The collection and transportation
of heat:
The components and systems depend on the power density, the level of power, and
the degree of temperature requirements for collection and transportation of
heat. Mechanical
elements for TCS:
In general, collection of the heat dispersed by any type of device through its fixation
elements and baseplate. With increasing power dissipation, the complete
baseplate has to be in contact with the spacecraft panel. The transfer of heat depends
on the parameters such as the surface finish, interface pressure, the types of
materials involved in difficult to control and quantify. The way to increasing
the conductivity through the interface surfaces include the use of synthetic
mats or metallic, and the application of the thermal grease. This last solution
has to be used with care because of the obvious potential contamination of
difficulties. Heat pipes:
The heat pipe is a device that allows efficient transport for thermal energy.
It consists of a sealed metal tube with a capillary structure on the inside, and
filled with a suitable working fluid. Heat is absorbed at one end by the
evaporation of the fluid, and released at the other end by condensation of the
vapour. The liquid is transported again back to the evaporator by the capillary
forces. The heat pipes commonly used on the spacecraft
are an aluminium or ammonia type that allows optimal temperature control in the
range of 0 to 40°C. The quantity of the heat transported by the pipe and it
determined by its dimensions and design, the equivalent thermal conductance is
constant and leading to the stable Conductance Heat Pipe. Cooling loops:
For greater power dissipation or more stringent temperature requirements, other
heat collection and transportation systems can be used. Various kinds of fluid
loops have been proposed and applied to cope with these situations. In single-phase loops, the refrigerating
liquid absorbs the heat from the heat dispersing items by increasing its
temperature, and transports it to the heat rejecting device where the fluid is
cooled down. A mechanical pump is essential to provide the hydraulic energy
needed for this process. The process of cooling loops, it has four types. There
are Single phase loop, two phase capillary loop, two phase hybrid loop, and mechanically
assisted two phase loop. Thermo electric
heat pumps:
Heat pumps have reversible mechanism that able to transfer the thermal energy
from lower to higher temperature bodies using extra source of energy. Only this
kind of heat pumps have been used in space, the basic feature of this pump is
the Peltier element, and it’s the connection through the metallic tab of type p
and type n semiconductor devices.
These kinds of heat pumps are normally
used for the control of tight temperature of the low power devices and the facilities
used for microgravity equipments. Many systems have been used and developed for
both manned and unmanned spacecraft.
The designing
phase:
some parameters used in the designing process of Thermal Control System. There
are,
the environment used for
spacecraft has to operate
the total amount of heat dispersed
on board the spacecraft
the distribution of the thermal dispersed
inside the spacecraft
the temperature of heat
requirements of the differ equipment items
the configuration of the spacecraft,
and its verification and reliability requirements
The
environment of Thermal control techniques:
for all the spacecraft, the incoming energy from the Sun and the heat send outs
to deep space are usually the major environmental interactions. Depends on the
spacecraft's attitude and orbit, other parameters can have a major influence on
the thermal control design. For sample, the type of the attitude stabilization
used can affect the TCS design. In general, spin stabilization is more benign,
as the rotation cause to an average of the flux inputs. Three axis stabilized
spacecraft needs a greater protection against short term differs in energy
input from the Earth or Sun.
Special
orbits
The design of missions for the long term observation of the particular phenomena
need a fixed, stable environment and tend to make use of stable orbits needing
low station keeping requirements, far away from any celestial body. Scientific
spacecraft like as scientific mission of SOHO and COBRAS SAMBA, are typical
kind of the class of mission. The spacecraft are Sun pointed and have one side fixed
illuminated and all other faces are opened to deep space. Serially, the Thermal
Control System design can be optimized likely to be easily and there are very
special temperature requirements for insufficient electrical power for the
heaters.
Deep space
and planetary exploration:
This class of mission includes most number of various sub scenarios depending
on the particular celestial body. In General, the mission duration and the need
for high intensive thermal conditions, like as cruises it’s very close or far
away from the low orbiting of the sun and very hot or very cold celestial
bodies and descents through the hostile of atmospheres, and survival in the high
intensive environments on the surfaces of the bodies visited. The challenge for
the Thermal control system is to provide enough rejection of heat capability
during the hot acting parts and still the survive the cold inactive ones. The
major problem is often the provision of the power and energy required for that
survival part.
The use of
the Thermal Control System is controlled by the technical or functional
limitations and compatible sources of all the devices used for a spacecraft
and, in the case of controlled missions, by the need to supply the crew with
suitable working surroundings. Almost all complicated equipment has specified
temperature ranges in which it will function rightly. Thermal Control System is
to maintain the temperature and stability of temperature of every item in the
spacecraft within those predefined limits for all mission parts and it using a
small amount of spacecraft resources.
The
environmental Interaction:
The outer layer of a spacecraft need secure from the local environment and
improved interaction with it, it involves:
·The increment of reduction
absorbed by environmental fluxes.
·The increment or reduction
of heat losses to the environment.
Heat
provision and storage:
In some of cases, to maintain the good temperature level and it has to be supplied
AND/OR a proper storage capability of heat has to be informed.
Heat
collection:
In many of cases, dispersed the heat has to be removed from the device in which
it is generated to avoid an unwanted increment in the unit's, AND/OR the
spacecraft's temperature.
Heat
transport:
In general, it is impossible to avoid the heat directly where it is generated,
and right means have to be used to pass the heat from the collection equipment
to the radiating equipment.
Heat
rejection:
The collection and transportation of heat has to be avoided at a suitable temperature
to a heat sink, which is usually the surrounding of the space environment. The
avoidable temperature depends on the amount of heat involved, the temperature
to be controlled and the temperature of the environment into which the device
send outs the heat.
The Role of Thermal Control Techniques in Robotic Spacecraft
Introduction:
The use of the Thermal Control System is controlled by the technical or functional limitations and compatible sources of all the devices used for a spacecraft and, in the case of controlled missions, by the need to supply the crew with suitable working surroundings. Almost all complicated equipment has specified temperature ranges in which it will function rightly. Thermal Control System is to maintain the temperature and stability of temperature of every item in the spacecraft within those predefined limits for all mission parts and it using a small amount of spacecraft resources.
The environmental Interaction:
The outer layer of a spacecraft need secure from the local environment and improved interaction with it, it involves:
The increment of reduction absorbed by environmental fluxes.
The increment or reduction of heat losses to the environment.
Heat provision and storage:
In some of cases, to maintain the good temperature level and it has to be provided AND/OR a suitable storage capability of heat has to be informed.
Heat collection:
In many of cases, dispersed the heat has to be removed from the device in which it is generated to avoid an undesirable increment in the unit's, AND/OR the spacecraft's temperature.
Heat transport:
In general, it is impossible to avoid the heat directly where it is generated, and appropriate means have to be used to pass the heat from the collection equipment to the radiating equipment.
Heat rejection:
The heat collected and transported has to be avoided at an appropriate temperature to a heat sink, which is usually the surrounding the space environment. The avoidable temperature depends on the amount of heat involved, the temperature to be controlled and the temperature of the environment into which the device radiates the heat.
In 1985, Enron was constructed the Natural Gas Company in Houston. Beginning Enron was a manager of interstate gas pipelines in the country. In 1989, Enron distinguished into the trading energy related investments. After some of years, Enron becomes the largest trader of energy in US and the UK. In 1994, Enron also successful in electricity in US as well. Enron goes future with a process to reconstruct its corporate look to a new, stylish-looking, more modern, and environmentally conscious type of company in 1997. It establishes a new corporate symbol and manages Zond Corporation; it is one of the best developers of wind energy power. The purchase leads to the control of the Renewable Energy Corporation of Enron. Enron also enters with new weather derivative products in addition to trade and energy. Enron is already buying and selling the pulp, cellulose, paper, plastics, metals, fertilizer and bandwidth.
Enron agrees to pay 100 million dollars over the period of 30 years for rights to new ballpark of Houston now it is called as the Enron Field. Enron Energy Services made its first billion dollar transaction with the Suiza Foods. After that Enron creates the first global Web based commodity trading site and also launches Enron Online. In 2000, a Fortune magazine congratulates Enron for the Most Innovative Company in America and it ranked 24th among 100 of best employers in the country. In the beginning of the same year, Enron ranked the 6th largest energy company in the world. In 2000, Enron and its new strategic investors are America Online and IBM launched the New Power Company, it is the first energy service provider of the country for small businesses and residential in US energy markets. After one year, Enron chief executive officer Jeff Skilling resigns his position. Former CEO and Chairman Ken Lay returns to their position atop Enron. In 2001, Enron reports 638 million dollars of third quarter of loss and announces 1.2 billion dollars reduced in shareholder impartial price, partly related to unlike partnerships run by its chief financial officer, Andrew Fastow. After few days Enron acknowledges that the Securities and Exchange Commission made an inquiry into a possible conflict of interest related to the company's operations. After few days later, Enron broke its relationship with Fastow's partnership. At the same year, Enron borrows more than 3 billion dollars, its boost the confidence of the customers and investors. After few days, Enron announces that the SEC inquiry has been advanced to the investigation. At the month of November, Enron obtains yet another 1 billion dollars in new loans for using its pipelines as collateral. After few days, the price of Enron's stock drops below 10 dollars a share down on December. The reports say that the collapse and stampede of Enron's share money. Enron's corporation was now firmly on the way to its end.
Enron announces that it made a 638 million dollars loss during fiscal year of 2001. At the same month, Andrew Fastow is forcing out to the chief financial officer because of his involvement into questionable business partnerships and transactions. Securities and Exchange Commission standard its questions into Enron's dealings into a formal investigation on Enron's accounting records and business transactions. Suddenly, Enron reconsider its financial statements. The revision leads to reduced earnings by an additional 586 million dollars for four years, due to losses with partnerships.
At the same month, Dynegy, smaller energy company, offers a plan for Enron and proposes a buy out of the Enron Company for 10 billion dollars in stock. Dynegy also agrees to pay 13 billion dollars more for Enron's debts. Finally, Enron agree with Dynegy.
In December, 2001 Enron makes bankruptcy. This is big Chapter of 11 bankruptcy case in the United States history. Its two major investors, J.P Morgan and Citibank, that the two banks provide 1.5 billion dollars in short term emergency funding. Enron announces that it will immediately layoff 4,000 employees from its headquarters. That the time many employees had lost up to 90% of their retirement savings as Enron's shares plunged.
At the same month Enron discloses that it paid more than 50 million dollars to its traders for leaving Enron as it intended to merge with Dynegy. Another process of Enron's revelations, the public finds out that Enron paid 55 million dollars in bonuses for bankruptcy. In December, Amalgamated Bank of New York, The bank claims that Enron's officials spitefully inflated the company's stock value, fraudulently gaining the most of money for themselves, using false financial records. At the same month, The US Department of Labor launches an inquiry into Enron’s mismanage of employee retirement pensions. The percentage of 70 to 90 of former Enron's employees lost their retirement savings in the company’s stock crash. After few days, the SEC begins investigation into the role played by Enron's independent auditors. The CEO of Arthur Andersen investigate that Enron might have committed the illegal acts in financial accounting practices; this statement leads to a criminal probation by the US Department of Justice.
In January, Enron and Dynegy, both of companies settle their dispute. Enron lost the legal battle and it turns over the ownership over the Northern Natural Gas Pipeline to Dynergy. The Department of Justice launches a criminal probation of Enron. Attorney General John Ashcroft and his Chief staff, David Ayres, refuse to participate in the investigation because Enron was a major contributor Ashcroft's failed bid.
Many observers blame the recent Enron's collapse on the free markets and deregulation and top management walking off with thousands of millions of dollars while employees lose their jobs, and customers get to look forward to more rolling blackouts and investors lose millions of dollars.
