NASA’s Balloon Program Office uses multiple types of balloons to lift science payloads into the atmosphere. The same is true for both U.S. and international commercial organizations. In general, a balloon used to launch a payload to an altitude of 18 km (60,000 ft) or more is designed for stratospheric flight. A few are even capable of briefly reaching into the lower part of the mesosphere, which is generally considered to be 50-80 km (164,000-262,000 ft), although such an altitude is not currently sustainable. NASA officials have said the zero-pressure balloon called the “Big 60” set a new sustainable record by reaching 48.5 km (159,000 ft) during an 8 hour flight on August 17, 2018, traveling well into the stratosphere and ascending 8 km (5 mi) higher than the next-largest balloon prototype.