How to build a fiberglass rocket, part 14: ground testing

The final chapter in the long saga of building the Darkstar Extreme: ground testing.

Actually, I don’t know whether I should have saved this step for the end. I’ve been looking at what some other folks do, and I’ve seen several people conduct ground testing as soon as the rocket is technically built, but prior to any kind of priming or painting, or adding other finishing touches. To be honest, that probably makes more sense because it’s bound to suffer some minor scratches and scrapes during testing, so better to do it “naked” and paint it later. Fortunately, I don’t care!

long blue rocket on wooden test stand, on grass - angled front view
testing time

Just to take a step back and recap what I’m even doing here: ground testing is important to test the electronics inside the rocket and make sure everything is wired up and working properly. I won’t go into the details of the electronics bay, but there are a lot of things connected to other things, and then there are more things. If even a single connection is loose or comes apart, the whole e-bay could cease to perform its basic function.

And by “its basic function,” I mean the flight computer (circuit board), connected to both a battery and an on/off switch, needs to be powered on and fire a charge at the right moment, which causes an electric match to spark, which causes some carefully packed black powder to explode, which causes the rocket to separate in a pre-determined place. And then it all needs to happen again to cause the rocket to separate in a different place. Parachutes deploy, rocket lands safely.

long blue rocket on wooden test stand, on grass - side view
might need a better test stand

Aside from generally checking that the electronics and wiring work correctly, ground testing is particularly important to determine the appropriate amount of black powder (BP) to use. There are different types of BP, and there are many online calculators that will tell you, based on the volume of your rocket’s interior space and your desired pounds per square inch (PSI), how much BP you should use exactly. However, actual conditions can vary, and it’s a good idea to test – and test again.

Ultimately, you want to use enough BP to ensure that the rocket separates, forcefully. Really forcefully. With verve. Anything less than this could cause a failure to separate, which means the parachute probably won’t deploy, which could be catastrophic for the rocket (and potentially any hapless bystanders). Of course, you don’t want to use so much BP that the explosion itself destroys your rocket, either. It’s a fine line. Your precious rocket hangs in the balance.

long blue rocket resting on box, on grass - side view
problem solved

I did multiple rounds of ground testing on different days (note the color variation and also choice of test stands in the different photos). On that note: never use a more elaborate test stand than necessary. Here I was, building a crude stand out of wood, like a sucker! I could have just been using a cardboard box all along. The angle is better anyway.

The calculator told me that I should use about 2.5 grams of BP, but I found that I needed to use closer to 3.0 grams to really separate the rocket forcefully. I also have a backup flight computer with its own separate charges, and for the backup I will use about 4.0 grams of BP. Gotta make sure it gets the job done.

rocket parts spread across grass in back yard, after separation
as god intended

It’s debatable whether this testing is really part of the rocket’s construction, strictly speaking, but in any event this was the final step before launching the rocket out in the field.

Now it’s time to fly!

High Power Rocketry: L2 Certification Flight

Officially level 2 certified!

rocket launching into the blue sky, with fire and smoke below
textbook flight

Fulfilling a 2020 goal

I really started getting into rocketry last fall, less than a year ago, and I had set some goals for 2020 when the year began. My goals included getting level 1 and level 2 certifications in high power rocketry (HPR) through the National Association of Rocketry (NAR).

I think 2020 threw some curveballs at just about everybody, myself included – but after a few false starts and delays, I was able to launch my first high power rocket in central Washington on a beautiful day in June, and as I wrote about previously, I got my L1 cert.

I deliberately chose and constructed a rocket that could be used for both L1 and L2 certification (i.e. it is capable of launching on a more powerful motor), and I built it to be dual deploy capable. I also had plenty of time to study for the written exam, which is required after the L1 certification but prior to the L2 flight. Timing is everything.

Because of this, I was able to do everything in a single day – L1 flight, L2 written exam (which I passed, of course), and L2 flight. I had more than six months to prepare for this day, so it’s not particularly impressive!

white rocket with orange and yellow parachutes lying on ground in green field
a safe landing

L1 vs. L2 flights

On the L1 flight – the maiden voyage – I didn’t want to take any unnecessary risks and decided to keep it as simple as possible, so I didn’t attempt using any electronics or dual deploy. The rocket separated through a simple motor ejection charge.

But for the L2 flight, I wanted to try the flight computer and dual deploy. I was a little nervous because while I checked and rechecked everything in advance, this was still the first actual attempt and there were a lot of firsts: first time using any flight computer or black powder charges, first time arming the electronics on the launch pad, first time using the ground station to communicate via radio with the rocket (using a laptop with the appropriate software and a connected Yagi antenna), etc.

Everything went smoothly, from the launch (see first photo above) to deployment of the drogue parachute at apogee and the main parachute closer to the ground. I recovered the rocket without any damage.

white rocket with text "improbable ventures" lying on ground in green field
mildly improbable

L2 flight data breakdown

What’s particularly cool is the flight computer not only fires multiple pyro charges (and therefore controls the rocket’s separation and deployment of two parachutes), but it also contains an altimeter and other sensors that record the rocket’s maximum height and its descent speed.

For my L2 flight, the rocket reached 3,506 ft, with a maximum speed of 599 ft/sec (Mach 0.5). In other words, the rocket’s max speed was about one-half the speed of sound.

The descent rate under the drogue parachute was 39 ft/sec, and under the main parachute it was 27 ft/sec. The HyperLOC 835 is a fairly lightweight cardboard rocket with a gross liftoff weight (that is, a weight including the motor, parachutes, and everything else inside) of only about 6 lbs, and this descent rate was more than sufficient for a safe landing.

All in all, this was a fantastic experience. A four hour drive each way made this a very long day, but it was absolutely worth making the trip. Inevitably, I also learned a tremendous amount – for example, how to set up a large rocket on the pad and launch rail, how to use the flight computer and ground station software, etc. I also learned what types of things that I could do better next time. Overall, I’m even more excited about future launches – trying out new techniques, flying on even more powerful motors, and capturing data with the flight computer to beat my own previous records!

The life and legacy of Wernher von Braun

I recently finished reading an excellent biography about Wernher von Braun. While browsing a used bookstore in Victoria, BC last year, I picked this book up on a whim. I really didn’t know anything at all about the man or his life, prior to this. In retrospect, I cannot believe I didn’t know anything, and I have to say I’m absolutely floored.

The book is Von Braun: Dreamer of Space, Engineer of War, by Michael J. Neufeld.

black and white photo of von Braun sitting at his desk with model rockets
Werner von Braun, the German-born American rocket engineer, with model rockets

The title really does a great job of summarizing the theme of the book. Von Braun’s life was in many ways a dichotomy between, on the one hand, his lofty intentions, a fascination with rockets and plans to use them for spaceflight and travel to the moon and distant worlds, and on the other hand, the darker side of his achievements, which were the creation of a weapon of immense destruction and war.

Pre-1945: German background and the Nazi regime

Von Braun straddled two worlds in many different ways, both literally and metaphorically. He was born and raised in Germany, received an education as an engineer and became an extremely effective and capable leader in engineering management – that is, leading large, complex engineering projects and organizations involving hundreds or even thousands of people.

As the Nazi regime came to power, von Braun was gradually pulled into its orbit (or intentionally gravitated towards it, depending on your view). He saw that the military and government were a powerful source of funding for the research and development of rockets, and von Braun seized the opportunity.

At Peenemunde, he developed rockets for the Nazi regime, including the infamous V-2, the world’s first long-range guided ballistic missile. The Germans used the V-2 during World War II to attack Allied cities, as retribution for Allied bombings of German cities (thus the German name for the rocket, Vergeltungswaffe 2, meaning “Retribution Weapon 2”). The V-2 was also the first rocket to travel outside the earth’s atmosphere into space. The rocket von Braun brought to fruition was therefore used to bring destruction during the war, but also for pioneering spaceflight, a familiar duality in von Braun’s life.

Von Braun joined the Nazi party and even met Hitler on several occasions. He rose in the party’s ranks and became an SS officer. And yet he never seemed particularly enthusiastic or dedicated to the Nazi ideology or cause. It was clear that his only passion was rocketry, and the Nazi regime was willing to pour vast amounts of money into his organization at Peenemunde. At the same time, he never seems to have strongly objected to what the Nazis were doing, although he likely wasn’t aware of the full horrors of the Holocaust at that time. Years (and decades) after the war ended, von Braun condemned the regime, but of course that was much easier to do in retrospect and seems opportunistic.

black and white photo of three men holding a large model rocket above their heads
William Pickering, James Van Allen and Wernher Von Braun hold a model of Explorer 1 in triumph after the successful launch of a US satellite

Post-1945: Spaceflight program leadership in the United States

After World War II ended in 1945, von Braun emigrated to the United States, one of several dozen scientists brought over as part of “Operation Paperclip.” He settled with his wife in Huntsville, Alabama, and with many other German workers as part of his organization. Von Braun lived in Huntsville for the next twenty years, raising a family there, and working for the US Army. He played a lead role in developing the Redstone rocket, which was used for the first live nuclear ballistic missile tests for the US, as well as the Jupiter-C rocket, which launched the first US satellite, Explorer 1, in 1958 (although this was not the world’s first satellite, which was the USSR’s Sputnik 1, in 1957).

Von Braun may have been opportunistic, but he thoroughly embraced his new American identity and believed that the US should lead the “free world” in the space race against the Soviet Union.

He later joined the newly created NASA in 1960 and played a major role in historic NASA projects, including the Mercury Redstone, Gemini, and Apollo programs. He was dedicated to the success of the Apollo program, and under his leadership, Apollo had a flawless track record for safety and success. The Apollo 11 lunar landing – the achievement of seeing humans actually set foot on the moon in 1969 – was probably the highlight of his life.

black and white photo of von Braun standing in front of enormous rocket engines
von Braun standing in front of the engines of the Saturn V

This is of course only a summary of von Braun’s life, and in this summary I am doing him an enormous disservice. Beyond his engineering, technical, and management genius, von Braun also increasingly became a popular household name as he began appearing in Walt Disney-produced documentaries in the 1950s about the future of spaceflight, and man in space. These documentaries themselves are fascinating, in retrospect, and are the subject of an entire separate post I plan to write.

A controversial legacy

Von Braun was a lifelong spaceflight enthusiast and strongly advocated for putting humans into space and going to the moon. It is safe to say that he is one of the most important individuals of the twentieth century: he basically led the development of the liquid fuel rocket into a mature technology, and he was directly responsible for the success of NASA’s Apollo program, among other accomplishments. And yet his rockets also have the legacy of destruction. He is ultimately responsible for the development of intercontinental ballistic missiles (ICBMs) and the dangerous cloud of nuclear war that hung over the entire world for the latter half of the twentieth century, and continues to hang over us to this day.

Intriguingly, this is a man who was an SS officer in the Nazi party and built weapons for Adolf Hitler, and yet also joined the US government and obtained security clearances, rose in its ranks, and personally met with multiple presidents including Dwight Eisenhower, John F. Kennedy, and Lyndon Johnson.

I highly recommend this book for a thoughtful, balanced study of von Braun’s life in much more fascinating detail.

How to build a fiberglass rocket, part 13: parachutes

Rocket recovery

The recovery system in a high power rocket is extremely important. Needless to say, launching a large rocket extremely high into the air is pretty fun. But that thing is going to come down again, sooner or later, and the recovery system you’ve designed and built for your rocket will determine whether it comes down like a ballistic missile or floats down gently for a soft landing. It could potentially injure or even kill someone. More importantly, your valuable rocket could be completely destroyed.

If the rocket separates in the air, even with no parachute, that’s a good start. A rocket separated into two (connected) parts loses its aerodynamic design; it will fall, but awkwardly and more slowly than if it were in one piece. Of course, if it’s heavy, it’s still going to hit the ground pretty hard.

Drogue vs. main

Better to separate and have a parachute. A single chute can be sufficient – it depends on the rocket’s expected altitude and how heavy it is. Ideally, though, the rocket will be capable of “dual deploy,” which just means deploying two separate parachutes, a drogue and a main.

person running in street, pulling orange parachute behind in the air
a running start

The drogue chute is smaller and deploys at apogee. The idea here is that, at apogee, the rocket’s speed has ground to a halt. It’s no longer shooting upwards, but it hasn’t yet started falling back down very fast either. The rocket separates at this point and the smaller drogue chute deploys, slowing the rocket’s descent to some degree.

After the rocket continues its descent and is closer to the ground, the airframe separates again and the main parachute deploys. This larger chute slows the rocket’s descent considerably and allows for a softer, gentler landing.

This order is important. You wouldn’t want to release the main (larger) parachute at apogee because even a slight wind would carry it very, very far away by the time it landed. But if you only used a drogue chute during the flight, the rocket’s descent would not slow sufficiently and it’d have a rough landing.

person in street, holding open orange parachute above head
I am actually being pulled backwards here

A weighty problem

This brings us to my current predicament. The Darkstar Extreme is a fiberglass rocket, and it’s pretty heavy, at roughly 14 lbs before adding the recovery system or the motor. That’s about what two gallons of milk weigh. Imagine the force it would take to accelerate two gallons of milk vertically, thousands of feet into the air – and likewise, the size parachute you’d need to significantly slow the descent of something that heavy.

There are online calculators that can help determine the right parachute size (diameter) based on the weight of your rocket and how fast (or slow) you want it to land. There are a lot of trade-offs in rocketry, some of which may not be obvious. All else being equal, for example, the softer the landing, the better – but there is a trade-off here. You can slow the descent and get as soft a landing as you’d like by increasing the size of the parachute. But large parachutes take up a lot of space. It’s increasingly difficult to stuff a gigantic parachute into your rocket without increasing the size of the rocket (and its weight, which then requires an even bigger parachute, etc.).

I ended up buying a 2 ft diameter drogue chute and an 8 ft diameter main chute, both from Rocketman Parachutes. In the above pictures, I opened them up as soon as they arrived at my house and ran around in the street trying to catch the wind and fly them like kites – with mild success.

They’re also a very vibrant orange color, which should make the rocket a little easier to see during its descent in the sky, and easier to locate once it touches down.

I’m looking forward to launching the Darkstar Extreme in the near future and seeing these parachutes deploy! I should also be able to capture a lot of data with my flight computer, so I’ll be able to tell how fast the rocket was descending with the drogue, as well as with the main chute.

High Power Rocketry: L1 Certification Flight

Finally! According to the National Association of Rocketry, I now officially have my level 1 certification in high power rocketry.

rocket launching into the air with fire and smoke below

I finished building my first high power rocket, the HyperLOC 835, back in December, but getting certified requires a successful flight and recovery of the rocket. But clubs don’t often host launch events in the winter months, and those that do are still subject to weather conditions (e.g., snowstorms). It’s helpful to have a club host a launch because you need (a) access to a large suitable area of land, (b) a waiver from the FAA to launch up to a certain altitude, and (c) launch equipment, such as launch pads and rails and an electric ignition system.

Clubs often start hosting launch events in the spring, but in spring 2020, COVID-19 hit, and things were cancelled or postponed.

I was finally able to attend a launch in June in south central Washington, about a 4 hour drive from where I live in the Seattle area.

I ended up launching the HyperLOC 835 on an Aerotech I-140 motor. The rocket is capable of dual deploy using a flight computer, but for this L1 certification flight I wanted it to be as simple as possible, so I didn’t use electronics. The recovery system was a parachute that deployed when the rocket separated using the motor ejection charge.

white and red rocket on launch pad
maiden flight

The weather looked ominous: it was cloudy, and we felt a few raindrops hitting us periodically, but it seemed to be holding steady.

The rocket launched, the parachute deployed, and it landed without a scratch in the tall grasses. The only tricky part was locating it. But since I was able to see the general area where it landed, it wasn’t too difficult to find.

yellow parachute in a sea of green tall grasses
a sea of tall grasses

Luckily the bright yellow parachute was pretty easy to spot from a distance, even though the rocket had sunk into a sea of tall grasses.

white rocket with text "improbable ventures" lying in tall grasses
a venture most improbable

Overall, it was a textbook launch and went as smoothly as could be expected! I’d estimate the rocket went about 1,700 ft in altitude, but as mentioned above, I didn’t use electronics for this flight so I can’t say for sure.

Immediately after this, I took the level 2 written exam, which is required prior to the level 2 certification flight, and I passed that (not difficult considering I’d had six months to study). It started raining more heavily, though, and we weren’t sure if we would need to call it a day and head out. But we waited another 30 minutes for the rain to stop, and then the skies cleared up and the sun came out. Perfect timing for my L2 certification flight, which I’ll summarize in my next post!

How to build a fiberglass rocket, part 12: primer and paint

All the difficult and time-consuming rocket construction steps are basically complete. The drilling and sanding fiberglass is done, the epoxy has cured, and technically, you can fly it “naked” at this point. But a painted rocket just adds that extra touch of class, and we are nothing if not classy.

Before getting started here, a couple of tips and some basic prep. There are a few parts that you might want to cover before spraying anything: things like the aluminum tip on the nose cone, the aluminum motor retainer, and the rail buttons. You can use masking tape to manually cover up these things pretty easily.

rocket disassembled on cardboard and grass, no paint or primer
“naked” rocket

Also, keep in mind that where a coupler slides into another section of the airframe with a snug fit, you don’t want to build up multiple layers of primer and paint, or things won’t fit at all anymore, without sanding the paint off. You may want to cover coupler ends with masking tape as well to save yourself trouble later.

So, to begin: lay out the rocket on cardboard or somewhere that you don’t mind getting turned into a rainbow of colors. Spray a thin layer of primer over everything (I chose a simple white primer) and use a quick back and forth motion. Don’t spray too close, and keep it continually moving while spraying, so that paint doesn’t build up too much in any single area. You can always come back and spray again and again, lightly with a thin coat each time.

rocket disassembled on cardboard and grass, white primer applied
applying primer

Of course, since the parts are lying on the ground, you can’t get underneath and will need to wait for them to dry and then rotate them. Depending on how much you’re able to coat the pieces each time, you may need to rotate them just once, or perhaps twice.

Finally, once everything has a nice layer of primer and it’s dry, you can begin spraying paint. The colors and design are totally up to you, but I would certainly recommend a high gloss finish.

rocket disassembled on cardboard and grass, painted glossy navy blue
roses are red, rockets are blue

In my case, I went with a glossy navy blue for the rocket body. I then used “sunshine yellow,” also glossy, for the fins and the vent ring around the e-bay. Note that it didn’t matter if the layers of navy blue got all over the fins, but once this was finished, I had to use more masking tape to very carefully and thoroughly mark off the fins from the rest of the body. I also used some brown paper grocery bags, tearing them up into approximate sizes to cover the rocket between and around the fins, with masking tape at the edges sealing it off to create sharp and exact lines.

I’m no expert painter; this is only the second rocket I’ve ever painted. But I think once finished, it turned out pretty well.

completed rocket standing vertically, painted navy blue with yellow fins
the rocket stands on end taller than you

Of course, this paint job is bound to get scratched, scuffed, and generally deteriorate over time. The rocket gets disassembled and re-assembled, and parts bump and bang into each other, and of course upon landing after even a single flight it will get dirty and a bit dinged, no doubt. I can always touch up the paint in the future when that happens, and it doesn’t really matter – it’s purely cosmetic. But it is fun and it just completes the look.