Since September 2021, a student team of the Akademische Raumfahrt Initiative Schweiz ARIS has started to design and build a hybrid engine, which will be implemented into a sounding rocket. In this new developed hybrid engine, the HELICOIL® Screwlock thread insert produces high-strength threads.
This hybrid engine will be implemented into the sounding rocket HELVETIA, another project of the ETH Zurich.
The primary objective is to improve the engine efficiency over the previous design in order to carry the HELVETIA rocket to its desired apogee. Through weight saving and changing the combustion reaction, a higher specific impulse is achieved. The ASTREA hybrid engine is designed to generate 6,000 N of thrust using a combination of nitrous oxide and acrylonitrile butadiene styrene. After a burn time of just 7 seconds, the engine has generated a total impulse of 40,960 N – enough to deliver a payload of 4 kg to 30,000 feet.
The hybrid engine consists of several subsystems such as a tank, a data acquisition and control system, a combustion chamber and an injector. This injector atomises the oxidising agent nitrous oxide from a liquid into a fine mist, which is then injected into the combustion chamber. This allows the nitrous oxide to react more easily with the fuel. In order to withstand the developed pressure, steel screws must be inserted into the aluminium injector component. However, the combination of steel and alumi¬nium often causes galvanic corrosion. This leads to broken threads and damages resultant the entire component. To prevent this situation, a heavy-duty and wear-resistant thread reinforcement is required.
Thread reinforcement has been inseparably linked to HELICOIL® for over 65 years. Wherever materials with low shear strength (e.g. aluminium, aluminium-magnesium alloys and fibre-reinforced plastics) are used, HELICOIL® thread inserts come into operation. They meet the requirements of national standards, aviation and military standards.
The HELICOIL® Screwlock thread insert is a wire with rhombic profile formed into an elastic spiral. It produces high-strength threads and has also a clamping area for captive screw locking. The steel screws can simply be screwed in. Even with frequent use, the wear of the nut thread is excluded and the longevity of the component is guaranteed. Currently, 12 HELICOIL® Screwlock with the dimension M8 are installed in the drive of the hybrid rocket.
The Spaceport America Cup, held in New Mexico (USA) is the world’s largest university rocket engineering competition. Each year more than 1,700 students gather in over 150 teams from around the world and compete to target altitudes of 10,000 and 30,000 feet with their own developed rockets.
This year the Cup took place from June, 21 – 25 and the ARIS team started in the highest category “Hybrid SRAD 30,000 feet” – and they did it. The rocket even reached an altitude of 33,800 feet. Congratulations to the team!