FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1962
1962 - 1892.PDF
392 FLIGHT Internatioiu. 6 September l%? Missiles and Spaceflight Depicted here to approximately the same scale are (from the left) the Polaris Al, the A2X-0I (first fight Al test vehicle) and the A3X-0I which was fired on August 7. This first A3 firing, from a land laun cher at Cape Canaveral, was intended to achieve a range of 1,995 miles. A malfunction occurred about three seconds after ignition of the second stage and the missile fell short of its planned range (photograph opposite) Polaris A3 "THE bullet shape of the Polaris A3," say Lockheed Missiles and Space Company, "is more than just a new look—the streamlined silhouette encloses a missile which is 80-per-cent new." Gone with the familiar champagne-bottle configuration are two-thirds of the bulk of the guidance package, the jetevators which steered the Al and A2 Polaris, the steel motor casings of the earlier models and a host of other items. The advances incorporated will give the A3 its most important addition—another 1,000 n.m. in range over the operational 1,500 n.m. A2, and more than double the range of the first generation Al. These improvements are the outcome of many Polaris flight tests —successful, partially successful and even failures. "While pre vious test flight programmes have been educational, and despite the fact that each launch taught us something, the challenge has gotten stringent," says Stanley W. Burriss, vice-president and general manager of the Missiles System Division of LMSC. He recalls that the programme has been accelerated twice since Lock- teed was named prime contractor in 1956. Not only has the time schedule been compressed, but leeway or tolerances which were acceptable in the development and manufacture of earlier versions are not permitted in the A3. A major factor in the successful acceleration of the work, without sacrifice of quality, is the mastering concept for gauging. In the development of the Al and A2 Polaris, the 7,000 subcontractors were required to meet very precise specifications. Ambient-tem perature differences at various locations in the far-flung contractor network could make fitting components together a problem. Under the mastering concept, a set of gauges or patterns are made and used as "yardsticks" by the various contractors, much in the way a template is used. While much of the new A3 is an outgrowth of earlier Polaris models, the longer-range missile has required extensive basic and applied research and development on the part of Lockheed, working with the Navy Special Projects Office. Among the innovations resulting from such pioneering work is the fluid-injection thrust vector control system. Subcontractors have developed the lighter and stronger glass-filament-wound motor casing, propellants with higher specific impulse, rotating nozzles and hundreds of other improvements to produce a submarine-launched missile which can reach any target on earth. It is clear that the jump from Polaris A2 to A3 is very much greater than that from Polaris Al to A2. Most of the basic design features are outlined in the accompanying table, and it is not difficult to believe Lockheed when they describe A3 as "an 80-per-cent new bird." Probably the most important changes have been made in the field of propulsion. Just a year ago (September 14, 1961, page 414) we reported at length upon the exceedingly ambitious design targets set by Aerojet-General Corporation for the Polaris A3 first-stage motor. According to American reports, the temperature and pressure are as high as 6,300/6,600°F and 800/900 lb/sq in. These figures are exceptional under any circumstances; but when combined with a long firing duration and a case of minimum weigh: the problems appear formidable. Missile range varies with com bustion conditions much as the range of an airliner varies with cruising turbine entry temperature, and calculations show that a reduction in temperature to 5,800/5,900°F would bring down the maximum range of Polaris A3 from 2,500 to about 2,300 n.m. Extensive research over many years has been necessary to perfect a glass filament-wound motor casing for the first-stage engine, and Aerojet seem on safe ground in describing it as the largest and strongest plastics case ever developed. Details of the propellant remain classified. There are four separate nozzles, as in earlier Polaris, since a single nozzle (unless of unconventional form, such as a "plug" configuration) would result in an increase in missile length. Final elimination of the expensive and—initially, at least- troublesome jetevators appears to be very welcome, quite apart from the fact that their drag is appreciably greater than that for other thrust-vector control systems. It can be seen from the table that Aerojet and Hercules Powder Co have, in conjunction with Lock heed and the Navy, steadily progressed from jetevators through swivelling nozzles to the ultimate scheme of liquid injection. Assisted greatly by the vast research programme for the Minute- man Air Force ICBM, the concept of swivelling nozzles on a high- performance solid motor is both lighter and more reliable than jetevator schemes, and the reduced drag confers a valuable in crease in range. Such nozzles are used on the first stage of the present A3. The second stage already employs liquid injection, which operates as sketched on page 602 of our April 19 issue. A suitable liquid—combustible or inert, according to nozzle condition? and propellants—is injected under high pressure through an appro priate port in the wall of the expanding nozzle. A strong inclined Shockwave is created, and the gas flowing through it is turned through an angle depending upon the angle of the Shockwave. The nozzle itself remains fixed. Lockheed were able to save time and money by using an "off- the-shelf" refrigerant, Freon, as the injected fluid. The Freon is injected into the four nozzles of the second stage, the amount oi fluid being controlled by varying the area of the holes. The injected Freon produces a shock wave, which in turn creates a high-pressure area on one side of the nozzle causing a deflection of the main rocket exhaust to result in thrust vector control. The inertial guidance sends signals commanding when and how much fluid is to be injected. This steering system sets the second stage precisely on its course, so that when the re-entry body and the warhead separate they wi '< be in a ballistic trajectory aimed at the predesignated target. Use of this relatively simpler and more efficient fluid vectoi
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
