02/05/96

Dear Glen:

 My name is Joe, I have a degree in Aerospace Engineering with a background in propulsion. I am writing in response to your "Manned Model Rocket Project" proposal which you submitted to my company. I must admit that when I first opened your package and read the title I was highly skeptical. As I read your proposal however, and did some number crunching with your various specifications, I came to the conclusion that the task probably could be accomplished for both reasonable cost and risk.

If you will bear with me I do have some comments and suggestions for you.

My first suggestion is you change the name of the project. I believe that you may have trouble convincing potential (non technical) corporate sponsors that you want to launch yourself in a large model rocket! I also feel that the term "Model Rocket" does not reflect the serious challenges that this project will pose.

 Ive enclosed some copies of photos that I took at Edwards AFB in 1979 when Budweiser sponsored a rocket powered car to break the sound barrier. I believe if they were able to obtain corporate sponsorship so should you.

 While your proposal to use a solid rocket to boost a mortar type vehicle is certainly feasible and probably could be done safely, I have drafted a proposal that I think would have some advantages.

Propulsion

Although solid propellant rockets are certainly easy to use, just light the candle and go so to speak they are not easy to design and build.

Some of the factors that must be considered are....

• What type of thrust time curve is desired?

  progressive?

  regressive?

  neutral?

• The trust time curve will determine the propellant grain geometry.
• The propellant must then be mixed and cast into the motor casing while molding the proper grain geometry and avoiding the formation of void spaces.
• Ideally the propellant should be degassed in a partial vacuum, and curved in a temperature controlled oven.
• This all must be done with approximately 200 pounds of highly flammable propellant.
• Of course the one major operational disadvantage of solids are their lack of controllability, once lit there is no stopping them!

 For the last year I have been developing hybrid propulsion systems for high powered rockets and have been very pleased with the results. The fuel grain (HTPB) is very easy to cast. With the use of plasticizers it can be poured easily like any liquid. A simple port burning fuel grain exhibits neutral burn characteristics. The fuel is virtually inert under normal conditions and poses no combustion hazard. the oxidizer, nitrous oxide, similarly poses no hazard under normal conditions and requires no preparation. The Nitrous oxide is simple injected into the combustion chamber and the motor is ignited! One of the other features I like about this system is its controllability. The motor can be started and stopped at will, a handy feature if your were to find yourself veering way off course. My test stand is computer controlled and I have consecutively started and stopped a motor up to three times. The motors can be throttled to some degree, and with some work I believe they could be throttled over a fairly wide range. (Not suggesting we necessarily develop throttleable motors for your project). Another attractive feature of the hybrid system is that it is reusable, and can be designed to be expandable, in the event a higher total impulse were desired at a late date!

 Ive enclosed sketches of two preliminary designs of hybrid motors for use in your project. The 5500 LB thrust motor design to be used with your mortar type airframe, and the 1500 LB thrust motor to be used in an airframe I propose and will discuss below.

 Airframe

I assume that the reason you specified the large diameter crew compartment and small diameter afterbody is to reduce the chance of striking the vehicleif you had to bail out while still in forward flight during an emergency situation. (e.g. if the parachute failed to deploy properly). One problem you may encounter in such a situation are the recirculation zones that exist behind bluff bodies like the crew compartment. These recirculation zones would tend to pull you in, putting you on a possible collision course with the fins or afterbody.

One way to avoid this hazard would be to build a vehicle that had no fins or afterbody. I propose building a conical shaped vehicle that is inherently aerodynamically stable and requires no fins. The vehicle would have an open canopy, and in the event of an emergency egress situation you would simple pull yourself up onto the head rest and lean backwards to let the slip stream slide you off the back of the vehicle like a sliding board.

Another advantage of the conical shaped vehicle is it structural stability. The load from the smaller forward sections are distributed over the larger areas of the sections immediately behind.

A conical shaped vehicle would also be very easy to build since it is composed entirely of straight lines. With the low acceleration involved (3 to 4 Gs) it could be constructed of anything from aircraft grade lumber to composite materials.

Please keep in mind that all calculations and proposals are preliminary and are not etched in stone. For example upon further examination it may be decided that a hydrogen peroxide solution or liquid oxygen may be preferred to nitrous oxide. Or perhaps a closed canopy may be desired over an open canopy. There is a lot of work ahead to be done! Please review this, and let me know what you think.

Good Luck

 Sincerely,

 Joe