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25 janvier 2013 5 25 /01 /janvier /2013 08:20

AEHF Satellite


January 24, 2013: Strategy page


 The U.S. Air Force finally had a success with its military communications satellite programs. The fourth AEHF (Advanced Extremely High Frequency) communications satellite is six months ahead of schedule and under budget. The first of the AEHF satellites was launched on August 2010. It achieved its initial orbit but then it was discovered that its main maneuvering rocket, needed to get the six ton satellite into its permanent fixed 36,000 kilometer orbit, was not working. Efforts to get the main engine going failed. The engineers then went to work and found a way to use the lower thrust maneuvering rockets to still get the AEHF bird into position. But the alternate method was slower and took about nine months. That was a small price to pay for a satellite that is supposed to last 14 years, once you get it in the right position. AEHFs will replace the older MILSTAR birds, providing more abundant and reliable (jam-resistant) communications.


The second AEHF bird has since been launched and a third is about ready to go up. Three more were ordered because the first three (costing about $2.2 billion each) performed as expected. The cost of the first three includes development costs, so additional ones will cost less than half as much.


While the AEHF are mainly to facilitate communications between headquarters in the United States and troops abroad, they are also up there to deal with the huge increase in wireless devices the troops are using. For example, the number of military radios has nearly tripled, to over 900,000, in the last decade. There has also been a huge increase in data transmission capability (“bandwidth”) from 46 megabits (million bits) per second in late 2001, to nearly ten giga (billion) bits per second now. This is just for troops in CENTCOM (the Middle East and Afghanistan). That’s 200 times more data being pushed through three times as many “wireless devices” (radios). This doesn’t even count the many cell phones and laptops used by troops in the combat zone, which often use civilian bandwidth. But it hasn't been enough.


The major consumer of all this new bandwidth is live video being generated by the increasing number of vidcams on the battlefield. These vids are being exchanged by the units cooperating in an operation. This huge growth in bandwidth began in the 1990s, when the U.S. armed forces moved to satellite communications in a big way. This made sense, especially where troops often have to set up shop in out of the way places and need a reliable way to keep in touch with nearby forces on land and sea, as well as bases and headquarters back in the United States. At the time of the 1991 Gulf War there was enough satellite bandwidth in the Persian Gulf for about 1,300 simultaneous phone calls (12 megabits per second). But while the military has a lot more satellite capacity now (the exact amount is a secret), demand has increased even faster. UAV reconnaissance aircraft use enormous amounts of satellite capacity. The Global Hawk needed 500 megabits per second and Predators about half as much. The major consumer of bandwidth is the live video.


UAVs have other sensors as well, as do aircraft. A voice radio connection only takes about 240 bytes per second and each of the multiple channels needed to control the UAVs use about the same. But it adds up, especially since the military wants high resolution video. Until recently (when the AEHF birds went up) the U.S. had far more demand for satellite communications than it could support. As a result, not all the Predator and Global Hawk UAVs in combat zones had sufficient bandwidth to send their video back to the United States. Data compression and using lower resolution was often necessary or using satellite substitutes (aircraft carrying transponders) to send the video to local users. The substitutes are becoming more common, simply because there is neither the money, nor the time, to get sufficient satellites into orbit.


While the larger UAVs need satcomm to send video back to the United States, most of the bandwidth demand now is for local use. Tanks, helicopters, and aircraft are all sending and receiving more vids, maps, and data of all sorts. AEHF is needed to get essential material to higher headquarters as quickly as possible. The basic idea is to keep everyone connected, all the time. More radios and other wireless devices are on the way, as well as more features any Internet user would recognize, all available while under fire. AEHF is an essential link in this data chain.

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