Tuesday was another successful day for the Stratos Team. The Faculty of Aerospace Engineering organized an inflight call with André Kuipers from the International Space Station. The event was also attended by Mark Rutte, the Prime Minister of the Netherlands. The national press covered the story and Frank Engelen, the team leader of Project Stratos was interviewed by ‘Vandaag de Dag’ in front of the new test bench of the hybrid propulsion team. The short interview can be seen here (06:23 t/m 07:52).

Before Mark Rutte entered Lecture Room A to talk to André Kuipers and students, we had an opportunity to show him the hybrid test bench. He was also so kind to take a picture with us.  Our work had left an impression as Mark Rutte referred to the test bench while talking to students in the Lecture Room.

A reception was given after the inflight call where we had the opportunity to present the test bench to representatives of the dutch space industry.

In May the Stratos II concept launcher was launched; a rocket to test components developed for the Stratos II project. Another successful launch of the rocket was performed on the 9th of September, after an aborted launch attempt in June.

After not being able to launch on the previous launch day in June, due to problems with other rockets that were also scheduled that day, only little work had to be done to prepare for flight in September. With only minor adjustments to the electronics and release mechanisms, the rocket was soon ready for launch.

This time the spectators could enjoy a successful launch: after ignition the rocket successfully left the tower. After 15 seconds the rocket reached apogee, and separated the nose cone from the motor. The separation of the nosecone and the ejection of the parachute worked flawlessly. Unfortunately, although the parachute folded in the squid bag did eject from the nose cone, the actual parachute deployment from the squid bag did not occur. This resulted in a rather rough touchdown and a flattened nose cone.

However all flight data stored in four SD cards survived, making this launch a success. We now know which subsystems perform as expected and which subsystems need a makeover.
As the remains of our rocket are no longer airworthy, a new concept launcher will be made. With the knowledge gained from the last launch we are ready to make the change from provisional prototypes to well designed components. These will also be designed to withstand the complete operating conditions of the final Stratos II. We are making good progress, but a lot of testing still lies ahead.

By Hein Olthof, Team leader solid propulsion group.

 

 

After a period of silence, the solid propulsion group started a new testing period. The goal was to further refine the propellant composition ALAN-7, and to characterize it. Three types of tests were performed: atmospheric burn tests, pressurized burn tests and shear strength tests. For the shear strength tests and the pressurized burn experiments, new test devices were developed and built. Several compositions were tested, the only difference between them being the binder components, while the total binder content in each composition was kept at 20%, which is the minimum required for good cohesion. From the shear strength tests and the atmospheric burn tests, it was found that increasing the polyester content in the binder combination will increase the shear strength, but generally yields a propellant with a less favorable burning behavior. A graph of the shear strength versus the polyester percentage can be found in Figure 1. A more elaborate analysis of the results is needed to judge which binder combination is most suitable for our needs. A very good result is the fact that each of the propellant samples ignited well. The problems we had with ignition in the past seem to be resolved.

 

For the pressurized tests, only one propellant was considered: ALAN 7.0. This composition was already flown in the Flaming Tiger rocket, but further characterization was needed in order to make a good motor design. Therefore, samples of this propellant were tested under pressure, in so-called Pressure Test Devices (PTD’s), with different values for the klemmung (burning area divided by the nozzle throat area). A high klemmung results in a high pressure, while a low klemmung gives a low pressure. Two types of grain geometry were tested. The end burner, which is a cylindrical grain, only burns on the front face. The core burner, which has a cylindrical hole in the middle, burns from the inside out, as well as on its front face. The first geometry gives a constant burning area, which eases calculations later on. However, to obtain a large klemmung value, the throat diameter needs to be very small, which increases the risk of clogging. The core burner has more burning surface and hence reduces this problem.
Some problems arose during the tests. Six PTD’s were prepared, of which only four ignited. The two that did not ignite had the same casing. During assembly, the ignition wires broke both times. This was caused by a flaw in the design, and will be solved later. One of the PTD’s did ignite, but suffered from severe leakage after the pressure sensor assembly came apart. The thrust that was delivered through the so created hole was enough to bend the 8mm steel tubing. The ignition was very fast, almost instantaneously, which is a good result. However, the pressure data have value only to the point where leakage started. One interesting observation was the occurrence of Mach diamonds in the exhaust for a short period of time. This gives nice photographs for presentations (See Figure 2)

 

Then, we had another good ignition, from a core-burning PTD with low klemmung. Due to this low klemmung, startup was slow, but a good stable burn resulted in a chamber pressure of 12 Bars.

The next test was an end burner, with a very small throat. Whether this was the cause or not: the pressure inside the PTD increased so much, that the solid, 3mm steel plates could not support the load on the endcaps and bended. This ruined the PTD, and reduced it to a nice museum piece. It has to be mentioned that this was the only PTD of the old design, with tension rods instead of threads.

Finally, another core burner with high klemmung ignited very fast, resulting in a steep pressure curve. The chamber pressure quickly reached 80 Bars, after which the safety valve was activated. Because of this, no full pressure curve was obtained, but the high pressure that occurred is very promising. Next to that, the burn was very stable, as was observed from the High-speed camera footage. A photo of the PTD at full pressure is given in Figure 3.

Over all, we look back at a successful test campaign, with more than enough data to analyze in the coming weeks and a lot of lessons learnt. And of course with some nice new pieces for the DARE museum: a charred burn test stand, some pieces of bent tubing and an destroyed PTD. This propellant clearly has potential!

Today at 14:22, Stratos II was brought one step closer to its goal of 50km when the latest test rocket, the Stratos concept launcher, left the launcher tower at ASK ‘t Harde and flew to an altitude of 1 km. The separation of the nosecone occurred near apogee and roughly four seconds later, the parachute was deployed. This test proved that the designed recovery mechanism works as it should. This represents a major step forward for the Stratos team.

 

As mentioned a few months ago we will launch a concept version of the Stratos II rocket. This Concept Launcher will only contain the upper part of the Stratos II rocket, being the nose cone and adjacent payload section. It will be propelled by the booster motor that powered Stratos I.

With this launch we hope to test our innovative separation, mechanism, the so called clamp band. A video of this system can be viewed below:

The original plan was to launch the rocket last year’s autumn. Unfortunately due to storage problems with the motors, we were not able to launch the rocket at that time. We had to wait for the next launch opportunity, which will be next on Friday the 13th. We will launch this rocket to an altitude of approximately 1 km at the artillery base ‘t Harde. We are confident in a successful flight, which will bring us one step closer to the launch of the final Stratos rocket.

Next Page »

• Inflight Call with André Kuipers — January 12, 2012
• Another succesful concept launcher launch — September 21, 2011
• Solid propulsion group update — August 19, 2011
• Successful launch of concept launcher! — May 13, 2011
• Concept Launcher ready for launch — May 3, 2011