lower gravity on the Moon (1/6th that of the Earth) and on Mars (1/3rd that of the Earth). Transportation What kinds of transportation will be necessary within the base and surrounding area? What kinds of trips will the crews need to make? How far will crews need to go? Do you need different methods of transportation for different purposes? What will you use for fuel? What equipment will you bring and what containers for returning samples will you need? Water Colonies will need a great deal of water for many purposes including drinking, washing, and watering plants. Where will you get the water? How will it be stored? A recycling facility may be needed. Energy and Production Equipment What energy source(s) will power the space colony? Will it be solar or nuclear? What about a back-up system? What kinds of production will take place at your colony? Will there be mining? Science laboratories? Telescopes? Fuel production systems? Water production facilities? How will they be integrated together? Activity Timeframe - 90 minutes Build a Space Base Materials Book or video about space colonies White paper Rulers Pencils, Colored Markers Parts for constructing a Lunar or Mars Base Model: Electronics from the interior of any old computers, TVs, VCRs, radios, tape decks, etc. Tin foil Styrofoam bricks of all shapes and sizes, meat packing trays Saran Wrap of all colors Wire, Wire cutters Toothpicks Glue Duct Tape, Scissors Almost anything! Legos with wheels (for rovers) A large piece of cardboard painted red on one side and gray on the other Two large tables (one for construction covered with newspaper) Boxes for the "parts" Chalkboard, dry erase, easel or large piece of paper Introduction to Space Colonies You may choose to read a story to the group about space bases to begin the session. It could be a fictional story like Are We Moving to Mars? or an article about future lunar bases like the one from Discover Magazine "What should We do with the Moon?" (see resources). Share the information included in this activity about the journey to Mars or building a lunar base. NASA handouts are included in this guide. You can show a video about space colonies like the introductory sequences in 2001. They are a nice introduction with few words, the first sequence to the orbiting space station is familiar to many, and the landing on the moon base is another good short sequence. Timeframe - 30 minutes. Designing Space Colonies Review with students the parts of a space base. If you have access to an overhead projector, print out on transparency paper the lists included this lesson. Have them design their own space base, for Mars or the Moon or for an orbiting station, on white paper (individually, in pairs, or in small groups). Discuss the different needs and considerations they have to consider in designing their colony. Timeframe - 20 minutes. Building a Moon Base or Mars Base Have the group choose either the Moon or Mars as the place for their base. The requirements will be similar. A large table with a piece of cardboard representing the lunar or Mars terrain can be painted red on one side and gray on the other before hand and flipped to the correct side. Each student should contribute one or more modules to the final design. Have the group divide up into teams for each of the different parts of the base. Using a chalkboard, easel or dry erase, or a large piece of paper have the group decide the rough locations of each of the base elements on a map. Discuss the scale of the modules so that they will relate to each other. For example, one inch equals one foot (or two), depending on the size of your table and base area cardboard. Then have each team build, using the parts in the "parts boxes", their piece of the base. Let them be creative! After the base is complete have the teams present their part to the rest of the group noting the dimensions, equipment, layout, purpose, etc. Timeframe - 40 minutes. Procedure 1. 2. 3. 4. 5. 6. 7. 8. 9. Review the Parts of a Space Colony section. Choose either the Moon or Mars base. Discuss the scale of the modules they will be making. Divide the group into separate design/construction teams • Laboratory Modules • Habitation Modules • Greenhouses • Solar Arrays and Communication Antennas • Surface Rovers • Resource Utilization Plants • Telescopes/Observatories • Supply Ships Review the parts or materials they have to work with. Have each team assemble parts and construct their module. Have the teams present their module to the group and place it within the base area. After the base is complete, have each team discuss their module: its dimensions, equipment, layout, and purpose. Take photos of your base and its designers! Follow Up Questions 1. Do you think we should build a lunar base before we go to Mars? Why? 2. Why should the building of a lunar base or a Mars base be an international project? 3. What are some of the problems that crews living on the Moon will have to face? 4. What hardships will the first space colonists on Mars have to endure? 5. If you were living in a space colony what would you miss most about Earth? 6. If you were born in a space colony on the Moon or Mars what would your life be like? How would it be different? Recommended Videos Destination Mars $16.00, Grades 7-12, 33 minutes, 1997, http://core.nasa.gov L5: First City in Space A 3-D IMAX movie, is about the first space habitat, based on these concepts (i.e., rotating for artificial gravity, and growing their own food) is a science fiction story about life aboard one of these colonies. 2001: A Space Odyssey. 1968 (Opening Space Station sequence, Moon Base Flyover sequence) Space Age, Vol. 1 - Quest for the Planet Mars. 1997 Space Age, Vol. 4 -To the Moon & Beyond. 1997 Books you can borrow from your library Non-fiction Cole, Michael D. Moon Base: First Colony in Space (Countdown to Space). Enslow Publishers, Inc. 1999. ISBN: 0766011186. Baker, David. Living on the Moon (Today's World in Space). The Rourke Book Company, Inc. 1989. ISBN: 0865923744. Uttley, Colin and Sara Angliss, Alex Pang. Cities in the Sky: A Beginner's Guide to Living in Space (Future Files). Copper Beech Books. 1998. ISBN: 0761307419. Asimov, Isaac and Greg Walz-Chojnacki. Space Colonies (Isaac Asimov's New Library of the Universe). Gareth Stevens. 1995. ISBN: 0836812255. Rickard, Graham.Homes in Space (Houses and Homes). Lerner Publications Company. 1989. ISBN: 0822521253. Brusic, Sharon. Kids and Technology: Space Colonization (Mission 21 Kids 4 Technology). Delmar Publishers. 1991. ISBN: 0827341024. Stewart, Gail. Living Spaces in Space (Living Spaces). The Rourke Book Company, Inc. 1989. ISBN: 0865921164. Clarke, Arthur C. The Snows of Olympus: A Garden on Mars. W. W. Norton & Company. 1995. ISBN: 0393039110. Wilson, Forrest. Build Your Own Moon Settlement. Pantheon Books. 1973. ISBN: 039482606X. Watts, F. Lunar Bases (First Books) by Sharon Cosner. 1990. ISBN: 0531108945. Cole, Michael D. Living on Mars: Mission to the Red Planet (Countdown to Space). Enslow Publishers, Inc. 1999. ISBN: 0766011216. Schraff, Anne E. Are We Moving to Mars? John Muir Publications. 1996. ISBN: 1562613103. Hamilton, John. Future Missions to Mars (Mission to Mars) Abdo & Daughters.1998. ISBN: 1562398326. Fiction Montgomery, Anson. Moon Quest (Choose Your Own Adventure, No 167). Bantam Books. 1996. ISBN: 0553566210. Kelch, Joseph W. Millions of Miles to Mars: A Journey to the Red Planet. Julian Messner. 1995. ISBN: 0671882503. Coville, Bruce. Space Station Ice 3. Archway. 1996. ISBN: 0671536419. Smith, L. Neil. Bretta Martyn. Tor Books. 1997. ISBN: 0312858930. Good Space Colony Internet Sites: Lunar Bases Exploring the Moon: Future Missions http://cass.jsc.nasa.gov/expmoon/future/future.html Lunar Bases and Space Activities of the 21st Century http://adsbit.harvard.edu/books/lbsa/ Lunar Base Quarterly Newsletter http://vulcain.fb12.TU-Berlin.de/koelle/LBQ/LBQ_index.html Lunar Base Article from Discover Magazine What Should We Do with the Moon? Cover Story, September, 1998 http://www.discover.com/archive/index.html International Lunar Working Group http://ilewg.jsc.nasa.gov/ LunaCorp http://www.lunacorp.com/ Artemis Project http://www.asi.org/ Mars Bases Mars Society Mars Antarctic Base http://www.marssociety.org/researchstation.asp Mars Society http://www.marssociety.org/ Mars Mission Images http://www-sn.jsc.nasa.gov/explore/DATA/MImages/MImages.htm Student Mars Habitat http://www.bestwax.com/htm/mars/index.html Missions to Mars http://www2.astrobiology.com/astro/mars/missions.html Terraforming Mars http://www2.astrobiology.com/astro/terraforming.html Technological Requirements for Terraforming Mars http://www.users.globalnet.co.uk/~mfogg/zubrin.htm Space Settlement Contests and Programs for Kids NASA http://science.nas.nasa.gov/Services/Education/SpaceSettlement/Contest/contests.html International High School Space Settlement Design Competition http://space.bsdi.com/ Spaceset - Hosted by the Jet Propulsion Laboratory, a small annual contest http://home.earthlink.net/~spaceset/ Mars Millennium http://www.mars2030.org The Mars Millennium Project, an official White House Millennium Council Youth Initiative challenges students across the nation to design a community yet to be imagined - for the planet Mars. Orbiting Space Colonies Orbital Space Settlements http://science.nas.nasa.gov/Services/Education/SpaceSettlement/ International Space Station http://station.nasa.gov/station/index.html Other Sites Biosphere 2 http://www.bio2.edu/ NASA Advanced Life Support Program http://pet.jsc.nasa.gov/ Designing for Human Presence in Space http://augusta.msfc.nasa.gov/ed61/papers/rp1324/rp1324.html Romance to Reality: Moon and Mars expedition & Settlement Plans http://members.aol.com/dsfportree/explore.htm BioBlast High School Program http://www.cotf.edu/BioBLAST/ BioBLAST® is a multimedia curriculum supplement for high school biology classes. It encourages students to conduct real scientific research, based on actual research now being conducted by NASA’s Advanced Life Support Research program. Hands-on laboratory investigations, computer simulations, and Internet-based telecommunications resources may be accessed via the BioBLAST virtual reality interface, which depicts a futuristic, moon-based research outpost. NASA Home Page http://www.nasa.gov
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