The Gas Replacement System (GRS) is a new technology that enables long duration flight of Super Pressure Balloons (SPBs) at nearly constant altitude. In the GRS, a storable liquid such as ammonia is carried aboard the balloon mission gondola and used to replace helium that leaks from a SPB. The ammonia can be used directly as a helium replacement gas, or it can be dissociated into a very low molecular weight nitrogen/hydrogen mix. In either case, the balloon remains fully inflated, and remains floating at nearly constant altitude. The advantage of using a storable liquid in this way, rather than as ballast, is that consumable mass is greatly reduced, being cut by a factor of 1.7 in the simple (S) non-dissociation system and 3.4 in the (D) dissociation system. Moreover, in a ballast system the floating mass of the balloon changes by the sum of the ballast and the leaked helium, whereas in the GRS the only the leaked helium is lost. Thus the floating mass of the system remains almost constant, with near constant cruise altitude being maintained as a result, Indeed, using the CRS the altitude excursion for compensating for a given amount of helium leakage being reduced by a factor of 8 compared to a ballast-dropping alternative. The GRS is a simple low-mass system requiring very low power. In the proposed program, the potential performance of the GRS will be analyzed, design options compared, designs developed and built for both S and D type units, and the concept validated by means of lab tests of GRS prototypes.
The primary purpose of the GRS is to enable SPB systems that can fly or long durations in the Earth’s stratosphere at near constant altitude, without need to drop ballast or provide replacement gas. By lengthening the duration of such missions, the science return and overall cost-effectiveness of the program can be multiplied accordingly. Such a system could also be used with extraordinary advantage to study Venus or Mars, not only by sounding its atmosphere, but by carrying remote sensing look-down instruments such as ground penetrating radar.
There are many commercial applications possible for GRS technology derived systems. SPBs are much cheaper than satellites, and flying at altitudes approaching 40 km, could enable remote sensing, cell phone, internet, and other forms of communications coverage over vast regions of the Earth, including Africa, Asia, and the world's oceans.