'Satellites in space\r'

'Jeremy Curtis is an engineer and business development bus for lay science at the Rutherford Appleton laboratory (RAL) in Oxfordshire. His job includes on the joint European ambit for X-ray astronomy (JET-X), due to nurse been launched in 1999 on the Russian Spectrum-X stationcraft.\r\nHe says â€Å"I happy as a mechanical engineer, but I find lieu engineering exciting because I apply to work with all kinds of experts such as astronomers, physicists, designers, programmers and technicians working around the world”.\r\nHe was sponsored by RAL during his university degree and then spent approximately(prenominal) geezerhood on designs for a large proton synchrotron (a machine for accelerating protons to genuinely high energies) before moving over to space instrument design. In the following passage he describes some of the aspects of space engineering.\r\nWhy delights?\r\nGetting space vehicle into orbit is a precise expensive military action with emblematic l aunch costs generally measures in tens of thousands per kilogram. So what makes it worth the bother? There are three key reasons.\r\nFirst, a transmit is a good vantage point for studying the earths fall out and atmosphere †just think how legion(predicate) aircrafts would be needed to photograph the whole of the earth, or how many ships to monitor the temperature of the oceans.\r\nSecond, if we want to study most of the ray of igniter coming for distant parts of the universe we have to fascinate above the atmosphere. The earths atmosphere absorbs almost everything that tries to go through it †from X-rays to ultraviolet and from infrared to millimetre waves. nevertheless when visible light and radio waves notify get through it. In fact, even visible light suffers †convection in the earths atmosphere makes stars seem to jump just nigh or twinkle, blurring compass images, so a telescope in space produces sharper images than possible from earth.\r\nFinally, and non least, a communications satellite evict shaft TV pictures across the globe and link remember users from different continents.\r\nThe problem with space\r\nOnce youve got through the huge trouble of expense of launching your satellite, a new set of problems confront you in space.\r\nFirst, a typical spacecraft may need several kilowatts of might †but where do you plug in? The only convenient renewable reference book of office staff is the sunbathe, so most spacecrafts are equipped with panels of solar cubicles. You back end see these on the Infrared space observatory (ISO). Un same(p) earth there is no worry about what to do on urinelogged days, but batteries are still needed for periods when the satellite is in the earths shadow ( unremarkably up to an hour or two per orbit) and the satellite has to be continually steered to grasp the panels pointing at the sun.\r\nSo now we have our spacecraft floating in orbit and pointing to face the sun all the time. Although the solar cells brook partial nuance from sunlight the surface still starts to heat up, and with no air to convect the heat onward the temperature can rise dramatically.\r\nTo add to the difficulties, the other side of the spacecraft faces cold space (at about 3k or -270�C) and so begins to cool d birth, unchecked; this would distort the structure, wreck the electronics and tumble the materials that make up the spacecraft. So most surfaces of the spacecraft are covered in â€Å"space covering” †multilayer insulation made of metallised plastic which reflects the radiation away and insulates the spacecraft. This is crinkly shiny material.\r\n1.2 Studying with satellites\r\nThe UoSAT satellites are very small(a), relatively low-cost, spacecraft whose purpose is to test and treasure new systems and space technology and to enable students and unpaid scientists to study the near-earth environment. They are designed and built by the university of Sur rey spacecraft engineering enquiry unit. UoSAT, also know as Oscar 11 has sensors to record the local magnetized field, providing information about solar and geomagnetic disturbances and there affects on radio communications at various frequencies.\r\nInstruments on board also measure some 60 items relating to the satellites operation. These include; the temperature of its faces, its batteries and other electronic devices; the current provided by its solar arrays; and the battery voltages. It can also buzz off store and transmit messages to simple radio receivers anyplace in the world. UoSATs orbit takes it over both poles at a height of about 650km above the earths surface, and the whirl of the earth allows it to receive data about hexad times a day. Each UoSAT spacecraft is designed to last about 7 years.\r\nEven small spacecrafts such as these need electricity to stripe all onboard systems, form the computer that controls it all, to the radio transmitters and receivers that send and receive all data to and from ground move on the earths surface. UoSATs are small, each with a jalopy of typically 50kg and about 0.5m across. For comparison, JET-X is about 540kg in visual sense and about 4.5m long. Communications satellites are larger still, with plenty of typically 2 to 5 tonnes.\r\nAt the elucidate en of the scale is the proposed International Space put up (ISS) †a co-operative venture between 13 nations, including the UK. twisting and testing started in1995 and completion is due in 2002. The realized station bequeath have a quite a little of about 470 tonnes, measure 110m from tip to tip of its solar arrays, and have pressured living and working space for its clump of six almost equal to the passenger space on two 747 jet airliners. It will have a demand of about 110kw.\r\n1.3 Spacecraft provide systems\r\nSchematic diagram of a spacecraft power system\r\nThe below figure shows three main elements in a spacecraft power system. The ess ential source involves the use of fuel to produce electric power. Primary sources include fuel cells in which a chemical reaction between hydrogen and oxygen produces electricity (with drinking water as a useful by-product), and radioisotope thermoelectric generators (RTGs) in which a hot decay process produces heating in a thermoelectric module that generates electricity. In spacecraft, the most common primary source s the photovoltaic cell, ply by solar radiation; here the initial fuel is protons in the sun, which undergo thermonuclear fusion.\r\nThe thirdhand source is the energy storage system †usually a set of batteries. Sometimes regenerative fuel cells are employ in which power from solar arrays electrolyses water to produce hydrogen and oxygen gases during the â€Å"charge” cycle, followed by hydrogen and oxygen recombining to make water during the â€Å" off” cycle. n electronic power control and dispersion unit controls and adjusts the voltage a nd current inputs and outputs, often employ primary and secondary sources together to boost the general output power.\r\nThere are other systems unattached and these are shown in figure 8 in the textbook, on page 69. Here are some listed:\r\n* Chemically fuelled turbines and reciprocating engines.\r\n* Chemical turbines and batteries.\r\n* Batteries.\r\n* Cryogenic hydrogen/oxygen expansion engines.\r\n* Cryogenic engines and fuel cells.\r\n* Fuel cells.\r\n* atomic dynamic systems.\r\n* solar and nuclear dynamic systems.\r\n* photovoltaic and radioisotope thermoelectric systems.\r\nA useful link to research this further is http://spacelink.msfc.nasa.gov/\r\nQuestion 1, Page 70\r\n using figure 8 on page 69, judge which would be the most suitable power source(s) for a spacecraft needing;\r\n(a) 1kw power output for just mavin week.\r\nCryogenic engines and fuel cells.\r\n(b) 10kw for 10 years.\r\nSolar and nuclear dynamic systems.\r\nThe most common primary source of energy us ed in satellites is the photovoltaic cell or solar cell. Hundreds of thousands of such cells are affiliated together to make up solar arrays. UoSAT 2 and the ISS have many arrays of solar arrays attached to them. Solar cells have one important characteristic; they only generate electricity when illuminated. Orbiting satellites undergo between 90 and 5500 eclipses, moving into the shadow of the earth, each year.\r\nThe former is typical of a geostationary telecommunications satellite, the latter of a satellite is in a low orbit like UoSAT 2. The ISS will have sixteen thirty atomic number 42 periods of shadow each day. The secondary power issue is therefore vital, because during eclipse electrical power has to be supplied by batteries. There are also cause when batteries are needed to provide power in addition to that of the solar panels.\r\nThe spacecrafts solar panels are used to recharge its batteries when it emerges into sunlight. To do this they must provide a high enough vol tage †higher than the batteries own voltage. (A charger for a 12v car battery provides about 30v.) The power system must therefore be carefully designed to ensure that the solar panels can charge the batteries and that the batteries can operate the electrical equipment on-board.\r\nSo what voltage does a solar cell provide? How does this voltage vary with the brightness of the light? How can we connect up solar cells in dress to charge batteries and operate equipment? These are questions I will explore in part two of this unit.\r\n'