Flight day 3 - Antares Ia
Date: 1.11.2009 (11:30 - 14:30)
Weather conditions: sunny, 20°C, light winds
Very limited time and technical challenges caused a project duration of more than twelve months until Antares Ia was ready for its first launch. All pre-flight tests were "pass" and now we waited for good weather condtions to conduct the first couple of flights. November began unusual warm and friendly so we took the chance to learn how the new systems would work under flight conditions.
The day before the launch we took a lot of pictures and some short movies for documentation in case the rocket would not survive the next day.
The launch site "Oesterberg" is a big meadow on top of a hill. When we arrived there almost no one was there. But until noon more and more walkers and other "visitors" arrived. Finally we were quite worried about their safety and decided to limit the launch pressure. In addition we tried to inform everybody about the upcoming launches but it would have been easier to catch a tiger by the tail.
We worked with a checklist to prepare the launcher and the rocket. This took some time but we wanted to make really sure that we didn't overlook something. Thanks to the warm and friendly weather there was no need to hury at all.
Launch 1: The pressure was already close to 11 bar when all of a sudden the rocket exploded with a loud BANG! The "upper stage" took off, powered mainly by compressed air and some foam, and touched the ground about 20 meters southeast of the launch pad. The flight duration was 3.5 seconds and the maximum height was approx. 12 meters. Since the data logger was switched on we could also see that the deployment timer worked. The complete upper part survived the disaster with minimal damage.
The lower bottle also left the launcher but having lost its base it didn't go very far. When it touched the ground one fin was dismantled.
The reason for the malfunction was easy to find: The base of the lower bottle was blown out. How this could happen was not clear. The pressure vessel had been tested with 12 bar a few days ago and passed the test without an issue. The broken pieces we found did not help much. Only after another bottle exploded during a pressure test some weeks later we have a first explanation. It seems that the reusable bottles get weaker with time and the base seems to be the weakest point. Tiny cracks around the base seem to indicate this.
It looked impossible but after a bit more than an hour the damage was fixed and Antares Ia was back on the launcher. Only the paint was missing and one fin was a bit flabby.
Launch 2: With respect to the explosion we decided to limit the pressure to 8 bar. Our goal was now to have a working rocket at the end of the day. Height did not matter so much.
This time everything worked well and Antares Ia took off in a slight arc. The seconds until the parachute fully deployed seemed to be endless but then - with a loud yell - the yellow bag glinted in the sunlight. After 20 seconds Antares touched the ground close to a thorn hedge but this didn't bother us any more. It was a nice flight to an altitude of approx. 67 meters - only 10% lower than simulated!
Launch 3: After a short discussion we decided to have a final launch with 9 bar. We aligned the launcher to the north in order to point the rocket away from the trail nearby. We also decided to replace the nozzle of type "A" with one of type "B" for more vertical alignment of the rocket in the launcher. When Antares was put on the launcher we discovered that the launch abort valve wasn't closed and water was already coming out. There was no other choice than filling the rocket again. During this procedure a lot of foam was produced and finally the whole pressure vessel was full of it.
When a pressure of 9 bar was reached we cleared the site and launched Antares Ia for the third time. It took off in a spectacular arc. At a height of only five meters the rocket flew already horizontal. Then it went down the hill. Luckily no one stood in the way. The rocket touched the ground on a falling slope which prevented severe damage. One fin and the nose cone were lost. Everything else was still in good shape.
Analysis of the data suggested that the instability was caused by the nozzle of type "B" and/ or the usage of foam. This was investigated during the next launch event.
All in all this was a very successful day. We had at
least one good launch proofing that the systems work well and Antares
Ia was still intact.
Next steps: Investigate the root cause of the instability.