I'm just saying any laser module/diode/driver would be too expensive for a (potentially) one-shot application, like this one, especially when there are better ways to deal with the situation, from cheaper materials and equipment, even if it's not that professional, and looks MacGyvered. If it works, it's good, even if it's dirt cheap.
I'm not really an expert, but I think rocket fuel would require slightly more than a pair of AA batteries, and ReNNo has a point: the batteries need to be heat-insulated at the very least, lest they freeze. Although I don't know how ling the balloon will be spending at that altitude, but I'm thinking the batteries will be frozen by the time it gets there...
Uhm, i had some meteo radio probe around (i gifted them away, had no balloons, just the electronic units) ..... they was using common 9V batteries, for work, and they go high enough for freeze too (also if not high as a good rocket )
But, as docs02d said, it's probably an one-time use, so, just as suggestion, insulating the battery inside a block of polystirene, may be enough for the use he want, and polystirene also weight almost nothing, and in these applications, also weight is important
I can't tape anything to the balloon. The latex is so thin and fragile it would burst. The balloon will expand from maybe 5 feet across at release to about 50 feet across at peak altitude.
I have toyed with using a rocket igniter in line on the string from the balloon to the payload and it seems that may be the best option. I have to carry 7.2 volts in lithium batteries for the camera, flight computer and radio anyway. 7.2 volts is plenty. I believe rocket igniters have an oxidizer built in but I'm not sure. The laser is attractive because it can reside on the payload and just point generally up at the huge balloon to burn a hole. In addition, I don't have to worry about a lack of oxygen.
From the last flight I know that extreme cold will drop the voltage on a battery (retards the chemical reaction) and of course I have plans to try and keep it warm.
Just so you know... in a near vacuum there is not really much air to carry away the heat so its less a problem than you might think.
Well, for the cold, the problem can be in the initial ascension part, when you're still in atmosphere, and the temp go under zero, but as i said, a good polistirene insulation can take care about that part (and 7,2V Li-Po batteries now are also cheap enough, and more light than steel cells)
Yes, the igniters, the commercial ones, have a part of oxidizer in the mix, but you can easily build yourself something that burn also in lack of oxygen, if needed ..... lots of mixtures contains oxidizers
Also the idea to cut the string is ok, if you don't care about the balloon (but i suppose that, without load, it can ascend enough to self-pop for expansion) ..... only, maybe use 2 of them for safety (redundance, redundance ), and add some burning mixture, for be sure that the flame is enough to cut the string without uncertain results (make some tests)
Interestingly enough.... On the last flight things were fine on the ascent which is about 800 Feet Per Minute. I expect the next flight to take about 2.5 hours to reach peak altitude.
On the descent however, the initial descent rates were close to 10,000FPM (a parachute doesn't do much above 80,000Feet) and as a result the temperature plummeted inside. I believe the increased airflow due to the high speed was wicking away the heat. As a result the voltage dropped on the battery and my camera shut down.
I'm thinking of buying a pool noodle to build payload bays. Eventually all this has to be shoved into a rocket.
Oh yes... I will have my very own DIY satellite. It's just a matter of time.
I was going to say, Estes model rocket igniters are basiclaly 4 AA-sized batteries running current through a small wire. That's less than the 7.2 volts you've got to run for your camera, anyway.(My dad was big on model rocketry until we remodeled the basement and the rocket room became my bedroom.)
The engines themselves are gunpowder-based, and gunpowder can ignite in a vacuum. It includes its own oxidizer.