We did it! We have launched and recovered our high altitude balloon IRBE-1! I can not say it was very easy because we had several problems that might have ruined our little near-space mission, but in the end everything went well! We are very excited that we got to launch our first HAB and also to participate in the GSBC. I finally found some time to sit down and write about the launch and I hope you will enjoy reading it and most importantly learn from our mistakes.
So we had the launched planned for 10th of april, but with just couple weeks to go we had a lot of programming and testing to do. We designed the boards three circuit boards for our payload:
- Data Logger board - SD card, RTC and temperature sensors
- Sensor board - Accelerometer/Gyro/Magnetometer/Pressure sensor
- Comunication board - RTTY transmitter, GPS and GSM module
Here is a picture of complete stack that was planned for launch.
Since these boards were basically home made, they did not have solder mask. This in turn caused several problems when soldering the SMD components. In fact these problems made us ditch the sensor board. In the end we got it working but because we had little time left before launch we decided not to take risk. Also the GSM module was removed from payload after we tested it and found that it randomly locks up the program. Again, we had little time to solve this problem and we decided to not use it. This was a quite bad thing. It meant that we had to rely only on RTTY transmitter and GPS when tracking the balloon and I do not recommend using only one wireless link for transmitting balloon coordinates, because you double the possibility of loosing your payload. We did it anyway, because we are crazy, but seriously don't do this.
So at the end we had only stellaris launchpad, data logger and communication boards, but without GSM module. This is very basic configuration for a HAB and we decided to stick with it because wanted to avoid any glitches caused by untested hardware or software. On the stellaris board we had to remove the reset management IC which did not allow the VBUS voltage to be lower than 4.38V. Since we had Li-ion batteries with voltage ranging from 3.7V to 4.2V, we removed U4 and connected batteries to VBUS. Thus we could run stellaris launchpad with li-ion batteries while using the original voltage regulator on the board. Please not that if you try to recreate this small hack with your stellaris launchpad, DO NOT leave the power switch on the ICD mode while connecting to PC via ICD usb. We did not try it, but it will probably set something on fire.
We had arranged the balloon launch from an Ventspils airport which gladly supported us in our activities. We also got a generous donation from a company AGA, that gave us 50l of 99% helium. Ventspils University College covered most of the expenses related to electronics. Combining all this made our project super cheep.
Soon enough came the launch day. When we arrived at the airfield, we discovered a problem that we had not paid much attention and it was the conductive material presence near the GPS antenna. And it turned out that we needed to rise the GPS module about 5cm above capsules cover, because the tin foil thermal insulation and other conductive bits made GPS loose the coordinates. We had the tin foiled cover and GPS tested earlier and it was fine, but as soon as we inserted it into capsule with cover on top, GPS went bananas.
Of course we did not know that in the beginning and so starts the spiral of problems that arose from this one. At the beginning we turned to software and ran a test code. Guess what happened after we found that it was physical problem? Off course we forgot to upload the flight code. This did not have catastrophic coincidences, but the GPS did not have flight mode enabled. So GPS would stopped transmitting coordinates after reaching altitudes above 12 km. Next chain-linked problem was the camera batteries. While we were trying different things solving the GPS problem, the batteries of cameras lost some charge in the process. We charged them up as much as we could but the daylight was burning so we had to launch the balloon or go home. Finally we figured out our main problem and so we taped the GPS outside the capsule. It worked again! Still we had to remove all the metallic bits from the top of capsule, like screws, fasteners and carabiners . This meant that we had to duct-tape the capsules cover. Overall this led to significant heat losses in the capsule during the flight. Next, the ropes had to be tied to capsule directly. This seamed like a "ok" idea at the beginning, but after the flight it turned out that one of ropes were in the way of IR cameras view. Talking about butterfly effect.
Never the less, we managed to get everything going and launched the balloon. The RTTY transmitted the GPS data the whole flight and we only lost signal after payload was landing at about 880 m of the ground. Also, it landed in Lithuania, country next to Latvia. Here is video footage of the launch and best of views from the air. I should point out that the HD cameras battery did not last very long. Only about 50 minutes off flight were recorded, but hey, it is our first HAB and it might have been much worse.
Our balloon recovery team followed balloon and just before they were closing in on the last received coordinates we received a call from a Lithuanian farmer Gediminas Ališauskas who found our balloon near his house. About 200 km away from the airport, balloon landed on a field owned by . He saw the message attached to payload and contacted us. Here picture of our balloon recovery team and Gediminas.
The recovered balloon payload was in very good shape. Altitude data indicate that our custom made parachute performed perfectly. Also the batteries of our stack lasted the whole flight. Here is some graphs that we managed to get from data recorded. Altitude graph was extrapolated to figure out approximated maximum altitude and time of balloon burst. This graph approximately matches the sudden external temperature changes which are probably caused by the drop. It can also be seen that internal temperature significantly impacts the battery voltage.
As I mentioned in previous logs, payload had a second camera, which was tweaked to take picture in near infra-red. I will publish those in my next log. Some processing needs to be done on those pictures first.
Despite several problems we encountered in our little project we managed to do most of things we wanted. We launched, the balloon, in flew and gathered some data and landed safely. Here are some things we learned:
- Test, fix, test, fix, test ... - This is how you should build everything! In our case, parachute was fully tested, the payload was not. Not surprisingly we had problems with payload and parachute worked perfectly.
- Take time to prepare - Do not rush anything. This will just get you in trouble, unless you like that sort of things.
- Make good thermal isolation - This will effect your electronics quite a bit, so don't skip on multi-layer isolation.
- Make payload modular - If all the electronics, cameras and batteries would be mounted on a panel or small rack it would be much easier to work with it. It is more complex to make it work than just sequential poping everything in the capsule, but it will save you a ton of time when you run into some problems and you will defiantly run into problems.
- Master power switch - When you have many devices with different power sources stuffed into a small box, you start to see how a master power switch would make your life easier. Just use one battery pack and power switch to supply all the electronics or make easily accessible switches for all your devices. In our case, the cameras were at the bottom of the capsule and it was real pain to remove all electronics and batteries, just to get to them.
- Antennas don't like company of metal objects - Like the thermal isolation, you will find this tip in almost every HAB tutorial, but it is very important that you take this into account. If you have similar capsule configuration like we did, try extending antennas further from capsule and defiantly test them.
Overall this was very fun and very useful experience. I hope that lessons learned in this project will help others and also prepare us for the next HAB project. I will add the IR camera photos in the next log and write about what it they are good for. If you wish to see some more videos and pictures, please go to our twitter and facebook pages (links are on the left side) and if you have any questions leave a comment below.
Core team members:
- Roberts Trops
- Endija Briede
- Jānis Šate
- Raivis Pabērzs
- Artūrs Orbidāns
- Mārcis Bleiders
Other team members:
- Liene Andrēviča
- Pēteris Bitāns
- Madara Sviķe