This discussion is intended help you understand potential projects a little better. Hopefully it will not limit your ideas, but expand them. This section may be updated and expanded.
The air pressure is 1% of that on the surface, near vacuum.
The Near Space Environment is much different than on the ground.
In getting to 100,000 feet the temperature may approach -60C (-75F)
The air is dry, the dew point may be 10C or more less than the temperature.
The water and dust content of the atmosphere may be negligible.
Winds may reach over 100 knots (>100 mph) near the tropopause (about 200mb (11870m, 39000 ft) in the figure below) – though not in the example below.
The Sun's intensity is about 30% greater than on the ground, and its spectrum includes more ultraviolet as this is above most of the ozone layer, and includes more infrared, which is absorbed by molecules in the atmosphere.
Just as sunlight received at the ground has been absorbed at some frequencies and wavelengths, looking at the ground through the atmosphere, both introduces additional absorption and additional solar light scattered by the atmosphere back to the camera or sensor. Remote sensing by light imaging can be both interesting and challenging.
Cosmic rays can penetrate to these altitudes.
The horizon is much further than near the ground. Where as near the ground you may be able to see a few miles, from balloon altitudes, it may be 350 miles, or more. Now only does the horizon influence how far away you can see, but at radio (FM, VHF, UHF) and TV frequencies, it determines you far away you can transmit or communicate. Long range communications is one of the challenges some ham radio operators are interested in.
We tend to classify projects as either scientific, or engineering. Artistic projects might also be proposed.
Scientific projects might further be divided into two types, Experiments and observations, or measurements.
An experiment is a way to test a hypothesis, and should be designed to be reproducible. Often this is accomplished by careful control of conditions, or repeated measurements. This can be difficult on a balloon mission, especially when there is only one flight, under limited control of conditions. Look on this as a challenge! Careful and perhaps extensive ground experiments, simulating important flight conditions, as well as multiple samples can help to understand what happens during the flight. In addition carefully monitor those conditions during the flight.
Some potential experiments might include, looking for changes in material properties due to cold, heat, pressure, ultraviolet exposure, etc. survival, mutation experiments due to similar conditions, chemical and chemistry changes due the changes in the environmental conditions.
An observation, or measurement requires understanding what you are trying to observe. Again ground testing helps to verify that you are measuring what you think you are measuring. Temperature measurements can be challenging since they often involve running electrical power into a sensor, as the sensor tries to trasfer heat with a tenuous atmosphere.
When working with new technologies it is also useful to demonstrate new and useful capabilities. Controlling conditions is an important issue with balloon experiments and missions. Pointing a sample toward the sun, or toward an astronomical object (Venus, Jupiter, Saturn or Mars, some angular distance or offset from the sun.) This might involve simply detecting the Sun to ascertain when data is valid. Or trying to roboticly control the pointing direction and extend observation time. Similarly pointing an antenna to a ground station, maybe using GPS to ascertain the payload position, and a compass to determine direction could enhance transmission ranges.