Open Source Modular Rocket Avionics Package

Cambridge postgraduate student [Adam Greig] helped design a rocket avionics system consisting of a series of disc-shaped PCBs arranged in a stack. There’s a lot that went into the system and you can get a good look at it all through the flickr album.

Built with the help of Cambridge University Spaceflight, the Martlet is a 3-staging sounding rocket that lifts to 15km/50K feet on Cesaroni Pro98 engines. [Adam]’s control system uses several Arm Cortex M4s on various boards rather than having just one brain controlling everything.

Each disc is a module that plays a specific role in the system. There are a couple of power supply boards sporting twin LTC2975 able to supply custom power to a dozen different circuits. The power system has a master control board also sporting an M4. There’s an IMU board with the guidance system — accelerometer, magnetometer, gyroscope, and barometer, all monitored by an algorithm that computes the rocket’s position and attitude in-flight. There’s a radio board with a GPS receiver and an ISM band radio transceiver for telemetry, as well as a datalogger with 10 thermocouple measurement channels. Engines are controlled by the pyro board which controls firing currents on four different channels. The vertical spacers also serve to transmit power and data to neighboring boards.

If you’re interested in learning more, check out the project’s code and schematics on [Adam]’s GitHub repository.

[Adam] is no stranger to these pages, with his Nerf Vulcan turret published a few years back, as well as his balloon tracking rig published more recently. Photos are CC-SA and can be found in [Adam]’s Flickr feed.

Books You Should Read: IGNITION!

Isaac Asimov described the business of rocket fuel research as “playing footsie with liquids from Hell.” If that piques your interest even a little, even if you do nothing else today, read the first few pages of IGNITION! which is available online for free. I bet you won’t want to stop reading.

IGNITION! An Informal History of Liquid Rocket Propellants is about how modern liquid rocket fuel came to be. Written by John D. Clark and published in 1972, the title might at first glance make the book sound terribly dry — it’s not. Liquid rocket fuel made modern rocketry possible. But most of us have no involvement with it at all besides an awareness that it exists, and that makes it easy to take for granted.

Most of us lack any understanding of the fact that its development was the result of a whole lot of hard scientific work, and that work required brilliance (and bravery) and had many frustrating dead ends. It was also an amazingly dangerous business to be in. Isaac Asimov put it this way in the introduction:

“[A]nyone working with rocket fuels is outstandingly mad. I don’t mean garden-variety crazy or a merely raving lunatic. I mean a record-shattering exponent of far-out insanity.

There are, after all, some chemicals that explode shatteringly, some that flame ravenously, some that corrode hellishly, some that poison sneakily, and some that stink stenchily. As far as I know, though, only liquid rocket fuels have all these delightful properties combined into one delectable whole.”

At the time that the book was written and published, most of the work on liquid rocket fuels had been done in the 40’s, 50’s, and first half of the 60’s. There was plenty written about rocketry, but very little about the propellants themselves, and nothing at all written about why these specific substances and not something else were being used. John Clark — having run a laboratory doing propellant research for seventeen years — had a unique perspective of the whole business and took the time to write IGNITION! An Informal History of Liquid Rocket Propellants.

Liquid rocket propellant was in two parts: a fuel and an oxidizer. The combination is hypergolic; that is, the two spontaneously ignite and burn upon contact with each other. As an example of the kinds of details that mattered (i.e. all of them), the combustion process had to be rapid and complete. If the two liquids flow into the combustion chamber and ignite immediately, that’s good. If they form a small puddle and then ignite, that’s bad. There are myriad other considerations as well; the fuel must burn at a manageable temperature (so as not to destroy the motor), the energy density of the fuel must be high enough to be a practical fuel in the first place, and so on.

The actual process of discovering exactly what materials to use and how precisely to make them work in a rocket motor was the very essence of the phrase “the devil is in the details.” For every potential solution, there was a mountain of dead-end possibilities that tantalizingly, infuriatingly, almost worked.

The first reliable, workable propellant combination was Aniline and Red Fuming Nitric Acid (RFNA). “It had the one – but magnificent – virtue that it worked,” writes Clark. “Otherwise it was an abomination.” Aniline was difficult to procure, ferociously poisonous and rapidly absorbed through skin, and froze at an inconvenient -6.2 Celsius which limited it to warm weather only. RFNA was fantastically corrosive, and this alone went on to cause no end of problems. It couldn’t be left sitting in a rocket tank waiting to be used for too long, because after a while you wouldn’t have a tank left. It needed to be periodically vented while in storage. Pouring it gave off dense clouds of remarkably toxic gas. This propellant would go on to cause incredibly costly and dangerous problems, but it worked. Still, no one wanted to put up with any of it one moment longer than they absolutely had to. As a result, that combination was not much more than a first step in the whole process; there was plenty of work left to do.

By the mid-sixties, liquid rocket propellant was a solved problem and the propellant community had pretty much worked themselves out of a job. Happily, a result of that work was this book; it captures history and detail that otherwise would simply have disappeared.

Clark has a gift for writing, and the book is easy to read and full of amusing (and eye-widening) anecdotes. Clark doesn’t skimp on the scientific background, but always in an accessible way. It’s interesting, it’s relevant, it’s relatable, and there is plenty to learn about how hard scientific and engineering development actually gets done. Download the PDF onto your favorite device. You’ll find it well worth the handful of evenings it takes to read through it.

Launch Pad for Air-Water Rockets is Good Clean Fun for STEM Students

We have fond memories of air-water rockets, which were always a dime store purchase for summertime fun in the pool. Despite strict guidance from mom to shoot them only straight up, the first target was invariably a brother or friend on the other side of the pool. No eyes were lost, and it was good clean fun that was mercifully free of educational value during summer break.

But now a teacher has gone and ruined all that by making an air-water rocket launching pad for his STEM students. Just kidding — [Robert Hart] must be the coolest teacher in Australia when Friday launch days roll around. [Mr. Hart] wanted a quick and easy way to safely launch air-water rockets and came up with a pretty clever system. The core task is to pump air into the partially filled water bottle and then release it cleanly. [Robert] uses quick-disconnect fittings, with the female coupling rigged to a motor through a bicycle brake cable. The control box has a compressor, the release motor, and a wireless alarm remote, all powered by a 12-volt battery. With the male coupling glued to the cap of a bottle acting as a nozzle and a quick, clean release, flights are pretty spectacular.

There are many ways to launch an air-water rocket, from the simple to the complex. [Robert]’s build leans toward the complex, but looks robust enough for repeated use and makes the launch process routine so the kids can concentrate on the aerodynamics. Or to just enjoy being outdoors and watching things fly.

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Copenhagen Suborbitals Launches Impressive Amateur Liquid Fueled Rocket

Copenhagen Suborbitals just launched their latest amateur liquid fuel rocket. Why? Because they want to strap someone to a bigger amateur liquid fuel rocket and launch them into space.

We’ve covered them before, but it’s been a while. While they make a big deal of being amateurs, they are the least amateurish amateurs we’ve come across. We’ll forgive a lot as long as they keep making great videos about their projects. Or posting great pictures of the internals of their rockets.

The Nexø I rocket they recently launched claims to be the first guided, amateur, liquid-fueled rocket. There is a nice post on the guidance system. It was launched from a custom built barge off the shore of Denmark, which allows them to escape quite a few legal hurdles around the launch. The rocket flew beautifully. That is, it went only away from the ground; no other directions. Also, it didn’t explode, which is a lot to expect from even the biggest players in the field.

Copenhagen Suborbitals continues to do amazing work. Hopefully their next rocket will be even more impressive… for amateurs, that is.

Steering High Altitude Rockets With Cold Gas

Amateur rocketry has been popular for ages, with designs ranging from small toy-scale model rockets to large-scale liquid fuel designs with steerable fins. A team out of Portland State works on some large-scale amateur rockets that can fly to very high altitudes. Since the atmosphere is thin the further the rocket flies, steering fins aren’t incredibly effective once the rockets reach high altitude. A team of students tackled this problem by designing a cold-gas reaction module to steer high-altitude rockets.

The team chose nitrogen as their cold-gas propellant, which is stored in a carbon fiber tank. After passing through a regulator, the gas is routed to several gas solenoids and then to a custom 3d-printed de Laval nozzle. An Intel Edison is used to drive the system, which calculates the rocket’s orientation with a MPU-6050. Control loops use the orientation information and fire gas through any of several nozzle ports to steer the rocket.

The system does have some limits: the solenoids are either on or off, not variable, and they aren’t incredibly fast. Even with these limitations, the team is confident that their module will work great when it embarks on its maiden flight in a brand-new custom rocket next year. The team was also awesome enough to make all of their design files open-source so you can build your own (although they warn that it’s a bit complicated and dangerous). Check out the video after the break to see a test-run of the cold-gas reaction system.

Thanks for the tip, [Nathan]!

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Apollo, the Everything Board

The best projects have a great story behind them, and the Apollo from Carbon Origins is no exception. A few years ago, the people at Carbon Origins were in school, working on a high power rocketry project.

Rocketry, of course, requires a ton of sensors in a very small and light package. The team built the precursor to Apollo, a board with a 9-axis IMU, GPS, temperature, pressure, humidity, light (UV and IR) sensors, WiFi, Bluetooth, SD card logging, a microphone, an OLED, and a trackball. This board understandably turned out to be really cool, and now it’s become the main focus of Carbon Origins.

There are more than a few ways to put together an ARM board with a bunch of sensors, and the Apollo is extremely well designed; all the LEDs are on PWM pins, as they should be, and there was a significant amount of time spent with thermal design. See that plated edge on the board? That’s for keeping the sensors cool.

The Apollo will eventually make its way to one of the crowdfunding sites, but we have no idea when that will happen. Carbon Origins is presenting at CES at the beginning of the year, so it’ll probably hit the Internet sometime around the beginning of next year. The retail price is expected to be somewhere around $200 – a little expensive, but not for what you’re getting.

Rocketduino, for high-G, high altitude logging


Although the thrill of launching rockets is usually found in their safe decent back to Earth, eventually you’re going to want some data from your flight. Everything from barometric pressure, GPS logging, and acceleration data is a useful thing to have, especially if you’re trying to perfect your craft. [zortness] over on reddit created a data logging board created especially for amateur rocketry, a fabulous piece of work that stands up to the rigors of going very fast and very high.

The design of the board is a shield for the Arduino Mega and Due, and comes with enough sensors for over-analyzing any rocket flight. The GPS logs location and altitude at 66Hz, two accelerometers measure up to 55 G. Barometric, temperature, and compass sensors tell the ground station all the data they would need to know over a ZigBee 900MHz radio link.

Because this is an Arduino, setting up flight events such as deploying the main and drogue chutes are as easy as uploading a bit of code. [zortness] built this for a 4″ diameter rocket, but he says it might fit in a 3″ rocket. We just can’t wait to see some videos of it in action.