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Aviation History
1964
1964 - 0842.PDF
FLIGHT International, 26 March 1964 481 satellite is in the northern hemisphere and, in addition, provides more stable radio signals for the ionospheric experiments. An unusual automatic temperature control system was built into the satellite. Vacuum insulation between instruments and the shell of the satellite shields the interior from the great variations of temperature on the outside. When the internal temperature of the spacecraft drops below the desired 70°F, eight mercury thermostats trigger an onboard power system fed by a special bank of solar cells which supply the power necessary to maintain the desired internal temperature. Such uniform internal temperature is expected to improve reliability and increase the operating lifetime of the satellite components. In the Laser experiment, a 101b array of fused silica glass reflec- tors is designed to return back to Earth light signals aimed at it from the Laser. Mounted on the satellite's body are 360 1 in dia- meter glass prisms known as cube-corner reflectors. These are constructed in such a way that light striking them from almost any angle will be returned to its source. They are arranged in the form of an eight-sided truncated pyramid, designed and built by General Electric Space Technology Center. A Laser mounted on an 18in diameter optical telescope housed in a 60ft high tower located 20 miles south of Wallops Station was to direct a pulsing beam of red light towards the satellite. Goddard experimenters planned to attempt the first illumination of the satellite reflectors during the early night-time passes over Wallops Island. This might occur as early as 36hr after launch. The planned orbital altitude of 750 miles was intended to place the beacon Explorer at a typical slant range of approximately 1,000 miles, where it would appear by reflected sunlight as a star of about the ninth magnitude—20 times fainter than a star which can be seen by the naked eye. The Laser system is mounted on an IGOR (Intercept Ground Optical Recorder) telescope normally used by Wallops personnel to track sounding rockets. Operators aim the telescope along the predicted path of the beacon Explorer and, when they see it, they flash the Laser light at a rate of one flash per second. If all goes according to plan, the reflector array is illuminated and returns a small portion of the light energy to the telescope. The reflected signal is automatically amplified by a photo- The satellite, solar paddles folded for launch, in place aboard the third stage of its Delta launch vehicle 20 Me, 40 Me, 41 Me J ANTENNAE il MAGNETOMETER UMBILICAL CONNECTOR < POWER SWITCH V; COMMAND LOGIC 40/41 M< TRANSMITTER CORNER REFLECTORASSEMBLY 324 Me, 360 Me ANTENNAS SOLAR CELLS / 136 Me, 162 Me ANTENNAS PAM COMMUTATOR '324/360 Me TRANSMITTER 162 Me TRANSMITTER MAGNETOMETER 20 Me ) TRANSMITTER DUAL OSCILLATOR BATTERIES Location of main elements of the ionosphere beacon satellite multiplier tube (a device that converts optical impulses to electrical signals). A digital counter records how long it took for the light signal to go and come back. In the event of overcast or inclement weather, illumination attempts were to be delayed until optical sightings were possible. The measurements of time between initiation of the light signal and reception at the photomultiplier gives the precise distance of the satellite for each second of time. These values are recorded at the telescope site and later sent to Goddard, where they are compared with distances calculated from other tracking instruments, such as NASA's space tracking and data acquisition network. These distance measurements are expected to be more precise than those obtained through other tracking procedures, and may be used to define the beacon Explorer satellite orbit more accurately. Results of the experiment may lead to a more definite determin- ation of the Earth's shape and development of improved systems for future optical tracking and communications. The Laser system employs a 6in synthetic ruby rod which becomes highly energized as it gathers energy from a xenon gas-filled flash- lamp mounted closely parallel to it in a barrel-like, metal-and-glass housing. The rod is designed so that both ends are polished to act as mirrors. The green light from the flash-lamp excites chromium atoms within the ruby rod which then re-emit red light of a uniform colour. As this red light is reflected back and forth inside the rod, the bouncing rays hit other excited chromium atoms and stimulate them to give off more red rays. It is from this stimulated emission that the Laser gets its name. These rays are in phase with each other and are parallel to each other as they bounce back and forth between the reflecting rod ends. This is known as "coherent" light, in contrast with random sources such as the Sun, electrical and neon gas lamps which have diffuse characteristics. Within a fraction of a millionth of a second this chain reaction builds to a powerful beam that "bursts" out of one end of the rod which has been made more transparent than the other. The Laser light can be directed into a narrow pencil beam which does not lose its effective strength before reaching the target. Among the ground stations involved in the beacon experiment are 11 in Australia (including one at Woomera), three in Canada and four in Britain. The United Kingdom stations are at University College of Wales, Aberystwyth; Nuffield Radio Astronomy Laboratories, Jodrell Bank; Royal Aircraft Establishment, Farn- borough; and a University of Exeter station at Sidmouth. ESRO in Business Following ratification by eight countries of the Convention setting up the European Space Research Organization, the final meeting of the ESRO Preparatory Commission (COPERS) and the first meeting of the permanent ESRO Council were sched- uled to be held on Monday last, March 23. Countries which have ratified are Switzerland, the Netherlands, Britain, France, Spain, West Germany, Sweden and Denmark.
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