دبیران هدایت کننده تلسکوپ فضایی هابل تصمیم گرفته‌اند که برای مطالعه و بررسی بر روی جرم آسمانی بعدی که توسط این تلسکوپ صورت می گیرد از افراد عادی کمک بگیرند . علاقه‌مندان درسراسر این کره خاکی می توانند با انتخاب یکی از گزینه ها به این هدف تحقق بخشند. شش گزینه وجود دارد که فقط می توان یکی از آنها را انتخاب نمود.
ادامه مطلب ...«ماهواره بر سفیر2» موشک حامل ماهواره از کلاس سبک است که می‌تواند ماهواره‌ای سبک را در مدار LEO قرار دهد.
کمترین ارتفاع مدار آن 250 کیلومتر و ارتفاع اوج آن در حدود 500 کیلومتر است. «ماهواره بر سفیر2» دو مرحله‌ای بوده و در هر مرحله از موتورهای جداگانه استفاده شده است.
بخش محموله نیز بر روی مرحله دوم نصب می‌شود، محموله متشکل از ماهواره، آداپتور و فیرینگ است.
فیرینگ پوشش محافظ دو تکه‌ای است که بر روی مرحله دوم نصب شده و ماهواره را در بر می‌گیرد و از آن در برابر شرایط نامساعد محیطی محافظت می‌کند، این پوشش به محض خروج از جو باز شده و جدا می‌شود. طول «ماهواره بر سفیر2»در حدود 22 متر، قطر آن 1 / 25 متر و وزن آن بیش از 26 تن است.
ادامه مطلب ...اهداف پروژه ماهواره ملی امید:
از آنجایی که پروژه امید اولین گام علمی در عرصه بومی سازی فناوری ماهواره بوده است لذا مهمتر و پیچیده‌تر از دستیابی به یک محصول بومی، ایجاد بسترهای لازم برای این صنعت خواهد بود. بر این اساس شناسایی صنایع داخلی و ظرفیت‌های موجود در خصوص تجهیزات ساخت، مونتاژ و تست ماهواره و ایجاد بستر فعالیت‌های فضایی در شرکت‌های خصوصی بعنوان اهداف بسیار مهم این پروژه بوده است.
اهداف مهم پروژه امید در راستای بومی سازی صنعت ماهواره:
- شناسایی ظرفیت‌های موجود در خصوص تجهیزات ساخت، مونتاژ و تست ماهواره
- ایجاد بستر فعالیت‌های فضایی در شرکت‌های خصوصی
- ایجاد فضای عملیاتی ساخت و تست ماهواره در تعامل با موشک حامل داخلی
ادامه مطلب ...
Atomic Bomb
Atomic Bomb, powerful explosive nuclear weapon fueled by the splitting, or fission, of the nuclei of specific isotopes of uranium or plutonium in a chain reaction. The strength of the explosion created by an atomic bomb is on the order of the strength of the explosion that would be created by thousands of tons of TNT (see Trinitrotoluene).
An atomic bomb must provide enough mass of plutonium or uranium to reach critical mass, the mass at which the nuclear reactions going on inside the material can make up for the neutrons leaving the material through its outside surface. Usually the plutonium or uranium in a bomb is separated into parts so that critical mass is not reached until the bomb is set to explode. At that point, a set of chemical explosives or some other mechanism drives all the different pieces of uranium or plutonium together to produce a critical mass. After this occurs, there are enough neutrons bouncing around in the material to create a chain reaction of fissions. In the fission reactions, collisions between neutrons and uranium or plutonium atoms cause the atoms to split into pairs of nuclear fragments, releasing energy and more neutrons. Once the reactions begin, the neutrons released by each reaction hit other atoms and create more fission reactions until all the fissile material is exhausted or scattered ادامه مطلب ...
Microwave Oven
Microwave Oven, appliance that uses electromagnetic energy to heat and cook foods. A microwave oven uses microwaves, very short radio waves commonly employed in radar and satellite communications. When concentrated within a small space, these waves efficiently heat water and other substances within foods.
In a microwave oven, an electronic vacuum tube known as a magnetron produces an oscillating beam of microwaves. Before passing into the cooking space, the microwaves are sent through a fanlike set of spinning metal blades called a stirrer. The stirrer scatters the microwaves, dispersing them evenly within the oven, where they are absorbed by the food. Within the food the microwaves orient molecules, particularly water molecules, in a specific direction. The oscillating effect produced by the magnetron changes the orientation of the microwaves millions of times per second. The water molecules begin to vibrate as they undergo equally rapid changes in direction. This vibration produces heat, which in turn cooks the food.
Microwaves cook food rapidly and efficiently because, unlike conventional ovens, they heat only the food and not the air or the oven walls. The heat spreads within food by conduction (see Heat Transfer). Microwave ovens tend to cook moist food more quickly than dry foods, because there is more water to absorb the microwaves. However, microwaves cannot penetrate deeply into foods, sometimes making it difficult to cook thicker foods.
Microwaves pass through many types of glass, paper, ceramics, and plastics, making many containers composed of these materials good for holding food; microwave instructions detail exactly which containers are safe for microwave use. Metal containers are particularly unsuitable because they reflect microwaves and prevent food from cooking. Metal objects may also reflect microwaves back into the magnetron and cause damage. The door of the oven should always be securely closed and properly sealed to prevent escape of microwaves. Leakage of microwaves affects cooking efficiency and can pose a health hazard to anyone near the oven.
The discovery that microwaves could cook food was accidental. In 1945 Percy L. Spencer, a technician at the Raytheon Company, was experimenting with a magnetron designed to produce short radio waves for a radar system. Standing close to the magnetron, he noticed that a candy bar in his pocket melted even though he felt no heat. Raytheon developed this food-heating capacity and introduced the first microwave oven, then called a radar range, in the early 1950s. Although it was slow to catch on at first, the microwave oven has since grown steadily in popularity to its current status as a common household appliance.
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