This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
Now there is also HIGH power rocketry (HPR). These are rockets with
motors up to type O (with greater than 40,000 Newton seconds of impulse).
There has been a lot of discussion about high power recently. You have to
be a member of either the NAR or Tripoli to fly rockets with H motors or
above. To fly with H or above both organizations require that you be
'certified' by safely demonstrating a successful flight with a high power
model in the presence of one or more 'qualified' members of the
organization. There is now a HPR safety code as well as the original
model rocketry safety code. There are expendable and reloadable
(discussed below) HPR motors available. They are increasingly
expensive as the power goes up ($13 for a G up to hundreds of dollars
for a really big (O) motor). High power rockets start where model
rockets leave off (i.e., > 1500 grams). High power models weighing
more than 50 pounds are not uncommon. The record weight for a high
power flight is over 1000 pounds.
Oh, yes, HPR requires a duly authorized, signed-in-blood (in triplicate,
etc.) FAA waiver for each day you wish to fly. It is ILLEGAL to fly
high power rockets without a proper waiver. See Part 10 of this FAQ for
more information on FAA waivers.
Depending on the type of motors you buy, use, and store, as well as where
and how you buy them, you might need some additional, FEDERAL, permits
for high power rocketry. More on this below, and a lot more in Part 1 of