Designing and Testing of a Bi-liquid Rocket Engine ... rocketry have evolved in Europe's tertiary education domain. Some of them are ... practice by working on their own experimental and sounding ... The main goal of this contribution is to raise awareness of the .... November 2015 Combustion chamber tests on full thrust.
2nd Symposium on Space Educational Activities, April 11-13, 2018, Budapest, Hungary
Designing and Testing of a Bi-liquid Rocket Engine with Graduate Students Christian Bach, Jan Sieder-Katzmann, Martin Propst and Martin Tajmar Institute of Aerospace Engineering Technische Universität Dresden Dresden, Germany Abstract — Germany’s student sounding rocket programme “STERN” (Studentische Experimental-Raketen) is a nationwide education programme initiated by the German Space Administration DLR (Deutsches Zentrum für Luft- und Raumfahrt) in 2012. The project’s objective is to promote young professionals for launcher systems and to establish a practical education of students in the field of aerospace engineering. In this context, eight university teams began to design, build and qualify their own experimental rockets including all subsystems from propulsion to payload. This wide approach makes the programme the biggest and most ambitious student sounding rocket project in Europe. After giving an update about the programme status and the conducted launch campaigns from ESRANGE (European Space and Sounding Rocket Range) in Sweden in 2015 and 2016 this contribution focuses on examining the challenges and benefits of this endeavour from the perspective of a participating university. References and comparisons are made to foreign rocketry programmes such as PERSEUS (Projet Etudiant de Recherche Spatiale Européen Universitaire et Scientifique) in France. One particular characteristic of the strategy of STERN is to give the student teams the freedom to develop and test the rocket engines themselves. The ethanol /liquid oxygen bi-propellant engine of TU Dresden might be the most complex rocket engine within the programme. The lessons learned from developing and verifying such an engine in a university environment are discussed. The paper rather concentrates on the operational and management aspects of the education project than on the technical characteristics, which have been described in detail in previous publications. Keywords—student; sounding; rocket; education; programme
I. INTRODUCTION In recent years, several hands-on activities in the field of rocketry have evolved in Europe’s tertiary education domain. Some of them are national endeavours, like the programme “Studentische Experimental RaketeN” (STERN) in Germany or the programme “Projet Etudiant de Recherche Spatiale Européen Universitaire et Scientifique” (PERSEUS) in France, others are local or regional initiatives, e.g. Delft Aerospace
Rocket Engineering (DARE) at TU Delft. These projects show great differences in how they are organised and conducted. This goes along with varying resources. Although their technological and scientific objectives distinguish from each other, they all try to improve education in rocketry by giving students the possibility to not only learn the theory, but to turn it into practice by working on their own experimental and sounding rockets. While the importance, benefits and challenges of hands-on activities in general have been discussed in previous work [1], this paper will concentrate on the specific requirements and challenges of rocketry projects. Therefore, section 2 will outline STERN as an exemplary rocketry programme including its objectives, participating teams and scope. Section 3 will detail how a specific project within STERN is conducted: the SMART Rockets project at TU Dresden. This is followed by a discussion of the main challenges for student rocketry in Europe in section 4. Finally, a conclusion is given in section 5. The main goal of this contribution is to raise awareness of the importance of practical education in rocketry and the challenges that need to be resolved in order to enable upcoming generations of professionals to gain the skills they need to ensure Europe’s access to space in the future. II. STERN Since the STERN programme has been described in detail in previous work [2], this section will focus on its overall scope and give an update on its current status. The programme is initiated and conducted by the German Space Agency (DLR) and funded by the Federal Ministry of Economic and Technology (BMWi). The main objective is to raise a new generation of well-educated and skilled young professionals, who will ensure Europe’s autonomous and cost-effective access to space in the future, especially within the Ariane programme. To achieve these objectives, DLR provides financial and administrative support for participating universities, which develop individual rocket systems. One key characteristic of STERN is that the student teams have the freedom to design full experimental rockets, particularly including propulsion systems. So far, the programme has launched two cycles. Since they have no dedicated names, they are simply referred to as “STERN 1” and “STERN 2” as outlined in the following subsections.
TABLE I. University Team
MISSION RESULTS IN STERN 1
Rocket
Engine
Propellant
Thrust [N]
Envisaged Apogee [m]
Reached Apogee [m]
HS Augsburg
HyCOMET
Hybrid
HTPB + N2O
1,000
5,000
-
HS Bremen
Aquasonic
Hybrid
PE + N2O
1,000
6,000
6,500
ZARM / Uni Bremen
ZEpHyR
Hybrid
Parrafin + LOX
1,800
10,800
1,500 [5]
TU Berlin
DECAN
Solid
AL + APCP
3,000
7,500
5,500 / 5,700a
Leonis
Hybrid
HTPB + N2O
1,300
5,400
5,700
SMART
Bi-Liquid
Ethanol + LOX
500
4,100
-
Cryosphere
Hybrid
HTPB + LOX
8,000
15,000
-
HyEnD
Hybrid
Paraffin + N2O
10,000
46,000
32,300
TU Braunschweig (ERIG) TU Dresden TU München (WARR) Uni Stuttgart
a.
A. STERN 1 The first round of the STERN programme was launched back in 2012. Eight universities participated in the programme with individual rocket systems [2]. Although most of the teams have already launched their rockets successfully and thus concluded their projects, the programme is still ongoing with at least one remaining university team. In the original schedule, a total project duration of three years for each team, who had individual kick-off dates, was foreseen. However, all projects have been extended to account for the high organisational and technical complexity. Three launch campaigns have been conducted at the European Space and Sounding Rocket Range (ESRANGE) near Kiruna in northern Sweden. No further launch campaigns are planned within STERN 1. The results of the first two launch campaigns, comprising 6 rocket launches by 4 teams in total, have been presented previously [3]. They took place in October 2015 and April 2016, respectively. The third and final campaign took place in October 2016 with two launches of equal rockets with the names HEROS 2 (Hybrid Experimental Rocket Stuttgart) and HEROS 3 by the Hybrid Engine Development (HyEnD) student group from the University of Stuttgart. The rocket has already been launched in the first launch campaign of STERN, but experienced a technical malfunction of the engine, which led to a non-nominal flight. The team made an extensive analysis of the failure and optimised the system for another launch attempt one year later. It turned out to be a very successful launch campaign, because HEROS 3 reached and apogee altitude of 32,300 m. “This set a new altitude record for European student and amateur rocketry and a world altitude record for hybrid rockets built by students” [4]. 0summarises the results of all teams and the launch campaigns that have been conducted within the STERN programme up to now. It can be seen that most teams achieved a successful flight. In average, the apogee altitudes reached during the flights were lower than the apogees that have been estimated in the beginning. The main reason for this is the elevation of the launcher at ESRANGE, which has been limited to 80° or, in the case of the ZARM Experimental Hybrid Rocket (ZepHyR), even to 75° by the authorities from the Swedish Space Corporation (SSC) due to the experimental nature of the rockets, which might impose a higher risk to the launch range.
DECAN performed two flights with two individual rockets
B. STERN 2 The second edition of STERN started in 2017. While eight teams have been supported in STERN 1, only 3 teams are supported within STERN 2 up to now. However, there has not been any official statement regarding STERN 2 from the DLR, so the technical goals of the programme remain unclear. The three teams of STERN 2 comprise HS Bremen with their rocket AQUASONIC II (project start 01.06.2017), TU Braunschweig with the rocket Leonis II (project start 01.08.2017) and Uni Bremen with their rocket ZepHyR 2 (project start unknown but the launch is envisaged for 2020). The duration of each projects is 3 years as it was planned for STERN 1. Instead of developing new rocket systems, the teams focus on enhancing and optimising the rockets flown in the previous projects. For instance, ZepHyR 2 will feature larger diameter and length as well as an increased thrust of 5 kN (compared to 1.8 kN), while the basic layout and propellants remain the same.
III. TU DRESDEN’S SMART ROCKETS PROJECT The SMART Rockets project at TU Dresden features a biliquid propellant combination with ethanol as fuel and liquid oxygen (LOX) as oxidiser and is thus the only one of its kind within STERN. Figure 1 gives an overview of the rocket design and subsystems. However, the project comprises much more than the rocket itself. To verify the complex propulsion subsystem, a suitable test bench needed to be developed, respective test plans had to be drafted and risk analyses had to be performed. Due to the particular complexity of this ambitious project, the objective was adapted and a stepwise approach applied. TABLE II. presents the timeline of the project. Moreover, it represents the extensive efforts in verifying the design of both the thrust chamber and the test bench itself. Significant delays result from manufacturing, which is further discussed in the subsequent chapter. Since testing is an iterative process and design changes are necessary before the next test campaign can begin, those delays add up drastically during the course of the project. TABLE II.
TIMELINE OF THE SMART ROCKETS PROJECT AT TU DRESDEN
Date
Event
End of 2007
Initial student theses on the test bench
August 2012
Begin of funding within STERN
September 2012 March 2013 December 2013
Start of rocket engine test bench setup Employment of two PhD students Rocket engine test bench operational
May 2014
Preliminary Design Review
July 2014
Initial test campaign, open combustions
August 2014
Test campaign on ignition
September 2014
First combustion chamber tests campaign
November 2014
Focusing project goal on engine development
March 2015 May 2015 November 2015 January 2016 February 2017 November 2017
Second combustion chamber test campaign First flight combustion chamber test campaign Combustion chamber tests on full thrust Delta-Preliminary Design Review First flight thrust chamber test campaign Combustion chamber tests for increased thrust
IV. CHALLENGES FOR STUDENT ROCKETRY The manufacturing of rocket components, especially considering complex parts for the propulsion system (e.g. cryogenic tanks suitable for LOX) is not just a technological, but also a management challenge. Usually, university teams have three options. The first is to purchase Commercial-Off-The-Shelf (COTS) parts. However, most products on the market are not suitable because they are either space qualified and therefore too expensive or they derive from another industry and do not meet lightweight design requirements. Another drawback of this option is that the students do not have the chance to design their own components. Thus, the learning effect is relatively low. The second option is to manufacture components inhouse, i.e. in workshops run by the university. This is often the cheapest solution, since the material generates the only costs in most cases. However, the manufacturing times are usually quite high and frequent delays occur. This could be avoided by outsourcing of manufacturing processes, which represents option three. Yet this approach goes along with higher costs, for which there is often not enough budget. Therefore, each project has to make a trade-off between these options and either plan resources accordingly or chose a design in which COTS parts can be implemented. The latter option might not be desirable for any educational project. Of course, the question of manufacturing is dependent on the source and amount of funding. The acquisition of funding is a challenge on its own. It seems basically two approaches exist. On the one hand, there are student teams like DARE, who invest a lot of effort to reach out to sponsors and build a network of supporters over the years. This means that they also have to implement outreach as a mandatory activity in order to represent their sponsors. Unless there is no existing network,
Fig. 1. Design and Subsystems of TU Dresden’s rocket
finding sponsors has to be considered a time and workforceconsuming task. In general, the success rate is uncertain and allows only partial funding by each sponsor. Other activities rely on governmental funding, such as STERN and PERSEUS, which are programmes conducted by the respective national space agencies of Germany and France. Usually, they provide full funding for the projects. Still, there are many countries where such programmes do not exist and even the established programmes seem to struggle. As presented in section 2, the number of university teams funded in the STERN programme dropped from eight in the first round to only three in the second. One reason might be that even though budgets for education exist within the agencies, educational initiatives have to compete with other programmes. This competition can be tough, because such initiatives do not seem to fit to classical funding policies. While the outcome and success of a research project can be measured easily, e.g. by the amount of published papers, the success of educational projects can only be measured indirectly and over a greater time scale, e.g. by comparing the careers of participants to those of non-participants. Thus, it is harder to demonstrate the impact of such programmes. Consequently, it is more difficult to obtain and establish research budgets. However, the need for funding is immanent for hands-on activities. This applies to rocketry in particular, as dedicated infrastructure is necessary for the conduction of verification tests, e.g. engine test benches, and for the launches themselves. Depending on system complexity, this can easily extend the scope of similar activities like CubeSat or payload developments. Even if this infrastructure is build, test and launch sites still have to be found, because they usually not rank among university standards. Existing ranges like Trauen, operated by the DLR, are accessible, but the test benches have to be provided and staff has to be paid. The DLR has built a test stand dedicated to student projects in Lampoldshausen. However, it is not suitable for any propulsion systems that require cryogenic flu-
ids and is limited to solid and hybrid engines [6]. Therefore, some student teams try to find and establish their own test site, e.g. at their home university. Although this is potentially the cheapest solution, it is difficult to achieve due to the inherent emissions of noise and exhaust gasses as well as safety regulations. While this is limited to an extremely narrow time period, usually in the order of some seconds per month, the responsible persons are often overly concerned when they hear the words rocket or combustion. Moreover, appropriate space is hard to find within existing university estates. Consequently, conducting the obligatory verifications is challenging, time consuming and contains a high risk of causing delays. But even if all verification has been done and everything is set for take-off, the right launch site still has to be found. This is considerably more challenging in Europe than in other parts of the world. While there is enough space to launch experimental rockets in the USA, even to higher altitudes, it is very challenging in Europe to find a place to launch at all. There are two launch sites north of the polar circle, ESRANGE in Sweden and Andøya Space Center in Norway. All rockets within STERN and PERSEUS are normally launched from ESRANGE. It is efficient to combine launch campaigns of several rockets. The main advantage of those sites is the experienced staff, whose support is particularly valuable for student teams. On the contrary, this makes launch campaigns relatively costly, adding to the high logistic costs due to the remote areas of the launch sites. Further challenges are the limited operation conditions as discussed in section 2 and that the launch site personnel has to be integrated in the development process from an early project phase on. It is advisable to let them participate in the preliminary design review and all subsequent meetings, to make sure that the rocket meets the requirements of the launch site. These requirements can be very different from range to range. For example, DARE launches frequently from the El Arenosillo base in southern Spain, where the implementation of an abort system that can be activated from ground is mandatory. Yet at ESRANGE, no active control or data uplink is desired. Thus, a rocket developed for a certain launch range might not be able to launch from other sites. Within public space in Europe, no further launch sites are known where flights to a reasonable altitude above some hundred meters are allowed and accessible for student teams. The only other option might be to launch from a restricted area. However, this goes along with its own challenges, because the military is not used to serve as a launch site provider for any type of civil research rockets. Further bureaucratic hurdles are imposed by the fact that most of these restricted areas are simultaneously nature protection areas. This might not apply for military activities, but any civil activity within the area has to comply with the respective regulations. This could prevent a rocket launch completely. Finding a place to test propulsion system or the right launch site are not the only common challenges that student teams have to overcome. There are other issues, ranging from documentation to the procurement of specialised parts, that most of the teams have to face. Some of them are part of engineering itself, so it might be justified to train them, but others might just be seen as another cause for delays while not adding any value to the project. Such issues could be minimised by estab-
lishing a close exchange between the teams, so that one team can benefit from the solution another team already found and vice versa. This could accelerate the overall progress within student rocketry. However, this requires a platform, which also needs to be moderated. Despite the possibilities of the digital age, it seems that no tools have been established, neither by individual teams nor by an agency. Another challenge for educational activities is the availability of students. As discussed in detail in previous work [1], students often do not get any credit for additional hands-on activities. Thus, they tend to focus on mandatory courses to complete their studies in time. This limits the participation in fields like student rocketry, even though such participation is considered to be highly appreciated by employers. Even if sufficient participation can be ensured, it is hard to conduct projects due to conflicting schedules. Participating students still have to attend lectures and pass exams. Therefore, their commitment to the project might be very limited. In general, a cyclic behaviour of commitment can be experienced, which is closely connected to the year’s study schedule. While commitment is high at the beginning of a semester, it decreases towards the exams, potentially forcing whole projects to pause. For longer projects, like in STERN, this means that progress cannot be planned easily and might be much lower than it would be for a continuous operation. In fact, this partly explains the delays discussed in section 2. For shorter projects, like the one-year-projects within PERSEUS, the challenge is to prevent any delays since the project cannot be extended, because the students will not be available anymore after the scheduled period. As for longer projects, new students would need to be recruited, creating further delays. This might be evident to students, but has to be communicated carefully to all stakeholders from the very beginning, since they might not be aware of these issues, which are not present in other research projects. Nevertheless, not only the student participation is a challenge. To enable a close and continuous supervision by university staff can be also an issue. Since most contracts of scientific researchers, particularly PhD students, are not permanent, there is always the risk to lose key personnel, which would heavily affect the project’s progress. V. CONCLUSION There is no single solution to the challenges that have been discussed in the previous chapter. It is also not the objective of this paper to present solutions, because any sustainable approach should be discussed by all stakeholders. Therefore, this paper wants to raise awareness for the challenges of student rocketry and give a starting point to spark such a discussion. It is evident that we have to foster future generations of space professionals and that hands-on activities do a great job in both motivating young people to pursue a certain research field and to better prepare the students for their professional careers. However, even established programmes like STERN and PERSEUS seem to struggle recently. This is not only unfortunate for the quality of space education, but imposes a threat to the future of the space transportation sector in Europe, which is already challenged by rising competition from North America
and Asia. In this situation, student rocketry is not a risk but an opportunity. If it gets the right support, it can play a vital role in Europe’s space strategy and allow cheap and easy research on novel technologies. But to do so, Europe needs to find a way to step forward. Obviously, the student teams cannot solve all problems on their own. National space agencies could help, but they usually operate within their country or the frame of bilateral agreements. Thus, an international entity is needed. A European student rocketry association could concentrate the ambitions across Europe, but it is questionable how such an institution could be created and funded. The European Space Agency could take a leading role here, but would need an increased budget for education and thus, the consensus of its member states. It seems that the Europe’s future in space depends on how they will acknowledge the value of education. ACKNOWLEDGMENT We appreciate the assistance and support by the DLR and the BMWi, who fund the project (REF.-Nr. 50 RL 1256) and all students contributing to the SMART Rockets project.
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