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STELLA Steps 'Out of the Box'
A new software capability may make it easier for research to be conducted aboard the International Space Station.

The EXPRESS Payload Simulator experiment -- demonstrated in May 2010 -- characterizes the functionality of Software Toolkit for Ethernet Lab-Like Architecture, or STELLA. In collaboration with the University of Tennessee at Chattanooga, the Boeing Company Payload Integration Team in Houston developed an experiment simulator and the STELLA experiment software interface. STELLA easily adapts Ethernet-based research software, used in ground laboratories, to software for conducting research in a space station EXPRESS Rack, or a standardized rack system used to house experiments. Ethernet is a trademark system for exchanging messages between computers.

STELLA captures experiment data and puts it in the correct formats -- ensuring that sending commands and receiving data from experiments conducted in space is as easy for researchers as working in their ground laboratories.

"ISS experiment software can be expensive and take a long time to develop, so the experience of being able to operate an experiment on the space station just like you operate it on the ground with off-the-shelf software is pretty incredible," said Amanda Rice, of Boeing, who is the experiment's principal investigator. "STELLA software provides an ‘out-of-the-box’ software interface for EXPRESS Rack payloads."

In order to send commands to a payload and receive data back, many specific data formats have to be met due to the complex designs of the space station ground systems and on-orbit avionics systems. Data has to be packaged based on very specific guidelines: it must have specific headers, frequencies and routing information or it will not be transmitted through the space station’s complex communication systems.

A subset of STELLA files is loaded onto a ground computer, in order for STELLA software services to allow the ground computer and the flight payload computer to communicate. From the ground side, researchers can press command buttons or type commands with software they are accustomed to using. "It’s unique that ground control data is transparently formatted by STELLA to be transmitted through space station ground and flight equipment," added Rice. "And likewise, a subset of STELLA files is loaded on the flight processor or computer, to enable the flight experiment data to be transparently formatted by STELLA for the return trip."

STELLA met all mission objectives in May 2010. "We were able to characterize how STELLA operates with the communications coverage available on station," she said. "We also learned key technical information related to the way we need to adjust the rates at which STELLA passes data, and are now incorporating those modifications."

For the experiment, Rice partnered with Jim Henry at the University of Tennessee at Chattanooga to get input from a researcher who is not familiar with current space station software. Henry utilized commercial, off-the-shelf, or COTS, software to operate a payload. By using a laptop aboard the station as the payload hardware, Henry wrote a COTS software application to gather information about the laptop such as temperature, utilization, fan speed and average audio level. He routed that information to a ground computer COTS software application. Also, using standard operating system functions, he transferred files between the laptop payload and the ground computer. Henry's COTS experiment software was easily integrated with STELLA to adapt it for use on a space station EXPRESS Rack.

"STELLA is just one little factor that will hopefully make it easier for future space station researchers," added Rice. "We have had a great deal of interest in it, and are eager to begin working with payload developers early in 2011."

by Lori Meggs
NASA's Marshall Space Flight Center