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EXPRESS Logistics Carrier

An ExPRESS Logistics Carrier (ELC) is an un-pressurized attached payload project for the International Space Station (ISS) that provides mechanical mounting surfaces, electrical power, and command and data handling services for science experiments on the ISS. ("ExPRESS" stands for Expedite the Processing of Experiments to the Space Station.) The ELCs are being developed primarily at the Goddard Space Flight Center in Greenbelt, Maryland, with support from JSC and MSFC. ELC was formerly called "Express Pallet" and is the unpressurized counterpart to the pressurized ExPRESS Rack. An ELC provides scientists with a platform and infrastructure to deploy experiments in the vacuum of space without requiring a separate dedicated Earth-orbiting satellite. ELCs interface directly with the ISS integrated truss Common Attach System (CAS).^{[1] [2]}

Within the electrical subsystem of the ELC, the ExPRESS Carrier Avionics (ExPCA) provides electrical power distribution to experiments, and data interfaces to the ISS. Within the ExPCA, the ColdFire-based flight computer, software, and related electronics comprise its "Flight Controller Unit" (FCU), providing the computing and communication resources as an ELC Command and Data Handling (C&DH) system with the following major goals:

• Provide a Low Rate Data Link (LRDL) interface to ISS to accept commands for the ELC and the resident experiments. The ExPCA is implemented as a Remote Terminal (RT) on the MIL-STD-1553 "ISS Local Bus." This interface also returns of housekeeping telemetry from the ExPCA and resident experiments back to the ISS.
• Provide a LRDL from the ExPCA to the experiments resident on the ELC to forward commands from the ISS to the experiments and to receive telemetry from the experiments for transmittal to the ISS. This is another MIL-STD-1553 interface, with the ExPCA acting as the Bus Controller (BC).
• Provide a High Rate Data Link (HRDL) between the ELC and the ISS. This interface is implemented as a Fiber Optical data bus with a capacity of up to 95.0 Megabits per second (Mbit/s). The primary function of this interface is the return on high volume experiment Science data from the resident experiments to the ISS.
• Provide an Ethernet Local Area Network (LAN) between the ELC and the resident experiments up to 6.0 Mbit/s per experiment. The primary function of this interface is the return of science experiment data from to the ISS, relayed through the HRDL.
• Support six analog input channels at each ExPA (ExPRESS Payload Adapter) location.
• Support six discrete command channels at each ExPA location.

Four ELC units are planned, with the first two lacking the avionics subsystems to support the experiment C&DH task, and the final two having full C&DH functionality.

ISS preparation for ELCs

On June 11, 2007, crew members of Space Shuttle Atlantis during flight STS-117, mission 13A, performed an EVA to install the S3 truss section that will support the ELC units.^[3]

ELC launch schedule

The current shuttle manifest shows that ELC-1 and ELC-2 will be transported to ISS on STS-129 Endeavour.^[4] The launch date is under review, but was originally set for July 9, 2009.^[5]

ELC-3 and ELC-4 are currently slated for mission STS-133 Endeavour, with ELC-5 being cancelled, in order to allow the MRM1 to be launched by STS-132.

NET: No Earlier Than

References

• NASA/Goddard Space Flight Center, ExPRESS Logistics Carrier Project Office, ExPRESS Logistics Carrier Operations Concept Document. ELC-OPS-000131