The carbon-fiber composite rocket shell with an aluminium interface holds all systems together and ensures structural stability. The nosecone is fabricated from glass-fiber composite to let radio signals from telemetry and GPS pass. Exchangeable CFRP fins with a foam core can be dismounted for transport and replaced if damaged. Couplers and the interface bulkheads have been optimized for the loads and manufactured from aluminium.

Redundant avionics trigger the ejection of the nosecone by pressurizing the parachute compartment with inert CO2. As a result, two parachutes are being ejected after each other: First, a drogue after apogee to stabilize and slow down the descent to less than 32 m/s. At 400 m above ground level, the main parachute is released to reduce the descent rate to less than 9 m/s and provide a safe touch down of the rocket.

To provide a live data feed throughout the flight, an X-Bee module transmits the position, system status, velocity, and position to a ground station. A WiFi transfers data within the rocket and the recovery position is acquired by a ublox GPS. The electronic hardware also stores the microcontroller and sensors for the control. All PCBs and the embedded software were student made and adapted for its use in the TELL mission.

Using the aerodynamic characteristics determined with a wind tunnel test, a student-developed algorithm controls the airbrakes that increase the drag to accurately reach the target apogee of 10’000 ft. The algorithm is solving a chance-constrained infinite horizon optimal control problem. Using Monte-Carlo simulations accounting for uncertainty and other effects, a look-up table is stored on the on-board memory and enables a simple implementation on a rocket with limited in-flight computation capabilities.

A commercial solid motor composed of Ammonium Perchlorate burns for 3 s and accelerates the rocket to a maximum velocity of 300 m/s with up to 10 g. This burn provides the energy needed to bring the rocket up to 10’000 ft. TELL is built for a reloadable Aerotech M2400T commercial off-the-shelf motor. The launch is initiated by an independent ground-based ignition system using electrical matches.

After flawless preparations TELL was installed on the launch rail at 11:20h. The waiting time on the launchpad exceeded one hour.

At 12:29h the ignition was successfully initiated, and the rocket lifted off. TELL cleared the launchpad nominally, but a tilt and/or rotation of the rocket could be observed after leaving the launch rail.

In the middle of the 3 seconds boost phase, the lower body of the rocket violently disintegrated, and the connection to the rocket was lost. Multiple debris could be observed. A catastrophe at take-off (CATO) was detected, and the range was closed.

The CATO was a great shock for everyone, but team TELL didn’t just take the hit and stayed on the mission. A detailed analysis on the ground with judges, experts of the competition and the manufacturer was conducted the same and following day and concluded a a malfunction of the rocket’s motor due to overpressurization from backside burning. The measured thrust curve suggested a non-nominal burning which was confirmed by the manufacturer. Most probably, just had the statistically possible bad fuel grain batch.

download the post flight analysis report

The parts of the rocket, including unburnt grain, could be recovered and were subjected to a detailed analysis. The outer structure was almost intact. The inner structure, the payload and the avionics, however, were heavily damaged. Surprisingly, no serious damage could be observed on the motor casing. The distorted lightweight fin section remains as a memorable artefact from the CATO.

The rocket TELL was equipped with a telemetry system and sensors in all compartments of the rocket. Post-processing of logged and transmitted data showed that the rocket experienced 16 g instead of 11 g in the short burn time until the CATO. This is 33 % more thrust than nominal.

The graph besides shows measurements from the accelerometers in the different sections of the rocket compared to the expected thrust of approximately 2400 N.

The recovered grains, the outside-burnt and burst insulation liner and the observed overperformance suggest that the fuel grain burned faster than nominal, which resulted in backside burning along the wall of the casing.
This created an abnormally high pressure in the motor and the threads of the rear closure of the motor casing weakened, leaving visible abrasion marks on the threads. As a result, the motor disintegrated, released all pressure (explosion) and stopped burning.
The intentional fail-safe mechanism by the failing threads at overpressure prevented further burning and a bigger explosion.

Check out the video of the take-off from multiple angles and see how the rocket looked like after launch!

Before the launch of the TELL rocket, the project manager tells more about the rocket and the organization.

We proudly represented our country with some raclette and chocolate in the desert of New Mexico.

Here’s a first look at the potential reasons for the break up on the ascent of our rocket during the launch.

Jonathan Firth (Exec. VP of Spaceport and Program Development of Virgin Galactics) was impressed by our airbrake design.

Before our rocket is inspected by the judges, it needs to get assembled first. Check out the timelapse of the assembly!

We arrived safely in El Paso. We met the vice president of the Experimental Sounding Rocket Association!

Time to explain what the Spaceport America Cup is and how our rocket actually works.

Find out in this video how we prepared for finding aerodynamic parameters of our rocket with the help and know-how from Formula 1 experts of Sauber Aerodynamics in Hinwil, Switzerland.

The nosecone of TELL 1 is made of glass fiber prepreg. The half-shell mould is closed after the layup and subsequently cured in the autoclave at CMAS Lab of ETH Zürich. Do not feed the students while building rockets!

It is the first time the team launches a Tripoli Level Two rocket. The self-built recovery worked perfectly, and the team had a blast in the beautiful Jura region of Switzerland.

With the help of our partners from industry and academia, the team figures out what the best final design of the rocket will be like. Thank you very much RUAG Space, Sauber Aerodynamics, Maxon Motor, ETH Zürich and HSLU for your education!

Christian explains to us how additive manufacturing helps to have a good idea of what the final object will actually look like.

Passion starts early: ARIS’s first rocket launched in Kaltrbrunn, Switzerland, with ARGOS. The rocket MESTRAL I tested our first electronics of the airbrake mechanism.