CHAPTER V

Construction

V.A. Ground procedures

1. Launching site

Carrying materials from Earth is very expensive, thus we must build in space a whole industry for bringing the material we need for the Space Settlement’s construction. The ground procedures will consist in preparing all the materials necessary for the Moon base and the L1 temporary base. We will also need to carry in space materials which can not be found on the Moon, Mars or appropriate asteroids. We will need powerful shuttles for carrying the crew, the engineers and the needed robots for the Space Settlement’s construction. The materials and the space shuttles will be launched from a site in India near the geomagnetic equator because workforce is less expensive and the gravity constant is minimal.

2. Launching techniques and automatic procedures

All the tools, robots and materials will be sent to the lunar base which was built before especially for this purpose. After the programmed robots extend the lunar base for living, the crew consisting in workers, engineers and doctors will arrive to the lunar base.

3. Means of transportation

In the early times, the astronauts were constrained to very difficult exercises, but nowadays almost any normal person can become an astronaut. The crew will be transported from the Earth to the Moon exactly like astronauts in common Space Shuttles.

V.B. On-orbit procedures

1. Using L1 as temporary deployment site

The building of the orbital settlement in L5 will involve the existence of a temporary “work camp” somewhere near the main construction site. This transit platform will function as anchorage zone for all materials and crews arriving both from the Moon and the Earth. For maximum efficiency, it must be placed between the two major bodies. As we said before, the orbit around L1 would be ideal for the temporary parking of shuttles, workers and materials during the construction of the space settlement, as it is relatively close to the Moon, the main source of materials (58200 Km). For better understanding its positioning, let’s consider the following example.

Two cosmic bodies of masses M₁ and M₂ respectively are situated at a distance (d) one from the other. On the line connecting the two bodies there is a point in which the gravitational field is null.

Therefore, the body will oscillate in respect with the law of linear harmonic oscillation. The equivalent constant of elasticity (k) is:

By matching this relation with the standard relation for the force of elasticity: , we can determine the oscillation period of the body of mass m.

In the case of our temporary transit platform between the Earth and the Moon, the equilibrium point is a little different from that in the situation above, as the body describes a circular motion around the center of mass of the Earth-Moon system.

 ;

 - the gravitational force of the Earth;- the gravitational force of the Moon

The speed of the deployment area in L1 must have a certain value, so that the Earth, the Moon, the transit platform and the center of mass of the Earth-Moon system will be permanently collinear. This can be accomplished only if the angular speed of the body in L1 is the same with that of the Earth and that of the Moon,

where is the orbital speed of the Moon around the center of mass of the Earth-Moon system (=1Km/s). The distance between the center of mass and the Moon is . Therefore,

By combining relations [5] and [8], the general relation becomes

We can determine r from relation [9] by using numeric examples.

The temporary station in L1 is then moved with the desired y in the direction of movement on its trajectory. The transit platform will still have two superimposed motions: a uniform circular motion around the center of mass of the Earth-Moon system and an oscillating movement along its trajectory, with the amplitude of y. The orbital kinetic momentum of the transit station will suffer small variations in module, but its orientation will remain constant. Therefore, the trajectory of the deployment platform will remain plan. 

2. Automatic and robotic devices

Extreme conditions in space and on the Moon, including heat and cold, radiation, and rough terrain, require robots that are mobile; have competent motion in hard or soft terrain; remain upright or are self-righting; and that are physically self-contained, durable, and autonomous. To accomplish our objectives the robots must be controlled by radio waves and hey must have intelligent algorithms having raised degree of autonomy. The robots operating with minimal Earth communication are essential for such a complex process of building the Space Settlement. Robots will pack the ore and this will be “launched” in the L1 zone, for temporary assembling. We have chosen this solution because it is hard to launch from the Moon big and heavy assembled parts of the Space Settlement.

For fuel saving we won’t use Shuttles for carrying components from Moon in space. We will launch the component parts of the Space Settlement with a “Moon Canon” thereby the energy used for lifting the Shuttle’s mass won’t be used.

This is an acceptable speed calculating that we save a lot of fuel not using Space Shuttles for carrying the materials. If the parts of the Space Settlement produced on the Moon base are launched with 868km/h on the direction Moon-Earth they will stop exactly in the L1 point which will be used for temporary base for assembling the Space Settlement.

3. Assembling procedures and facilities

As we said before, the robots will assemble the Space Settlement in the L1 zone. First of all they will assemble the central body (The 0 gravity body) ,then the “pipes” which connect central body with the torus, then the torus and then finally the mirrors and the Photo Voltaic cells.

4. Temporary life sustaining

Keeping many people in good conditions for a long period of time is very difficult. The numerous numbers of robots is very important thus a little number of people will be needed for the construction.

The Shuttle carrying persons who must stay in space for supervising the robots activity will be located in the L1 zone and it will have a revolution motion around the L1 point which will need a small amount of fuel for trajectory corrections.

V.C. Building and life sustaining materials

1. Material properties

Titanium

The most important material for the construction of the space settlement will be the Titanium Oxide. For the construction of the torus , the 0 gravity center and the annexes we will use an amount of    88980425100 kg of TiO_2.

In the table below we will enumerate some of the Titanium Oxide properties.

We will also use silicium , lead and other metals for the functional completeness of the Space Settlement.

Aluminium

Pure aluminium is a silvery-white metal with many useful characteristics. Alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Strength on pure aluminium  has a tensile strength of between  49 MPa and  700 MPa depending of alloying type and the heat treatment. Aluminium is a very good conductor of electricity, also being non-magnetic and non-combustible.

Copper

Copper is an excellent electrical conductor. Most of its uses are based on this property or the fact that it is also a good thermal conductor.

Nickel

Nickel is silvery white and takes on a high polish. It is hard, malleable, ductile, and a fair conductor of heat and electricity.

Nickel gives glass a greenish color. Nickel plating is often used to provide a protective coating for other metals, and finely divided nickel is a catalyst for hydrogenating vegetable oils.

For the electromagnetic coils we will use supermalloy for its high magnetic permeability properties.

a. Earth composition

Earth is a very good source of materials, but taking objects in space from Earth requires a large amount of energy. Any material which is already in space has an enormous potential value relative to the same material that needs to be brought up from Earth. It is more than 10 times easier and cheaper to bring an object into low Earth orbit from the surface of the Moon than from the surface of the Earth. This is why we will take only the strictly necessary resources from Earth, as oxygen, water and construction materials for the lunar and orbital temporary base.  

b. Lunar resources

The Moon is another potential source of materials. The Lunar regolith contains some useful ores, in particular TiO2 and FeO. However, the ore quality is not as high as that of some asteroids, and the moon is almost totally without volatiles. Water ice has been discovered on the moon, but its precise quantity is unknown, and the moon is still without any known good supplies of carbon, nitrogen, and helium.

The first resources which will need to be extracted from the Moon are discussed below:

Aluminium

Aluminium is one of the moon’s resources. It’s a light, good electrical conductor, the most widely used conductor material on Earth, even more than copper.

Being light, it helps building large structures rotating for creating artificial gravity.

It can also be used as material for building mirrors, because aluminium mirrors are good reflectors, being able to compete even with those made out of asteroidal nickel. Atomized aluminium can also be used as a good fuel, when burned in oxygen.

Aluminum mirrors are good reflectors and could compete with those plated from asteroidal nickel. Atomized aluminum powder also makes a good fuel when burned with oxygen. Indeed, it's the fuel source of the Space Shuttle's solid boosters. On the Moon, it could become the primary fuel source for chemical rocketry of material to and from orbit (though we would need a different kind of rocket since the Space Shuttle solid boosters use aluminum in a kind of rocket we can't make from lunar materials).

There is also a disadvantage. This metal expands and contracts with temperature much more than ordinary metals, creating a problem in creating large structures on the moon made out of aluminum, which would be exposed to extreme day/ night temperatures. That is also why the equipment used in lunar extraction of minerals is not made out of aluminum, and steel (an iron and carbon alloy) is better used for any metal structure.Iron (steel) is better used on the Moon and other such places for metal structures.

The Moon has concentrations of aluminum in an easy to process mineral form: anorthiteEven if on Earth the main aluminum ore is the bauxite (containing 25% aluminum), on the moon the most occurring mineral containing aluminum is the anorthite(20% aluminum) and it is possible and feasible to process it(the procent of anorthite in the lunar crust is important from 78% to 80% on the landsites of the Appolo16 mission).

Calcium

The extraction of aluminum anorthite,  would make calcium look only as a byproduct, the anorthite being a calcium-aluminum silicate CaAl₂Si₂O_8.Calcium is one of the most abundant elements in the lunar soil. Calcium and calcium oxides are useful in the production of ceramics, but calcium is also an excellent electrical conductor( it’s not used un Earth as such because it burns in contact with the atmospheric oxygen as all the metals found in his group of elements e.g. Magnesium in flashbulbs) in vacuum environments.

At [20C, 68F], calcium will conduct 16.7% more electricity than aluminum, and at [100C, 212F] it will conduct 21.6% more electricity through one centimeter length and one gram mass of the respective metal. Compared to copper, calcium will conduct two and a half times as much electricity at 20C, 68F, and 297% as much at 100C, 212F.”

Like copper, the calcium metal is easy to manipulate. It has half of aluminum’s density,  but it’s not good as a construction material because it is not strong at all. Calcium slowly sublimates in vacuum. Calcium doesn't melt until 845C (1553F).

Titanium

Titanium is a high strength metal. It offers more strength per unit weight than aluminium and it is used for military aircraft and missiles.

Titanium mineral, ilmenite, FeTiO3 (iron titanium oxide) is one of the most attractive economical resources available on the lunar surface. Ilmenite grains of high purity found in the lunar soil make the separation process easier. These ilmenite grains average 53% TiO2, 44% FeO, 2% MgO and 1% of impurities.

Although utile: TiO2(titanium dioxide) is more desirable, ilmenite is also considered to be a commercial ore for producing titanium which we consider to use in the process of building the space settlement. Ilmenite minerals also trap solar wind hydrogen very well, so that processing of ilmenite will also produce hydrogen, a rare element on the Moon which can be used on the space station in the combustion cells.

Ilmenite is not found in large quantities on Earth’s crust, but in lunar soil the purity and quantity  of this mineral is significant.

Iron

Iron is an often encountered metal source on the Moon. It is obtained in the processing of ilmenite (see titanium above). Free iron grains also exist, and they can be extracted in an easy manner, by using magnets.

The Lunar mineral composition is shown below:

Lunar Mineral Composition

Lunar Ice

Sunlight doesn’t reach the lunar poles, because of the moon’s inclination of the rotation axis, almost 1.6 degrees. The temperatures inside these craters are around 50K(-223 Centigrade or -370 Fahrenheit).

The south pole is a lot poorer in water than the north one(50% more than in the south pole).

The first estimative figures of hydrogen, which existed in water ice: 0.3 to1% in 5000 to 20000 square kilometers at the south pole and 10000 to 50000 square kilometers at the north pole. After looking deeper into this problem, a theoretical quantity of six billion metric tons of water is concentrated in a small number of lunar polar craters.

Of course almost pure water is expected to be found at a very low temperature, this giving an extremely interesting problem: mining ice water.

The material must be resistant in this cold situation,  but the properties of the material must be exceptional.

The mining surface must be heated before starting the mining. The mining of the material must be slow, and the vehicle and it’s attachments must be warmed also.

Another option is to enclose an area an to heat the water there, bring it to the state of vapor, and then collect it into pipes and transport it into tanks.

The south pole is permanently kept in shadow, but the north one isn’t. It has shadowed areas, and the options of mining sites (sunlit rims of a polar crater) are many.

c. Asteroid resources

While the Moon's gravity field is one-sixth that of Earth's, it is still enormously higher than that of an asteroid. This will make taking materials from asteroids a lot cheaper than launching them from the Moon. Still we must consider only bodies that have been nudged by the gravitational pull of nearby planets into orbits that cause them to enter the Earth's vicinity (Near-Earth Objects (NEOs)). In terms of orbital elements, NEOs are asteroids and comets with a perihelion  distance less than 1.3 times the Earth-Sun distance. However, the vast majority of NEOs are asteroids, called Near-Earth Asteroids (NEAs). NEAs are subdivided into the Aten, Apollo, and Amor groups. The ones of interest for the construction of the orbital colony are those that have a high metal content and a high volatile content. The carbonaceous chondrites fit this description. These asteroids can contain sizable amounts of high quality metal ore, and significant deposits of volatile compounds, particularly water and carbon. The C1 and C2 types of carbonaceous chondrites are particularly suitable for our purposes and will be one of the main sources of building materials. The composition of the C1 and C2 types are summarized below.

Asteroid composition

3. Material exploiting and processing

The different kinds of raw materials needed for building the space settlement will have to be efficiently exploited and processed with minimum effort and energy consume. That is why we must consider only the most reliable technologies for obtaining metals from lunar and asteroid ores.   

a. Magnetic separation

Magnetic separation is a procedure used to obtain free metals from the ores found on asteroids and other celestial bodies.

Asteroids are rich in free nickel-iron rocks, which are also found on the surface of the Moon but in smaller quantities (which are traces of old asteroid impacts).

The process is approximately the same on both sources (moon and asteroid):

The first step is the grinding of the rock, and then the smaller particles are put through magnetic fields to separate de silicates from the nickel-iron grains. This last procedure, after repeating this last process the nickel iron grains achieves a high percentage of purity. Material is dropped onto magnetic drums. The silicates and weakly magnetic particles don’t stick to the drums, but the magnetic ones do until they are scraped off the magnet. The centrifugal grinder consists of a very rapidly spinning wheel that accelerates material down its spikes against an impact surface. The impurities remaining on the magnet surface are eliminated from the metal particles stuck on the magnets’ surface.

An efficient detail is that of giving the drums a high speed, high enough to flatten metal granules on impact. The centrifugal grinding must be used again before advancing and repeating the process of magnetic separation. Most of the shattered impurities will be small quantities of little silicate granules which could be sieved out.

This method can also be used to separate minerals with weak magnetic proprieties. This is an adaptation of  the process used on Earth, the difference being that a lower gravity found in space could determine a greater magnetic beneficiation.

Magnetic permeability

There are three types of magnetic proprieties.

Paramagnetic materials are those who attract the lines of a magnetic field, become polarized, and in consequence attracted. Those who repel the lines are called diamagnetic, and the third type of substance is the one who isn’t affected by magnetic lines. Paramagnetic materials can also be Ferro-magnetic or feebly magnetic.

In conclusion, the main principle of magnetic separation is the different magnetic permeability of minerals.

b. Thermal separation

This process is used in extracting volatiles elements and compounds from asteroids, where they are often found.

The solar oven is a chamber heated by means of solar heat. At high temperatures, the volatiles leave the material. In space conditions (windless space and no gravity), the oven mirrors can be made out of aluminum foil. The gasses are captured and guided into pipes who take them into chambers situated in low temperatures (space shadow, no sun). The chambers are put in a series, the farthest being the coldest one. In this manner water is able to condense in the first one, and the other gasses float and condense in the next ones.

In this way, we can obtain rocket fuel, in the form of oxygen and hydrogen separated from the gaseous mixture. It is also possible to obtain a hydrogen-carbon compound which is used as fuel, methane gas (CH₄): C + 2H₂ => CH₄.

The chambers used for the storage of low temperature solid gasses can be manufactured from the free nickel iron metal. The solar oven can be used to melt the metals in space. The tanks don’t need a high pressure, because the gasses are frozen solid in space.

c. Electrostatic separation

The first step in this type of separation is the separation of material pieces of the same size. This separation can be done by sieving by screens, and consequently passed through grinders, and sieved for a second time, in order to achieve uniformity.

The second step is using static electricity, charging the mineral grains and separating them by passing them through an electric field. This separation method is using the principle that different minerals have different electrostatic affinities, more exactly each mineral absorbs a different quantity of charge, depending on structure and composition. The material must pass this process for a few times, for obtaining a better separation of the minerals. This process doesn’t alter the mineral in any way. It offers only separation.

The electrical charge can be made in several methods:

• Charging the sieving screen
• Charging any surface that they come in contact to
• Using an electron beam as they fall

This choice must be made depending on what type on mineral we wish to separate, each mineral having a different response to different methods and working conditions.

The separated material is put aside in special compartments. It is called the “concentrate”, and the output is called “tailing”.

This type of separation is used in obtaining the separation of not only one mineral. We can use more than one compartment, and the streaming material will split in multiple streams, depending on the charge they possess and the type on interaction with the magnetic field.

Space vacuum increases the speed and rate of this process, lacking wind, and giving the possibility of creating stronger energetic fields (10 times stronger) than in Earth’s Atmosphere. Also the lack of moisture is a factor that speeds up this process. Water makes the grains stick together, and also changes the minerals’ electrical properties (conductivity),   reducing differences between minerals (This process on Earth is preceded by roasting the mineral probe). The low gravity on the Moon (1/6 of Earth’s gravity) also helps the separation process by decreasing the speed of the separated grains’ fall and as such, increasing the speed of the separation.

For the Solar Power Satellite (SPS), the General Dynamics report states: "The presence of large quantities of fine glass particles in lunar regolith is particularly relevant to the recommended use of foamed glass as primary structure for the SPS solar array and antennas. Foamed glass is commercially manufactured from fine particles of ground glass by the addition of small quantities of foaming agents and the application of heat. Thus, beneficiation of lunar regolith to recover the large amounts of fine glass particles may permit the direct production of all of the foamed glass needed for the SPS with few or no intermediate steps required to prepare the glass for foaming."

This method can also be applied building the space settlement.

d. Electrophoresis

Electrophoresis for the separation of minerals can be achieved only in no gravity conditions. It is a simple process, but it’s performances are better than the electrostatic one, but also a much slower one.

The schematic shown below explains how the process works.

There is a chamber filled with a fluid. An electric field is created between the two opposite walls by charging them with different charges: one positive, and one negative. The mineral probe is put into the fluid. The probe’s grains will float facing the no gravity conditions. The electric charges created by the electric field passing through the two opposite walls are collected by the minerals’ molecules. In this manner the minerals will migrate through the fluid to the position between other types of minerals (two isoelectric materials a higher and a lower one). Each mineral forms a plane of substance parallel to the walls and to the other minerals’ planes.

Earth’s gravity creates a large disadvantage, because it creates convection currents, and at the same time, gravitational settling. This was the reason why some electrophoretic experiments which were unsuccesful on Earth have been succeded in space, thanks to the lack of gravity.

One of the most exploitable properties of lunar soil is the wide range of isoelectric points of the minerals. No two minerals have the same isoelectric point or, in practically all cases, even similar isoelectric points. This property of lunar soil makes it an ideal candidate for electrophoretic separation; it means that for a given suspension material each mineral phase will separate and form a discrete band within the electrophoretic chamber.

e. Electrolysis of minerals

Electrolysis is the procedure decomposing a material in compounds, using a voltage. Electrolysis of minerals separated metal, oxygen, and/or their oxides. There are two electrodes: the anode (+) where the oxidation reaction occurs, and the cathode (-),

where the reduction reaction occurs.

The selection of electrodes and voltages and even additives are extremely important in order to achieve the wanted result. The ore is melted. The electrodes are put in. The metals go to the negative electrode (cathode) and oxygen to the anode (+).

The process can be written in the following way for ilmenite.

Total electrolysis of ilmenite: FeTiO₃

         3* |   anode (+)          O^2- => O⁰ (gas)+2e^- [oxidation]

                 cathode (-) Fe²⁺ +2e^- => Fe⁰ (liquid)[reduction]

                                         Ti ⁴⁺ +4e^- => Ti⁰  (solid)[reduction]

     Total process:

      3O^2- + Fe²⁺ + Ti⁴⁺   => 3O⁰ + Fe⁰ + Ti⁰

Aluminum, calcium, sodium , potassium and manganese will be liberated in vapor form, iron and silicium may be liquid or solid depending on the bath’s temperature, and

 titanium will be deposited under a solid form.

f. Vacuum distillation

This is a process strongly related to the electrolysis. The resultant metals in the process of electrolysis are heated to the different liquefaction or boiling point to extract each one separately.

By means of the last two processes oxygen can be extracted from lunar soil.

g. Glass fabrication

Lunar and asteroidal materials can be used in the process of obtaining a great variety of glass structures: fiberglass, foamed glass, clear glass, and also materials used for the fabrication of walls, pipes and other construction materials.

On the lunar surface natural glass particles are more often found than on Earth’s surface, because of the lack of water (H₂O) existing on our planet’s satellite. Lunar glass can be separated from other minerals by using electrostatic beneficiation.

Glass produced on earth is heavily contaminated by water vapor in the atmosphere, this contributing to the  low mechanical proprieties (britteling material, weak, and non resistant to shocks). This fact has lead to research concerning “anhydrous glass”, manufactured in the absence of water and which can be used in structures thanks to it’s improved mechanical proprieties.

Foamed glass is the highest resistant glass manufactured yet, and whose mechanical proprieties make it usable in space construction.

It’s fabrication scheme can be seen below:

Source: General Dynamics/Convair report for NASA and US Dept. of Energy on making    solar power satellites from lunar materials. Slightly reworded by Mark Prado

Strong mechanically glass-ceramics can be manufactured by using FeO(from the lunar soils rich in this substance). The glass has a dark colour. Colourless glass can be manufactured by using anorthite (CaTiO₃), with small additions of CaO or SiO₂. This kind of glass is resistant to large changes of temperature, the expansion coefficient is a lot less than in other types of glasses.

Glasses,  will be produced in the process of high speed cooling of  melted material, to create a different crystalline structure. In order to obtain a higher resistant glass foamed glass will be reinforced with nickel-iron steel, so that structures made out of this material could support a wider range of tension and compression. To withstand radiation, Pb²⁺ ions must be introduced in the process of glass fabrication.

h. Generating plastic and rubber

Laminates and rubber are essential building materials, without which the interior layout of the Settlement will be impossible to achieve. Both plastics and rubber are light, flexible and durable, improving the functionality and esthetics of the different compartments of the Colony.

There are two possibilities for generating rubber and plastic. The first one is using Carbon to create carbochain polymers; the second involves the processing of Silicon. Both methods have their advantages and disadvantages.

The Carbon based products are much more durable and flexible than those based on Silicon. Transforming Carbon and Carbon composites into plastic entails a long row of chemical processes, each of them with its own coefficient of efficiency. The major impediment is the lack of organic matter (which is known to contain great amounts of Carbon) on both Moon and NEOs. The insignificant amounts of Carbon found on the Carbonaceous Chondrite Class C2 asteroids are not a reliable source of raw materials for this kind of composites. As carrying organic matter from Earth isn’t an economically feasible option, we must consider creating rubber and plastic from Silicon based composites. Still small amounts of Carbon and water vapors can be used in generating the strictly needed high endurance rubbers. The process is shown below:

The resulted hydrocarbon composite contains  

   is the most suitable hydrocarbon for generating rubber and plastic. Therefore we must disassociate it from the rest of the mixture.

We can resume the whole chemical process to a more simple form:

Hydrocarbon mixture

The separation of the different hydrocarbons contained in the raw composite can be achieved by liquefying the initial mixture and than distilling it.

As we said, the most efficient way of creating plastic and rubber is obtaining them from Silicon, which can be extracted in huge quantities from both Moon and NEOs. More exactly, we will use silanes, which are analogous to hydrocarbons. As the basic building block of hydrocarbons is the methane (CH₄), that for silanes is silane (SiH₄). The main structure of the compounds will be SiH₃-(SiH₂)_n-SiH₃.

Silicons can be prepared in more than one way. The most commonly used method is reacting chlorsilane with water. After condensing, the obtained hydroxyl intermediate will form a polymer –type structure.

Alkoxysilanes, chlorosilanes and other silicone precursors can also be used for obtaining polymer type structures. The chemical process involves the reaction of elemental silicone with an alkyl halide: Si + RX → R_nSiX_4-n.

Raw silicon rubbers will be cured using different peroxides. For improving the poor tensile strength of silicones we will use reinforce fillers, such as silica in the form of silica fume or even carbon black. It is known that silicones have better fire resistant properties than other types of rubbers. Still we can improve this quality by adding flame retardants such as aluminium trihydrate or zinc compounds. Heat stability can be achieved by adding ferric oxides. As we must also consider esthetics, different organometallic compounds can be used as pigments.

The main advantages of this type of rubbers are the good thermal conductivity, the ability to repel water, the constancy of properties on a large temperature scale, the excellent resistance to oxygen, ozone and sunlight, the good electrical insulation, the low toxicity and low chemical reactivity, the good flexibility and the anti-adhesive properties. The good thermal stability does not allow properties such as volume, resistivity, power factor and dielectric strength to be affected by the different changes in temperature. Silicons are flexible at low temperatures and tend to stiffen at higher temperatures.

Silicons will have multiple uses onboard the Settlement, including applications in mechanical engineering, electrical engineering and medicine.

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