On Thursday the 3th of May 2012, the hybrid propulsion team of the Stratos II project (named Dawn) successfully tested their flight engine. This hybrid rocket engine has been developed based on the research they have done during the whole span of the project. Now finally they are ready to go for the first attempt in the history of DARE to launch a hybrid rocket engine.

The team has kept to their original design of an engine with a sorbitol fuel grain and a nitrous oxide oxidizer. To store the oxidizer the tank concept developed during the Spacecraft Engineering Minor this year was used. This tank has been integrated together with the combustion chamber, the feed system and the fill valves into one sleek looking rocket body. This whole setup was tested during the static ground test of this Thursday.

The group had performed a similar test a few weeks before, however that test was unfortunately not a success. There the servo mechanism that opens the main valve did not function properly and so it was not able to open the valve at the correct speed. This time however there was no apparent problem what so ever with this system. The servo had been replaced by a new one, the bracket attached to the valve was made to fit tighter and the actual flight electronics were implemented and integrated into the rocket. This all together made that the whole system behaved like it was designed to. The valve opened correctly, which can be seen from the very steep increase in thrust at the start of the burn. This is a good property of the system as a high thrust at the beginning means that a rocket equipped with the engine will quickly accelerate to exit its launch tower with enough speed to be sufficiently stabilized by its fins.

The attempt at the first launch of a hybrid rocket engine of DARE will take place during the 19th and 20th of May on a launch day near Leipzig, Germany. The team will now work further on the preparations for this launch day to make sure that they can conduct this launch successfully as well.

On Friday, March 30th, the first BEM, or Ballistic Evaluation Motor (see the previous solid six post: from desktop to tabletop) has experienced its inaugural firing! An 8-second burn with a roaring sound and a huge flame marked the start of a new test campaign. The concept of the BEM seems to work as we hoped.
For the first test, a conservative nozzle and propellant configuration was used, to ensure that during the first test the pressure inside the combustion chamber would not reach a very high level. The purpose of this test was to verify the working of the BEM and to check whether the thermal design has produced a reusable motor, so that we can do a lot of tests during a short period, at minimal cost.
We started the day at the workshop, where we did a pre-calibration of the pressure sensor and packed everything we needed on a cart. Then we headed out for the test field. After a long period of nice weather, today a stiff wind was blowing and the sky was heavily overcast. However, this did not diminish our good mood and without further hesitation we started to work. We put the test bench with the motor firmly on the ground and fortified the setup with sand bags, to ensure that the surroundings of the test setup remain safe, even if something unexpected, such as a motor explosion, would happen. The firing line was unrolled to the command post, 60 meters away. And finally, the cameras were set up to provide the highly desired video footage of the test. All preparations were finished at 10:30, just in time for the people that had morning lectures to join the spectacle.
When the countdown reached T minus 0 seconds, the motor burst to life. A bright, two meter long flame erupted from the exhaust and lasted for a full eight seconds, spreading sparks towards the sandbag shield that we set up 5 meters away. Then the motor noise died out as quickly as it had started, leaving the crowd with big smiles on their faces. After every sign of smoldering had disappeared, the site was declared safe by the safety officers and the crowd came in to take a peek at the scorched grass. No signs of leakage or other kinds of damage were visible and it could be concluded that the test was a success. To celebrate this, cigars were shared with the public in true rocketry tradition.

A close inspection during dismantling of the motor revealed that indeed very little damage occurred on the reusable parts: the liner that protected the casing from the heat in the combustion chamber was largely intact. The casing showed no signs of overheating, however the next test will prove if this is actually the case: aluminum may undergo a heat treatment during a burn, which may weaken the material. However, looking at the condition of the thermal liner, it is believed that this did not happen. The endcap and the igniter assembly were in pristine condition after cleaning and also the nozzle and nozzle retainer, the parts that have to withstand the highest heat load during the burn, were in great condition. A lot of hard residue was found on the divergent part of the nozzle: a sign that the combustion may not have been as complete as we hoped for. However, overall it was concluded that this motor could easily be used a second time.
From the recorded pressure data, it was found that the pressure inside the combustion chamber was indeed very low: even lower than we had expected on beforehand. As a result, the burn duration was long, as we found from the video footage: an impressive 8 seconds. A good, steady pressure curve was obtained, showing that we had a complete and fairly quick ignition and no combustion instabilities. A characteristic exhaust velocity of only 1172 m/s was deduced, considerably less than the 1450 m/s which is theoretically achievable. This shows that the combustion efficiency was low, only 80%. However, it is believed that this increases dramatically at higher pressures.
Overall, we can conclude that this experiment was a very good start of a new test campaign, and we are eager to perform more so that we can obtain more data and present more and better pictures. A quick impression of the test is given by the photos below. For a video compilation of the test, I would like to direct you to the DARE youtube channel: .

As mentioned in the last update of the Solid Six, we are confident that our new propellant, ALAN-7, is ready for use in a real rocket motor. And that is exactly what we are going to do in the coming weeks!
During the last months, we have been working on the design and production of a re-usable and flexible motor design. Flexible means that the propellant and nozzle geometry may be changed without having to produce a complete new motor. This makes it possible to test our propellant in a wide range of operating conditions.
In its standard configuration, the motor contains 1.2 kg of propellant in a BATES-grain configuration. This will hopefully result in a steady burn of about 2.5 seconds, wherein the motor produces almost 100 kg of thrust. Altering the nozzle geometry may lead to longer or shorter burn times, with lower or higher thrust.
The motor consists of an aluminum casing with an aluminum endcap and a nozzle with interchangeable insert. Currently, the nozzle is made of graphite, but experiments with different materials will also be conducted. During our research with the Pressure Test Device, we discovered that erosion of the steel nozzle can be quite severe under certain conditions. Different materials may be more resistant to the flow of hot gas and thus provide a better nozzle.
Next to the motor, a special test bench is developed to record the thrust that the motor produces. This device is made of square steel tubing, which makes it strong and rigid. It is designed to be easily transportable from and to the test field. This makes testing easy and therefore, many tests can be conducted in a short time.

We have finalized the fabrication of the motor this week and the result is Catia-perfect. Some photos are attached to this blog to give an impression of the overall result. The test bench is being fabricated at the moment and will be ready next week.
New blogs will be posted when the first test results are in!

 

Fabrication in progress

The motor fully assembled

Even though the average temperature outside was far below the freezing point the Dawn team of DARE pushed on with the planned igniter test last Tuesday the 7^th of February. This was needed as since the recent project, which was part of the Spacecraft Engineering Minor of the TU Delft, it was found that the igniter that was in use by the team was not as reliable as once thought.

 

The old igniter, which consisted of a NiChrome wire with magnesium strips, had worked consistently during all Dawn tests during 2010 and 2011. However, during the tests of the minor project the igniter failed to work more than 50% of the time. The cause of this might be due to the change from a horizontal to vertical orientation of the engine, because of the use of a different valve, because of higher oxidizer tank pressures or maybe simply because of environmental reasons: All Dawn test were conducted in warmer times of the year. Most likely is that it is a combination of the mentioned factors but either way, a new ignition system needed to be designed.

The eventual system tested consisted of a small igniter made of a mix of nitrocellulose and graphite, surrounded by a larger amount of steel wool. This igniter has now proven that it can light the engine, even at the low temperatures of last Tuesday. Compared with the old NiChrome igniter this system also has the added benefit that it requires only a small amount of electrical power to ignite, whereas the old system needed a very high current to function.

 

The test of Tuesday was conducted on a snow-white Architecture field on the TU Campus. The temperatures started of around -10°C to -8°C in the morning but rising to around a comfortable -5°C in the afternoon. Next to the difficulties that such cold weather brings to the human body, it also influenced some of the test equipment. For example, one of the valves was found to be leaking very slowly, probably due to shrinking of the sealing rings because of the temperature. This problem was however solved by greasing the valve with Krytox. Furthermore the leak detection spray that is frequently used by the team was found to be frozen and could unfortunately not be used.

 

In conclusion, it was a rough environment to do an engine test, but the Dawn team can now celebrate that they have found an igniter that looks very promising, even at these low temperatures.

 

Slow motion videos of the tests can be found here. There is unfortunately no other footage of the tests as the camera regularly used for this did not work because of the low temperatures.

In the past few months the hybrid propulsion group has been working along with other fellow students in a minor at the TU Delft. A minor is a semester during which students can choose to specialize in a field or discover new areas non-related to their field of study. The minor not only allowed more students to discover rocketry but to get closer to a flight ready design.

One significant improvement was the design of a vertical test bench with reduced friction and restrains movement in the vertical direction thus allowing for more accurate data gathering and analysis. Further integration resemble to a ready design was made by designing an in house developed tank to hold the oxidizer. To ensure the safety one tank was tested up till its burst pressure at 147.9 bars and the second tank was tested to be leak tight to at least a pressure of 95 bars. These test were performed at the company Advanced Lightweight Engineering

A heating system was added to be able to heat the tank to an operating pressure of 60 bars and obtain comparable data. To perform this a coil of heating wire was wrapped around the tank and epoxy was applied to the outside of the tank and the tank was insulated. The coils were equally spaced to prevent spot heating. Once all design and production was completed hot fire test were performed as shown in the picture below.

Three successful hot fire tests were performed with HDPE and sorbitol both fuels using nitrous oxide as oxidizer. Problems were encountered with the ignition of the engine, as it did not behave in the same way as in horizontal test setup. In the following weeks this problem should be resolved. The hybrid propulsion group will now work further to integrate this propulsion system into a rocket.

 

Next Page »

• Dawn flight engine ready to go — May 13, 2012
• Solid Six – First BEM test is a success — April 5, 2012
• Solid Six – From desktop to tabletop — March 1, 2012
• New ignition system for the Hybrid engine — February 20, 2012
• Hybrid propulsion update — January 12, 2012

• Stratos II capsule (6)
• Stratos II electronics (1)
• Stratos II hybrid propulsion (6)
• Stratos II promotion (6)
• Stratos II solid propulsion (3)
• Stratos II team (6)