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National Aeronautics and Space Administration

Goddard Space Flight Center

Scientific Balloons

Balloon Program Office


Zero Pressure Facts Graphic

Zero Pressure Balloons (ZP)

Currently the balloons most used for conventional and LDB missions are called zero-pressure balloons. The zero-pressure balloon carries the scientific instrument to a density altitude that is determined by the total mass of the system (suspended mass + balloon mass) divided by the fully inflated balloon volume. The balloon is only partially filled at time of launch and expands to its full volume as the balloon approaches its float altitude. NASA currently uses helium as the lifting gas.

The zero-pressure balloon has openings to the atmosphere, called vent ducts, to release the excess gas called free-lift, which provides the lifting force during ascent. The balloon continues to float at its equilibrium-density altitude until there is a change in the radiation environment, such as sunrise/sunset, upwelling earth flux, etc. At sunset, the gas cools, the volume decreases, and the balloon descends (about 30-50k-ft) to a lower equilibrium altitude based on atmospheric lapse rates and the radiation environment. Altitude can be maintained by the reduction in total system mass through release of ballast, which nominally amounts to about 8 percent per day. Flights thereby are limited by the total available mass that can be used as ballast.

Super Pressure Facts Graphic

Super Pressure Balloons (SPB)

A super pressure balloon is made with a non-extensible material and is a closed system to prevent gas release. By the time float altitude is achieved, the free-lift gas has converted into super pressure. Variations in the radiation environment produce changes in the super pressure, but not in the balloon volume, therefore the balloon continues to float at the same density altitude. As long as the balloon is super-pressured, it will continue to float at a constant density altitude.

This type of balloon will play an important role in providing inexpensive access to the near-space environment for science and technology. It will offer ultra-long duration missions on the order of 100 days or more at mid-latitudes. SPB will also offer greater stability at float altitude with minimal altitude excursion during the day/night cycles when compared to that experienced on Zero-Pressure (ZP) balloons. This added stability and extended durations at mid-latitudes will enable new science missions that currently are not feasible with ZP balloons. Therefore, balloon-borne telescopes, operating in the regions of the spectrum - namely X-rays and ? ?-rays that canít be studied as effectively at the poles because of the strong background of charged cosmic rays funneled in by Earthís magnetic field, will be enabled to venture into new science and discovery missions onboard a super pressure balloons. For more details on SPB and current status, click here

Super Pressure vs. Zero Pressure flight Comparrision Model

NASA Code 820

Scientific Balloon Update

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