To be read after Lesson 11

Space Cooling

A new method of cooling that can generate cryogenic tempera­tures of 200 °C below zero without the use of electricity and with almost no moving parts has been tested at the Jet Propulsion Labo­ratory in Pasadena, California. The refrigerator used for the pur­pose was recently tested to — 253 °C, only 20 degrees above absolute zero, the lowest possible temperature.

In space such cooling system could increase the life of future space station refuelling ports by cooling the large liquid-hydrogen fuel tanks which are likely to be in service.

In future earth applications it could be used for cooling hydro­gen-powered cars and planes, as well as for cooling superconduct­ing motors and computers.

According to the JPL (Jet Propulsion Laboratory) experts the key lies in the use of hydrides, materials that interact with hydro­gen. These materials absorb tremendous amounts of hydrogen gas at room temperature. The engineers of the JPL have taken advan­tage of this property to build a series of devices that act as compres­sors and provide a continuous cooling stream of liquid hydrogen.

The system saves weight in space since it can use direct solar heat instead of electricity from heavier, inefficient electric systems. Because it has so few moving parts and uses the same supply of gas in a closed cycle, it could operate for many decades. Because of its long potential lifetime, the system could be used to cool infrared sensors during missions to the other planets, which may take 10 years or more to complete.

The Propulsion Challenge¹

Magsails are a form of solar sails that use a completely different type of physical interaction with the Sun. Magsail is a simple loop (петля, контур) of high-temperature superconducting wire carry­ing a persistent² current. The charged particles in the solar wind are deflected³ by the magnetic field, producing thrust. Although the thrust density in the solar ion wind flux is 5,000 times less than the thrust density in the solar photon flux⁴, the mass of a solar sail goes directly with the area, whereas the mass of the magsail rises with the perimeter of the enclosed area.

The effective cross-sectional area of the magnetic field around the magsail is about a hundred times the physical area of the loop. As a result, preliminary calculations show the thrust-to-weight ra-

tio of a magsail can be an order of magnitude (порядок величины) better than a solar sail. Recent thermal balance calculations indi­cate that a properly Sun-shielded⁵ cable can be passively main­tained at a temperature of 65 К in space, well below the supercon­ducting transition point for many of the new high temperature su­perconductors.

Notes to the Text

Problem, difficulty, invitation to see which is better

Continuing

Cause to turn away from

Flow

Protected

Computer Graphics

Computer graphics are known to be pictures and drawings pro­duced by computers. A graphics program interprets the input pro­vided by the user and transports it into images that can be displayed on the screen, printed on paper or transferred to microfilm. In the process the computer uses hundreds of mathematical formulas to convert the bits of data into precise shapes and colours. Graphics can be developed for a variety of uses including illustrations, archi­tectural designs and detailed engineering drawings.

Mechanical engineering uses sophisticated programs for appli­cations in computer-aided design (CAD) and computer-aided manufacturing (CAM). In the car industry CAD software is used to develop, model and test car designs before the actual parts are made. This can save a lot of time and money.

Basically, computer graphics help users to understand complex information quickly by presenting it in more understandable and clearer visual forms. Electric engineers use computer graphics for designing circuits and in business it is possible to present informa­tion as graphics and diagrams. These are certain to be much more effective ways of communicating than lists of figures or long expla­nations.

Today, three-dimensional graphics along with colour and com­puter animation are supposed to be essential for graphic design, computer-aided engineering (CAE) and academic research. Com­puter animation is the process of creating objects and pictures which move across the screen; it is used by scientists and engineers to analyze problems. With appropriate software they can study the structure of objects and how it is affected by particular changes.

A graphic package is the software that enables the user to draw and manipulate objects on a computer. Each graphic package has its own facilities, as well as a wide range of basic drawing and paint­ing tools. The collection of tools in a package is known as a palette. The basic geometric shapes, such as lines between two points, arcs, circles, polygons, ellipses and even text, making graphical objects are called «primitives». You can choose both the primitive you want and where it should go on the screen. Moreover, you can specify the «attributes» of each primitive, e.g., its colour, line type and so on. The various tools in a palette usually appear together as pop-up icons in a menu. To use one you can activate it by clicking on it.

After specifying the primitives and their attributes you must transform them. Transformation means moving or manipulating the object by translating, rotating and scaling the object.

Translation is moving an object along an axis to somewhere else in the viewing area. Rotation is turning the object larger or smaller in any of the horizontal, vertical or depth direction (corresponding to the x, у and z axis). The term «rendering» describes the tech­niques used to make your object look real. Rendering includes hid­den surface removal, light sources and reflections.