Based on a hybrid 6U VMEbus and a CompactPCI rugged open-systems architecture, the first-generation SMU that’s flying in the Global Hawk is packet-based. The second-generation SMU, while also packet-based, goes further by tying its buses together with a fabric interconnect. The SMU’s architecture is designed such that upgrades can be made to interconnect switch technology without having to requalify the software, or redo the software from scratch. Curtiss-Wright makes both SMU and Integrated Mission Management Computer (flight control) systems aboard the Global Hawk.

Road to a Global IPv6 Network

Because the SMU packetizes the data that moves from system to system or within the system, all the systems it connects to can be tied together with a fabric such as switched Gbit Ethernet. And because it’s Internet Protocol (IP)-based, the subsystem blocks can be virtually linked to each other onboard the UAV as well as system on blocks anywhere in the world. The ultimate goal is to leverage the advantages of IPv6. With IPv6, a centralized router is no longer needed, and organizations like the U.S. Military can have a huge network that’s spread around the world, without a need for different subnets.
Being networked-based makes the SMU platform very generic from the perspective of software. Hardware upgrades to the unit to support higher-speed sensors have no impact on the software. The packetized data can also link over the myriad variety of I/O aboard the Global Hawk. Whether it’s Fibre Channel, Gbit Ethernet, MIL-STD-1553 or even RS-422, if the data is moved in a packetized form it doesn’t really matter what the physical link is.

Much of that slower legacy I/O could move to faster, more easy to work with protocols, by taking advantage of some other interfaces that are now standard in a commercial environment—such as USB or Firewire. So far, designers at Global Hawk prime contractor Northrop Grumman are avoiding those consumer high-speed interfaces because of the risk that they could disappear from the market over the long term.

Powering Down on the Tarmac

According to Curtiss-Wright’s, the second-generation SMU, although providing triple the capability of its predecessor, does draw double the power compared to the older version. Meanwhile, the subsystems the SMU links to are likewise drawing more power. That added power means more heat dissipation. And while that heat can be expelled via air-cooling when the Global Hawk is aloft, when the UAV is sitting on the tarmac the problem can be acute.

With that in mind, Curtiss-Wright has written its Board Support Package for the SMU’s boards to accommodate power management features. That means that, while on the tarmac, the box can be powered up without really running at full speed. The CPUs can go idle because there is typically no application being executed while the UAV is on the ground. The box can essentially be put to sleep—aside from some self-checking—until the higher application calls for it.

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