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CHAPTER 1: 700 Years of Black Powder War Rockets

Saltpeter is the main ingredient in “black powder”, the other two ingredients being charcoal and sulfur. The net reaction from burning an oxygen-balanced black powder mix can be summarized as:

2KNO3 + 3C + S 3CO2 + N2 + K2S

Saltpeter is naturally occurring potassium nitrate, KNO3. Saltpeter forms from water-soluble urea, CO(NH2)2, and white semi-solid uric acid, C5H4N4O3, which are the end products of protein metabolism found in the urine of mammals and of birds, reptiles and insects, respectively. The urea and uric acid react with KCl in wet soil and atmospheric O2 to form KNO3 in solution. Deposits of clear, solid crystals of potassium nitrate are left on the surface of the ground as the water evaporates. Historically large deposits of saltpeter were available in arid regions of China and India but less so in Europe where frequent rains washed it away.

Since saltpeter, charcoal and sulfur are all relatively common, their uses—both individually and in finely ground black powder—go back to antiquity. Written reference to mobile fire works such as pinwheels, ground and water skimming “rats”, fountains and fire arrows date back to at least 1045 A.D. Detailed descriptions of gunpowder preparation, storage and military use in explosive and incendiary devices are preserved in Chinese records of the period. An edict of 1067 A.D. prohibited export of saltpeter and sulfur to withhold them from potential enemies. The “fire arrows” were incendiary devices consisting of a conventional arrow with a bamboo or paper cylinder containing loose grains of black powder attached to the shaft near the front. These were not rockets, merely conventional arrows with black powder attached to set fires. A fuse was lit before release of the arrow. The earliest unambiguous reference to actual self-propelled rockets appears in Arab descriptions of “Chinese arrows” in 1240 A.D., however it is widely believed that the Chinese used actual rockets to rout the Mongols at the battle of Kai-fung-fu in 1232. Records of fuel-rich black powder mixtures more amenable to use in hard-packed rocket propellant grains appear in Chinese records at about this time. These early Chinese rockets were small, the length of standard arrows, with a doubly-barbed iron arrowhead dipped in poison and feathers on the trailing end of the shaft. In appearance they departed from a standard arrow primarily in the presence of the cylindrical rocket motor strapped to the shaft a short distance behind the arrowhead. The rocket motors were bamboo or paper cylinders filled with tightly compacted black powder with a variable diameter hole drilled down most the length of the propellant grain. A clay plug with an opening matching the width of the wide end of the propellant grain hole served as the nozzle. The propellant burned from the hole outward toward the walls of the cylinder. As the propellant burned, the hole grew wider, increasing the burn area which increased the pressure and thrust as well. The widest part of the hole would burn to the wall of the cylinder first and run out of

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propellant, preventing a further rise in pressure as propellant continued to burn along the narrower length of the hole. This evened-out the overall propellant burn-rate and thrust somewhat, preventing the cylinder from rupturing due to excessive combustion pressure.

As the stick grew longer on later rockets, the feathers on the end of the stick were dropped. Rockets were equipped with explosive or incendiary warheads and grew larger in size. Military use of black powder stick rockets quickly spread to India where they were employed on a large scale. The Anlo-Mysore Wars were a series of wars fought in India over the last three decades of the 18th Century between the Kingdom of Mysore and the British East India Company. The British were impressed by the Mysorean rocket artillery made from iron tubes by the enemy armies of Tipu Sultan and his father Haidar Ali. The military tactic developed by Tipu Sultan and Haidar Ali was the use of mass attacks with rocket artillery brigades on infantry formations. The regular Rocket Corps in the Mysore Army began with about 1200 men in Haidar Ali’s time. Tipu Sultan wrote a military manual called Fathul Mujahidin in which 200 rocket men were assigned to each brigade of infantry. The areas of town where rockets and fireworks were manufactured were known as Taramandal Pet (loosely “the Sky Market”). The rocket men were trained to launch their rockets at an angle calculated from the diameter of the cylinder and the distance to the target. Wheeled rocket launchers were capable of launching a salvo of rockets simultaneously. Rockets were of various sizes usually consisting of a tube of soft hammered iron about 8 inches long and 1.5 to 3 inches in diameter strapped to a shaft of bamboo. A rocket carrying about a pound of well-packed black powder had a range of almost 1000 yards. In the Second Anglo-Mysore War, at the Battle of Pollilur (1780), Colonel William Braille’s ammunition stores were detonated by one of Tipu Sultan’s rockets, contributing to a British defeat. In the Third Anglo-Mysore War of 1792, the Rocket Corps of Tipu Sultan’s army had reached its ultimate strength of about 5000 men. By the Fourth Anglo-Mysore War the British were “so pestered with the rocket boys that there was no moving without danger from the destructive missiles. The rockets and musketry from 20,000 of the enemy were incessant. No hail could be thicker. Every illumination of blue lights was accompanied by a shower of rockets, some of which entered the head of the column, passing through to the rear, causing death, wounds and dreadful lacerations from the long bamboos of 20 or 30 feet. Some had protruding iron points or steel blades. The blades made the rockets unstable towards the end of their flight, causing the blades to spin around like scythes, cutting down those in their path”. The latter referred to maple-seed-like auto-gyration of the sword blade as propellant consumption lightened the nose.

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This relica of a Mysorean sword rocket has a 10” long x 2.3” diameter case with a 40” metal blade bound to it. Despite the ultimate defeat of the Mysores, the British had been sufficiently impressed by the Mysorean rocket artillery to begin a vigorous reseach and development program at Royal Arsenal, Woolrich beginning in 1801 under William Congreve. Stick rocket development reached its climax in Congreve’s large family of rockets weighing from 6 to 300 pounds and having metal casings with diameters from 113/16 to 8 inches. The largest rocket was 6’ 4” long and had a warhead weighing almost 50 pounds. Guide sticks extended from 6 to 27 feet and broke down into multiple sections for ease of transport. Most widely used was the 32 pound rocket with the gunpowder charge housed in a 3’ 6” long iron casing that was 4” in diameter. Range was about 1000 yards. All the rockets were based on standardized black powder composition and manufacturing techniques. Black powder charges were rammed solid into the steel casings; then a hollow tapered core was bored out to give a large burn area. A permanent firing range at Woolrich, England and extensive testing assured quality control and optimum performance. Congreve first demonstrated his rockets to the Prime Minister and War Secretary in September 1805 and the missiles were used against the French Navy at Boulogne beginning in November. Congreve believed rockets to be an important force multiplier because large numbers of big bore projectiles could be rapidly fired by a limited number of military personnel. From Britain black powder rockets spread through much of Europe.

A 100 pound Congreve rocket on display at the National Air and Space Museum in Washington, D.C. The pointed warhead was an incendiary designed to embed the tip in the target and then leak a flammable liquid which was ignited by a pre-lit fuse.

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A recreation of the firing of Congreve rockets on land

France, Russia, and Austria were among the serious investigators of rocket weapons. Tripod launchers such as this one (below) from Austria were typical. The complete family of Congreve stick rockets is depicted on the following page.

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Isaac Newton’s Second Law of Motion put rocket science on a quantitative computational footing.

His Law of Gravitation did the same for orbital mechanics. Rocket “science” moved toward a theoretical footing based on Newton’s Second Law published in Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) in July 1687. Newton’s Second Law states “Force equals the rate of change of momentum” which is perfect for quantifying the dynamics of a rocket motor. Force = Thrust = Rate of Change of Momentum = Mass Flow Rate x Velocity. It can’t get any simpler than that. Newton’s explanation of the dynamics of launching a satellite, including calculation of orbital and escape velocities, appears in A Treatise of the System of the World, 1728. William Moore, an instructor at the Royal Military Academy at Woolrich, correctly calculated the velocity at burnout and the maximum altitude of a rocket of constant burn rate and thrust fired vertically in vacuo. He did this in response to a prize offered in 1810 by the Academy of Copenhagen and published the results in 1813 in his officially sanctioned book A Treatise on the Motion of Rockets. Moore’s formulas are still found in modern textbooks: T = Mp/t . Vexh so Vexh = Tt/Mp from Newton’s Second Law

where: T = thrust Mp = mass of the propellant consumed t = burn time Vexh = average velocity of the exhaust Vbo = Vexhln(Mo/(Mo-Mp)) – g t where: Vbo = velocity of the rocket at burnout Mo = initial mass of the rocket

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g = acceleration of gravity (32.174 ft/s2 = 9.80665 m/s2) ln = “the natural logarithm of” H = Vexht(1 + (Mo-Mp)/Mpln((Mo-Mp)/Mo))-1/2gt2 + 1/2Vbo

2/g where: H = maximum altitude reached by the rocket In the vacuum of space away from gravitating bodies, the change in velocity, V, from an individual stage of a multistage rocket is given by: V = Vexhln(Mo/(Mo-Mp)) This simplified form of Moore’s equation is the so-called “Rocket Equation” usually credited (incorrectly) to having been first published by Russian Konstantine Tsiolkovsky or American Robert Goddard, neither of whom had been born when Moore’s Treatise was published. Likewise the idea of multi-staging to achieve higher velocities had been demonstrated by powder rocket practitioners long before being “discovered” by spaceflight visionaries of the late 19th and early 20th Centuries. A rocket’s “specific impulse”, Isp, is defined as the total impulse, Tt, divided by the weight of the propellant consumed, Wp = gMp. Specific impulse is used as a measure of rocket engine performance since it is directly proportional to the exhaust velocity: Isp = specific impulse = Tt/(gMp) so Vexh = Tt/Mp = gIsp Compared with heavy cannons, rockets offered greater mobility, longer range and much higher rates of fire. Unfortunately black powder rockets were also unpredictable—even erratic—in flight. The propellant was sensitive to humidity, temperature and the proper placement of the fuses. Acceleration of the rockets was therefore not consistent from one to the next, so the ascent angle of the projectiles and their height above the ground varied greatly. It was not unusual for the missiles to strike the ground prematurely and rebound in a new direction, sometimes becoming a hazard to those who launched it. In land campaigns they were frequently found to be ineffective against anything less than large, high-density (i.e. “easy”) targets. The rockets’ incendiary nature and longer range did, however, seem to favor their use in naval engagements. A rocket-armed ship stood a good chance of setting an opponent’s wooden sailing vessel ablaze before coming within range of the enemy ship’s guns, or of setting fire to a coastal city from beyond the reach of shore batteries. Rockets were even better suited to small, maneuverable shallow-draft boats with too light a displacement to carry heavy cannons. Such boats were used to particular advantage by the British during the Crimean War (1853-1856). The boats, lowered from larger ships, would work the shallow waters and cover of coastal rocks and trees to gain surprise in close-in attacks against ships in harbor and against stores of ammunition, food and other supplies stockpiled nearby for shipment. Without rockets, these small craft would have had no weapons of large caliber.

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“The Use of Rockets in Fire Ships” from A Treatise on theGeneral Principles, Powers, and Facility of

Application of the Congreve Rocket System by William Congreve

Shallow draft rocket boats from the same military manual

Stick rockets’ poor accuracy was due in part to the slow ignition and uneven burning of black powder grains, but also to the basic asymmetry of the side-mounted stick. Congreve moved to alleviate the latter with the introduction of a center-mounted stick and a tubular launcher in 1815. The stick was screwed into a threaded hole in the base of the rocket. Five exhaust ports surrounded the central threaded hole.

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Congreve rockets with center-mounted sticks and small fins

Two versions of Hale spin-stabilized rockets requiring no sticks

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English inventor William Hale dropped the stick altogether in his spin-stabilized rockets introduced in 1844. In the initial design a central exhaust port was surrounded by five smaller nozzles canted at an angle to put the spin on the projectile. A later version featured three equally spaced exhaust ports 120 degrees apart which discharged the flow down half-cylinders that allowed the gas to expand off them only in a counter-clockwise direction (as viewed from behind). Hale rockets gained quick favor in the U.S. and Austria but not Britain. Congreve rockets of the center-mounted-stick variety and spin-stabilized Hale rockets were both used by U.S. troops against the Mexican army at the battle of Vera Cruz in 1847. Both types of rockets were launched from tubes or open troughs. Advances in cannons—rifled barrels, breach (.vs. muzzle) loading, and stronger, heat resistant metals from the Bessemer steel process—substantially improved the accuracy, firing rate, muzzle velocity and range of tube artillery while making cannons (somewhat) lighter and more mobile. Rockets could no longer compete effectively as large caliber weapons and rapidly faded from the world’s major battlefields by the early 1860s. They played little part in the U.S. Civil War (1861-1865) and had virtually vanished altogether as weapons of war by the end of the 19th Century. 1887 and 1888 saw the introduction of two key developments by Swedish inventors that would lay groundwork for the later re-emergence of rockets. Alfred Nobel’s double base gun propellants based on nitrocellulose and nitroglycerin and Gustaf de Laval’s converging-diverging supersonic nozzle would make possible a new class of rocket motors with almost three times the specific impulse of the best black powder rockets to date. Robert H. Goddard of the United States would be the first to systematically investigate use of the new nozzle and propellants in rockets beginning in 1914.