Week 2: War Rockets

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Rockets spent the next several centuries almost entirely as weapons before anyone thought about pointing them at the sky for other reasons.

History

By the 1700s and early 1800s, rocket weapons had gotten serious upgrades. The Kingdom of Mysore, in southern India, fielded iron-cased rockets that could survive much higher internal pressure than the old paper-and-bamboo designs — meaning more range and a heavier payload. British forces who encountered them were impressed enough that a British officer, William Congreve, reverse-engineered the idea into his own standardized iron rocket a few years later.

Forces

This week introduces a simple but critical ratio: thrust versus weight. A rocket needs enough thrust to overcome its own weight — plus friction and drag — or it simply won't leave the launch rod with any useful speed. Too little thrust, and a rocket can wobble off unstable instead of flying straight.

Math

T/W = Thrust / (m·g)

Worked example (metric): a small model rocket has a mass of 60 g (0.06 kg) and uses a motor with about 10 N of average thrust. T/W = 10 / (0.06 × 9.81) = 10 / 0.589 ≈ 17:1 — well above the safe minimum.

Advances

William Congreve standardized his iron-cased rocket design in 1804, adding a long stabilizing stick — a crude but effective early answer to the stability problem we'll dig into properly in Week 7.

Key Date

In 1780, Mysorean rockets were used against British forces at the Battle of Pollilur — one of the most striking early demonstrations of rockets as a battlefield weapon.

Safety Note

A minimum thrust-to-weight ratio of about 5:1 is considered the threshold before a rocket is launch-safe — below that, it may not clear the rod fast enough to be stable. This is exactly why we check a motor's thrust curve against a rocket's weight before every flight.