SHIELDING,WASTE and FIRE Protection

SHIELDING

Beside other things, shielding is vital in the safety of the space station and the colonists who will live there. We know that in space there are many risks, from all kinds of radiation to meteoroids and meteor showers. Because of this, we will need a suitable protection against all of them. The radiation protection can be split in two parts:

The passive shielding will be formed all around the space station. It consists of 4.5 – meter thick layer of Lunar soil, and after that a second layer of two heavy metals Limonite and Barium. The outside radiation will not be able to penetrate the two layers of the passive shielding. Why should we use Lunar soil? Well, the Lunar soil was chosen because, all future space stations will be built on the Moon, or in space. It will make no difference if we use soils from other planets or moons. But we should be sure that they don’t contain any traces of radioactive metals or other kinds of pollution. Secondly, it will not harm the Earth because it will not be dug from it. The two heavy metals Limonite and Barium on Earth are used in building walls for nuclear power plants, storage pits, nuclear shelters and etc. From this we know that they have the quality of repelling and not letting the radiation to pass through the metals. Like the soil, Limonite and Barium can be found everywhere in the galaxy. Picture 1 shows an intersection of a space station wall, with details of the passive shielding.

Picutre 1

Besides the passive shielding, the space station we will have to have an active shielding too. The difference between the passive and the active shielding is that the active shielding creates an Electro-magnetic field with strong potential to change the trajectories of charged particles. The active shielding is also known as the plasma core shield. The idea is to put an electron well in the center of the space station. Inside this well about 10 C of electrons spiral along the lines of magnetic force will hold the metallic habitat at positive potential of 15 billion volts. This enormous electrostatic potential repels the protons and other cosmic ray nuclei from the habitat, and will cast off the cosmic ray spectrum for energies below 7.5 GeV/ nucleon (15 GeV for protons). The plasma core is new an it has some difficulties in some areas of it. Until extensive work is done to study all of these problems, the plasma core shield cannot be claimed as a practical solution to the radiation problem in space. In Picture 2 we can see an intersection of a space station wall, with detail of the passive and active shielding.

Picutre 2

Meteoroids and meteor showers pose a great risk to the space station as well. If the space station is in orbit on some planet then the planets atmosphere can be used as a shield against meteors, but if the space station is in space, well that is another thing. Tiny and small meteors can be harmful because they can only bend the wall on the space station or make small holes that can be fixed. Large meteors can cause serious damage or in some cases destruction to the space station. Bumpers can provide protection. They will absorb most of the meteoroid impact. In Picture 3 we can see the bumpers and how will they react if a meteor strikes them.

Picutre 3

When a meteoroid strikes, the bumper will absorb the impact and nothing happens to the station. It will be better to have a double skin of meteoroid bumpers. When a particle strikes the station, the other shield takes the force of the blow.


WASTE

Even on a space station, waste will be produced. If we don’t find a suitable solution, waste can be a big problem for the colonist. We will have to find a way to remove or to reuse the waste that will be produced. The waste generated on the space station are of four general types:

For long duration missions the best method for dealing with the waste is to recover and transform the waste to useable products as much as possible. Some methods are specific for the type of waste while others can process waste of virtually any type. The question that prevails is why the waste should be recovered not simply vented in to space. Venting it to space on longer duration missions is prohibitive, because that way we will get rid of the waste but in the same time we will lose mass and pollute space with waste.

Metabolic waste
For long duration missions metabolic waste (liquid and solid) can be recovered. Water can be recovered by dehydration but this process leaves the solid portion of the feces. Ideally this would be converted to fertilizer for plants which would provide a significant portion of minerals and food requirements. Metabolic waste also can be recovered in to CO2 and H2O, but this recovery is not good because large amounts of O2 and energy will be consumed for this process.

Other solid waste
Other solid wastes (paper, disposable dishes, paper cups etc.) consist primarily of paper and plastic, so if they are made from recycled materials (recycled paper or recycled plastics) they can be recycled in special plant on the space station so the same paper or plastic will be “going around in a circle”. For the dishes Japanese scientists invented a very practical item, edible dishes. The dishes are made from rice that is pressed in large pressing machines under significant pressure. After this you have an ordinary dish, like any other dish but this one you can eat. For other solid waste we will have to find alternatives how to reduce the amount.

Liquid waste
Sources of liquid waste include urine and brine residues from some of the water processors. Converting the liquid wastes we can make very useable products. One of those products is to reclaim water from urine as a feed to the electrolysis cells. Electrical energy must be consumed for the reaction to proceed. The Oxygen Generation Assembly (OGA) consists of 18 electrolysis cells constructed using ion exchange membranes and a conducting polymer termed a Solid Polymer Electrolyte. Oxygen is produced at ambient pressure and vented to the cabin. Hydrogen is produced at slightly elevated pressure as a potential supply source for a carbon dioxide reduction system (Sabatier Reactor). With this we are able to reuse the liquid waste, make oxygen and at the same time make hydrogen for the Sabatier Reactor from which we can make water.

Gaseous waste
Sources of gas waste include metabolic gaseous wastes (CH4, H2S, H2, CO, CO2) and byproducts from various chemical processes. The gaseous wastes may be removed or transformed to H2O and CO2 by the atmospheric trace contaminants control assembly.

Fire Protection

Fires on space stations can be disastrous and the potential for fires must be minimized. Using materials, which are resistant, and designing a habitat and its systems to not propagate fire reduces the likelihood of a major fire. Even so, the possibility of a fire cannot be totally eliminated. It therefore becomes important to detect a fire as early as possible.

Detection of incipient fires

The sense of smell is a sensitive and reliable method of detecting a fire, which is available on all human space missions. However, fires may occur during sleep periods, and as space habitats become larger not every module will be continually occupied. Therefore, reliable automatic methods are needed. Those methods include flame detectors based on visible, infrared and ultraviolet emissions and smoke detectors based on detecting the particles emitted by burning materials. Due to spurious alarms by the fire detectors, there have been missions where the sense of smell was the only reliable method. Because of this, improvements are needed in discriminating between smoke particles and other particles. Some of the newer technologies developed to detect fires are ionization detectors and photoelectric flame detectors. Another promising method being developed uses an expansion chamber to detect condensation nuclei produced by particles given off by heated materials prior to combustion.

Suppression of fires

Fires can be suppressed by removing the oxidizer (by suffocation) or the fuel (by shutting off the flow) and/or by removing the heat required for combustion to occur. The methods that are used on Earth (including water, foam, CO2 and Halon) cannot be used on the space station because of the consequences after use. For example, if we suppress fires using water, electrical failures may result and likewise, using foam creates a cleanup problem. .The best fire suppression for the space station will be usage of CO2. This is the best solution because CO2 can effectualLY suppress a fire and makes the cleanup process a relatively simple task. Other methods of fire suppression include N2 and depressurization of the habitat.

Cleanup after a fire

Any fire will create byproducts, which may be hazardous. The degree of hazard depends upon the types of materials burned, the temperature of the fire and the type of suppressant used to extinguish the fire. Removing those byproducts from the atmosphere is essential. The best method for cleaning up after a fire depends in part upon the severity of the fire and the amount of byproducts produced. For a severe fire which produces a lot of smoke particles the best method may be to depressurize the affected area of the space station by venting the contaminated atmosphere out to space. If this is not possible other solutions must be used. If the fire is in an area where decompression or suffocation of the fire with CO2 is not possible then the method using water will be used, and the contaminated atmosphere will be cleaned from the contamination system that will be onboard. For a smaller localized fire some type of portable contamination system device may be able to remove most of the contaminants from the atmosphere so that the trace contaminant system can safely remove the remaining contaminants. Surface contamination by potential corrosive combustion byproducts may also result, depending on the material burned and the suppressant used. Those byproducts will have to be removed without causing additional contamination by wiping the surfaces with a solvent or a neutralizing agent to prevent corrosion. Other methods and systems will be designed by the colonists on the space station or settlement. They will be designed by their specific needs.

Author: Vladimir Simonovski