One Little Cloud In The Blue Sky

On Saturday I helped with a school launch by Greg Tomlin, who drove here from Coventry with his SKYBLUE payload and a minibus full of excited schoolchildren. It was their first launch, but not Greg’s, as he’d launched twice before with his previous school.

Predictions were for a fairly gusty and showery day overall, but with a chance of launching in the morning before the wind got up and the clouds and rain arrived. Landing predictions were also good for the morning, but poorer later as the winds would take the balloon down to the Severn Estuary. I ran through several permutations of balloon size and gas fill, and finally opted for a 1600g balloon with a standard ascent rate of 5m/s.  To help keep the flight away from a watery end, I chose a slightly undersized parachute so the final descent wouldn’t drift too far south.

Greg kindly offered a free ride for one of my trackers if I had anything to test, and I did. I’ve been working on a tracker that uses a servo-controlled parafoil to guide a payload to a specific landing spot. I’ve run this through emulated flights but hadn’t flown it for real, so this was an opportunity to do just that, with the fallback of another tracker in case things went wrong (which they did!). So, I quickly put together RTLS1 (Return To Launch Site), without servos of course, but with all the software intact.  Hardware was an original Pi Zero (I didn’t want to fly a camera this time) and prototype PITS Zero board with LSM303 compass/accelerometer connected.  As an extra test, I added code for a BME280 pressure/temperature/humidity sensor. Together with the RTLS compass data, and various landing prediction and flight control values, there was quite a lot of telemetry to send, so I opted for a 140 bytes/second LoRa mode for transmission.

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I had another reason to fly something. My wife’s maiden name is Cloud, so last year I bought a cloud necklace, with the intention of sending it up to near space so she owned a very high-flying cloud! I hadn’t got round to actually flying it, but with our 30th wedding anniversary in a few days this was a good opportunity! The launch day also turned out to be the 12th anniversary of when Julie’s dad died, so it was particularly poignant. To add one more coincidence, he used to be a CB operator with callsign “Skyblue”.

With Greg and team en route, I prepared for launch so we could get the balloon flying as soon as possible (delays would mean a higher chance of a wet landing). So when they arrived, I had my tracker online and payload sealed with line attached, groundsheet out, balloon tied to the filler, and lines tied to the parachute. Greg and his team wasted little time in getting cameras started, tracker running and online, and payload sealed up and tied to the parachute and my payload.

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Meanwhile I inflated the balloon. The wind by now was quite gusty, but with quiet periods where I could get on with filling with gas and checking the neck lift.

After sealing the balloon sealed and tying it to the payloads, I took the balloon out to the field, followed by Greg and his team carrying the payloads, parachute and line. Out in the middle of the field, the wind was quite gentle and as I let up the balloon it wasn’t far off being vertically above me. Holding the lower (my) payload …
IMG_1970… I took a few steps downwind and launched. The entire flight train that rose into the grey sky above.

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Back in the house, I checked the transmissions and map. initially the live prediction was a bit alarming, showing a landing south-east of the Severn (I’d aimed for North-West), but then I remembered that the live predictor generally assumes a burst altitude of 30km, and ours should be 36km or so. Also, the initial ascent rate with hydrogen is lower than the average, whilst the predictor assumes the ascent rate will be constant.

With a fairly high flight landing not far away, we didn’t have to rush into the chase vehicles. So we had time to watch the flight progressing, and I had time to finish getting my chase car set up. Part of that was starting up my LCARS-based touchscreen, and when I did I noticed that the RTLS1 position wasn’t updating. A quick check of the telemetry showed that it had stopped at about 12km altitude, which was a very strong indication that the GPS wasn’t in flight mode. It later turned out I hadn’t re-enabled that code after disabling it for my emulated tests. Oops. At least the SKYBLUE1 tracker was still working fine, and I knew that RTLS1 would start sending the correct GPS data once the flight descends back through 12km, and that I would have plenty enough test data from it anyway.

Once it was certain that the landing point was going to be west of the Severn, we drove down to Monmouth to wait for the balloon to burst. Parking at a convenient and free location (Lidl !), Julie bought some supplies as we all watched the flight proceed and then burst. We waited a few minutes for the predicted landing position to stabilise, and then set off for the most likely landing area. We had to change our target a couple of times, and were a couple of miles away when the flight landed (which isn’t bad considering the how narrow and windy the roads are in that area!). My LCARS system had a last position of 166m altitude which was only 46 metres above the landing position, and 4 metres below the road near that position! I later found out that my home receiver had a last position of 368 metres altitude, which again was very good considering the hills between the launch and landing sites.

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Using that last position, we drove through a small forest (usually a bad sign when chasing a payload!) to a track which, according to the satnav, was the closest pint we could get to by road, with the payload about 350 metres away. I still had no signal from either tracker, which seemed very odd as normally I’d get a signal 1km or so away. With a single tracker I’d wonder if the tracker didn’t survive the landing, but it seemed unlikely that both trackers would stop. So we kept going in the hope of getting a signal further along the road. We still couldn’t get a signal so parked up and got out the Yagi which, with radials horizontal (meaning the payload was on its side or the aerial was squished against the ground) finally got a good, decodable signal. Tapping that into the satnav, we were directed back to that track we passed earlier. So we parked up, and Greg and I went to the adjacent house to find out who owned the land that we’d just dropped our payloads on, and to gain permission and hopefully directions too!

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With that done, we opted to walk down the track, which got progressively more muddy and after a while wasn’t getting us any closer to the payload. By then we managed to get satellite mapping loaded on my phone, and it became clear that it was going to be better to go back to the house and find a different route. When we got there I chatted with the landowners – a retired couple in the house – and they couldn’t have been more helpful. The husband was recovering from an operation, but the wife offered to come out with us, so once a quick rain shower subsided she got her wellies and we all followed her down a footpath and across (in single file!) a field to a second field where the children soon spotted their blue payload. They seemed pretty excited!

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I, of course, was relieved that I hadn’t lost Julie’s necklace!

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Back at the house, the SKYBLUE team showed some of their photos to the landowners, and after some more chat we all left.

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Julie and I decided to stop in Monmouth to have lunch by the river.

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So, a very good flight, and I now have lots of real data to peruse before I start testing my RTLS project with a parafoil.

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One Response to One Little Cloud In The Blue Sky

  1. Bill Harvey says:

    Dave – another inspirational flight for the children and a sentimental one for you and your good lady wife. I managed to follow this successfully yesterday from a hill in North Devon, my first mobile attempt.

    Since my first balloon flight this week my wife has become very interested. She hadn’t realised what fantastic results could be achieved (photos etc) and what a great experience it can be for the children involved.

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