Delft Aerospace Rocket Engineering (DARE) is one of the world’s most ambitious amateur rocket-building clubs. Based at the technical university in Delft, The Netherlands, its 130 members share a big dream: to reach outer space. Using materials and technologies from Oerlikon Metco, they have moved a significant step closer to their lofty goal.
Until 2016, the students from Delft held the European altitude record for a rocket built by students. That year, the record was snatched from them by the team at the University of Stuttgart, Germany. With the Stratos III, DARE’s largest project, they hope to bring the record back to The Netherlands — and build on the momentum generated by the Stratos I and Stratos II+ rockets’ success. A flight altitude of 32,300 meters will achieve this goal. However, the group working with Felix Lindemann, the Stratos III team leader, is aiming for a good deal more: “If everything works right, then our rocket will achieve a flight altitude of 60 to 80 km,” he explains.
The engine as an influencing variable
He notes that “a prognosis like this is always a bit risky.” That’s because flight altitude potential depends on quite a few considerations. The air density at the launch site and the wind conditions in the atmosphere are just two of the variables. Each has considerable influence but can be calculated with only limited accuracy.
What can be controlled by the rocket builders (and is therefore of decisive importance) is combustion time: how long the engine burns. It must generate the necessary thrust, and every tenth of a second of combustion time results in more meters in altitude. For this reason, the engine is being thoroughly tested during the development phase, Lindemann explains: “At the moment, we have achieved a combustion time of 15 seconds for the rocket engine. Our goal is to increase this to 28 seconds.”
However, a longer combustion time also means higher temperatures at the nozzle. The flame in the combustion chamber is about 3,000 K hot, or somewhat more than 2,700 degrees Celsius. At the outlet of the nozzle, the temperature is still about 2,000 K. “This temperature is influenced by the shape of the nozzle, which, in turn, is also a significant factor for the thrust,” says Felix Lindemann. “The nozzle must not become deformed under any circumstances, even when subject to such a high thermal load.”
In order to optimize the engine and the ignition sequence, test nozzles made of graphite are being manufactured first. This material provides sufficient thermal stability, but is too heavy for later use in the actual rocket. Consequently, Lindemann’s team is working with a hybrid structure for these components in which only the parts that are subject to the greatest thermal loading are made of graphite. However, the calculations are turning out to be a challenge: “It’s important to understand that we are working at the very limits of what is technically possible as to whether and how many components in the nozzle can be replaced — and whether this will prove worthwhile in the end,” he says.
Material and technology from Oerlikon Metco
Oerlikon Metco is providing the young researchers with support in the development work. The company is supplying a highly temperature-resistant titanium alloy powder to DARE project corporate partner 3D Systems, which is building the nozzle outlet using the additive manufacturing process with laser melding. The demands for temperature stability would not be met by titanium alone: “In order to reduce the thermal load, Oerlikon Metco had the idea of additionally coating the component with yttrium-stabilized zirconium oxide at their Swiss location,” says Felix Lindemann. And he is pleased at the current status of the development work: “Two nozzles have already been tested and the results are very promising: At least the two last centimeters of the so-called ‘divergent section,’ meaning the outermost part of the outlet, can be replaced with this material.”
The rocket is not yet ready for launch. Many tests are still pending before the exact launch date can be determined. As things stand today, though, all should be ready by the early part of 2018. Until then, Lindemann says, the students have a good deal to do, as “70 hours per week and sometimes more is the standard for members of the core team.”
DARE is no “extra-curricular” activity. Semester breaks are being sacrificed and semesters on leave invested. But an enthusiastic student member says it is worthwhile: “We love what we are doing here. We have a great deal of freedom in the project and are able to develop and make decisions ourselves. That includes from the start to the finish — in fact, from the design of the individual components on to the testing.”
And what about the competition with the other student teams? “Oh, that shouldn’t be taken too seriously. We exchange information and now and then there are team members who worked in a team from a different country just as enthusiastically — as I did as well.” Felix Lindemann smiles slyly: “But we’ve made great progress in Delft. With the Stratos III we’re going to get the record back.”
DARE and Stratos III
Delft Aerospace Rocket Engineering (DARE) was founded in 2001 at the Delft University of Technology, the Netherlands, and today has about 130 student members. With numerous projects, DARE offers students the opportunity to gather practical experience in the development and the construction of rockets as of the first year of studies. Stratos III is the largest of the more than 100 rockets which have been launched into space since the founding of DARE.
Thermal Barrier Coatings (TBC)
Thermal Barrier Coatings (TBC) reduce the transfer of heat and isolate the substrate. The low thermal conductivity and the high thermal coefficients of expansion of Oerlikon Metco’s coating solutions offer decided advantages: Longer service life of the components at the permissible, higher temperatures and a significantly improved degree of thermal efficiency.