WASHINGTON — Replacing faulty electrical wiring that runs behind the James Webb Space Telescope’s (JWST) primary mirror could delay assembly of the flagship observatory’s primary optics package, although the overall mission remains on schedule, a NASA official said April 8.
NASA and JWST prime contractor Northrop Grumman discovered 76 harnesses that bind electrical cables together had “nicks or cuts” that were caused by the wiring, Eric Smith, JWST program director, told an agency-chartered advisory panel meeting at NASA Headquarters in Washington. The damage was close to the connectors that allow the wires to plug into the telescope components they power, Smith said.
The fix, Smith told the NASA Advisory Council’s science committee, is to replace the cables and associated hardware. Until all that new wiring is ready, NASA and its contractor will not be able to install all 18 of the primary mirror segments on the telescope’s backplane.
The backplane, made by Orbital ATK of Dulles, Virginia, holds the JWST’s primary mirror steady and houses its four main science instruments and other hardware, such as thermal control systems. Smith said the backplane structure is slated to arrive in August at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, where JWST is being put together.
At that point, engineers will be able to install at least some of the mirror segments, because “you can actually begin putting some of the mirror down before you have to put the wire harnesses on,” Smith said.
Once all of the mirror segments are installed, engineers at Goddard will couple the telescope’s optics, known as the Optical Telescope, with its the four main instruments, which will fly in a bundle NASA calls the Integrated Science Instrument Module.
This integrated optical and instrument package is not slated to begin cryogenic testing at the Johnson Space Center in Houston until 2017, but the wiring problem is an example of the sort of small, unforeseen development hiccups that government auditors have repeatedly warned could snowball into bigger issues during JWST integration and testing.
“[A]lmost 4 years of integration and test remain ahead, which is when schedules tend to slip and problems are most likely to be identified,” the U.S. Government Accountability Office wrote March 5 in its annual report on NASA projects with a lifecycle cost of $250 million or more. “[N]ew problems that cause delays to any of these elements or major subsystems would negatively affect the overall project schedule,” GAO wrote.
JWST is set to launch in October 2018 aboard a European Ariane 5 rocket. The flagship-class observatory is expected to cost nearly $9 billion, including five years of operation. Smith said April 8 that despite the wiring and other problems, the project is still tracking toward an on-time, on-budget launch.