A SPACE OASIS
One of the top ten entries in the Honeywell Fiesta Bowl Aerospace Challenge was created by a local homeschool team consisting of five 7th and 8th grade students – Megan Barlow and Chris Minsky of Desert Hills, Aaron MacInnis and Dominic Martel of Glendale, and Peter Olsen of New River. Their written report covers everything from controlling life support systems to the types of snack foods to have on board. The paper contains a great deal of scientific information and technical details, so it was obviously well-researched, and it also includes quite a few unique ideas, so they certainly gave their project a lot of thought. I told them that I would like to feature their report in my column, but at over 30 pages in length, I had to edit it to make it fit. The condensed version will take up two columns as it is. Even though this was just a hypothetical project, it goes to show how much planning is needed to build a real space station!
This report is dedicated to the scientists, engineers, and astronauts who are making living in space a reality; and to the next generation of space scientists, aerospace engineers, and astronauts.
Our mission in space is experimenting with plants to solve world hunger and for the crew on the station. Another goal we would like to accomplish is medical discoveries in micro–gravity. We will also be harnessing solar energy for power, by collecting it and beaming it down to Earth.
Artificial gravity on space stations is often seen in science fiction stories such as 2001: A Space Odyssey, Rendezvous with Rama, Star Wars, and Babylon 5. For practical purposes and health reasons, artificial gravity will most likely be needed for any prolonged space habitation. This will eliminate the long term effects of weightlessness on humans.
Artificial gravity can be generated in space by centrifugal force, which is created by spinning the spacecraft. To achieve this, the station does not have to spin very fast. For creating the spin, the easiest way seems to be to attach small thrusters in balanced pairs around the rim of the station.
It wouldn’t matter which way the station rotates, because there is no up or down in space, so the people wouldn’t notice if they were “upside down.” But if they looked far ahead or behind them, they would see the floor curving up. People living in space would gradually learn to move away from a feeling of “up or down” to a more circular perspective.
Design And Structure
Building a space station is an engineering challenge, especially when it has to be assembled in outer space. All construction materials will have to be transported to the site. The Earth can be a source of building materials, but it costs a lot of money to launch supplies up from Earth. It would be easier to get the needed materials from the Moon because it has no atmosphere to go through and its gravity is much weaker. Nearby asteroids would also be good sources for materials.
If the space station is going to be rotating, it should have a rounded shape. The three main shapes that can be used as rotating space stations are: sphere, cylinder, and torus. A torus (donut or ring shape) is the best choice. The structure is strong and compact, and is more economical to build than a large sphere or cylinder, due to its smaller surface area. The torus shape allows for a lot of useable floor space at a uniform gravity level, without requiring a large amount of interior atmosphere. The center hub can be easily accessed from all parts of the station.
To simulate Earth's normal gravity, the entire torus will rotate around a central pole. The central pole is attached to the outer ring by four tubes which double as access routes. Each transport tube will be like an elevator, its mass being driven by electromagnetic fields, a “mass driver.” The central pole will be the zero-gravity area where crops and crystals are grown. The docking and launching zones will also be in the zero gravity area.
Thick cables attached from the torus to the central pole help maintain the rigidity of the torus. Additional stability is provided by many criss-crossing guy wires pulled taught, as on a suspension bridge, both in-plane and out-of-plane, to prevent flexing of the toroidal ring.
A rotation and mass balance officer will be in charge of four tuned mass rotational dampers. The cylindrical heavy metal dampers made of iron or nickel slide along the outside of the transport tubes. The mass balance officer can, using computer-aided controls, slide the dampers between the center hub and the outer ring to maintain a stable rotation if it gets out-of-sync under shifting loads. This works similar to a figure skater holding her arms out to slow down or pulling her arms in toward her body so she can go faster. Many types of dampers like this are already in use on tall skyscrapers and suspension bridge towers, to keep them from swaying in the wind.
A space station needs a steady supply of power. Electricity is used for climate control, lighting, food preparation, computers, communications, and other equipment. We have decided that the electricity needs of this space station will require nuclear and solar as the main sources of power.
We have designed it so that our nuclear power plant is safely separated from the inhabited part of the station. It can be shut off or even detached in case of an accident. We don’t think the disposal of nuclear waste will be a problem, either. The nuclear waste can be easily discarded using Magnetic Rail Guns that use magnetic rails as the propulsion mechanism. This allows higher initial velocity than rockets and is cheaper. We can shoot a tightly sealed canister of nuclear waste into the sun on a schedule. It won’t affect the sun at all.
A main economic reason that justifies this space station endeavor is the collection and distribution of abundant solar energy to supply power for Earth. Normally, “only 40% to 50% of solar energy reaches the earth's surface. 22% of solar energy is absorbed in the atmosphere and between 30% to 40% is reflected into space.” Some sort of system must be designed to fully utilize the sun as energy and beam it down to Earth. Large solar collectors can be built to convert sunlight to electricity which can then be beamed to Earth using microwaves and/or lasers. We expect the sale of solar energy to help pay for the station.
Shielding is one of the most important functions on a space station. Without shields the station would overheat, be destroyed, or radiation would penetrate the station and affect all organic matter by increasing cancer risk.
The two types of shielding are passive and active. Passive shields are usually bulk shields that absorb solar radiation and dispose of the radiation. An active shield is an exterior body that protects the craft from solar radiation and deflects solar particles by way of magnetic fields, plasma shields and electrostatic fields.
The Oasis space station will be in orbit at an altitude of 500 km (310 miles) above Earth. It will be in Low Earth Orbit, but slightly higher than the current ISS which has a mean altitude of 373 km (232 miles). This will avoid most of the space debris that is floating around.
Space shuttles will be an important link to Earth. The Oasis space station must have a safe, efficient transportation terminal to allow fast and easy access of space shuttles, along with their cargo and passengers. It seems hard to believe, but objects in orbit around Earth are moving at tremendous velocities. Positioning a shuttle close to the space station while orbiting the Earth at such a high speed can be pretty tricky.
Docking systems are simpler when the station is not rotating. Here is a way it can be done. While the station is rotating around the tubular pole, the pole itself is not rotating. (Imagine a wheel on an axle.) The docking port is on one end of the pole, far enough away from the main structure to satisfy safety concerns.
A ship comes in and the docking arms are extended. They grab onto the ship and help guide it to the docking port. With a soft thud, the ship makes contact and is coupled to the station. The ship remains attached to the outside of the station. Once the ship is docked at the port, the airlock door opens up and the people go through.
Since the pole is not rotating, there is microgravity inside this part of the station. So the arriving traveler is weightless when he first enters. He has to haul himself hand over hand through the airlock. There are more handholds all the way along the interior of the tube. The visitor arrives at a spherical chamber at the axis of the space station. From there, several tubes head off in different directions to other parts of the station. Moving through one of these tubular tunnels, he is getting closer to the ring of the torus and feels himself starting to get heavier.
As Arthur C. Clarke wrote in 2001: A Space Odyssey, “Faint and ghostly gravitational fingers began to clutch at him, and he drifted slowly toward the circular wall. Now he was standing, swaying back and forth gently like seaweed in the surge of the tide, on what had magically become a curving floor. The centrifugal force of the Station’s spin had taken hold of him; it was very feeble here, so near the axis, but would increase steadily as he moved outward…..Not until he reached the passenger lounge, on the outer skin of the great revolving disk, had he acquired enough weight to move around almost normally.”
Atmosphere is made up of a combination of gases and pressure. The Earth’s atmosphere contains about 21 percent oxygen, 78 percent nitrogen, less than 1 percent of argon and carbon dioxide combined, and trace amounts of other gases. The astronauts will need a steady supply of oxygen to survive. Their bodies will use the oxygen, exhale the carbon dioxide, and won’t do anything with the nitrogen or argon. But pure oxygen is highly combustible, so nitrogen must be added as an inert gaseous buffer. If an outside hatch is opened or if the hull is breached, the airlocks will have to close quickly when the pressure drops.
Supply vessels can deliver pressurized tanks of oxygen and nitrogen to start with. But the air in the storage tanks will not last long. The MIR space station generated most of its oxygen by using electrolysis to break down water into hydrogen and oxygen. Lithium perchlorate candles were burned to generate supplemental oxygen when more than three people were onboard MIR. Lithium perchlorate produces oxygen through a chemical reaction when heated. But the oxygen-generating candles only burn for 5 to 20 minutes, and a defective one can catch on fire.
In our case, there is a better way. We will have plants on board. Plants naturally convert carbon dioxide into oxygen. So while the astronauts inhale oxygen and exhale carbon dioxide, plants take in carbon dioxide and produce oxygen. We will have to be extra careful when figuring how many plants we need to produce enough oxygen for each astronaut, based on what happened in Biosphere 2. Biosphere 2 was constructed in Oracle, AZ in the late 1980s to see if eight people could sustain themselves in an airlock-sealed environment such as a space colony. It was 2.3 acres in size, the largest closed ecological system ever built. Biosphere 2 was stocked with over 3000 species of plants, fish, trees, etc. However, their mission ultimately failed because the plants didn’t produce enough oxygen to support all eight team members. They ended up having to bring in air from the outside, which is something that we won’t be able to do.
It has been found that it takes ten square meters of plants to recycle just one astronaut's air. That would fill up a small bedroom. So a crew of 100 astronauts would need 1,000 square meters of plants. Our space station will have to be very big to hold all of these plants. But remember, that's not all we need plants for. We will be producing our own food in hydroponic gardens. About 50 square meters of crops can produce enough food to support one astronaut. A crew of 100 would need 5,000 square meters of hydroponic gardens—five times more than is needed for air! So those same plants that are grown for food will produce more than enough oxygen to breathe.
For many years, NASA produced drinking water by mixing hydrogen and oxygen in a fuel cell using electrolysis. This made enough water for rehydrating foods as well as drinking. This process also produces electricity as a byproduct. But the Oasis will need a lot more water than that just for its hydroponics sector. A supply of water could be brought to the station to begin with, but it would be impractical to always have to transport the water. So it is essential for the space station to become self-sufficient and resourceful when it comes to water.
The crew members of the current ISS are able to get by with less than 8 gallons of water a day per person. Their water is recycled from every available source. Waste water can be recycled from showers, hand washing, food preparation, moisture in the air, perspiration, and urine.
Water conservation will have to be strictly practiced, and personal water use may even be rationed. For example, astronauts can limit their need for showers by taking sponge baths using a special soap that does not need rinsing. They can wash their hands with premoistened towelettes or a washcloth rather than leaving the water running. Clothes can be dry cleaned instead of laundered. These are just a few of the ways we can conserve water on the space station.
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