One problem for high-altitude balloon projects is the CoCom limit on how high and how fast a GPS will operate. To prevent GPS modules from being used in very fast moving weapons (such as ballistic missiles) GPS receivers are not allowed to operate at: 1. Higher than 60,000 feet 2. When traveling faster than 1,000 knots The second restriction doesn't matter for GAGA-1, but the first does. GAGA-1 will have a maximum altitude (balloon dependent) of more like 100,000 feet. Different manufacturers implement the CoCom limit in different ways: some use an AND rule (>60,000 ft and >1,000 knots) and others use an OR rule (>60,000 ft or >1,000 knots). For high-altitude ballooning it's ideal if the GPS uses AND. Unfortunately, this information is shrouded mostly in mystery and it's only through actual flights and testing that people have managed to determine which GPS receivers are AND and which are OR. For GAGA-1 I have two GPS units: one in the Recovery Comp