FAQ : Frequently Asked Questions
This FAQ has not been updated in many years.. It was borrowed from Ray Calkin's old aRocket.net website in 1998 (with his permission) after having been put together by contributors to the rec.models.rockets newsgroup. It could really use some updating. If you are kowledgable, up to the task, and have the time, please let me know via the comments form. You will be given full credit for the update, and a 6-pack of the beer of your choice, for your efforts. Thanks! :)
This FAQ is not intended to be a complete course in rocketry. It covers some basics and has pointers to further information but from there, it's up to the reader. If there are any errors or if you know of something that really should be included, please email it the authors: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org.
Some parts (it should be obvious which) are the authors' opinions. Feel free to disagree. While the authors tried to ensure the accuracy of the information in this FAQ, we make no warranty, express or implied, as to the validity or usefulness of anything that follows. You pays your money and you takes your chances.
TABLE OF CONTENTS
- Rocketry Classes
- Internet Resources
- Frequently Asked Questions
Ammonium Nitrate: Solid rocket oxidizer
Ammonium Perchlorate: Solid rocket oxidizer
Change in velocity
Expendable Launch Vehicle
Gross Lift Off Weight: total rocket mass at the moment of lift off
Hydrogen Peroxide: liquid oxidizer/monopropellant
Hydroxyl-terminated polybutadiene: Solid rocket fuel/binder
Fuel and oxidizer ignite spontaneously upon contact
Destiny Specific Impulse: product of specific gravity and specific impulse
Thrust Force * Time
Specific Impulse: Thrust force per unit weight flow of propellant
Final mass (after propellant burn) divided by initial mass
Monomethylhydrazine: liquid fuel related to hydrazine
Propellant mass divided by initial mass
Reusable Launch Vehicle
Red Fuming Nitric Acid: liquid oxidizer; nitric acid with 5% - 20% nitrogen dioxide
Kerosene like fuel of higher purity for use in rocket engines
Single Stage To Orbit
Two Stage To Orbit
Unsymmetrical Dimethylhydrazine: liquid fuel related to hydrazine
Extra volume of gas above propellants in the tanks
The kind of rockets everyone fooled around with as a kid. It uses only premanufactured, solid motors from class A to G. Restrictions: GLOW not to exceed 1500g; Each motor not to exceed 62.5g propellant and/or 160 NS impulse; Total propellant not to exceed 125g; No metal structural parts.
HPR - High Power Rocketry
Scaled up model rocketry, using the same basic methods for construction, though metal parts can be used if necessary. It uses only premanufactured solid or hybrid motors from H to O. There are no weight restrictions, but each motor may not exceed 40,960 NS impulse and the total impulse may not exceed 81,920 NS.
Anything that falls between HPR and professional rocketry. This includes liquid fueled engines, metal structures, building your own motors, and just about anything else you can think of. There are no formal definitions or requirements, other than the laws of physics and your government.
Different people have used this to mean different things, but essentially it's the same as amateur rocketry.
Rocketry conducted for profit, usually by governments or large corporations.
NAR - National Association of Rocketry
The organization that regulates model rocketry in the United States.
TRA - Tripoli Rocketry Association
High power rocketry organization in the United States.
CAR - Canadian Association of Rocketry
The organization governing model and high power rocketry in Canada.
PRS - Pacific Rocket Society
One of the leading amateur rocketry organizations.
RRS - Reaction Research Society
The oldest amateur rocketry group in the United States, which operates a 40 acre test site north of Mojave, CA and Edwards AFB.
ERPS - Experimental Rocket Propulsion Society
Experimental Rocket Propulsion Society.
Books on Spacecraft Design and Spacecraft Systems
A listing of recommended reading on several spacecraft topics.
Blue Sky Rocket Science
This site focuses on solid propellants, with information on formulations, mixing and testing.
The most comprehensive model rocketry site on the net, it also has a few tidbits about amateur rocketry.
Rocketry.Org (This web site)
This web site, focusing on experimental and amateur rocketry.
DARTS Rocket Tracking System
A sophisticated computerized radar system for tracking rockets.
"How to Design, Build, and Test Small Liquid-Fuel Rocket Engines"
A great, but old, book on designing, building and testing small liquid fueled rocket engines.
The newsgroup dedicated to discussion of space hardware and technology. Occasionally, there are threads of interest to amateur rocketry.
This newsgroup is primarily for model rocketry and HPR so in-depth discussion of amateur rocketry wouldn't be appropriate, but occasionally something turns up that is of interest to amateurs.
The AUSROC Project
One of the most advanced (and certainly best documented on the net) amateur rockets ever built. Their detailed design report is very informative.
A DOS program that allows you to experiment with different combinations of fuel and oxidizer.
A graphical front end for PROPEP that makes it much easier to use.
The folks who publish the mammoth set of industrial sourcebooks have put their database on the web. Once you register you can search for suppliers absolutely free.
Chemical Propulsion Information Agency
Run by Johns Hopkins University for the US Department of Defense. This web site has a searchable database of citations from 16,000 technical papers.
Which is best for amateur rocketry: solid, liquid, or hybrid propulsion?
The question gets a lot of debate. As with anything else, it depends on a number of factors, and there's no definite answer. Factors that should be considered include: your personal background and knowledge; size of rocket; impulse required; specific impulse desired; thrust; monies available; reliability factor; materials and equipment available; legal aspects; etc.
Generally, very small rockets (up to several kg or tens of kg) are easiest to build as solids or hybrids, and a lot of the technology is already available. Liquids provide the highest specific impulse and are most economical in larger sizes but are more complex. Hybrids tend to bridge the gap between liquids and solids, providing better impulse in mid-size than solids and being simpler than liquids.
"How do I build rocket motors?"
There is no easy answer to this. You need to buy the books, join an amateur group, do the research, and understand what you're doing. Blindly following a recipe you found is asking for the sudden removal of your extremities.
"Where can I get LOX?" (liquid oxygen)
Check with welding supply companies in your area or with the local outlets of Air Liquide and Praxair, listed in the Suppliers section. If all else fails, medical supply companies sell it for respirators, though you'll pay through the nose (pun intended) and they may have restrictions. Price varies widely, so shop around.
"Where can I get transducers, DAQ boards, valves, fiberglass, etc?"
Check out the suppliers section below and the yellow pages in major cities. If you can't find what you want, try the Thomas Register at a university library or online (see the Internet Resources section above.)
"Putting a rocket into orbit looks easy. How come no amateur has done it yet?"
Short answer: Because it ain't easy, not even close.
Long answer: There are several inter-related reasons: Scalability, Materials, Methods, Development, Cost, and Time.
SCALABILITY: Some rocket components are impractical on a small scale, for instance turbopumps and hydraulic systems. Rockets also suffer from the effects of the cube/square law as they get smaller, particularly tanks.
MATERIALS: There is a sliding scale of price and performance: steel,aluminum, alloys, fiberglass, graphite, and someday, buckytube. Generally, the higher the strength to weight ratio, the higher the price. Graphite fibre is *expensive.* And if you go cheap, performance suffers.
METHODS: Advanced manufacturing techniques are likely to be out of reach of the average amateur. Not many of us have a filament winding machine in the garage. And the best way to implement regenerative cooling is to machine the coolant passages in the walls of the engine, fill them with wax,electro-deposit a "roof" and then melt the wax out. That's beyond the capacity of any amateur I know. If you contract for those kinds of jobs, you drive the price way up, and if you use simpler methods, performance suffers.
DEVELOPMENT: You can't buy a kit, slap the pieces together, and put a satellite in orbit (not yet anyway.) This is real R&D: you're going to have to build a prototype, test it, build another, test it, build another and soon. For each of three stages. And things go wrong: valves stick, plumbing leaks, rockets blow up. And then there's the support equipment; you're going to have to build a test stand, data acquisition system, fuel loader, launch pad, tracking system and more. All of this takes time and, yes, money.
COST: The big one. All the other factors contribute to the cost, and it adds up in a hurry. How much would it cost to do a "Sputnik?" More than $25,000. Some groups have spent that much already, and are still nowhere near orbit. $100,000 is probably in the ballpark. (Note: that's the cost of the entire program, not just the flight.)
TIME: The key word here is "amateur." These people are not paid to build rockets. They have regular jobs and only do it in their spare time. This doubles or triples development time.
Short answer #2: If that still doesn't convince you, try it yourself.
"What materials should I use for my rocket motor?"
In Appendix C of Huzel & Huang there is a brief description of the materials being used in modern rocket engines.
"Why don't we start a newsgroup for amateur rockets instead of a mailing list?"
Mailing lists have a very strong self-selection factor; you have to want to join up. Moving to a newsgroup would bring a higher profile, but it would also bring the spammers, flamers and the truly clueless. The average IQ in USENET has been plunging in recent years, with no sign of bottom. Most of us do not want to be pestered by endless repetitions of Question #1.