Launch Campaign Stratos II Day 8

As many of you have read or seen our story on social media or on the Livestream, today the launch of the Stratos II rocket was planned. The day started very early. All teammembers set their alarm at 5:30 so that we could start the final rocket assembly early and have the possibility to launch in the morning. This would only be possible, however, if the wind would shift to South-West direction early in the morning. Unfortunately the wind only changed to this favourable direction at the predicted time of 14:00. This meant the team had to wait.  While waiting it was possible to already roll the Stratos II rocket out of the hangar to the launch tower, mount the rocket to the launch tower and set the tower up-right.

Stratos II roll-out

Stratos II roll-out

All systems of the launch site have been standby the whole day for the launch. This included ambulances and firetrucks in case of non-nominal situations, a helicopter for the locating of the rocket  directly after launch, radar and optronics systems for tracking purposes (which were also visible on the Livestream) and 3 ships of which 2 from the coastguard and 1 from the launch site INTA to retrieve Stratos II once it has landed.

The launch was initially planned for 14:00 local time (CEST) after the delay due to the weather. At 14:00 the starting procedure for the rocket launch was planned. However, at 13:30 it was decided by the team to switch the batteries of the cameras, which will provide livestream footage from on-board the rocket. One of the two cameras on-board is the payload from Delft Dynamics and is powered by the rocket’s umbilical while on ground and the other one is a standalone camera which operates on batteries.  The rocket was dismounted from the tower, the capsule fairing was removed while the rocket was still on the launch tower and camera’s batteries were switched. From the control center the cameras on-board were tested and after this check the rocket was mounted again. The team was ready for the next launch window at 16:00. In the meantime the first weatherballoon was deployed to measure the preliminary wind speed and wind direction. Until the launch this weatherballoon would be tracked by the radar system.

Testing the videolink with the camera on-board the Stratos II rocket.

Testing the videolink with the camera on-board the Stratos II rocket.

At 16:00 when the launch procedure was about to start it was decided to wait until the second weatherballoon which was sent up 1 hour before. This activity took longer than expected, but at 17:00 the data was finally in for the accurate wind profiles to be inserted in the simulations for the flight path. The simulations are an essential part of the launch. Without it, the pin-pointing of the exact location of the rocket will be difficult.  Click here if you want to know more about the simulations team of the Stratos II project

At last after a long day of waiting and delays, at 17:00 it was finally time to start the next step in the procedure of the launch which is to start filling the tank with the nitrous oxide, after a “Go/No-Go” meeting with the INTA crew about the continuation of the launch.  Half an hour later the pressurization of the tanks was started. The laughing gas was pressurized to 50 bar. In parallel to this activity, the simulations were running.

"Go/No-Go" meeting

“Go/No-Go” meeting

Launch aborted

At 18:15 the pressurization was completed. However, a leak was visible on the Livestream during the detachment of the feedlines. This is normally not a problem, because it is not uncommon to lose some oxidizer after cutting the oxidizer feed line. This is all taken into account. When launching the Ariane rockets it is also visible that some oxidizer is being vented (=leaked) prior to launch.

Parallel to the small amounts of oxidizer being vented, a problem occurred with the flight termination system. A couple of minutes before lift-off there was a sudden loss of signal.  These two problems created a much bigger issue. This is because the flight termination system needs a clear signal but as long as this is not obtained, the digital safety protocols built into procedures prohibit the rocket from being launched. And thus the oxidizer remained leaking out of the tank. As the rocket  stood on the launch platform heated up by the sun more and more nitrous oxide began venting from the tank, now in increasing volumes. The oxidizer in the tank almost reduced to half while the problem with the flight termination system was being fixed.  In the end, after the oxidizer in the tank was reduced from 75 kg to 40 kg, it was decided to abort the launch by the Mission Control Center. The decreased amount of propellant would lead to decreased and undesirable performance. Furthermore, for these conditions no simulation data was available and it would thus be unsafe to launch the rocket without an initial trajectory prediction

View at the Mission Control Center

View at the Mission Control Center

Flight Termination System Malfunction Causes

There is a small probability that the flight termination system malfunctioned due to the fact that it is close to the tank, just like all the other electronics. The oxidizer that vents out of the tank, which is about -60 degrees Celsius, would also cool down the flight termination system causing it to malfunction. Another possibility is that the flight termination system operates in frequencies that interfere with the frequency used by the launch site INTA or by the Delft Dynamics payload which transmits camera footage from the on-board camera live to the ground for the Livestream.

Solutions

The rocket is dismounted after waiting one hour, to let the oxidizer be vented entirely from the tanks. This was required due to the fact that the pressurized tanks can cause a safety risk. Of course the entire Stratos II team was disappointed after the “No-Go” of the launch. But there was not much time to feel sad. The team immediately started to think about possible solutions.

Disappointment after launch abort

Disappointment after launch abort

It has been decided to cut the feed lines of the oxidizer only 30 seconds before launch instead of 10 minutes. Now you may wonder why the team has not done this before. The reason is that this activity has always been a very trivial procedure, mainly because the venting of the oxidizer does not occur usually with our tanks and therefore it was decided to remove this activity out of the critical period (30 seconds before launch) to 10 minutes before launch. The events of today have proved that this needs to be revised. Therefore for tomorrow it has been decided to keep the time of cutting the oxidizer feed lines to 30 seconds before launch.

The problem with the flight termination system will be solved by first performing another radio-frequency compatibility test to check whether the frequencies used by Stratos II rocket do not interfere with the launch site’s frequencies. This test has been performed on Wednesday (Day 7). It is however possible that something has changed in the meantime, so therefore the test will be performed again on Friday (Day 9). If it turns out that this is not the problem, then it will be checked if the  Delft Dynamics payload is causing the loss of signal of the flight termination system. If this is the case then the Delft Dynamics payload camera will be turned on 35 seconds after the launch, when the flight termination system is no longer needed.

Safety is very important within DARE and therefore Stratos II will only be launched if the safety of everyone is not at risk.

Preparing for Launch on Friday

In addition to solving the issues with the flight termination system and the venting of the oxidizer, it has also been decided to replace the igniter of the rocket motor since it could have been damaged by the moist from the from the oxidizer. The igniter is technically gunpowder therefore any moist on it would decrease its performance. The entire rocket’s feed system is currently being tested. Tomorrow the capsule team will then again assemble the rocket after all of the electronics are placed inside the capsule for a rf compatibility test and a test to check the interference with the payload from Delft Dynamics.

The next and final launch window is tomorrow on Friday the third of October. Time is still undetermined so stay updated through our social media and Livestream.

In case you would like to stay up-to-date with all of our activities follow us on twitter (https://twitter.com/DARE_TUDelft) or like our facebook page (https://www.facebook.com/DelftAerospaceRocketEngineering) and be sure to check our Livestream (https://www.youtube.com/watch?v=QqnL04-8fps) and sign up for the text message notification (http://dare.tudelft.nl/stratos-ii/stratos-ii-launch-livestream/). The text message notification worked very well today and we will send the notification tomorrow as well. If you have signed up once you do not need to sign up again.

Note that the livestream which is embedded on the dare.tudelft.nl website will be overloaded due to the huge amount of visitors. If this is the case then the youtube link will still work!

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