| Solid rocket motors are normally classified by their total impulse by a lettered classification scheme. This includes everything from model rockets up through the Space Transportation System and beyond.
The total impulse of a motor is essentially the product of its thrust and burn time (this is a simplification). Since thrust is normally measured in Newtons and time in seconds, the usual unit is the Newton-second (N-s).
Motors of G class and smaller are currently essentially unregulated in the US. Motors up through J class require a Level 1 high-power rocketry certification from one of the two sanctioning bodies -- the National Association of Rocktery and the Tripoli Rocketry Association. Motors up through K class require a Level 2 certification and motors larger than this require a Level 3 certification. At the time of this writing, there are fewer than 500 Level 3 certified individuals in Tripoli and a comparable number in NAR.
Please note that the above certification requirements apply to launching rockets using these motors. There are separate regulations for posession of low explosives such as the ammonium perchlorate composite propellant used in most solid rocket motors, and which are far too complicated to go into here.
The standard classes are:
From (N-s) To (N-s) Class Comment
0.625 1.25 1/2 A
1.25 2.5 A
2.5 5 B
5 10 C common model rockets
10 20 D
20 40 E
40 80 F
80 160 G
160 320 H level 1 certification required
320 640 I
640 1280 J level 2 certification required
1280 2560 K
2560 5120 L level 3 certification required
5120 10240 M
10240 20480 N
20480 40960 O
40960 81920 P largest common hobby motors
81920 163840 Q
163840 327680 R
327680 655360 S
655360 1310720 T
1310720 2621440 U
2621440 5242880 V
5242880 10485760 W
10485760 20971520 X Space Transportation System (shuttle) SRB
20971520 41943040 Y
41943040 83886080 Z
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