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).

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). The FCU runs the free open-source real-time operating system (RTOS) RTEMS and provides 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 housekeeping telemetry from the ExPCA and resident experiments to the ISS.
• Provide an 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 transmission 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 them all having full-up avionics subsystems to support experiments' C&DH task. Manifested on ELC-2 is the first ELC-based payload, Materials for ISS Experiment (MISSE-7).

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.

ELC launch schedule

The current shuttle manifest shows that ELC-1 and ELC-2 will be transported to ISS on STS-129 Atlantis. The mission launched on November 16, 2009.

ELC-3 is currently slated for mission STS-134 Discovery, launching on September 16, 2010. ELC-4 is currently slated for mission STS-133 Endeavour, to launch July 29, 2010. ELC-5 has not been manifested yet. MRM1 to be launched by STS-132 currently has the manifest where ELC-5 would have launched.

Launch date	Mission	Shuttle	ELC
16 November 2009	STS-129 (ISS ULF3)	Atlantis	ELC-1 and ELC-2
29 July 2010	STS-134 (ISS ULF5)	Discovery	ELC-3
16 September 2010	STS-133 (ISS ULF6)	Endeavour	ELC-4

References

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