Projects are essential to progression. The completion of certain projects allow for newer and more ambitious undertakings. To keep focus aligned and concentrated, DanSTAR organises all of its work into projects that the entire team focuses on. Keeping the amount of active projects low means that effort can be put into progressing in specific areas such as either rocket development or launch rail design.
The Dragonfly Project
Although development the rocket Dragonfly is a huge part of DanSTAR, the actual Dragonfly project is larger than the rocket itself. Within this project, we are developing a new engine, new flight electronics, updating our mission control software, updating the test stand, and much more.
The Dragonfly rocket is 4,5 meters long and consists of an aluminum air frame with a carbon and glass fiber exterior. Weighing in with a dry weight of approximately 50 kg, the entire rocket is extremely light-weight, allowing it to reach the desired altitude of approximately 9 km.
Upon reaching its apogee, the nose cone is ejected using pressurised CO2 which lets the drogue chute fall out of the nose cone volume. After falling to around 500 m above ground level, a pin is released which allows the drogue chute to deploy the main parachute. This event reduces the falling velocity of the rocket to 20 km/h.
The rocket is powered with a bi-liquid propulsion system running on nitrous oxide and a custom isopropyl alcohol blend. These propellants are fed to the rocket engine Gnome Child using a 300 bar pressure-regulated cold gas inert feed system of pure dinitrogen. The propellant tank itself is a common bulkhead duplex/316 stainless steel component, which has been carefully engineered and pressure-tested to withstand immense pressures above 50 bar if neccesary during operation.
The rocket is passively guided with three aluminum fins. The decision to passively guide the rocket was made to reduce complexity and the working load on an already burdened electronics and software team as an active guidance system would otherwise have had to be developed. This neccesitates a high exit velocity when leaving the launch rail, which requires a high start accelleration that then imposes another series of challenges to solve for.
Gnome Child is the name of the rocket engine that propels Dragonfly upwards for the approximately 16 seconds long boost phase. During this period, the rocket sees acceleration of more than 3G as the fuel tanks empty. Around 18 kg of pure propellant is burnt in this period.
The engine is kept cool with an advanced regenerative cooling system, meaning all of the fuel is circulated around the combustion chamber immediately before being injected into the engine. This has a two-fold advantage in that the engine is kept cool, but the fuel is also heated up, reducing the energy needed for evaporation.
This is done in close cooperation with Danish Technological Institute who gracefully offered us the opportunity to 3D print the engine in metal. 3D printing is a new and emerging technology within rocketry that allows for complex designs of cooling systems within the actual engine itself that could not be manufactured with traditional methods. This means DanSTAR is on the forefront within actual rocketry development, and it allows our students to get hands-on experience with state-of-the-art technology before graduating.
RICHARD is short for Robust Internal Controller for High Altitude Rocket Dragonfly. This is our internal flight computer, which additionally also controls the test stand. Sometimes refered to as the flight stack for its many stacked PCBs, it utilises STM32 microcontrollers for a low learning curve and reliable platform to work with. The stacked PCB design allows for easy iterations of individual computer models and adding new features a breeze.
The internal communication is done with a modern CAN interface, the same also used in the automotive industry, which allows the boards to communicate quickly and easily among eachother, ensuring infomation is where it’s needed when it’s needed.
The multi-board design consists of an actuator board, temperature sensor board, pressure sensor board, telemetry board, high-power board, low-power board, and lastly the main board. This configuration has all the functionality that is needed within Dragonfly during flight and recovery, and controls everything from the auto-ignition sequence to recovery events.
When used on the test stand, a test stand board is added to the stack, which increases the amount of connected sensors and valves that can be controlled.
The launch rail is a quarter ton heavy and 13 meter tall behemoth structure that DanSTAR had to develop from scratch to facilitate launching a rocket the size of Dragonfly. The launch inclination can be adjusted down to a single degree because of its special hinge construction. This means DanSTAR can carefully decide the rocket flight direction, which is helpful for safer launch events.
The structure itself consists of a steel center piece and legs with an aluminum mast. This ensures most of the weight is located at the bottom of the structure, making it stable even in windier conditions. The mast is in constant tension because of the steel wires which keep it firmly in place when the launch rail is deployed.
The launch rail is able to be completely disassembled, which is a requirement for shipping it to the US, in order to distribute the shipping weight throughout several flight cases.
Initially, the demo engine was meant to showcase DanSTAR’s abilities in design and operating its own rocket engines. The engine is quite small and works on simple principles, but this is perfect in order to get a grasp for what matters and what doesn’t in rocket engine design. Additionally, it serves as a tool for testing the the test stand, as this engine can withstand severe hard starts and burn durations of more than 10 seconds without being actively cooled.
The copper chamber works as a heat sponge, absorbing the immense heat that is created inside the chamber during operations. This is widely refered to in literature as capacitive cooling.
Nominal thrust: 300 N
Nominal chamber pressure: 20 bar
Chamber diameter: 44 mm
Throat diameter: 11.6 mm
Chamber wall @ thinnest location: 27 mm
The nozzle of the engine can be unbolted to install an almost fool-proof ignition system deeply inside the engine for reliable engine ignition.
The demo engine is outfitted with a thorough sensor suite, capable of sensing feed pressure for both the oxidizer and fuel as well chamber pressure. It has 6 thermocouples located deeply inside the chamber wall to measure temperature at critical locations.
The test stand is probably the most important piece of equipment that DanSTAR has developed. At its core, it’s a sturdy and portable steel frame with a fluid system, but in reality it’s a complete test bed for testing everything from fluid system components to software implementation. It’s a perfect and purely terrestrial replica of the Dragonfly rocket, which allows for highly accurate tests which simulate the systems inside the rocket. The key difference between the test stand and the rocket, besides being aerodynamically challenged, is the control suite. With its load cell, flow meters, and added solenoid valves it allows for much better measurements and control than what is available on the rocket.
Although the test stand project officially finished when the demo engine was successfully fired in the end of 2018, it will never truly be complete as it serves as a canvas to test new ideas in all aspects of rocket engine development and control.
In order to achieve live communication, we wrote our own mission control software. This piece of software is written from the bottom up, contains several thousand lines of code, and allows us to monitor the vitals on the test stand before, during, and after engine test firings. With the click off a button every single valve on the test stand can be actuated exactly to the position that is required and the live sensor feedback will tell you about the system response.
Additionally, the mission control software also transmits the auto sequence parameters to the engine controller so that the flight stack can operate the engine autonomously and automatically turn of the engine if operation falls outside of specified parameters. Mission control is constantly iterated on as features get added and removed according to requests from the mechanical and electrical team.
The test stand’s fluid system is intended to emulate the one as seen in Dragonfly. This provides a test bed with close to the same conditions present as in the rocket itself, and build on the principles of ‘test as you fly, fly as you test’ laid out by Copenhagen Suborbitals.
Similar to the rocket, it contains three large volumes. A 10 L tank for storing the 300 bar dinitrogen, a 35 L insulated nitrous tank, and a 15 L fuel tank. This is approximately three times as large as seen on the rocket, allowing for quick turnover times between hot-fires by reducing fueling time as well as enabling longer duration engine burns to be test.