FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1963
1963 - 1026.PDF
995 t LIGHT International, 20 June 1963 Missiles and Spaceflight THIS IS THE FIRST MESSAGE SERT COAST TO COAST VIA AM ORBITING BELT Of OIPOLES X rftOM THE HIT LIRCOLR LAB SITE AT CARP PARKS REAR SAW FRARCISCO TO THE RIT LIRCOLR LAB SITE AT WESTTORD MASS. 8REETIRSS AND CONGRATULATIONS OR THIS LORS AWAITED EVERT. THE OUICK BROW FOX JURPED OVER THE LAZY D06S BACK 1234967SM CP SERDS TRE OUICK BROWN FOX JURPE0 OVER THE LAET DOSS BACK 125456789R CP SERDS Self-explanatory teletype example of West Ford communications. Voice and high-speed digital data transmissions have also been successfully effected THE QUICK BROWN FOX JURPED OVER THE LAZY DOSS BACK ttt4»«?BM CP SENDS THE OUICK BROW FOX JURPED OVER THE LAZY DOGS BACK I234H78M CP SENDS be used in this experiment is about 501b, which yields approximately 400 million dipoles. The length of the dipoles is determined by the radio frequency at which the maximum reflecting strength is desired. Specifically, the dipole length is one-half the radio wavelength at the desired frequency. For this experiment, at frequencies in the vicinity of 8,0OOMc/s, the wavelength is about 1.5in and so the dipole length is about 0.75in. The thickness of the dipoles is selected to optimize the effects of solar pressure, which is the chief force tending to perturb the orbit, such that orbital life is finite and limited, yet long enough to permit testing. The distribution of dipoles in the belt will be exceedingly diffuse. Average separation between individual dipoles, after the belt is established, will be more than one-quarter mile. If all the dipoles were joined end to end, to make a single fibre less than 0.001 in in diameter, the fibre would extend less than one-tenth of the distance around the orbital path. If all the dipoles were laid out to make a flat sheet of material less than 0.001 in thick, it would cover only about half of a 5yd strip of a football field. It would take 25 times this amount of material to cover a single Project Echo balloon 100ft in diameter. Because the dipoles are tuned to the frequency of interest, they give a remarkably strong reflection at that frequency. Each dipole fibre, almost invisible to the eye, reflects as much as a flat (untuned) reflector with an area of about 2cm2 when viewed at right angles to its length. Since the dipoles will be tumbling about in random orientations, the actual reflecting strength in orbit will, on the average, be only about one-fifth of this. The dipoles are released by the dispenser gradually, over a period of about one day. At one time or another during this period, they will have been spun off in all directions relative to the orbital path: some towards the Earth, some away from it, some in the forward and backward directions, and some to either side. The velocity with which the dipoles are ejected will vary over a selected range, but the velocity of any dipole relative to the dispenser will be very small compared to the velocity of the dispenser in its orbit. The end result of this process is to place each individual dipole in its own orbit, each one minutely different from the others, but all lying within a rather narrow range to form a thin belt that follows the original orbital path in which the dispenser is launched, at an altitude of about 2,000 miles. Approximately 60 days after launch, it is estimated that the belt will be about 8km (5 miles) wide and about 40km (25 miles) thick. Subsequent dimensions and location of the belt will depend on factors, such as solar pressure, that are to be evaluated in the course of this experiment. The package (illustrated on page 993), consists of a cylindrical stack of 18 discs mounted on a hollow central shaft. Each disc, about 4.5in in outside diameter, is made up of a large number of dipole fibres, closely packed like cord-wood parallel to each other and parallel to the central shaft. The dipoles are embedded in naphthalene, a hydrocarbon solid commonly used as the principal ingredient in moth balls, which sublimes (turns to gas) when exposed to the atmosphere; when exposed to very low pressures in space, naphthalene sublimes more rapidly than it does at normal atmo spheric pressure. After the launch vehicle has achieved an orbit that is suitable for the experiment, a radio command signal from the ground causes the package to be ejected from its sealed canister by two concentric coil springs. The main body of the package is in fact divided into five parts; an end piece, which carries a telemetry package and two discs of dipole fibres, and four other stacks of fourj discs each. There is thus a total of 18 discs in all. Each stack of discs is clamped with a force of about 2,3001b between two end plates on a central shaft. The hollow interior of this shaft has spiral grooves, like the rifling in a gun barrel, which mesh with spiral ridges on the central shaft of the canister. As the package is ejected, these spiral groves cause the central shaft of the package to spin, and the spin is imparted to the package of dipole stacks. Soon after ejection, the five parts of the package are separ ated one from another by small springs. These five shorter spinning sections will operate similarly but independently and should have greater dynamic stability than a single long, thin stack. The spin imparted to the dipole package at the time of ejection is vital to the dispersal of the dipole fibres: the spin supplies the force that impels individual fibres to fly off the stack, as they are released by the gradual vaporization of the naphthalene. Each fibre then has a velocity that is very slightly but perceptibly different from all the others, and it is these very small differences in velocity that cause the fibres to diffuse slowly along the orbital path to form a thin, narrow circular ring. The radio telemetry package is the square box at the left in the drawing, which also shows the two discs of dipole fibres attached to it. The four curved long wires are the transmitting antennas. This package contains instruments to measure temperature, spin rate, and tumble rate. In addition, three small spring-loaded rods press against the face of the nearest disc of dipole fibres, at different distances out from its centre; as the dipole fibres spin off, the disc shrinks in diameter, allowing one rod after another to pop out, and giving a crude but simple and reliable indication of the rate at which dispensing is taking place. The flat T-shaped package at the right contains circuits to signal that ejection has been effected (upon radio command from the ground) and to indicate the velocity of ejection. This package, along with the canister and other associated hardware, remains with the parent vehicle on which it is bolted. The entire assembly weighs about 901b, of which 151b is the telemetry package, 501b is copper dipole fibres, and 251b is all the rest of the mechanism. Related Activities The attempt to establish a test belt of dipoles in orbit is of course an essential part of the West Ford experi ment, but a belt in itself would be useless without the special equip ment and techniques that have had to be developed. The ground terminal facilities and measurement techniques, and related theore tical and experimental studies in the laboratory, have required an expenditure of effort at least as great as the development and testing of the dipole dispensing technique. These other activities have yielded a number of results that are significant in their own right to various fields of science and engineering. High-power trans mitters, very sensitive receivers, and large precision reflectors, as well as the aerial control and signal processing techniques that have been developed for this project, will find applications in many other branches of electronics and communication technology.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
