The last day of the launch window is finally upon us. The whole team knows that it is now or never. For today our trajectory simulation experts have kept a close eye on the weather. It was found that the launch window would be open until 14:00. After 14:00, the wind speed would increase which means that it is not safe to launch the rocket anymore. This of course needs to be verified by the weatherballoons right before the launch.
Unfortunately the life of a rocket engineer does not include a good night sleep. The electronics team and the propulsion team stayed up until late at night to fix all of the issues (4 am). The capsule team went back to the camp site early because they had to take the first steps the next morning for preparation of the planned FTS tests.
On the launch day (October 3rd), after the rocket was assembled and mounted onto the tower, another set of tests were performed on the Flight Termination System (FTS). It was found that the system did not work. After many stressful moments with the fear that the last launch opportunity could be missed, the cause of the error was located. It was found that the resistors in the negative feedback amplifier of the FTS were mixed up. This happened after the repairs that took place after the launch scrub the day before. The wrong resistors resulted in a high gain in the amplifier. This again caused the signal received to be amplified significantly such that the signal clipped. After the problem was found the FTS was taken out of the rocket, resistors were soldered in the correct configuration and then reintegrated again.
Testing the Flight Termination System
Attempt to Launch
The team knew that there was still time to launch the rocket as it was 12:00 am at this point. Some final checks were performed and the rocket remounted on the launch tower. At 12:30 a final confirmation was given that we had a “go” for launch at 13:30. The launch control center was set-up, mission control center was manned and the other crew members sat at the conference room to enjoy the nice footage by the Radar & Optronics System. Two minutes before the launch procedure it was however found that the Flight Termination System did not work anymore. The signals were not received by the rocket. These signals are crucial to continue the rocket’s flight. When Stratos II doesn’t receive the signals the flight will automatically be terminated within 3 seconds. The Optronics Control Center can immediately terminate the flight if safety can not be guaranteed. This is done by sending another signal to the FTS in the rocket. This safety mechanism will make sure that the rocket is terminated before any accidents can happen. Finally it was decided that the mission would be aborted by the mission controller in the Mission Control Center. The mission controller (Geert-Henk Visser) asked for a formal decision from the Flight Director (Rob Hermsen). The Flight Director gave a “No-Go” for the launch as launching without the FTS is not an option for both INTA and DARE.
A “No-Go” after FTS malfucntion
It was decided after the “No-Go” that the FTS would be tested one more time with the Intermediate Frequency Amplitude of the signal (IFA, this is comparable to the volume of the signal) increased by the INTA team, as requested by us. It turned out that the FTS worked and that we had a “Go” for launch! The Mission Control crew was ecstatic with joy, but there was no time for celebration. The rocket was not launched yet and the oxidizer was leaking out of the tank. At this point it was decided to speed up the launch procedures, without discarding any safety protocols, due to the fact that the oxidizer was leaking every second counted. The Range Safety Officer (Robert Werner) started syncing the launch countdown timer with all the control centers by counting down and marking the time over the communication devices. This was repeated a few times to make sure the countdown was synced perfectly. With only a few seconds to go until launch the whole team started to countdown together! 5, 4, 3, 2, 1, 0… The button was pushed…. But no launch. It was immediately visible that the rocket suffered from an engine misfire. The Flight Director decided to immediately abort the launch to ensure full safety.
Condensation on the rocket after engine misfire
Frost forming near the main valve
Analysis of the failed launch
The misfire has been determined to be caused by the main valve being frozen. The main valve is located between the tank and the combustion chamber (as can be seen in the picture above). This is sealed off to make sure that the liquid nitrous oxide only flows through the valve and not around it. It did however flow around it, resulting in the valve getting frozen by the extremely low temperature of the nitrous oxide. The rocket has already been tested once with the nitrous oxide running through the valve. This test went perfect when it was conducted in Delft a few weeks before the launch campaign. The seal worked fine and the valve did not get frozen. However, the seal did break before launch. It is assumed by the team that this seal was broken due to the fact that the rocket was disassembled multiple times, with every disassembly the chance of the seal being broken increases. The seal is designed to be reliable, but it is not reliable enough after disassembling the rocket multiple times. Increasing the reliability for all possible scenarios is something which needs to be investigated by the propulsion team. In addition to the problem with the main valve of the propulsion tank, the FTS also needs to be checked. It turned out that the signal amplitude of the FTS was set too low, as explained in the previous paragraph. More tests should be run before the launch to determine an optimal Intermediate Frequency Amplitude of the signal.
Moments after the launch attempt
Conclusions
The conclusions that can be derived from this launch campaign are: first and most importantly, the FTS needs to be more reliable. A complete redesign of the FTS might be favourable over fixing the issue. Secondly the leaking of the oxidizer tanks needs to be addressed. Either the leaking needs to be completely fixed or the leaking should be minimized as much as possible.
It can also be concluded that all the teams of the Stratos II project worked very well and efficiently together. The INTA crew has inspected our work over the past days and were very pleased with our professionalism. They especially considered us very competent with safety critical activities. They are very positive about a possible launch in the near future. We will need to discuss this with the entire Stratos II project team. The sponsoring will be a critical issue for a possible launch in the future. Therefore we will inspect potential sponsoring options in the coming weeks. In case you are reading this and feel like you can help us out with our mission or whether you or your company want to cooperate with us, then please contact our External Relations team (externalrelations@dare.tudelft.nl).
