2.3.1 Program Goals
The goals for the development of the NASA Super-Pressure Balloon (SPB) are
related to supporting a specific science mass lifted to a set stable altitude for an
extended duration. The program level requirements for the SPB are as
follows:
• It shall be capable of lifting 1,000 kg (2,200 lb) of science instruments.
• It shall be capable of sustained flight altitude of 33.53+ km (110,000+ ft).
• It shall be capable of sustained flight with an allowable altitude variation of
plus infinity (no limit on height) and minus 1,524 m (5,000 ft) during normal operations. (Rare, extreme low temperature events shall allow an occasional dip to lower altitudes.)
• It shall be capable of sustained flight duration of up to 100 days.
• Its function and performance shall be independent of science mission
type.
2.3.2 The Balloon
In view of the program goals, it was determined that the SPB would be designed
to be flown at any latitude on the globe regardless of day/night cycles, including
mid-latitude flights. It will fly at a constant density altitude with a known mass of
payload hanging from the balloon. It always maintains a positive internal pressure
in relation to the environment in which it is floating. The SPB is a sealed structure
filled with a measured and specific amount of helium lifting gas. The balloon rises
after launch and the helium expands as the ambient pressure falls with increasing
altitude. When the balloon reaches the desired float altitude the extra helium isn’t
vented but fills out the shape and pressurizes the balloon. The initial helium load
is the amount needed to lift the entire flight system plus some extra to provide an
upward force. This extra helium is sufficient to pressurize the balloon at the float
altitude but not so much as to cause it to rupture.
The SPB is designed to fly with a positive internal pressure at all times. When
the Sun heats the balloon during the day, it has a higher internal pressure. This is
also called the differential pressure since it represents the difference in pressure
above that of the atmosphere where it is flying. As the balloon cools down at night,
the differential pressure is much lower, but remains above ambient. The differential pressure range of the SPB is up to 180 Pa (0.0261 psi). Although this is a rather
small internal pressure, it is enough to keep the balloon flying through the night.
As a result of maintaining near constant volume, the SPB has greater stability at
float altitude, with minimal altitude excursion during the day/night cycles. This
improved stability and extended duration allows mid-latitudes science missions
that are not feasible using ZPB.
2.3 Super-Pressure Balloons (SPB) 17
The goals for the development of the NASA Super-Pressure Balloon (SPB) are
related to supporting a specific science mass lifted to a set stable altitude for an
extended duration. The program level requirements for the SPB are as
follows:
• It shall be capable of lifting 1,000 kg (2,200 lb) of science instruments.
• It shall be capable of sustained flight altitude of 33.53+ km (110,000+ ft).
• It shall be capable of sustained flight with an allowable altitude variation of
plus infinity (no limit on height) and minus 1,524 m (5,000 ft) during normal operations. (Rare, extreme low temperature events shall allow an occasional dip to lower altitudes.)
• It shall be capable of sustained flight duration of up to 100 days.
• Its function and performance shall be independent of science mission
type.
2.3.2 The Balloon
In view of the program goals, it was determined that the SPB would be designed
to be flown at any latitude on the globe regardless of day/night cycles, including
mid-latitude flights. It will fly at a constant density altitude with a known mass of
payload hanging from the balloon. It always maintains a positive internal pressure
in relation to the environment in which it is floating. The SPB is a sealed structure
filled with a measured and specific amount of helium lifting gas. The balloon rises
after launch and the helium expands as the ambient pressure falls with increasing
altitude. When the balloon reaches the desired float altitude the extra helium isn’t
vented but fills out the shape and pressurizes the balloon. The initial helium load
is the amount needed to lift the entire flight system plus some extra to provide an
upward force. This extra helium is sufficient to pressurize the balloon at the float
altitude but not so much as to cause it to rupture.
The SPB is designed to fly with a positive internal pressure at all times. When
the Sun heats the balloon during the day, it has a higher internal pressure. This is
also called the differential pressure since it represents the difference in pressure
above that of the atmosphere where it is flying. As the balloon cools down at night,
the differential pressure is much lower, but remains above ambient. The differential pressure range of the SPB is up to 180 Pa (0.0261 psi). Although this is a rather
small internal pressure, it is enough to keep the balloon flying through the night.
As a result of maintaining near constant volume, the SPB has greater stability at
float altitude, with minimal altitude excursion during the day/night cycles. This
improved stability and extended duration allows mid-latitudes science missions
that are not feasible using ZPB.
2.3 Super-Pressure Balloons (SPB) 17