In Afghanistan, there's a growing crises with supplying the troops. This is especially true as more and more American personnel enter the country, and are dispatched to increasingly remote bases and outposts. There are over 300 American bases that have to be supplied either by truck, or by air. There aren't enough helicopters to do this, and it's often too dangerous (because of the Taliban, the terrain or the weather) to do it by road. So air drops are increasingly favored. But even here, there are problems.
Often, accuracy is needed for the drops (because of the presence of hostile forces or very rough terrain). Air dropped supplies have landed, on average, within 185 meters of the aim point. However, the new GPS guided pallets can land within 50 meters of the aim point. So when greater accuracy is needed (or it has to be done at night), a GPS guided parachute rig is used. But there is now a problem with getting these GPS parachute guidance systems back. The rigs are built to survive 20-30 drops, and even though helicopters visit the isolated troops periodically, and can bring back the several hundred pounds of equipment that comprises each GPS rig, there are still too many of them stranded out there. The army is even considering using UAVs to carry cargo, and to land and recover GPS parachute rigs.
Another problem is the many mountain peaks and ridges. The GPS guided rigs go for the spot on the ground, and navigate between the aircraft they were dropped from, and that GPS locations down there, without being able to detect and avoid any mountainous terrain that's in the way. Because of this, airdrop supervisors and pilots have to carefully plan the drops. There are several solutions to this in the works, including flight planning software that will calculate the optimum altitude and location for making a drop. There are still problems with unpredictable winds (that overwhelm the guided parachute's ability to compensate.)
Meanwhile, the need for airdropped supplies grows at a rapid rate. In all of 2003-7, only 8,500 tons were dropped, with 98.5 percent of the drops being successful. But in the last two years, the use of air drops has skyrocketed to over 10,000 tons a year.
There are several systems that use GPS to guide parachute drops. The air force has developed JPADS (Joint Precision Airdrop System) and ICDS (Improved Container Delivery System). Both of these are systems whereby pallets of supplies are equipped with GPS, and mechanical controls, to guide the direction of the descending parachute for pinpoint landings. After the pallet is pushed out of the aircraft, but before the parachute is deployed, the pallets first release a parafoil (a parachute that can be controlled in such a way that the user can gain altitude and travel over long distances), and the pallet descends at about 44 meters a second (from an altitude of about 6,000 meters, safely away from any ground fire), guided towards the landing point. When a few hundred meters over the programmed drop zone, the parafoil is released and the parachute deploys, bringing the pallet (with up to five tons, or more, of supplies) down within 50-75 meters of the programmed landing point. A single C-17 can deliver up to 40 pallets this way, to many different landing zones. JPADS has release point information (calculated using current weather conditions) sent to the C-17, along with GPS landing coordinates for the pallets. This GPS data is transmitted to each pallet via a wi-fi type system.
The new system was developed from earlier precision para-drop systems. All rely on GPS to give accurate landing information, and easily manipulated parafoils to provide the maneuverability. The aircrews find it fascinating to push a bunch of pallets out, then watch as they form into "flocks" and head off for their various drop zones. For the troops on the ground, it's a convenient way to get supplies, no matter where they are out in the boondocks.
Before the development of GPS guided air drops, a large percentage of air dropped supplies were lost, either by falling into enemy hands, or into things that destroyed them (especially water). With the new delivery systems, it's possible to do night drops, which is preferred when you don't want to alert nearby enemy troops. Often, you can accurately drop pallets without the GPS systems, if you have a large flat drop zone, daylight, and calm winds. But if conditions are difficult, you now have GPS guided drops.