What is a superpressure balloon?
“I read that ‘superpressure’ balloons can maintain their altitude high up in the atmosphere day and night. Is that possible, and how would it work?”
A superpressure balloon constantly maintains a higher pressure inside the balloon than in the air around it, no matter the temperature.
With an ordinary balloon, when the temperature falls, the pressure inside is also reduced, becoming lower than the pressure outside, so the balloon becomes compressed. A balloon’s lift depends on its volume: when it increases, so does the lift and vice versa. So ordinary balloons lose height during colder nights, unless their weight can be reduced by losing ballast.
A superpressure balloon maintains its altitude by means of two factors: a carefully-measured quantity of helium, and an external shell that keeps its shape in spite of increasing or falling pressure. Although temperatures fall at night, the volume is not reduced, so it can hold its altitude. During the day the balloon will climb a little, but this is restrained since the lift reduces with altitude.
Hence, superpressure balloons stay around the same altitude all the time. That is beneficial for scientific studies, allowing measurements to take place under uniform altitude conditions.
NASA plans to launch the SuperBIT superpressure balloon in 2022. The balloon will be the size of a soccer stadium, and will glide at an altitude of 4km, pointing a telescope into space to make measurements relating to dark matter, among other things. Superpressure balloons also formed part of Google’s abandoned plan of balloon-based Wi-Fi (Project Loon), and have been used to carry out studies of Venus’ atmosphere.