Derek Deville Answers Your Questions on Rocketry

Derek Deville Answers Your Questions on Rocketry 33

Posted by timothy on Monday November 07, 2011 @02:34PM from the not-just-a-weekend-thing dept.

After his amateur rocket flight in the desert (to 121,000 feet!), you asked rocket enthusiast Derek Deville about the project. Derek's responded to a selection of the best of those questions; read on below for his replies.

Education
by Maladius

Where/how did you learn the information needed in order to pull off a feat like this? Related: How long have you been working on these types of projects?

Derek Deville: I got started in High Power Rocketry in 1996 after finding out about Tripoli, the national hobby rocket organization. I started attending Tripoli launches in West Palm Beach (I live in Miami) and quickly got certified Level 1 and 2. With that I could fly rockets up to "L" power (5,120 N-s) which have about 5 lbs of propellant. I started a chapter of Tripoli in South Florida and got a waiver to fly to 25,000' in a tomato field about 20 miles south of Miami. Shortly thereafter I got my Level 3 certification which opened the door to any size rocket. For the next 7 years I flew rockets almost every month, logging hundreds of flights with every increasing size and power. I took a hobby course introducing me to making my own propellant. That got me hooked.

I started talking to all the guys that were making the biggest hobby motors and started tinkering with even larger motors of my own. By 2000 I was making "P" motors with about 50lbs of propellant in them. This was on the high end of what the hobby was doing. I wanted to take it even further. I started doing a lot of research with AIAA and reference textbooks. I connected with several of the hobby rocket motor manufacturers such as Paul Robinson, Frank Kosdon and Gary Rosenfield. I also connected with some of the related scientific community such as Professor Terry McCreary and Charles Rogers. From these folks and my independent studies I was able to further my understanding of propulsion science.

In 2001 Korey Kline found me through my hobby exploits and invited me to join Environmental Aeroscience Corp (eAc) in developing a hybrid propulsion system for SpaceShipOne. It was the opportunity of a lifetime. For several years we fired some of the biggest and best hybrid rocket motors ever made. Hybrids use a solid fuel grain and liquid oxidizer such as Nitrous Oxide. In some ways these are similar to solids, but mostly they are a breed all their own. In 2004 after completing our work with Burt Rutan, Korey and I were asked to join the Civilian Space Exploration Team. We originally intended to make a large hybrid for them for their SpaceShot, but they weren't able to control the dispersion to the satisfaction of the FAA, so we switched to a solid.

Korey insisted that a full scale motor be test fired. During that process we learned a lot. We made an "S" motor that flew to space in March 2004. That was and remains the largest successful amateur motor ever made. The Qu8k motor is one third scaled down version of that motor. Because of the CSXT experience, I had even more data for my motor design and was able to go into Qu8k with higher confidence.

Theory vs Practical Experience
by Toonol

How much of the design of your rockets come from trial and error, and how much from more formal principles of rocketry? Or, in other words, how much of the planning comes from deliberate application of physics, ballistics, etc., and how much from past experience?

DD: The vast majority of the Qu8k design came from deliberate application of design principals. This is particularly true for the propulsion system, flight simulation and vehicle structure. The important thing that comes from past experience is knowing what the failure modes are so that I can design and test as necessary to prevent them. There are aspects of the rocket that come from rules of thumb generated from many years of experience. One example is the area of venting necessary for the payload section. I can ballpark the required area but it doesn't take into account all the variables. It is a function of the volume of the payload section, how quickly the rocket changes altitude (outside pressure) and what pressure the nose retention system can tolerate. All I can do in a case like that is make a best guess.

Thoughts on N-Prize, doable?
by foolish_to_be_here

I'm very impressed. Great job. Question: Do you have any comments on an N-Prize sort of launch? Do you feel it is achievable at even one orbit? If so are you part of a team?

DD: I am not part of any N-prize team. I do not think that the goals are achievable as defined. The tracking portion alone is a mammoth undertaking, and from my rocket experience I know that the expense of a launch vehicle will far exceed the stated budget.

Balancing work, family, and play?
by thermopile

I was impressed and somewhat humbled by all the different activities you had featured on your website. Do you ever sleep? In all seriousness, how do you (appropriately) balance work, family, and play time? In looking at your website, you seem to do at least two of those (family + play time) very well.

DD: Thank you so much. I am passionate about all three. My family is the top priority. A lot of the groundwork for my current ‘play' came before the family. I am a little OCD so when I get into something I really commit. Work had been engrossing for the past two years and I had to back-burner hobbies. I saw a break in work coming and took advantage of that to do Qu8k. This project was conceived in July and the work was done between August and September. Now I'm back to working and family. I can't wait for the next opportunity to do more rockets.

Machinery
by vlm

I looked at your website pictures; clean shop (cleaner than mine, anyway); Curious what type of equipment you used to build it. I see a Bridgeport-style knee milling machine, a large unidentifiable lathe with a quick change toolpost. Chinese or classic American heavy iron? Nice smoke off the carbide (carbide, unlike HSS, can be pushed hard enough to make the cutting oil burn without wearing the cutting edge) Looks like all manual machines, no CNC? TIG welding the aluminum or ? Did you CAD it all up or build as you get parts? Is something like this rocket light enough to manhandle around the shop or are their engine cranes involved, or a custom cradle of sorts?

DD: The machine shop is at my employer Syntheon. We have a Haas Mini Mill CNC but it was not used for any of these parts. We did all the CNC work on the ProtoTrac which looks just like a standard mill but has a controller attached. The manual mill and lathe were the primary tools. As you can see we had to get creative to work with 8 foot long parts. The CAD model is fully featured. The models were being refined during the fabrication due to the short timeline. The motor is the only part that started to get too heavy to handle comfortably. Once the propellant was poured it weighed 256 lbs. I actually ended up injuring my back from moving it too much. And yes, TIG welding for the fins.

Passive vs active stabilizing
by jd

For low-altitude rocketry, passive stabilizing is just fine. When you start getting to the heights your rocket is reaching, it's hard to imagine that this is still the case, yet your diagrams on your website show no active mechanism for keeping the rocket upright, the base fins for stability and that's about it. (Actually, given the wind sheer, it would be almost as bad to be blown horizontally yet remain vertical. To fix that, you'd need full-blown guidance.) To be fair, though, the diagram is hellishly crowded and you may well have kept the details to what would be the most interest/use to the most people.

So, are you using active mechanisms in your current rockets and, if not, are you planning on adopting any in future projects?

DD: For the type of Class 3 waiver that I was flying under, you can't use active guidance. Anything other than simple fin stabilization requires a full blown launch license which needs a range destruct and so much more.

I make sure that I have at least 1.5 calibers of stability at all Mach numbers and at least a 7:1 thrust ratio off the pad to keep things pointed straight up.

Temperature/Pressure
by Maladius

I noticed you said the temperature at its lowest was -32C, and the pressure was only 93 Pascals. Did you need special electronics/cameras in order to operate under these conditions?

DD: Since the exposure time was low, the only thing I was concerned about was the pressure. I tested the electronics function in a vacuum chamber before the flight.

Accuracy and difficulty
by planckscale

To what accuracy is the thrust nozzle lathed? In the rocketry movie October Sky, I recall that the nozzle/motor was the most important build. Which component required the most math/sweat/swearing?

DD: The nozzle was outsourced to a company that could CNC lathe graphite. They hold +/- .005 but that wasn't critical. I could easily tolerate two or three times that on the throat diameter given the overbuilt nature of my motor casing. This is a function of the type of propellant used and for me I my propellant is relatively insensitive. As a general rule though, we held tight tolerances on all the parts.

The thing that gave me the most grief was the fin can. The tube for the fin can needed the ID turned which required a lathe much bigger than what we had, so I had to outsource that at great expense. Then the welding of the fins caused the tube to deform and I ended up spending hours grinding on this finely machined ID to make it fit over the motor. To make matters worse, this was one of the last parts fabricated so I was working on it right up until the shipping deadline.

Rocket Assists
by jd

There are a lot of projects that aim to give rockets an assist at the start. NASA has experimented with ski ramps (and is back to them again) but has also played with turbine-assisted ramjets and variants thereof. ScaledX opted for a hybrid liquid/solid fuel motor, to get the controllability of liquid fuels with the oomph and reduced weight of solid. Have you considered any non-standard design or are you more in the "keep it simple" camp?

DD: I have worked with hybrids a lot. I prefer solids for simplicity. The objective of this launch was success. I did everything I could to reduce risk wherever possible. I have concepts for more exotic mixed propulsion systems in the future, but flying them without ground testing is crazy and I don't have access to the right test facilities now.

Oldest and newest flight technologies
by deathcloset

I (and many others) have been thinking about balloon-assisted launch systems recently. Balloons seem like an excellent and flexible launch element which could offer a ton of altitude and avoidance of at least some friction. Have you heard of or considered this?

DD: I am familiar with these schemes. I have not explored this at all. As tricky as it is to get this right while on the ground, I can't imagine doing it in the air.

Spinning
by notKevinJohn

Of all the rocket launch videos I have seen, your had by far the least amount of spin on the way up, no doubt due to precision engineering/machining on your part. Have you ever considered launching a camera with a wide angle lens that could see 360 degrees around rocket and then removing the spin from the resulting video with software?

DD: I haven't thought of that method, but have discussed several other methods. I think the main issue is that with any system, if the camera is panning rapidly, with any normal exposure time the view will be blurred by motion. I recently saw this roll stabilizing system which I think shows great promise. And yes, lots of effort went into making the fins as straight as possible to reduce roll.

Potential range
by mattr

23 miles is a great feat, congratulations!

I'm a layman but having read about the stroke victim in Antarctica I got curious about the application of aerospace technology to emergency transport, rescue, communications, observations, and whether focus on these issues could help attract funding to civilian engineering teams.

For example, it is apparently 5430km from Wellington, NZ to the Amundsen-Scott South Pole Station, and more like 6000km from Australia. What would it take (team, cost, time, technology) to build an emergency aid rocket, or rocket-assisted aircraft that could be set on stand-by to deliver for example a medicine, part or surgical tool to the Pole Station? Since the South Pole is not actually west of anywhere you can't take advantage of the Earth's rotation. Is it even possible to reach the Pole with a suborbital vehicle? If it was something like a scaled up, navigable version of your current rocket, what kind of stresses, temperatures would the payload experience (would medicine have to be kept warm? would anything mechanical get warped by the vibration/shock?)

DD: Wow, that's a whole lotta question. The first thought that comes to mind is that I don't want to be in the station the rocket is pointing at in case something goes wrong. The next thing is that I don't think an unguided rocket would have the accuracy required. I think you could get there with a big enough rocket, but I don't think it would be cost-effective.

Developing interest in rocketry?
by Registered Coward v2

As an old-school rocket hobbyist — one of the good outcomes was furthering an interest in science and engineering. Personally, model rocketry influenced my decision on which university to attend (one of the professors there was heavily involved with the NAR) and design to study Aeronautical and Astronautical Engineering. How can we foster the same interest today, given the attacks on rocketry by various well meaning, but misguided, agencies?

DD: Things have been looking up for rocketry. Recently Tripoli (the other national rocketry club) along with the NAR successfully sued the BATFE to get APCP (our most common propellant) taken off the explosives list.

I hope that the video of Qu8k can be shown in schools and used to inspire kids to dream big. I am working with the Symbyosis Foundation on a student payload project. They will be soliciting payload ideas from high schools and universities. The top concepts will get funded and get a chance to fly onboard the next flight of Qu8k. If anyone reading this can help spread the word, please direct interested parties to symbiosis-foundation.org/speer/speer.html.

Limits on GPS for Civilian Use
by PhunkySchtuff

How do you get around the restrictions on civilian GPS. While I'm sure this was taken into account, civilian GPS receivers are limited to speeds quite a bit below the speed achieved, and altitudes of around half of the achieved altitude:

"The U.S. Government controls the export of some civilian receivers. All GPS receivers capable of functioning above 18 kilometres (11 mi) altitude and 515 metres per second (1,001 kn) are classified as munitions (weapons) for which U.S. State Department export licenses are required."

3,516 km/h is just over 975 m/sec and you estimate an altitude of more than twice the restricted altitude.

Even if it's a soft fail in the GPS module and it cuts back in when the "out of spec" conditions are no longer experienced, it would still make it difficult to record the maximum altitude if you're 18+km above that which a regular GPS will register.

DD: When these Cocom limits are properly implemented as an "and" condition then the data will resume when the speed drops below 1000 knots even if over 18km. The gps data dropped out for me way before these limits were hit so it's safe to say this wasn't the problem for me. It was a concern before the flight and I had intentionally selected hardware the I believed had proper implementation. There are ways to get permission to have these limits removed, but I don't think that I'll be worrying too much about gps for altitude data on my next flights. I am starting to work with some folks to create a low cost radar system that I think will work better for altitude measurement. I think the main role of gps in rockets will be to assist in recovery which worked wonderfully for Qu8k as we were able to drive straight to the rocket on the ground.

controlled airspace?
by element-o.p.

What, if any, notifications, waivers, etc. were required to penetrate controlled airspace in the launch area? At the very least, you would have penetrated Class A airspace (between 18,000MSL and 60,000MSL over the entire contiguous 48 states), so I presume you had to have FAA approval?

DD: I had a Class 3 waiver that ran concurrent with the BALLS rocket launch waiver which extends to 150,000 feet. Together we were required to make several notifications to the FAA. As a matter of fact, two representatives of the FAA were present during portions of this year's BALLS launch.

next launch?
by rastos1

Three questions regarding next launch: Where? When? May I come? (Well, in fact it's too far away for me, but I'd love to ;-) )

DD: There will definitely be a next launch! I am not sure if it will be an exact repeat of Qu8k, a stretch version, a two-stage version or something completely new and even bigger. It may even be more than one of the mentioned possibilities. Only time will tell. If you would like to contribute in some way please contact me and let me know what you can offer and I'll keep you informed as things move ahead.

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