[amsat-bb] USNA Party Balloon Success!
bruninga at usna.edu
Sat Apr 28 08:55:29 PDT 2012
Party Balloon success!...
Everything possible went wrong! A disaster of monstrous proportions. But finally got it all working and just wanted it gone! We released it about 1545 which means we missed getting off the academy before the afternoon's formal parade and lost 30 minutes going out gate 1 and 3/4 of the way around the yard through Annapolis traffic. But everything worked perfectly after release. The balloon was just about making land over Kent Island 8 miles away before we even got onto Rt 50.
With Friday afternoon beach traffic we were chasing the whole time. Thomasson was bragging about his altitude prediction when it reached his 6500' altitude as we crossed the Bay bridge. We were still 16 miles behind it at Easton with
Fick making time in all the traffic as the driver. Several minutes later Thomasson ate crow as it passed through 8000' and was speeding up to 45 MPH.
Headed south on 50 towards Easton we were still 16 miles behind it as it overflew Easton. Then we noticed the altitude descending. It was down to 6500 feet...
Since we were beyond the Choptank (last water body) and descending slowly we decided not to send the cut-loose command and ride it down. When we got in about 4 miles range we began to see the wireless camera again and could see chicken coops below. At 2000' we turned on a farm road and told the other car to go to the next road and turn. It passed over us and we got a solid visual.
Radioed to Mids in other car and they got a visual. Ballester and Garcia got to within 100 yards at touchtown.
We did send the cut command at about 1000 feet just to see if it worked, and it was acknowledged but the payload remained attached. It landed in a field and the bright red balloons flopping about 10 feet high in the breeze made it a walk in the park to get to. The release had worked, but the parachute had gotten entangled in the one balloon that had burst and so they came down together.
Cleary one of the 5 balloons had burst at 8000' and started the descent. With the balloon chards hanging down where the parachute was also hanging down, it is clear that entanglement was certain (bad planning). Next time, we will
widely separate the balloons from the payload and chute to avoid this.
But all systems worked well and gave great proof of concept for the next one. The payload was about 320 grams (0.6 lb)consisting of two Lithium 9v batteries a complete APRS digipeater and command/control/telemetry plus a 2.4 GHz wireless camera. Mission duration was under 2 hours, distance about 50 miles just slightly within the attention span of a student ;-)
You can see the track on the web page http://aprs.fi and enter the callsign W3ADO-11 and then ask for the appropriate number of hours of history. The balloon landed at 2123z or 1723 EDT after a 98 minute flight.
Our joy and enthusiasm were destroyed, however, after a parking lot formed on the bay bridge returning. All lanes were blocked for several hours.. doubling the time of the entire mission. Yuk!
Having now flown two party-balloon missions, I am happy with the results compared to Latex balloons. The missions are very different profiles, but they meet our educational goals quite well. Here are some thoughts. I am not a balloon expert (only my 3rd attempt in 20 years) so take these opinions with your own grains of salt.
1) 3' dia party balloon (unfilled. On line) cost under $2 each. Making a 5 balloon launch about $10 for the balloons.
2) Mylar Balloons have a high mass to lift ratio so these are all LOW ALTITUDE missions. Even with zero payload, the MAX altitude is around 25,000' where the full balloon can only support its own weight no matter how many balloons.
3) OUr first mission was an extremely small 50 gram payload with HF oscillator and some CW telemetry, attemting a 10 day around the world flight. Since it went over the atlantic toward africa, who knows what happened to it. You could only year the milliwatt XMTR within line-of sight (about 100 miles)...
4) Helium loss through Mylar appeared to be around 1% per day compared to higher rates through latex.
5) Mylar balloons are an order of magnitude less vulnerable to UV rays which will almost always burst laytex after several hours exposure at high altitude.
6) Mylar are fixed volume. THey get to a fixed height, where they are over-pressure and remain there (unless they burst).
7) Below 10,000' temperatures are not an issue with electronics compared to the -60C temps for the typical high altitude flights.
8) I use clear plastc bottles for the enclosure and the temp inside remains high (solar heating). Even at 8000' the temp never got below about 40C. We must use water proof containers because of all the bay and waters around.
9) This second mission used a full APRS system, wtih GPS and 2.4 GHz wireless camera using the Byonics MT-TT4 all-in-one APRS circuit board all in under 0.6 lbs including waterproof botttle container and chute.
10) WIth these mylar constant-pressure designs, extreme care must be used in underfilling each balloon exactly the same. Any balloon that is slightly higher than the others will rise to a HIGHER Pressure and will be the first to burst.
The jury is still out as to whether a long duration mission is possile. Ours will always go immediately to the Atlantic and at the low altitude, will take days to reach anyone in Europe (Our last went headed for africa where no one was listening).
** A ballast release mechanism is reuired for long duration. We attempted a clever block of Ice (sublimation mass loss), but dont know if it worked, because no one reported hearing it in Africa?)
11) The amount of over pressure at equilibrium altitude is equal to the amount of excess lift. So it is a difficult balance. Too little lift and you need an extremely large launch area. Too much and you are sure to burst.
12) IN fact, with a modest excess-lift on our intentional shout duration mission, maybe there will always be a FIRST TO POP as in our case. This was perfect though. The loss of one balloon gave an almost balanced up and down profile . No need for a chute.
13) The bright red multiple balloons (all full, except the one shreaded one) make for a highly visible descent and recovery. If we had cut the payload loose, the chances of finding a clear plastic bottle with nothing around it but a tiny chute woiuld have been 1% of the success of finding 4 waving balloons!
14) Observing this, we thought about maybe using multiple string cutters for our next mission to control descent by cutting loose balloons. But cutting loose only eliminates about half the mass as letting one burst. When it bursts, it loses lift, but the mass (nearly half the total lift) remains with the payload making descent better.
SO, maybe the plan next time will be to slightly overfill one balloon to assure a first-to-pop, and therefore have an automatic descent! Still we will have a payload cutter just to make sure we can release before the Atlantic!
FINALLY, The abuse these party balloons can tolerate are an order of magnitude greater than Latex. We launched in a 20 MPH wind! After walking all 5 balloons from the classroom, across a road and through a narrow chain-link fence gate in that 20 MPH wind (3 times!) they survived. Just prior to release, I noticed it was still transmitting all 3 packets at a 10 second rate! We had to bring it all back indoors, cut loose the payload, go reprogram it, and then re-assemble and go do it all again!
With multiple balloons, we fill a spare, so that if we busrt one, we can quickly tie in a replacemet in the field. If they all survive getting to the launch point, then we release the spare to see exatly where the winds are going, so we can find the best spot to clear the 100' high light posts surrounding the field.
Photos of this last mission will eventyally make it to the http://aprs.org/balloons.html page.
But right now, I'm burned out.
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