Complex sentence: SOFIA is a Boeing 747SP airliner, formerly flown commercially by United Airlines and Pan Am, modified to carry a 2.5 meter diameter reflecting telescope for infrared astronomy observations at altitudes of about 41,000 feet (~ 12 km) in the stratosphere.
Split into simpler sentences: SOFIA is a Boeing 747SP airliner, formerly flown commercially by United Airlines and Pan Am. This telescope is designed for infrared astronomy observations at altitudes of about 41,000 feet (about 12 km) in the stratosphere.