Faced with the complicated job of putting together the $8.8 billion James Webb Space Telescope, NASA and lead contractor Northrop Grumman are starting to run practice assembly tests using a "pathfinder" telescope.

The technique was used during the construction of NASA's Chandra X-Ray Observatory, which launched in 1999, and was apparently quite successful because the telescope remains scientifically productive today, said Jon Arenberg, James Webb Space Telescope (JWST) chief engineer at Northrop Grumman.

"It helps us do a number of things, obviously how to handle such a large structure, how to attach the mirrors," Arenberg told Space.com. "So this allows us to wring out a 140,000-lb. [63,500 kilograms] stand and robot assembly process." [Photos: Building the James Webb Space Telescope]

"This is an example of practice makes perfect, so we practice, practice, practice so when we get the flight hardware, it goes off as smoothly as possible," he added.

The pathfinder's design is fairly similar to that of the actual JWST, but there are some differences, Arenberg said. For example, the pathfinder lacks two winglike parts on either side of a backplane that holds a large part of the telescope together.

Hardware tests

JWST is the highly anticipated successor to NASA's iconic Hubble Space Telescope. When it's up and running, the infrared-optimized JWST will probe the atmospheres of exoplanets, study the universe's first galaxies and investigate how stars and planets form, among other things, NASA officials say.

But the telescope has received criticism for cost and development overruns. Around the turn of the century, JWST was projected to cost up to $3.5 billion and launch no later than 2011, according to a U.S. Government Accountability Office report released in 2014.

The coming months will be crucial to the success of JWST, as components are starting to be completed and shipped for testing and assembly.

One major sign of success came in July, when load testing was finished on the observatory's primary mirror backplane support structure, the device that holds the telescope's mirror segments and science instruments. The backplane support was scheduled to be shipped to NASA's Goddard Space Flight Center in Maryland at the end of 2014 to be placed in its clean room and begin receiving mirrors.

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James Webb Space Telescope Assembly Practice Runs Start