Space: Small Size Matters


June 15, 2011: Six years ago, the U.S. Department of Defense began developing very small satellites. The smallest ones so far are called CubeSats. That is, their volume is no more than one liter (10x10cm or 4.1x4.1 inches) and weigh no more than 1.3 kg (three pounds). The military got the idea from the increasing use of commercial nanosatellites (which weigh no more than 6.8 kg/15 pounds). The U.S. military launched its first CubeSats last December (piggybacking with a larger bird). CubeSats can be used for photo or electronic surveillance, or communications. The rapid advances in communications and sensor technology during the last decade have made it possible to build a useful reconnaissance satellite weighing less and less. A tiny satellite like this would include solar panels, to provide power. British firm Surrey Satellite Technology LTD pioneered this technology a decade ago, and made it possible to get scientific satellites in orbit for a fraction of the usual price.

These tiny satellites also have the advantage of being much more difficult to be tracked from the ground. If there are successful satellite attacks, then the nanosatellites can be sent up to replace the lost birds. The lightweight satellites (Surrey has a line of standard small satellites, from CubeSats to 200 kg minisats) can be put in orbit using smaller, solid fuel, boosters. The U.S. Navy proposed using the ICBMs fired from SSBNs (ballistic missile carrying nuclear subs), which can be put to work much more quickly than the usual liquid fueled launcher. But the solid fuel ICBMs can only put a ton or so (usually less) into orbit. With CubeSats and nanosatellites, this is not a problem. With Surrey's standard nanaosatellites, sold ready for the installation of your own payload, it's pretty clear what the military minisats would look like, and how they would get into orbit.

For the last decade, the U.S. Air Force has been developing and launching lightweight (under half a ton) TacSat reconnaissance satellites. The first one (Tac Sat 2)was launched seven years ago, while TacSat 3 went up two years ago, and was providing data to combat commanders in Afghanistan until earlier this year. Troops on the ground could communicate with the TacSat, which provided photo-reconnaissance.

TacSat is not alone up there. There are a number of lightweight photo satellites in use. Two years before the 109 kg/240 pound TacSat 1 went up, Israel launched the 300 kg/660 pound Ofek-5. While TacSat 1 had only an infrared camera, regular camera, (both low rez) and a radio signals collection package, Ofek 5 had a one meter resolution digital camera, good enough to tell the difference between a tank and a car and spot a group of tanks assembling for attack.

The 400 kg/882 pound TacSat 3 had a wider array of sensors, including a hyperspectral (can detect a large range of light sources) imager, an Ocean Data Telemetry Microsatellite Link and the Space Avionics experiment. TacSat 3 sensors have a four meter resolution, but the ARTEMIS hyperspectral sensor can detect vehicles hidden in forests, as well as buried roadside bombs.

The problem with these microsatellites is cost. The cheapest way to launch these small birds is via a solid fuel ICBM (preferably one that is being retired). Even there, the launch cost is going to be about $20 million per satellite. That's why even smaller satellites became popular, because they were compact enough to be piggybacked with a larger satellite. This is becoming the most common way to launch the nano birds, keeping the cost down to under $10,000 per microsatellite. 




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