Sunday, August 2, 2009

Physics Research Paper

In order for an astronaut to be able to ‘live’ in space, the environment in which they occupy must be similar to that of their original location, Earth. The Controlled Ecological Life Support System (CELSS) of a human bearing space craft consists of many aspects.

The seven main different aspects are:
• Atmosphere Control, Supply and Recycling
• Water
• Temperature Control
• Light
• Food
• Waste Removal
• Fire Protection

Atmosphere Control, Supply and Recycling
Within the space vessel the following is needed for a crew to survive:
• An atmosphere similar to Earth – achieved by using liquid oxygen and nitrogen tanks to produce a gas mixture consisting of approx. 78% oxygen and 22% nitrogen at the correct pressure of 14lbs/in2 throughout the ship.
• Breathed out carbon dioxide removed - by chemically using soda lime. The carbon dioxide is trapped in the soda lime by a chemical reaction and removed from the air.
• Contaminating or trace gases removed - trace odours, dust and volatile chemicals from leaks, spills and out gassing are removed using Filters and charcoal canisters
• Normal humid environment – a cabin heat exchanger is employed to separate water from the air using a centrifugal force

Water is created using Fuel Cells (Refer to Power – Page ??). It is then passed through a hydrogen separator to remove any excess hydrogen that may reside in the newly formed water. The water is then stored in pressurised tanks and can be used for various activities. Water is continuously being created, and any excess water is dumped overboard.

Temperature Control
As inside the vessel, the electronics provide enough heat, the temperature control system must be able to carry out the following two tasks:
• Distribute the heat so that sections of the ship do not freeze from the cold of space
• Get rid of the excess heat
The two ways this can be achieved is by using passive or active methods.
Passive methods are generally very simple require very little maintenance however do only carry a small heat load. These include the use of insulation and electrical heaters.
Active methods are much more complex, require frequent maintenance but can bear many times greater heat load than Passive methods. These more effective methods include the use of Heat Sinks (Cold Plates), Heat Exchangers (Fluid Cooling), Radiators and ammonia boilers.

The space vehicle in which the astronauts reside must be very well lit. Taking the American Space Shuttle into perspective, we see that fluorescent floodlights are used in the crew compartment, external floodlights are used to light the cargo bay and the control panel of the ship is backlit to improve viewing ease.

Food must be very carefully stored to prevent rotting or other type of wasting. The most common forms of storage that would be feasible and used in such a vehicle are dehydration, low-moisture and heat stabilised. These would then require a way to reverse the process and also require the following resources:
• food storage compartments
• food warmers
• a food preparation area with warm and cold water outlets
• metal trays to hold utensils and food in place

Waste Removal
Removal of debris and potentially dangerous items is an important factor up in space. Various different waste collection methods are available, though some better than others. An extremely effective method of waste removal includes the separation of liquids from the solids. The liquids are then discarded overboard while the solids are brought back to Earth where they are destroyed. This is effective because not only does it work for objects such as wipes and detergents etc, it can also be employed as a way to deal with toilet waste.

Fire Protection
Fire over all things is probably the most dangerous possible problem while in space. This means that the vehicle must be equip with not only extinguishing utilities, but with various methods of prevention.
A possible system to deal with fire could include:
• area smoke detectors
• smoke detectors in each rack of electrical equipment
• alarms and warning lights
• non-toxic portable fire extinguishers
• personal breathing apparatus - mask and oxygen bottle for each crew member
After a fire occurs, the atmosphere control system works to remove any remaining particles of dust or smoke that may be left in the air.

The crew of a space craft require the ability to talk to both the mission centre on Earth and each other while carrying out tasks on the outside of the vessel or in payload modules.

To communicate to the Earth from the vessel, and also the opposite, communication satellites situated approximately 35,700 km above the earth are used. These tracking satellites relay the signal between a very tall radio transmitting/receiving tower and the space craft, which can be in two possible bandwidths:
• S-Band – Used for voice, commands, telemetry and data files
• Ku-Band – High bandwidth channel used for video and the transfer of two-way data files

In order to communicate with the other members of the crew, a UHF frequency can be used to transmit and receive voice. A spacewalker’s spacesuit is fitted with a personal headset and microphone enabling communication between the shuttle and him/herself. As in the American Space Shuttle, plug-in audio terminals can be located throughout the crew compartment making it much easier to communicate with other astronauts on opposite sides of a ship.

Energy Sources
The two types of energy sources that spring to mind when a space ship is mentioned would have to be, solar energy and generated power.

Solar energy are commonly used in applications such as satellites and telescopes which are aimed to stay in space for a long period of time and are frequently moving in the sun’s path. By being able to charge batteries using solar energy, a satellite can function a set period of time away from direct contact of the sun.
However when it comes to space vehicles, a guarantee cannot be made that the sun will be frequently encountered and therefore solar power would be an unreliable energy source

Generated power using devices such as fuel cells is more effective for such an application and has many other uses. Fuel cells are made of:
• The anode side – negative post which conducts the freed electrons from the hydrogen so they can be used on an external circuit
• The cathode side – positive post which collects and conducts electrons back from the external circuit. Here they recombine with the hydrogen ions and the oxygen molecules to form the water used on the vessel.
• The electrolyte – A specially treated material used and placed between the cathode and anode sides to prevent the conduction of electrons, forcing them to take an external course
• The catalyst – A special material used to speed up the reaction of the oxygen and hydrogen. Usually made of a very thin coat of platinum powder on carbon paper or cloth. The surface is made coarse so that the maximum surface area possible is in contact with the hydrogen or oxygen.
They are grouped in a stack of cells (similar to a battery) and create approximately 0.7 volts each. Although this is a small figure, when hundreds of fuels cells are grouped together, a large voltage can be attained.

Computers and Navigation
A space ship is known by most people as a very complex piece of equipment; however the computers used on such a vessel are not as high tech and up to date as a great deal of people think.

Issues such as solar wind and high energy particles come into play when up in outer space. A modern day processor has tracks so thin that if a high energy particle just managed to pass through it, chances are it would totally break a track and render the computer unusable. To accommodate for such interferences, computers are required to contain appropriate parts which lessen the chances of damage. These include older, slower and larger processors, low density memory chips, and other similar hardware.

In space travel, a single error can lead to disaster. This is why onboard such vehicles the use of multiple computers and the utilisation of methods such as fuzzy logic are important. These computers monitor equipment and control critical adjustments during launch and landing.

They also perform tasks such as:
• Operation of the craft
• Interface with the crew (Using laptops)
• Caution and warning systems
• Data acquisition and processing from conducted experiments
• Flight manoeuvres

The navigation of the craft is done mainly by the computers, however the information needed to fly the vessel is fed to the computers by the crew. Global positioning devices are also used to recognise where the vessel is and an approximate speed of travel. The use of gyroscopes comes in very useful when trying to identify the direction of heading.

A rocket is a device which is based on the principle by Newton that “to every action there is an equal and opposite reaction”. A rocket is designed to throw a large mass in one direction and benefit from the reaction force in the opposite direction.

The high pressure gas that a rocket fires out in one direction can be seen as the mass. It comes from the weight of the fuel that the rocket burns. Even though the fuel changes in form from a liquid or solid to a gas, its mass does not change. This burning process causes the gas to expand and shoot out at an extremely high velocity (between 8000 and 16000 km/h).

Single-stage Rockets
These types of rockets are very commonly used on missiles type objects. They are simple rockets do not go through more than 1 stage of fire. The two different types of single stage rockets are solid-fuel and liquid-fuel.

Solid-fuel Rockets
Solid fuel rockets were designed with a very simple concept behind them. A rocket the burns very quickly but not explode. The fuel is lined around the edges of the cylindrical rocket with a tube drilled down the middle. When the fuel is ignited it burns away the fuel from the centre towards the outside casing until it is all exausted.

These solid fuel rockets have 3 main advantages:
• Simple
• Low cost
• Safe compared to many others
But also have 2 disadvantages
• Thrust cannot be controlled.
• Once ignited, the engine cannot be stopped or restarted.
These disadvantages allow us to see why these types of rockets are used in short term applications such as missiles or booster systems.

Liquid-fuel Rockets
Liquid fuel rockets work in a similar way as solid fuel rockets. A solid fuel rocket burns a solid fuel and an oxidiser, where a liquid fuel rocket burns a liquid fuel and an oxidiser. However they are no where near as simple as solid fuel rockets. They require a pressurised gas feed for the carry of fuel and oxidiser to the burning chamber, piping to cool the engine, and are required to carry the oxidiser as well as the fuel onboard the rocket. A real modern liquid bipropellant engine has thousands of piping connections carrying various cooling, fuelling, or lubricating fluids.
Liquid Fuel Rockets have 4 important advantages:
• Most powerful type of rocket in terms of gross thrust
• Can be built with many variable factors
• Level of thrust can be controlled
• Can last much longer than Solid fuel rockets
However they also have 2 major disadvantages:
• Extremely intricate and complex, have a large window for error
• Nitric acid used onboard is extremely corrosive and dangerous

Multistage rockets
Multistage rockets were developed with one thing in mind, efficiency. The main principle was to discard what had been used to minimise weight and increase overall speed. To do this, the rocket is split into many ‘stages’. These stages can be either solid fuelled or liquid fuelled. By jettisoning the used sections, the weight of the rocket is decreased and the mass ratio of the rocket is increased. To get the payload to its desired height in the most efficient manner, it is better to raise the propellant weight ratio by discarding unnecessary parts one after the other, not to lose reliability by making the system too complicated. Most rockets these days are built on a 2 or 3 stage design. Multistage rockets were used in the Mercury, Gemini, and Apollo programs as well as the current Space Shuttle.

Cluster Rockets
Developing a large rocket engine powerful enough to soli lift a rocket is quite an expensive process. A more cost effective and secure method of thrust is brought by through the use of cluster rockets. These rockets are basically a group of many small engines that work together to lift the craft. The engines used can be previous designs from existing rockets which cuts costs and time in development. The main advantage is that if one of the 20+ engines fails, the flight is not disrupted and can continue as normal. Another advantage includes the fact that only one fuel tank is required and shared among the engines, thus making the craft lighter than a multistage rocket.

Solid Fuel
The fuel used in a solid fuel rocket has to follow one main principle, to burn very fast but not explode. A very simple fast burning compound can be made by taking gun powder and decreasing its burning speed (explosiveness). This sounds quite obvious and is used as a common fuel in home made fireworks. Perfect examples of solid fuel rockets are the 2 SRB’s (solid rocket boosters) used on the American Space Shuttle. These have a much more technical mix of chemicals compared to the gun powder formula. The ingredients of the fuel are essential for performance and other special needs such as burn time and thrust.

The SRB’s contain the following mixture as a fuel (percentages by weight):
• 69.6% - Ammonium perchlorate (oxidizer)
• 16% - Aluminium (fuel)
• 0.4% - Iron oxide (a catalyst)
• 12.04% - A polymer (a binder that holds the mixture together)
• 1.96% - An epoxy curing agent
This mixture burns at approximately 4.2 tonnes per second! Together the SRB’s contain about 1 million kg of fuel mixture and provide a thrust of 2.41 million kg (23.4 million N)!!

Liquid Fuel
In most liquid-propellant rocket engines, a fuel and an oxidiser is pumped into a chamber where it is burned and forced out one end. But just exactly what is the fuel and oxidiser? There’s no one answer for fuel, because based on the needs and availability of chemicals it changes. However, the oxidiser used in most liquid fuelled rockets has been oxygen. It is one of the most abundant chemicals available on earth and works well as an oxidiser with many other chemicals chosen for the fuel.

The most common chemicals used for a fuel alongside liquid oxygen as the oxidiser are:
• Liquid hydrogen – Used currently in the Space Shuttle main engines
• Kerosene – Used in the Apollo Program for the Saturn V first stage boosters
• Alcohol – Used by the Germans in their V2 rockets
• Gasoline – Used by Goddard on his early rockets

However, as oxygen is not the only possible oxidiser, another recently used combination was Nitrogen tetroxide and monomethyl hydrazine in the Cassini flight system.

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