In Afghanistan, it's become quite common to supply the many troops out in the countryside via air drops. When accuracy was needed for the drops (because of the presence of hostile forces or very rough terrain) a GPS guided parachute rig is used. A problem has developed in getting these GPS rigs 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.
This is becoming an issue as 30,000 more U.S. troops are being sent to Afghanistan, and most of them will be stationed in isolated bases in the back country. Last year, over 5,000 tons of supplies were air dropped by U.S. Air Force C-130s and C-17s. That's more than was dropped in all of 2007. And it's even more this year, and will increase considerably next year. In all of 2003-7, only 8,500 tons were dropped, with 98.5 percent of the drops being successful. Accuracy is important in Afghanistan, with all the hills, gullies and forests. Air dropped supplies have landed, on average, with 185 meters of the aim point.
To insure this accuracy, 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 of supplies) down within a hundred 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.