The Mark III EIP ship-side connections are backward-compatible, mechanically and electrically, with the Mark I. The Mark III EIP is a drop-in replacement for all the aircraft in the fleet, including the ER-2 and WB-57, which have the most stringent power and volumetric requirements.

ER-2 and WB-57 pilots control instruments exclusively from the cockpit, and the new EIP carries forward an interface to the cockpit switch panel for those and other aircraft. Unmanned installations substitute an onboard Master Payload Control System (MPCS) in place of the pilot, which is software controlled through a communications link. Whether aircraft are manned or unmanned, for safety, the controls for avionics and the switches to power instruments are hardwired and isolated from those for instrument communications, data collection, and instrument adjustment in flight.

The new EIP supports all the legacy data protocols of existing instruments, but the primary data interface for new payloads is an aircraft’s payload Ethernet network. Each EIP incorporates an Ethernet switch with four 1000BASE-T and eight 10/100BASE-T ports available to instruments. In a typical installation, two 1000BASE-T ports are consumed by the ring network backbone, leaving ten of the ports available for payloads.

Each Mark III EIP contains 12 commercial solid-state power controllers for distribution of 28-V DC power, the Ethernet switch card, and four custom printed circuit boards that tie everything together. Sierra Circuits fabricated several of the boards in the Mark III EIP. NASA airborne instruments typically operate from 28-VDC or three-phase, 115-V, 400- Hz AC. The EIP itself does not switch, protect, or measure AC, but merely distributes the current from shipside to four outputs for instruments. That duty is consolidated on a single custom board, instead of a conventional terminal-block implementation, which would have consumed too much space. The total AC power available is 17.25 kVA, with a wide safety margin for transients.

There are five connectors to power instruments. Four of them each include two circuits of three-phase AC (15 A per phase) and two circuits of 28-V DC (15 A apiece). Those connectors duplicate the pin assignments of the Mark II power interface designed for the Global Hawk, and provide the same supply of AC and DC as the Mark I EIP. The fifth socket, whose pinout duplicates that of a power connector on the Mark I, supports legacy instruments, providing up to 40A of 28-VDC on each of two circuits.

Each Mark III EIP supports up to four scientific instruments for simultaneous data acquisition. There are multiple bays in each aircraft to house one or more EIPs and their associated instruments, a NASDAT, and for the Global Hawk UAV, a MPCS.

Airborne measurement systems had to be designed for particular NASA aircraft based upon observation requirements, but thanks to the Mark III EIP, they can now be flown universally on the many different aircraft of the fleet, which increases mission flexibility and the number of research flight opportunities. Moreover, the ability to network instruments within and among aircraft in flight, in coordination with satellitebased instruments, opens opportunities for far more detailed definition of the atmosphere. Using the Mark III EIP, NASA Airborne scientists can acquire more data simultaneously than ever before to better comprehend our environment as a whole.

This article was contributed by Joshua B. Forgione, Electronics Engineer, NASA Ames Research Center; Carl Sorenson, Sensor Engineer, NASA Dryden Flight Research Center; and Amit Bahl, Technical Director, Sierra Circuits, Sunnyvale, CA. For more information, Click Here.

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