Friday, 24 July 2015

The TT7-40 Launch

To summarize right at the beginning. What could have gone wrong did go wrong. However, let's take it step by step.

The parameters for the flight were as follows.
Location: Roznov pod Radhostem, Czech Republic
Time and Date: July 22, 2015 10:00 CEST ISH (8:00 UTC)
Payload: RFM22B custom tracker, Mobius ActionCam, 150g
Balloon: Hwoyee 1600g
Gas: helium
Telemetry: 434.301MHz, RTTY, 100 baud, 500Hz shift, 2 stop bits, ASCII 7, parity none
Modeled Prediction: 42119m, 3.5m/s ascent speed (185g Free Lift), 10m/s descent speed

As I mentioned in previous articles, I had been waiting for the right conditions in the stratosphere which in deed came with the start of the summer. However, since about the end of June, I have been inspecting predicted trajectories for upcoming days with little success. The wind patterns kept being undesirable for a good part of the month. Until the 22nd.
Since I was expecting a +40km flight and I aimed for slower ascent speeds, I used these settings. I had some doubts about the predictor's accuracy in the +35km region and I thought the landing spot might actually have been quite close to the launch site.
The filling this time was quite fast and apart from an occasional gust that had to be taken care of uneventful. Concerning the fill, that would turn out to be an issue later, I ceased filling right when the weights leveled off and started slowly rising suggesting the problem originated in the calculation.
Mobile internet connection wasn't initially cooperating either. But eventually it managed to get the telemetry to Habitat.
That meant that I could turn on the camera, close and tape the payload and prepare for the actual launch.

Due to the wind I decided to try a technique I had read about on UKHAS. One person stands holding the balloon with his back to the wind. Another person holds the payload down the wind. The balloon gets released first and by the time it passes the payload it is hopefully high enough to pull the payload straight up without hitting the ground.
 At about this point I grew a little suspicious of the balloon's ascent speed.
Farewell balloon.
Shortly after that, it became obvious that the balloon is ascending only at about 1m/s instead of 3.5m/s. That sort of threw all the predictions out of a window and I began to speculate about it's fate. I wondered whether it could enter float, or descend back to ground again later on. Eventually, I reckoned it would be best to watch the ascent speed develop, because it tended to rise a little. One thing that may have contributed to the slower ascent rate was the fact that on that day the ambient temperature turned out to break the record high. It was well above 30°C already when we launched. As long as I had the telemetry feedback, I had something to work with.
And that brings us to the second major cock-up of the day. Despite all the successful freezer tests with the now insulated RFM22B, at about 1729m the transmitter failed and went into a carrier. That basically meant the end of that day's adventure, because, based on my previous experience, when the RFM22B goes, it goes for good (until a hardware reset - unplugging and plugging the battery).
I went home and laid out the equipment on the terrace to watch the carrier signal slowly die-out. My last hope was that the balloon would ascend to at least about 20km into a layer of winds that would bring it back west towards me.
During one of my periodic checks, I noticed the signal was back. And in the following checks, I saw the angle on the antenna and its mast, that I tried to position such the SDRsharp showed the strongest signal, slowly rise. At that point, I started searching the sky with a pair of binoculars.
And there it was! After almost 5 hours we made contact again. This time, however, only visual. Eventually, I was able to see the balloon with the naked eye.
At about 15:45 I watched the balloon flyover the launch site and my home.
Earlier, I made a few predictions with slower ascent speeds. The above picture shows 42000m burst, 2m/s ascent speed and 10m/s descent speed. Based on these and the time of the balloon's flyover over my house, I estimated that the balloon eventually reached about 2.5m/s average ascent speed and had flown as far east as the High Tatras, Slovakia.
I then kept periodically checking the signal for any change. I had no idea whether it was still rising or it had entered float and could potentially continue for hours.
At about 16:10 the carrier signal seemed a little different to me. And at 16:23 it disappeared. After another check 10 minutes later with no sign of the signal, I reckoned the change in the carrier's appearance meant the balloon had popped and the payload had been falling. While it's disappearance meant it had fallen below horizon. Based on the time elapsed from the flyover and the expected burst, I thought it may have actually landed around the city the original prediction pointed to. That made me think that perhaps someone would find it and call my phone number written on the payload.
Towards the evening when the ambient temperature decreased to sensible levels, I couldn't just let it be so I took the antenna with the notebook and drove to a higher ground where I wanted to search for the signal and perhaps specify the direction of the landing site. I didn't hope for anything. Just couldn't let it be without at least trying. At the top of the first hill, I found no trace of any signal.
However, the second attempt on another hill surprised me with a suspiciously strong signal on the right frequency.
That started an evening of signal chasing through woods and fields
The signal getting stronger and stronger.
Close to the signal's epicenter in the middle of a wood.
Eventually, I localized the signal to a small wooded area in between two grass fields.
However, it was already getting dark and I couldn't see much underneath the trees. I decided to come back again the next morning.
The next day, I found nothing on the ground. The signal strengthening and weakening helped me to specify the location to this group of trees. Unfortunately, it seemed that the payload landed at the top of one of them. That would correspond to the fact that I was able to see the signal from that far away. Had it fallen to the ground, I might have not been able to capture it at all.
One of these treetops hosts the payload.
However, not even after 2 and a half hours of searching the trees with binoculars from all possible angles I wasn't able to actually see it. At that point and with a thunder storm closing on me, I decided to leave. The current idea is to wait for a windstorm to pass and go search again. The payload must be somewhere at the top hidden behind leaves and branches out of my sight. None of the trees is climbable without special equipment which I don't have, nor the experience to do so. If that fails, I'll wait for the fall and when the leaves are down, I might be able to at least see the payload. Unfortunately, the equipment will have been most likely destroyed by then.

It is a shame the telemetry didn't last longer. It would have been interesting to see how the ascent speed progressed throughout the flight. That could have told me more about to what extent it was due to the extremely high ambient temperature and to what extent was underfilling the balloon to be blamed.
Quite coincidentally, despite the heavily altered trajectory, the actual landing spot was fairly close to the original prediction. A very favorable wind pattern that took the balloon away and brought it back at a comparable rate and distance. Given the launch at 10:47 and the implied burst at about 16:10 with the signal disappearing at 16:23 we arrive at little over 5 hours 36 minutes of total flight time. The burst altitude will, however, remain a mystery.
And that's the story of TT7-40. The result is no altitude data and no video recording. Only memories. Hopefully, at some point, there will be an update on the situation of some sort. Until then...
"She's, out there.
Setting up a camp.
Alone, in a strange galaxy.
Maybe, right now, she's settling...
... for the long nap.
By the light of our new sun.
In our new home."

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