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jan 15, 2001 For a long time I have been thinking about hobby rocketry. I always played with model rockets when I was a kid, trying to make something that would go faster and higher. I had this one rocket called the silver bullet, which housed a cluster of 5 class C solid rocket engines. The trick in lighting this rocket was to get all 5 engines started before the rocket, which was obnoxiously light, left the launch pin! If you only got a partial fire, the rocket would circle around and around and invariably end up broken somewhere. I learned quickly to use a car battery instead of the whimpy 4 double A battery thing they give you. That usually got things started in a hurry. Besides, with a good car battery, if you ran out of solid rocket igniters, you could always just bend a piece of wire and use that! The logical place to graduate is into the sport of high power rocketry. These are the groups that require FAA clearance to launch their rockets 50,000 feet into the sky. They can usually be found on the Black Rock Desert, which is a dry lakebed where you could walk for miles and not get anywhere. They launch both solid and liquid propellant rockets there where the margin of error is 30 miles wide and over 100 miles long. But I got to thinking. First there was the space race between the United States and Russia, which culminated in moon landings. I think that the next big space race will be for the model rocket hobbyist. The High Power Rocketry crowd has briefly gotten into space, but I think that the next goal is going to be a successful earth orbit. After that it'll be on to the moon and back. So how would one get a model rocket into orbit? Well, we will have to answer several critical questions first. How do you drive the rocket up there, how do you track it, and how do you get it back? Well, for a successful orbit, you don't really need to get the rocket back. You can always just go for the orbit, but it would be cool to take the orbiter back home with you at the end of the day! The way I see it, the high power rocketry people have proved one thing. For whatever reason, be it permits or thrust to weight ratio, it is less than practical to shoot a rocket off of the earth and into space for orbit. (yes, NASA did it, but they had less limited resources.) So I got to thinking about it and I thought why not use one or more atmospheric balloons to transport the rocket into the upper atmosphere. It is not unusual to attain altitudes of 100,000 feet with an atmospheric balloon. In this case, you would avoid having to propel the rocket through thick atmosphere where most of your fuel would be used up just counteracting gravity and drag. At 100,000 feet, most of your fuel will be used getting the rocket up to orbital velocity rather than counteracting friction with air. Orbital velocity is somewhere in the neighborhood of 11 km per second, so you probably want to start an arc after a horizontal launch from the balloon to clear a good bit of the remaining air. The less air you have to push out of the way, the more energy you can use to get the rocket up to orbital velocity. Getting up to 11 km per second from a virtual stand-still will take some time, but considering that combustion in the upper atmosphere where there is less air pressure gives greater speeds, you have a bit more working for you than at sea level! So let's say that we get into orbit. How do we know we're there, and for that matter, how do we control the rocket? NASA has access to a world wide network of communication equipment called the Deep Space Network, which is used to track and communicate with the Space Shuttle and other objects in orbit around the earth. We won't have that, so our flight control is going to have to be on board the rocket in the form of a computer. Whenever the rocket is in range, we'll have to batch transfer statistics and commands. For this reason, an orbit that tracks the same course on the ground each revolution would be ideal. How does the rocket know where it is? Well, we stick a $100 GPS receiver in it and hope that the rocket stays within the footprint of the GPS satellite system. GPS satellites orbit at an elevation of 11,000 nautical miles and circle the globe in 12 hours. Seeing as we will probably be below 11,000 nautical miles, we can use GPS for macro navigation and positioning data. Micro navigation would likely be done with one or more gyros with course correction done by rudder fins and small retro jets. Computers are fast, cheap and small. The only possible problem that we would run into running a solid-state computer in space is shielding. We're probably going to have to sacrifice a bit of weight and get some lead to cover the electronics. Regular satellites use hardened circuitry, but that's going to be a bit expensive for our purposes. We'll also forgo the use of a nuclear reactor for power in favor of some lithium batteries. Reentry should really be just a calculation of when to fire the retro jets to force the orbit to decay. After the initial entry where the rocket will get quite hot, we fire a small drag chute and wait until we have 5,000 feet of altitude before firing the main chute. We'll probably want to target an ocean and possibly inflate a balloon to keep the ship from sinking. Then any kind of radio transmission should be sufficient to find the rocket. Now for a dose of reality. NASA has a relatively perfect safety record. Yes, they have had disasters, but when you look at the total number of successful manned and unmanned missions NASA has had, the number is exceptionally low. On the other hand, almost half of the high power rockets fired in Black Rock Desert have some sort of failure. Now we're not transporting a human into space and back here, but you get the idea. To combat the lack of aeronautical spec machining and meticulous design by world class engineers, the hobbyist rocket community will have to build hundreds of crafts capable of making the flight. By shear numbers, one of those rockets will eventually make it. Once we reach orbit, the moon is not far away. If you consider the time it took for NASA to move from their first manned orbit (Feb 20, 1962) to landing man on the moon (Jul 20, 1969) we are only talking about 7.5 years. I'm willing to bet that the time duration between a model rocket hobbyist sending an unmanned craft into orbit and an unmanned rocket to the moon will be less than 7.5 years. Granted, there was quite a bit of political pressure to put a man on the moon in the 1960's but I'd argue that a hobbyist's passion would close the gap more quickly. Imagine being the first hobbyist to send a model rocket to the moon! May 17, 2004 Today the first model rocket has reached space. (100km altitude) See http://www.civilianspace.com/ for news. |
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