In a previous post, I made the assertion that trees eat rockets. I would like to add to this assertion that lakes, ponds, and other sundry bodies of water consume rockets.
Every rocketeer seems to be afraid of something. Many are afraid that their parachutes will never deploy or will deploy at the wrong time. Some are afraid that their fins will flutter, break, or be completely ripped out of their rocket on the ascent. Still more are deathly afraid of the motor CATO. Me? I’m afraid of trees (but only in the context of rocketry). I am convinced that all the trees near launch sites are rocketvores, and I’ve lost my fair share in unreachable branches. I am further convinced that the more expensive and/or less common a rocket or part is, the more like it is to get eaten by a tree. Just the other day, my brand new crayon rocket with a nice new Stratologger found its way into a tree about a hundred feet up. Had it stayed aloft a half second longer, it would have cleared the trees and landed in the grass.
I’ve also landed a nosecone for the SpaceX Falcon 9 in a tree. Unfortunately, the nosecones for that rocket are not a commercially available component, so I found myself scrambling for a solution to the missing part dilemma (see the previous post). In some respects, losing a single component is more disappointing than losing an entire rocket since there is closure in knowing that the whole thing is gone rather than just a part.
Let it be known that if I ever own a flying field, the first thing I’m going to due is take a chainsaw and raze the place to the ground for a mile around. Of course, then, I’d have the rocket that drifts a mile and a foot into the trees…
There is no question that additive manufacturing technologies like 3D printing are going to be game-changers in the aerospace industry and manufacturing in general. In the past, most components for aerospace were made using subtractive manufacturing. Processes such as drilling and facing remove material from a piece of stock to reveal a part. Naturally, this leads to a lot of wasted material. Furthermore, to create all part features, multiple processes may be required—one side may need to be faced, two sides may need to be drilled, and one of those sides may need to be counterbored. Already, four different processes are required to create the listed features, processes that cost time and money. With subtractive manufacturing, some features such as cooling channels in turbine blades are practically impossible to make. For this, manufacturers rely on castings, a basic form of additive manufacturing where molten metals are poured into molds. Still, the molds must be made using subtractive processes, presenting the same dilemma as before.
Enter 3D printing. Technology like 3D printing works by depositing layers of material onto a surface to build up a three-dimensional body, much like stacking LEGO bricks to create a much larger model. Of course, rather than depositing large bricks, 3D printers deposit fine layers of material as little as 20 microns in thickness one layer at a time. Because each bit of material is added to a part rather than removed, any physically possible feature, externally visible or invisible can be created using 3D printing. Better yet, the entire part can be created in a single process (not counting finishing processes and coatings) without having to change tooling or part orientation. The process is not instantaneous like printing off a document on an inkjet printer, but it is comparable to the time it takes to make a part with multiple features using subtractive processes. The technology also minimizes wasted material since only necessary material is added to a part. Current 3D printers can make parts out of a variety of materials from thermoplastics to aerospace metals. (It is worth noting that each printer is compatible with a narrow band of materials, so your average desktop 3D printer can’t print a metal nozzle. You’ll need a much more expensive Direct Metal Laser Sintering (DMLS) printer for that.)
The cost of 3D printing has dropped significantly as the technology has developed. You can get a basic Makerbot 3D printer, which prints using ABS or PLA thermoplastics for about $2,000. The models shown in this post were printed in PLA using Makerbots owned by Georgia Tech, and you can see that the quality of the parts is pretty good.
If additive techniques can be applied to so many different fields, I figured why not bring 3D printing into rocketry? Not to be confused with addictive rocketry, which I have found to be an also-truth, additive rocketry has proved to be quite useful in making a variety of parts for my rocket fleet. I’ve made a replacement nosecone for the SpaceX Falcon 9 kit (download my model for free) and a custom transition unit for 3.9 inch body tubes that the Georgia Tech Ramblin’ Rocket Club stocks to 3 inch body tubes. Unfortunately, I have been unable to flight test any of these components, but they appear to be much sturdier than the paper components I typically work with. I am currently in the process of designing an entire rocket to be 3D printed. Since the printer work space is limited, the rocket will be printed in three 6-inch segments and glued together where appropriate, but no other assembly besides parachute, shock cord, and motor installation is required. I am excited to see how it performs.
I am also using 3D printing for my Level 3 project. Rather than using composite skin reinforcements or tube stiffeners, which are either out of my realm of expertise, are too costly, or both, I intend to use 3D printed plastic stiffeners to add strength in shearing situations. This simple, cheap, and lightweight solution promises to add strength where extra strength is required so as not to cause shearing tears in the thin cardboard couplers. I hope this will also aid in accelerating the shear failure of my nylon shear pins during parachute ejection. Below is a picture of the stiffener for riveted inserts. (I’d like to be able to disassemble the rocket for transport since I have a small car, but I’d like it to stay together for the duration of flight.) Each riveted joint will be bound by two rows of 0.163″ nylon pop shank rivets in a hexagonal formation.
I used a similar design for the shear pins. Each shearing section is held together by three #2 nylon screws. These stiffeners are designed to be glued to the interior of a 5.38″ cardboard tube coupler so they don’t interfere with the coupled fit. The shear pin stiffeners are shown below.
Not pictured are some 3D printed drill guides for drilling holes for the rivets and shear pins. Since precision alignment will be critical for the proper function of the stiffening inserts, I took the liberty to print out the tooling to make the job easier. Yet another great use for 3D printing in rocketry!
Today, December 14, 2012, marks the 40th anniversary of the end of man’s greatest adventure. It is hard to believe that forty years have passed since Astronauts Gene Cernan and Harrison Schmitt lifted off the surface of the Moon—forty years since humans have impressed their footprints in the lunar soil. We have not dared to send man beyond Low-Earth Orbit since 1972, despite an explosion in technology and potential. Having a space station in an easily-attainable orbit is not a bad thing, and the ISS has certainly contributed significantly to our understanding of science, but our prolonged stay, fearful to venture beyond the safe confines of the horizon, has set back our ventures beyond the surly bonds of Earth.
Apollo XVII was, perhaps, the grandest of the science missions. A J-mission, Apollo XVII featured the longest total lunar surface EVA time, the largest lunar sample return, and the longest lunar flight. Commander Gene Cernan and LM Pilot Harrison Schmitt, the only astronaut formally trained as a geologist, performed three EVA’s, gathering vast amounts of valuable information about the Moon. When it was all said and done, the two had each spent over 22 hours on the lunar surface outside the protection of the Lunar Module. While Cernan and Schmitt were on the surface, Command Module Pilot Ron Evans was busy taking observations and performing experiments high above the lunar surface.
So why aren’t we going back. The technology is there. We know how to get to the moon, and we could theoretically accomplish the task fairly readily. With superior computing power, more efficient propulsion technology, and lighter, stronger, more magical materials, the Moon is a very easy target for a nation that went from having no space program to speak of to delivering humans safely to other worlds in less than a decade. Sadly, it is not politically advantageous to have a vision for space. We no longer seem to be at odds with a foreign power, seeking to claim victory in space. We pay Russia millions of dollars to deliver our astronauts to the same old Low-Earth Orbit, and we do not take seriously the Chinese ambitions in space.
It saddens me to see how we’ve lost the dream. So close is the Moon to our grasp, yet we don’t reach farther. We could see farther by standing on the shoulders of giants, but we’ve given up the vision. We’ve stopped exploring. Sadly, Gene Cernan’s final words before departing the Moon did not invoke a new exploration or a golden age of space, but we can always wish.
“I’m on the surface; and, as I take man’s last step from the surface, back home for some time to come — but we believe not too long into the future — I’d like to just [say] what I believe history will record. That America’s challenge of today has forged man’s destiny of tomorrow. And, as we leave the Moon at Taurus-Littrow, we leave as we came and, God willing, as we shall return: with peace and hope for all mankind. Godspeed the crew of Apollo 17.”
~Gene Cernan, Apollo XVII Commander