These balloons are being developed to keep payloads aloft at high altitude for weeks or even months at a time. The balloon is over pressurized relative to the external atmosphere, and is reinforced with tendons for additional strength. This balloon does not use ballast to adjust the height of the balloon, and maintains very close to the same altitude even at night.

Note that is balloon is quite large. NASA intends the super pressure balloons to lift payloads far in excess of our Mars payload, hence the size is much greater.

From NASA:

• Zero-Pressure Balloon
• Balloon is inflated though side of balloon
• When the balloon reaches float altitude, “excess” helium vent out ducts
• Balloon uses Load Tapes to carry suspended load
• Balloon shell made of 0.8 mil single layer co-extruded LLDPE film
• Requires diurnal ballast (6-8% of system mass) to stay floating overnight

• Super Pressure Balloon
• Balloon is inflated though apex fitting
• When the balloon reaches float altitude, “excess” helium pressurizes the balloon
• Balloon uses Load Tendons to carry suspended load and resolve pressure forces
• Balloon shell made of 1.5 mil co-extruded LLDPE film
• Ballast not required for diurnal cycle and to stay floating overnight

For more information, see the Super Pressure Balloon page.