Boeing Wideband Global System satellite. Credit Boeing
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By Erik Seedhouse
Since the space race of the early 1960's, the U.S. government and others have increasingly utilized military satellites as a key component of military strategy and national defense for the purposes of communication, navigation, surveillance, and reconnaissance.
With the need for increased bandwidth capability, the numbers and sophistication of this class of satellites is increasingly dramatically. The reason for this growth is threefold. First, for all users, the size of the Earth requires multiple satellites to be placed in orbit in a constellation to cover areas of interest and constellations typically need a minimum of 3 to 4 satellites to provide adequate communications coverage. Secondly, for existing users, upgrading satellites is not feasible, which means new capabilities are required and new satellites means new launches. Thirdly, more countries are recognizing the advantages of military satellite communication (MILSATCOM) capabilities and are looking to implement, or expand, their networks.
Globally, the trend in the utilization of military satellites is to provide more interoperable, network-centric communications, a requirement driven by the bandwidth of current operations and the projected bandwidth of future conflicts. For example, in Desert Storm, 542,000 troops occupied nearly 100 megabytes per second of MILSATCOM bandwidth whereas at the height of Operation Iraqi Freedom, 350,000 troops consumed 3.2 gigabytes per second of bandwidth - a thirty-fold increase in the space of a decade. Fortunately, technology is keeping pace with the desire for higher bandwidth, as evidenced by the deployment of the Wideband Global Satellite (WGS) system, a constellation of highly capable military communications satellites that are the Department of Defense's (DoDs) highest capacity communications satellites. The WGS also provides a new two-way Ka-band service, and 39 125-MHz Channels via a digital channelizer/router, with 2.1 gigabytes per second capacity.
A number of technology advances have enabled these increases in bandwidth. For example, communications satellites are being deployed with phased array antennas which can be electronically scanned over their search volume very quickly; all the elements in the array may be used in conjunction to produce a very narrow, high-resolution beam, or a broader, lower resolution beam. In addition, the array elements can be driven in smaller groups to produce multiple beams. A second type of electronically scanned array is the Active Electronically Scanned Array (AESA). In this system, each element is driven by a transmit/receive module, which contains discrete components, thermal management technology and several monolithic microwave integrated-circuits (MMICs) feeding a beam-forming network that feeds a radiating element. As the technology develops, more functionality will be incorporated into the MMICs and the number of MMICs will decrease.
Another major class of military satellite is the Global Positioning Satellite (GPS). The U.S. has its own Navstar GPS system, the Russians have GLONASS, the European Union (EU) will eventually have Galileo, and China is implementing its Beidou system, providing location and timing data to its home turf (there are ten satellites in place with six more to follow). A future development in U.S. GPS capability is the United States Air Force (USAF) GPS-2F constellation of 12 satellites that will provide around-the-clock, ultra-precise navigation and timing services for military and civilian users. This next generation of GPS satellite provides improved accuracy through advanced atomic clocks, a more jam-resistant military signal and a longer design life than earlier GPS satellites. The GPS 2F will also increase precision navigation and timing to combat forces, increase the signal power, precision and capacity of the system, and form the core of the GPS constellation for years to come.
On February 10th, 2009, a U.S. Iridium communications satellite (Iridium 33) collided with a Russian Cosmos 2251 communications satellite, an event which added hundreds more pieces of debris in orbit and highlighted the need for more precise tracking of space objects. Space debris has become a growing concern to the military since orbital space junk can inflict severe damage upon orbiting assets. The debris is of particular concern for micro and nanosatellites, which, because of their small size, have limited protection.
To combat the problem of space debris, the USAF is working on projects to track orbital debris. One of these projects is the Space Fence, a $3.5 billion project to replace the Air Force's VHF radar fence (which currently tracks orbital debris) by deploying ground-based S-band radars. Supplemental to the Space Fence, the USAF is building the Space-based Space Surveillance (SBSS) system, a satellite constellation designed to track orbital debris from space. Fitted with agile digital optical sensors mounted on high-speed, two-axis gimbals, allowing controllers to swivel cameras quickly between targets, the SBSS was launched from Vandenberg Air Force Base on 25th September, 2010. It completed on-orbit testing three months later and is set to revolutionize U.S. space situational awareness.
Operational Responsive Space-1 (ORS-1), the latest USAF battlefield reconnaissance satellite blasted off atop a Minotaur 1 rocket at from NASA's Wallops Flight Facility in June 2010. The 'eagle eye in the sky' ORS-1 spacecraft is the first operational satellite created by the Air Force's Operational Responsive Space Office (hence the satellite's name). The $226 million spacecraft, which went from design and development to orbit in just 32 months, is outfitted with a customized version of a sensor called SYERS-2, similar to the system carried by U-2 spy planes. SYERS-2 provides high-resolution imagery day and night across seven wavelength bands, and will improve warfighters' situational awareness in real time.
Future trends: faster, better, smaller, cheaper
At a time when defense budgets are being cut, the era of multi-billion dollar military satellites is most likely over. Instead, governments are looking for cheaper alternatives such as microsatellites.
Microsatellites*, which are defined as weighing between 10 and 100 kilograms, are a tenth of the cost of their larger cousins and are much easier to sell to budget sensitive procurement officers. This class of satellite is also much cheaper and faster to design, build and launch, although there are question marks when it comes to their reliability and longevity. One of the reasons for their rapid development timetables is their use of commercial-off-the-shelf (COTS) technology, which sometimes makes the assembly of these satellites analogous to a Lego set.
DARPA, the Pentagon's R&D division, is an enthusiastic proponent of microsatellites. Its Microsatellite Demonstration Science and Technology Experiment Program (MiDSTEP) is currently developing advanced technologies and capabilities to demonstrate the next suite of high-performance microsatellite technology. For example, one of MiDSTEP's projects is the Microsatellites Technology Experiment (MiTEX). MiTEX has flown two technology demonstration satellites to investigate lightweight power and propulsions systems, COTS components, advanced communications, on-orbit software, and avionics.
Another DARPA microsatellite innovation is Systems 6 (Future, Fast, Flexible, Fractionated, Free-Flying Spacecraft), designed to divide the tasks performed by large satellites and assign each task to a dedicated microsatellite which would operate in clusters. The advantage of the Systems 6 fractionated approach is the reduction in program risk, faster deployment and greater survivability.
While DARPA is focussing on developing the potential of microsatellites, the current trend in the US Army is the development of nanosatellites. In April 2009, the U.S. Army's Space and Missile Defense Command/Army Forces Strategic Command (USASMDC/ARSTRAT) took delivery of eight SMDC-ONE nanosatellites. Weighing less than 5 kilograms and costing less than $1 million to produce, the SMDC-ONE satellites can be refreshed frequently by launching replacements, which permits rapid technology upgrades and reduces the unit reliability requirements significantly. The Army launched its first nanosatellite on December 10th, 2010 onboard a Falcon-9 booster as a secondary payload; the launch marked the first launch of an Army-built satellite in more than 50 years.
Over the past four decades, military satellites have become absolutely critical to national security. Most estimates suggest the U.S. has roughly 122 satellites dedicated to national security. However, a substantial number of these satellites are nearing the end of their life spans and replacements are slow to come. Meanwhile, as the future of America's large and expensive cutting-edge spy satellites remains less than certain, the new breed of microsatellites is hitting the scene. While military dominance of the satellite business will be a key to America's success in the coming years, the U.S. is not the only military in the microsatellite game; Nigeria and Turkey, not normally known as leaders in the aerospace industry, both recently began such projects, and Russia has also launched microsatellites. In the space race years of the 1960s, the satellite game was a clash of superpowers, but today, smaller nations and private interests are increasingly involved, which suggests that America's approach of keeping an eye on the national interest from space may soon need to be reviewed.
* Microsatellites are just one category of small satellite. Other categories include nanosatellites (1 to 10 kilograms), picosatellites (0.1 to 1 kilogram) and femtosatellites (less than 100 grams).