ABOUT MOTORS
Basic Rocket Motor Knowledge
About Rocket Motors
Rocket motors come in many sizes. They are measured in total impulse and are designated by letters of the alphabet. Each letter designates a range of total impulseThe total thrust produced by a rocket motor across its full burn time. Usually expressed in Newton-seconds.
Levels one through three: reference to the three levels of high power rocketry certification. Unless you are in Canada, Eh?
Tripoli Rocketry Association, Visit TRA
National Association of Rocketry, Visit NAR
Low Power Rocketry | |||
---|---|---|---|
A | B | C | D |
1.25Ns ⟹ 2.5Ns | >2.5Ns ⟹ 5Ns | >5Ns ⟹ 10Ns | >10Ns ⟹ 20Ns |
Mid-Power Rocketry | ||
---|---|---|
E | F | G |
>20Ns ⟹ 40Ns | >40Ns ⟹ 80Ns | >80Ns ⟹ 160Ns |
High Power Rocketry
Certification Level 1 | |
---|---|
H | I |
>160Ns ⟹ 320Ns | >320Ns ⟹ 640Ns |
Certification Level 2 | ||
---|---|---|
J | K | L |
>640Ns ⇒ 1280Ns | >1280Ns ⇒ 2560Ns | >2560Ns ⇒ 5120Ns |
Certification Level 3 | ||
---|---|---|
M | N | O |
>5120Ns ⇒ 10240Ns | >10240Ns ⇒ 20480Ns | >20480Ns ⇒ 40960Ns |
Their potential power is indicated by a letter. However a motor of any given energy range might be configured to deliver only the middle of energy range rather than the full amount. That’s because you don’t always want the full amount. The motor manufacturer’s charts give you this information. The letter is followed by a number. The number tells you what the average thrust is. An example would be an I170 or an I240.
We are used to speaking in terms of horsepower and such, however, that’s only part of the equation, the amount of time applied given the amount of horsepower is needed to figure the total energy used. In rocketry, we use a different measurement and it is related to the total energy of the motor, i.e., power and time. Rocket motors are rated in Newton-seconds, however if you divide it by 4.45 and you will get pound-seconds. In other words so many pounds of force for one full second.
Hopefully, you are not lost and have acquired a good grasp of the concepts discussed to this point. To help you better comprehend all of this, here we will give you a little contrived comparison that makes it simple to understand.
Think of the term Newton•seconds
The typical unit of measurement for rocket thrust. One newtonsecond is one newton of thrust maintained for one second.

Interpreting Rocket Motor Codes
Model rocket motors approved for sale in the United States are stamped with a three-part code that gives the rocketeer some basic information about the motor’s power and behavior. For example, an Estes B motor might be stamped:
- The letter B specifies the impulse class.
- The number 6 tells us average thrust is 6 Newtons.
(6 Newtons equates to 1.3 pounds of thrust.) - The 4 gives us the delay time between motor burnout and the firing of the ejection charge for recovery.