Monday, 26 September 2011

Launch Day

Well that was a bit dramatic...
Rain and wind really did put a dampener on things to begin with, and caused us a few issues, but WDHAB was going, ready or not.
There were some successes, and there were some failures. I was never one for doing 'the normal' thing and full experimentation was the key here. Hopefully some lessons can be learned and a few ideas taken on-board by others.

Set up at the launch location went well, but the main WDHAB payload just wasn't getting the altitude. It had never failed before. Typical. Restarting, unplugging, cold starting the GPS didn't seem to make a difference, though I thought it would pick it up eventually anyway.... but alas no joy - sod it, launching anyway, especially as the balloon was inflated by this time.

The balloon didn't quite get to the neck lift I was wanting, it's possible the rainwater resting on it may have contributed (not sure) but the cylinder ran out with approx. 3KG lift. I was aiming for 4KG for a shorter flight, as the minicams and the WDHABmini payload only have short battery lifetimes.... anything to maximise the chance of recovery. The prediction was reasonable, but it had a little further away landing point than I had wished, the winds were definitely strong - some of the decodes indicated ground speeds of 65 mph.

WDHABmini first. This was a very lightweight payload - approx 50g. it was literally gaffer taped to the side of the main payload box. The intention to see how it behaved 'open to the elements' - the result: badly.
1)The cold affected the transmission frequency dramatically, and it was very difficult to keep tuned it.
2)The temperature also affected the 'shift' for the RTTY tones, and the initial 425Hz rapidly reduced to sub 300Hz and varied throughout.
3)The batteries were small Lithium Sulfide, light weight, but not all that powerful. It seems that though transmissions were steady at normal temperatures, the fluctuations badly affected them and their life was short as well as reduced power output to drive the GPS/transmitter effectively.
4)The GPS unit trialled on the mini payload was of a Venus type, and it does seem to have failed above a certain height (possibly battery power related), though I think further trials wouldn't go amiss.
The mini payload indicated how the components were affected by the temperature, and some sort of thermal control/insulation definitely helps.

Both payload antennas were dramatically affected by the wind - silly I know, but upon retrieval it looks like one of the radials actually came off and the other antenna was blown flat. This would likely have explained the weaker than expected signal strengths, but also indicates the skill of the radio receivers who were able to pick up anything at all!
Reinforcing the antenna, or altering the design is a whole new area to work on.

The balloon payload went out of range quite quickly from the launch site until we got to the other side of the Malvern Hills, but by then it had made considerable distance and the signal was rather weak. Cup of coffee and then it was off to try and keep up!

WDHAB just about worked - in that; it went up, came back down, was found and had taken pictures :)
The habhub predictor was rather accurate - that was a great success.
The addition of a standalone GPRS GPS tracker was inspired; and saved the day.
The Canon CHDK script worked well, as well as the other Ricoh interval timed camera with auto bracket.
The styrofoam boxing with additional sticky pads worked really well in securing the cameras, radio, batteries and flight computer and seemed to maintain acceptable temperature ranges.
The main GPS on WDHAB has now seemed to have properly died :( It has survived many outings in model aeroplanes and has been tested throughout the development of the payload. So I'm disappointed about this. The reported 'no altitude detected' of 99999999 never changed throughout the flight. It also seems that it too was either affected by the height restrictions, or not enough battery power to get a lock (which I think is unlikely) which is unusual for a ublox (and in airborne mode). Further investigation required.

The rain looks like it shorted out one of the minicams, and another minicam just didn't function (probably my soldering not surviving). Luckily the third worked well. An example of redundancy helping, but showing that water potentially will find a way to cause problems! No holes in the top of your payload if you can help it!
The wind and rain really made setup quite difficult, thanks to the other half and my brother for standing around holding the balloon and not flapping too much when stuff wasn't going quite to plan!

Looking at the times from the pictures, the payload was in flight for about 2 1/4 hours, which was about half an hour longer than I predicted - due to the slight under-inflation. On the plus side, it probably went a touch higher than intended. A few pics below.

Retrieval was made from a farmers field, who himself was rather interested in what the strange box was. This was near Melton Mowbray and was quite a drive from the launch site!

Many thanks for the trackers from the UKHAS and assistance on the IRC.
WDHAB2 will be re-engineered, and will have differing goals. Hopefully this has been helpful to the wider HAB community :) any questions, give me a shout.


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