Launching a weather balloon, a camera and a Raspberry Pi to the stratosphere

why people don't attach rockets to such balloons? It is a very old idea, yet nobody so far seems to be doing it. Launch from 30km height without atmospheric drag to speak of would make reaching real space much easier. Is there some obstacle for doing it?

Was really hoping to see video of the descent!

In the US, it is not legal to drop objects from amateur high altitude balloons. That includes launching projectiles from them.

Laws relating to high altitude balloons vary from country to country, so I don't know the reason for people not doing it outside the US.

Speaking of laws, at the minimum some things you should probably check before sending up a balloon is your country's laws on:

• What notification you have to give, if any, and/or markers you have to place on the balloon so that it won't interfere with air traffic as it passes through the altitudes airplanes and helicopters use.

• What methods of communication with the balloon are allowed. Many in the US us GSM cellular devices hooked to GPS units, but from what I've read that it is not legal to use cellular devices from high altitude balloons.

The best approach in the US is to get a Technician class amateur radio license (and if you are the kind of person who can put together a decent payload for a high altitude balloon, you can learn enough to easily pass the radio license test in a couple evenings). You can then use amateur radio frequencies and equipment for your telemetry, and you are even allowed to build your own radios. A transmitter can be pretty simple and cheap to build if you are willing to transmit your data in Morse code (like, a transistor, a crystal, and a handful of resistors and capacitors and such). If you are sticking an Arduino or Pi or some such in there, that can easily convert the data to Morse and send it, and automatically decoding it on the ground with a computer is not hard.

Everything else I've seen seems to be either illegal, or involves using unlicensed bands where you are legally limited to very low power which could be annoying (especially if your balloon lands far away from where you expected, and you are trying to track it down with radio direction finding). When you make licensed use of the ham bands, you can use a good amount of power (but only up to what is necessary to accomplish the mission).

In the UK, from what I've read, the ham option doesn't work. Hams are not allowed to transmit from aircraft, and that includes balloons. Not sure what the best legal method of operating there is.

• What constraints there are on the balloon. In the US there are regulations on, among other things, total weight of the complete system, total weight of the payload, and on the size/weight ratios of the components of the payload, and on the strength of the ropes attaching the payload to the balloon.

There's a UK group preparing to launch a small rocket from a high altitude balloon; they've built apparatus to do ground testing of release and ignition and guidance systems under realistic conditions of temperature soak and air pressure. Photos and description of the development process:

[1] https://www.flickr.com/photos/registerparis/

[2] http://www.theregister.co.uk/science/lohan/

may be cutting 2 trees in general isn't that big a deal in some situations, but looking at the photo it was definitely overkill in that situation - these trees were easily climbable and once up there it would be enough just to cut the branches the payload stuck onto.