Skydiver record attempt: 'Fear keeps you awake'
Adventurer Felix Baumgartner is planning to skydive from an altitude of 120,000ft (36.6km) this summer.
One of his advisers is US Air Force Colonel Joe Kittinger, who currently holds the record for the highest freefall for his 102,800ft (31.3km) leap in 1960.
Here they both explain the appeal of jumping from such a height.