Motors for model rockets, high powered rockets, and amateur rockets are classified by total impulse into a set of letter-designated ranges, from A (the smallest, though 1/2, 1/4, and 1/8-A motors are also available), up to O as the largest. A is from 1.26 newton-seconds to 2.5 N·s, and each class is then double the total impulse of the preceding class, with B being 2.51 to 5.00 N·s. Engines classified beyond O are in the realm of amateur rocketry. In this context, the term amateur refers to the rocketeer's independence from an established commercial or government organization.[1]
The impulse designation for a specific motor is based on the alphabetic code. For example, the letter (M) would represent the total impulse of between 5,120.01 and 10,240.00 N·s of impulse.
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Class Total Impulse
(Metric Standard)Total Impulse
(Imperial Standard)A 1.26-2.50 N·s 0.29-0.56 lbf·s B 2.51-5.00 N·s 0.57-1.12 lbf·s C 5.01-10.00 N·s 1.13-2.24 lbf·s D 10.01-20.00 N·s 2.25-4.48 lbf·s E 20.01-40.00 N·s 4.49-8.96 lbf·s F 40.01-80.00 N·s 8.97-17.92 lbf·s G 80.01-160.00 N·s 17.93-35.96 lbf·s H 160.01-320.00 N·s 35.97-71.92 lbf·s I 320.01-640.00 N·s 71.93-143.83 lbf·s J 640.01-1280.00 N·s 143.84-287.65 lbf·s K 1,280.01-2,560.00 N·s 287.66-575.30 lbf·s L 2,560.01-5,120.00 N·s 575.31-1150.60 lbf·s M 5,120.01-10,240.00 N·s 1150.61-2301.20 lbf·s N 10,240.01-20,480.00 N·s 2301.21-4602.40 lbf·s O 20,480.01-40,960.00 N·s 4602.41-9204.80 lbf·s P 40,960.01-81,920.00 N-s 9204.81-19409.60 lbf·s Q 81,920.01-163,840.00 N-s 19409.61-38819.20 lbf·s R 163,840.01-327,680.00 N-s 38819.21-77638.40 lbf·s S 327,680.01-655,360.00 N-s 77638.41-155276.80 lbf·s T 655,360.01-1,310,720.00 N-s 310553.81-621107.2 lbf·s U 1,310,720.01-2,621,440.00 N-s 621107.21-1242214.40 lbf·s V 2,621,440.01-5,242,880.00 N-s 1242214.41-2484428.80 lbf·s W 5,242,880.01-10,485,760.00 N-s 2484428.81-4968857.60 lbf·s X 10,485,760.01-20,971,520.00 N-s 4968857.60-9937715.2 lbf·s
In many countries, the sale, possession, and use of model rocket motors is subject to rules and regulations. For example, in the United States, high-powered motors (above 160 newton seconds) are restricted by industry convention to purchasers who possess the requisite certification, though this is not a legal restriction. In the United States of America, the two recognized organizations that provide high-power certifications are Tripoli Rocketry Association and the National Association of Rocketry, both of these organizations have three levels of certification which involves building progressively more complex and higher powered rockets and taking a test of safety rules and regulations. The U.S. government regulatory documents surrounding high-powered rocketry are FAA FAR Part 101 and NFPA 1127.[2] In Canada, the Canadian Association of Rocketry has a 4 step certification process, but all three organizations accept the other's certifications if a flyer shows up at a high-power launch and wishes to fly under their sanction. Some states restrict the maximum impulse to a G motor. The United Kingdom Rocketry Association employs a similar 3-level system as Tripoli and NAR, and UK fliers may require governmental approval to obtain larger motors or to possess large quantities of them.
Level 1 certification qualifies you to purchase and use H and I engines, Level 2 certification J, K, and L engines and Level 3 certification M, N, and O engines. Note: Canada adds another step in between, and has a Level 4 which is the same as US Level 3.
The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives established laws after September 11, 2001, which required that an individual must hold a Low explosive Users Permit (LEUP) to have a high-powered motor in their possession. Following a 9-year long lawsuit brought by TRA and NAR against the BATFE, these laws were overturned in a federal court in 2009, and U.S. citizens no longer require governmental approval to purchase APCP solid rocket motors.[3]