i took a look at that pongsat thing, and i'm interested :)
just some off-topic questions:
is it possible for european students too?
where do they get sent of to space?
and now on topic:
how will you get the power? because a pingpong ball is very small, and batteries can be big
if you use a pressure sensor you can measure the pressure and calculate the altitude, that way you have two things at once :)
i think you'll have to push to get all this inside, i don't think many more sensors will be possible
For the offtopic questions:
I imagine it would be possible for European students. The september mission is full. There is another mission scheduled for April. The pongsat needs to be shipped to california, and it launched from Nevada. You could email the maintainer of the PongSat program and ask him if being in Europe would limit you. The only limiting factor would be cost of shipping the ball back to you.
and the onTopic:
Still learning as I go on this for power and sensors?
This page seems like a good starting point: