Show that foil balloons can float at altitude. Previous pico flights have shown that you can carry out low altitude flights with foil balloons however each time one balloon has burst resulting in descent. The current thinking is that the reason we havent' previously achieved float is that the balloons have had too much lift, they reach burst altitude before float altitude. For this flight the aim is to carefully get a slow ascent rate of approximately 0.5m/s.

• Arduino168
• Ublox5 GPS with patch antenna
• Radiometrix NTX2 434.075Mhz
• 2xAA
• Built on stripboard

Total mass = 87g (inc antenna + insulation)

• Filling was undertaken in a closed barn, to reduce any wind.
• As we were going to add ballast to get the target ascent rate we filled one balloon first, made sure it could lift 25g (1/4 of payload mass + a little bit more), we over filled slightly.
• We measured the total lift of the first balloon and then aimed to get each balloon to lift that much. It was easy to add He but we didn't attempt to empty out He as we feared it might push out the internal seal.
• Once we had all the balloons filled we then measured the ascent rate and added further mass until we had roughly 0.5m/s.
• Bluetack is a good material to add and subtract mass. We found that it needed a further 44g of ballast and so added a small bottle and some water which had a total mass of 44g.
• Once everything was filled we just waited for the rain to stop - being in the barn meant that the balloons were safe.
• For launch we just too everything outside and released it.

Once the balloon was released we went back to the barn to track. Early on we found that the signal strength wasn't as good as previous flights and there was fading with an oscillation of approximately 2 seconds. This made data collection challenging requiring us to rig a yagi on a pole to maximise our receive abilities.

To compensate for this poor signal strength it was necessary to collect all the partial strings and calculate and combine the data to get the flight profile. The ascent rate was a relatively stable 0.5m/s apart from an usual section where the acent rate increased and then held for a few minutes only to continue ascending. As we passed 6km altitude and were at the edge of our reception range we noticed that the balloon had begun to float - this was confirmed but the reconstruction of the partial strings.

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• The setup was very easy - having a large indoors space to fill made getting the mass, lift and ascent rate much easier. This is vital for these foil balloons which small error margins.
• The data shows that we did manage float for about 10 mins before we lost radio contact - this is great news but we'll need a further flight with a sustained float to actually prove it.
• Low altitude flights are hard to track - its difficult to get the widespread listeners as you do need to be quite close or have a good setup. This wasn't helped this time by what was most likely an antenna problem on the payload.
• Often we could hear the RTTY but weren't able to decode the data - some morse in this situation might have helped.