By John Keller
MELBOURNE, Fla. - Northrop Grumman engineers are modifying the electronics aboard the U.S. Air Force E-8C Joint Surveillance Target Attack Radar System (Joint STARS) aircraft to accommodate an ever-increasing amount of commercial off-the-shelf (COTS) components.
Over the past three years the avionics blueprint for Joint STARS has evolved rapidly from proprietary technology such as the Digital Equipment Corp. VAX computer and Computing Devices International programmable signal processor to open-systems components such as the Digital Alpha microprocessor, VME backplane data bus, and Fiber Distributed Data Interface network, better known as FDDI.
U.S. Air Force officials awarded Northrop Grumman contracts in June worth $132 million to install the latest Digital Alpha servers and workstations aboard the Joint STARS radar aircraft, as well as fiber optic cabling and standard 19-inch electronics racks, says Alan Metzger, chief engineer of the Joint STARS computer replacement program at the Northrop Grumman Electronic Sensors and Systems Integration division in Melbourne, Fla.
The contract covers upgrading electronics on the third development E-8C aircraft, and engineering documentation necessary to upgrade all E-8Cs, although purchase of hardware and installation or retrofit of systems into fleet and production aircraft will be covered in future contracts.
Future COTS implementations aboard Joint STARS are likely to include the Microsoft Windows NT operating system, the Analog Devices 21060 SHARC digital signal processor, and industry-standard Raceway high-speed multiprocessor interconnect invented at Mercury Computer Systems Inc. of Chelmsford, Mass., Metzger says.
In essence, Northrop Grumman engineers are overhauling the avionics foundation of Joint STARS to accommodate rapid turnover of COTS devices as new generations of equipment become available.
"There are nonrecurring engineering things that have to happen for us to go down the COTS road," explains Sam Densler, program manager of the Joint STARS computer replacement program at Northrop Grumman. "We are making modifications to the airplane as well as to the racks themselves to allow us to go to the COTS solution this time and in the future. The modifications are made to the airplane, rather than to its boxes."
As part of the upgrade, engineers are installing converters in the aircraft`s power-distribution system to switch it from its existing 115 volt, 3-phase, 400 Hz configuration to a 115 volt, 60 Hz system, which accommodates COTS electronics, Metzger says. The exact power converters to be involved in the power-system upgrade have not been selected.
The original electronics baseline for Joint STARS involved five Digital VAX computers with their associated VAX VI proprietary backplane - three operating and two "hot spares" - as well as the 10 base 5 Ethernet network, and the VAX VMS operating system.
The conversion of Joint STARS avionics to COTS began in 1994 with a follow-on project to full-scale development, Metzger says. That project involved switching from the VAX to 133 MHz beta versions of the Alpha microprocessor. "Since then we have decided to stay with Alpha, but the speeds have increased dramatically," he says.
The most current upgrade involves replacing the five VAX computers with two Digital Alpha 8200 servers - one operating and one hot spare. The Alpha 8200 is based on the open-systems PCI backplane data bus and printed circuit card form factor, unlike the VAX which has a proprietary data bus.
In addition to the Alpha 8200 servers, the upgrade calls for Digital Alpha Station 600 workstations based on PCI and the 440 MHz Alpha microprocessor. Computing hardware for the servers and workstations will fit into standard 19-inch racks, Metzger says.
While the computer components will be standard COTS, engineers will package these subsystems in ruggedized enclosures for electromagnetic interference shielding, shock-mount isolation, and cable disconnects, Metzger says.
Data will flow between servers and workstations over FDDI fiber optic links via a Digital GIGAswitch, he says. The optical fiber selected will also support Asynchronous Transfer Mode, Gigabit LAN, or Fiber Channel network protocols in future upgrades, Metzger notes.
Each Alpha 8200 chassis will house disk controllers and fiber connect interface cards to the GIGAswitch and to memory channel communications to the hot-spare 8200, he says.
Adjacent VME chassis will house all supplemental I/O such as the Mil-Std 1553B data bus interface, discrete and analog I/O, and the system`s time source module.
"Our aircraft is the Boeing 707, and we have made great strides in using COTS where applicable," Metzger explains. "I don`t think COTS is applicable for all applications, but we do have a relatively benign environment, and it looks like COTS will work."
The U.S. Air Force Joint STARS aircraft is receiving a new generation of COTS computers, data networking, and power distribution.
