High Altitude Balloon Experiments in Technology.  The HABET Project fly high altitude balloons to altitudes well over 100,000 feet.  That's over 20 miles up.  In contrast your typical commercial airliner is usually at 20-30K feet and most military crafts don't exceed 60,000 feet.  At those altitudes you are near space and above about 90% of the Earth's atmosphere.  This means you can get some great pictures of the Earth and do some exciting research at a fraction of the cost for launching a normal rocket.