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Leonardo Times MARCH 2013PROJECT STRATOS
Stratos I that flew in Kiruna, Sweden in 2009 was the first rocket designed and produced by DARE capable of reaching the stratosphere. Stratos I flew on an in-house developed solid rocket fuel com-bination of KNO3 and industrial sugar. According to radar and telemetry data, the rocket reached a height of 12.3km, whilst also collecting scientific data using electronics situated in the nose cone. This meant that Stratos I broke the European Amateur Rocket Altitude record [1]. Rem-nants of the flight capsule are still being displayed in the hall of the Electrical Engi-neering, Mathematics and Computer
Sci-ence (EWI) faculty at TU Delft.
After the successful launch, the team was in a euphoric state. Straight after the flight capsule was retrieved and returned to Delft, the team started discussing a fol-low-up project. The team members knew that they had the capability to design, manufacture and launch rockets to ex-treme heights (on an international level), and this gave them such a confidence that DARE came up with a new and even big-ger challenge: becoming the first student team ever to reach space. A preliminary study concluded that with a higher specif-ic impulse and an increased performance of the propulsion system, it was possible
to reach the Kármán line – the boundary of space – at 100km altitude. Additional calculations showed that the solid rocket fuel used in Stratos I (Isp=120s) needed to make way for a type of fuel with a specific impulse of above 180s. Thus developing a new propulsion system and a new type of rocket fuel was essential.
It became clear that redeveloping a pro-pulsion system and reaching an altitude of 100km was more feasible if done step-wise. The team decided that the most reliable way to reach space was to first develop a new propulsion system and fly this system on a rocket half-way to space
Reaching space with a student-built rocket
In the spring of 2009 a team of 15 TU Delft students travelled to Kiruna, Sweden with
only one goal: to launch the rocket Stratos I they had been working on for 2 years to
an altitude of over 12km, thereby claiming the European Amateur Rocket Altitude
record. These students were part of Delft Aerospace Rocket Engineering (DARE), a
Dream Team of the TU Delft involved in research, development, manufacturing and
launching of rockets. However, this record-breaking launch was not a single project;
it was the first part of a larger endeavour of which the primary goal was to become
the first student team in the world to reach space with a student-built rocket.
TEXT Maarten Haneveer, BSc Student Aerospace Engineering
PROJECT STRATOS
Student project
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(50km) and after that continue on to the ultimate goal of 100km. The initiative of two diff erent rockets, Stratos II (50km) and Stratos III (100km), was born. This en-deavour towards the altitude of 100km, consisting of the research, development and manufacturing of the three Stratos rockets, was named Project Stratos.
STRATOS II
Since Stratos II will reach the lower end of the mesosphere – one of the most poorly understood parts of the atmosphere – its secondary mission is to be a research rocket. Space agencies such as NASA use research (or sounding) rockets [2] to con-duct measurements and carry out scien-tifi c experiments during its suborbital fl ight. Stratos II will provide 12 payload slots and advanced electronics, thereby striving towards the professionalism of corporate sounding rockets.
The vastness of Project Stratos calls for a large team: technical teams working on electronics, propulsion, simulations, telecommunications, aerodynamics and recovery, but also non-technical teams operational on payload acquisition, spon-soring, public relations, logistics and launch site communications. More than forty DARE members, from multiple fac-ulties, each with their own strengths, are currently actively partaking in one of Proj-ect Stratos’s many sub teams. Each diff er-ent sub team is led by a team leader, and together with two project managers they have to ensure the entire project and all its members are on the same wavelength, whilst also keeping up the pace in devel-oping their respective subsystem. This combination of member’s contribution to (non-)technical aspects and management functions results in a dynamic yet eff ec-tive cooperation between the teams. As mentioned, Stratos II needed a far better performing engine to guarantee reaching the 50km altitude. In the middle of 2012 two propulsion teams could pro-vide propulsion systems meeting all re-quirements. These teams were the Solid Six (solid rocket fuel) and Dawn (hybrid rocket fuel). Obviously, each team wanted their system to propel Stratos II, however due to safety, cost and reliability consider-ations, only one propulsive system would be chosen. Trade-off tables were made, weights were given to criteria and long nightly meetings with the team leaders were held to ensure the right propulsion system would be chosen. The result of weeks of revising all aspects and argu-mentations of both teams led to the de-cision that Dawn, the hybrid team, would provide Stratos II with its propulsion sys-tem.
HYBRID PROPULSION
A solid rocket motor makes use of a solid fuel and oxidizer combined into a single
grain. This makes these types of rockets relatively simple but also less effi cient in the amount of thrust they produce for every unit of propellant compared to, for example, liquid engines. Liquid rocket engines, using liquid fuel and oxidizer, are far more complex but off er better performance than solid motors. A hybrid engine, like the one developed by Dawn, combines properties of both solid and liquid engines. Hence it is more effi cient than a solid engine but less complex than a liquid one. The development of the hy-brid engine gained a lot of momentum during the DARE minor of 2011, in which a complete working test bench was created and valuable data was acquired (Figure 1). The knowledge gained during the minor and the corresponding fi re tests (Figure 2) resulted in the fi rst hybrid engine con-cept.
(Figure 3) is a schematic representation of the hybrid engine. The numbers repre-sent the diff erent subsystems. The largest volume in the engine is for the oxidizer tank (1). This will be an aluminium tank in which N2O will be stored under pres-sure. N2O is also known as nitrous oxide or laughing gas. Below the tank is the feed system (2), which connects the tank
to the engine. It contains a special valve that can be opened (and shut) remotely using an electronic system. When the valve is opened, oxidizer will fl ow through the pipes of the feed system towards the combustion chamber. The N2O fi rst passes the feed system to the injector (3). The in-jector is placed in the combustion cham-ber (5) where it vaporizes the incoming nitrous oxide, making the oxidizer react more easily with the solid fuel grain. Subsequently the igniter (4) is set off by an electrical current, igniting and heating up the combustion chamber and fuel inside it. When the N2O enters the combustion chamber, it will be hot enough to start the reaction with the fuel. The fuel and oxidizer will start to burn, and form gas-ses and build up pressure inside the com-bustion chamber. These gasses are then expelled through the nozzle (6), which, due to its shape, will accelerate the gas-ses immensely and thus propel the rocket. In June 2012 the Morning Star rocket was launched successfully near Leipzig, Ger-many. The Morning Star used the concept engine described previously, and was the fi rst rocket launched by DARE to contain a fully working hybrid engine (Figure 4).
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Figure 1. Thrust Curve of Dawn Hybrid Engine
Figure 2. Dawn Engine Test Fire 12-sept-2012
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Leonardo Times MARCH 2013Another great benefi t of the hybrid en-gine is the choice of fuel and oxidizer. Separated, nitrous oxide and Sorbitol are inert and therefore a lot safer to handle. Furthermore, travelling abroad to a yet to be determined launch location will be easier as less certifi cations are needed for the logistics of the hybrid engine. Cur-rently, the Dawn team is making a full scale hybrid engine. This engine will be used for full scale engine testing at TNO in April, from which the fi nal character-istics can be calculated. Once these tests are done, the hybrid engine is ready to be used in Stratos II.
The hybrid engine largely defi nes the characteristics and dimensions of the rocket. According to the current design and choice of engine, Stratos II will be a single staged, hybrid (N2O and Sorbitol + additives) engine driven rocket with a maximum velocity of around 1000 m/s and a maximum acceleration of 5G for the duration of 18 seconds. The capsule will be 160mm in diameter and by means of a coupler connected to a 200mm engine section. The total height of the rocket is designed to be 5.5m, containing 99.6 kg of fuel and oxidizer within. Further charac-teristics of the Stratos II are a specifi c im-pulse of 190 and a total thrust of 10,000N. In (Figure 5) a detailed fl ight plan is illus-trated. Once the rocket is launched, it will accelerate to its maximum velocity and af-ter 18 seconds engine burn-out will occur. From there on Stratos II will decouple its engine section and continue coasting to
its apogee of 50km, whilst sending down in-fl ight data. Once the capsule starts re-turning to Earth, the fl ight computer will initiate the recovery system which will bring the capsule containing the scientifi c payloads safely to the ground, from where it will be retrieved and brought back to the team.
The launch described cannot be possible without the use of sophisticated fl ight electronics and a durable capsule. These two components ensure a safe environ-ment for the launch crew, the rocket and for the safe return of the payloads and are therefore of signifi cant importance for the success of the project. Let’s elaborate a little bit more on them.
ELECTRONICS AND CAPSULE
The electronics segment include the fl ight computer and a ground station, built on experiences gained from Stratos I and de-velopments within DARE over the last 2 years. The fl ight computer works in two-fold: execute the rocket fl ight plan and provide power and communication for the payloads. Consisting of various sub systems such as a transmitter, a measure-ment board, a storage board and others, connected by a backbone and controlled by a master control unit (MCU), the fl ight computer monitors and controls the fl ight and is capable of routing the data re-ceived from the measurement board and the payloads to the storage board and the transmitter, which in turn sends the data back to the ground station.
These electronics are situated in the top
of the capsule. Another function of the electronics is the ignition of the hybrid engine and the activation of the recovery system. The recovery system consists of a dual parachute system. A small drogue parachute will deploy fi rst to decelerate the capsule after apogee and the main parachute will then be deployed to en-sure a safe landing. This system reduces the shocks on the capsule whilst simulta-neously reducing the footprint of the cap-sule. The electronics, payloads (Figure 6) and recovery system are all situated inside the capsule which, in the top part, is made of glass fi bre to ensure radio transparency for the telecommunications. With an ac-celeration to 5g in 18 seconds and top speed of 1000m/s, one can imagine that high compressive loads and temperatures (up to 450°C) are exerted on the capsule. Therefore, a strong yet light skeleton and deployment system have been designed for the internal structure of the capsule. On the tip of the nosecone heat-resistant materials are being added to cope with the high temperatures and preventing the cone from melting mid-fl ight.
PAYLOAD AND SPONSORING
Combining all the technical aspects results in a rocket reliable of reaching and deliv-ering payloads to a 50km altitude. The payload section consists of 12 slots with Standard PC/1-4 (Pumpkin) CubeSat PCB dimensions, each with a nominal power supply of 1W, SPI compliant communica-tion protocol and availability of 2kB/s stor-age data rate. Slots can be bought up by private, educational or industrial entities Figure 3. Schematic Overview
Dawn Engine Figure 4. Dawn Team with Hybrid-powered Rocket (Morning Star) in Leipzig
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for use of experiments of their choosing. Suggested scientifi c research and techno-logical experiments that can be executed during fl ight are magnetic fi eld and up-per atmosphere radiation measurements, testing of navigation, positioning and at-titude determination systems and of elec-tronic systems/sensors designed for space and astronautical operations. At the mo-ment of writing, (international) interest has been shown in this project and con-tacts regarding potential payloads have been initiated.
Even though Project Stratos is a student team and therefore has no labour costs, the materials, logistics, tests and PR still have to be accounted for. Luckily there are many companies and organizations interested and willing to invest in Project Stratos. The main sponsor, Dutch Space, largely sustains the continuity of the proj-ect whilst also exchanging their knowl-edge and experience, proving themselves to be of vital importance to the project. Other companies, such as TNO and TU Delft, respectively provide test sites and workshops. The help of these companies and organizations helps continue the dream for the 100km, and simultaneously results in a professional involvement with the industry.
LOOKING AHEAD
Many technological challenges have been solved by the hard-working DARE rock-etry enthusiasts since the start of the proj-ect. Full scale motor tests are scheduled in April and a launch is scheduled at the end of 2013. However, preparations for the launch side, logistics, payloads, spon-soring and PR have to be made in order to continue the project smoothly once Stratos II is rolled out. In the upcoming months (social) events are planned to get Project Stratos out to the public, calls for payloads will be intensifi ed and potential partnerships are being sought to increase the fi nancial security of the project. Fur-thermore, a concrete launch site will be acquired along with the corresponding certifi cates and logistics will be dealt with. Project Stratos is currently recruiting new team members excited in collaborating
on these organizational aspects of the project.
DARE is certain that the hard work of all the teams of the past years and the up-coming months will result in a successful launch of the Stratos II rocket at the end of 2013. From thereon DARE will be one step closer to attain the title of being the
fi rst student team in the world reaching space.
For more information on joining Project Stratos, sponsorship and payload opportu-nities, as well as news or updates about the project, please visit ProjectStratos.nl or send an email to info@projectstratos.nl.
Figure 5. Stratos II Flight Plan
Figure 6. Payload Section Design
References [1] http://www.hobbyspace.com/Rock-etry/Advanced/records.html [2] http://sites.wff .nasa.gov/code810/ D ARE D ARE
