Reconfigurability and extended data rates drive satellite communication payload designs

Story

September 30, 2014

Space platforms are not often associated with flexibility. Once launched and in orbit, satellites do not see many payload repairmen flying up from Earth. Therefore, systems onboard must work for 15 years or more. Designers build in redundant components and systems in case the electronics are damaged by cosmic rays or other threats. Now thanks to advanced software architectures, extended bandwidths, and high-performance FPGAs, military SATCOM payload designers are getting that flexibility.

“Reprogrammable technology allows operators more flexibility in a satellite’s mission,” says Jill Krugman, a spokeswoman for Lockheed Martin. “With a 15+ year lifespan, needs change throughout the course of a satellite’s life and the ability to dynamically modify a mission assures that our satellites deliver value as long as they are in orbit.”

An example of this is “the reprogrammable processor designed by Lockheed Martin,” she continues. “It is the only technology of its kind being offered on the commercial market today. It is used on the A2100 satellite, which has served both commercial and military customers. The A2100 is the common framework behind the Advanced Extremely High Frequency, Mobile User Objective System, Geostationary Operational Environmental Satellite Series-R, and GPS III satellites,” she says.

The fully reprogrammable mission processor enables users to modify payload configurations and performance in-orbit, suppress interference, and adjust satellite-to-ground communication, Krugman says. Today, satellites typically amplify incoming signals and route them back to Earth, but reprogrammable technology will enable signals to be processed and routed to multiple users and locations. For example, if a thousand mobile calls came into a single satellite, the onboard processor can switch all those calls to discrete users and locations, she adds

“Military satellite users are looking for flexibility through reconfigurability,” says Peter Cash, director of the Space, Defense, and Avionics Frequency and Time Division at Microsemi in Aliso Viejo, Calif. “They want to be able to quickly reconfigure payloads in orbit. Right now the methods for reconfigurability are pretty limited particularly in severe radiation environments.”

Engineers at Northrop Grumman in Redondo Beach, Calif., leveraged reconfigurability in the protected commun-ications payload for the U.S. Air Force’s third Advanced Extremely High Frequency (AEHF) satellite.

“The payload’s software-based communication network architecture allows us the unprecedented ability to reconfigure assets as needed for an evolving battlefield,” says Stuart Linsky, vice president of communication programs, Northrop Grumman Aerospace Systems. “This software-based architecture has enabled Northrop Grumman to deliver new capabilities our leaders and warfighters requested through the Milstar constellation for all 20 years since the launch of the first Milstar in February 1994.”

FPGA or ASIC

Much of the reconfigurability in satellite payloads is enabled by radiation-hardened FPGAs such as those from Xilinx and Microsemi.

“To enable reconfigurability, designers are using multiple transceivers and in parallel with multiple FPGAs,” says Chuck Tabbert, vice president of sales and marketing at Ultra Communications in Vista, Calif. “For example, they may use a Xilinx space-qualified FPGA with 16 lanes at 2.5 gigabits per second [Gbps] and multiplex those channels into one transceiver, enabling a 40 Gbps electrical-to-optical conversion for point-to-point solutions.”

“For the implementation of digital logic, two fabrics solutions dominate the land-scape: ASICs or FPGAs,” says Tony Jordan, vice president of Product Marketing and Applications Engineering at Aeroflex Microelectronics Solutions in Colorado Springs, Colo. “System designer trade-off power, operational frequency, size, schedule, design risk, flexibility (i.e.: ability to reprogram on orbit), and cost when selecting a digital fabric. Mission and budget requirements will ultimately dictate the selection of the digital technology. Perceived ease of on-orbit reconfiguration, flexibility, and limited or one-time use payloads drive system implementers to FPGAs. ASICSs have a decided advantage in power, performance, and recurring cost,” he continues.

 

Figure 1: The radiation-hardened UT90nHBD ASIC from Aeroflex provides logic and memory bit advantages for satellite communication payloads.

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“Satellite communication payloads opportunities remain a focus market segment for Aeroflex,” Jordan says. “We are developing standard products to meet with future requirements and on the ASIC side our 90-nanometer capability offers very attractive logic and memory bit densities, as well as gigabit-per-second serial communication solutions. We look forward to new architectures that will take advantage of these capabilities.” (See Figure 1.)

Extending data rates

One thing satellite designers want even more than reconfigurability is more bandwidth. The demand for more and more information over existing frequencies is forcing satellite designers to extend the bandwidth of new commercial and military payloads.

“Data rate demands really depend on the mission platform,” Tabbert says. “If you are talking about sensing applications in low Earth orbit for the intelligence community then there will be requirements for more bandwidth between sensors and computers. However, interesting things are happening with communication payloads when it comes to bandwidth. Communication payloads are demanding greater and greater throughput due to mobile communication devices.”

Northrop Grumman engineers used crosslinks to enable extended data rates (XDR) on their AEHF communication payloads on both sides of an AEHF satellite. This was not possible with only two AEHF satellites on orbit, says a Northrop Grumman spokeswoman. Testing involved establishing communications networks between combinations of AEHF terminals on the ground that use Milstar’s medium data rates and other terminals equipped to handle the wideband AEHF XDR. They exercised and further proved payload software that configures worldwide networks (see Figure 2).

 

Figure 2: One Advanced Extremely High Frequency (AEHF) satellite will provide greater total capacity than the entire Milstar constellation currently on orbit. Photo courtesy of Northrop Grumman.

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“One AEHF satellite will provide greater total capacity than the entire Milstar constellation currently on orbit,” the spokeswoman says. “Individual user data rates will be five times improved. The higher data rates will permit two-way, jam-resistant transmission of tactical military communication such as real-time video, battlefield maps, and targeting data.”

“Military satellite payload integrators are challenged trying to send more information bits in a given frequency spectrum; enhanced digital electronics is key to meeting this challenge,” Jordan says. “Enabling digital technologies optimize logic and memory per unit area, and afford the system designer with gigabit-per-second serial communication capabilities [‘fat pipes’]. Satellite payload programs require small footprint [pin count] fat pipes to reduce payload size and mass. For example, advanced architectures will interface giga-sample per second ADCs and fast DACs to digital processing elements using these small footprint fat pipes. Four pin, single-lane, gigabit-per-second CML SerDes are now replacing eight pin LVDS-based solutions while providing upwards of 2x the performance,” he continues.

“The increased data rate demands bode well for suppliers of fiber optic components,” Tabbert says. “Fiber optic interconnected networks are winning when data rates per channel are 2.5 Gbps and above from a size, weight, and power [SWaP] perspective. That said, just as you should never bet against silicon in the semiconductor world, you should never bet against copper solutions in the interconnect world.

“The military satellite market is constant and bandwidth requirements are always increasing,” Tabbert continues. “The commercial fiber optic community is fielding 100 Gbps solutions right now and I expect the satellite and avionics markets to follow close behind. Ultra Communications’ standard X80 platform, which is a 40-gigabit fiber optical transceiver, is used across all market configurations – for space avionics, missiles, and ships. 40 gigabit box-to-box connectivity is hard over copper interconnects and fiber wins the SWaP trade-offs.”

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Leveraging commercial manufacturing processes

With the demand for more data and enhanced flexibility comes the never-ending demand for reduced costs. Nothing is ever inexpensive when it comes to space, but system integrators are leveraging commercial manufacturing techniques to improve time to market and reduce development costs where possible.

Commercial practices have long benefitted the military satellite market, Krugman says. As mentioned previously, the A2100 serves as the framework for multiple government satellites. “To that end, we will continue to derive military applications from the A2100 as we modernized the system for the commercial world including advances in digital design, manufacturing, and 3D printing.”

Northrop Grumman leveraged commercial practices during the manufacture of specialty compound semiconductors for the AEHF fifth and sixth satellites at its advanced microelectronics wafer fabrication facility in Manhattan Beach, Calif. The more than 36,000 integrated circuits produced at the facility enable production to ramp up on a broad scale for both payloads, says a company spokeswoman.

“By implementing commercial best practices in making military integrated circuits, we’re able to generate further cost savings for the Air Force,” Linsky says. Each payload contains some 18,000 high-frequency monolithic microwave integrated circuits (MMICs) for frequency conversion, amplification, and switching, he says. They are integrated throughout the payload’s major subsystems that enable real-time mobile, global access such as anti-jam uplinks and downlinks, secure crosslinks, and super high gain Earth coverage antennas.

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