NASA is also awaiting delivery of a second instrument that was delayed nearly a year, the Near-infrared Camera (NIRCam) built by Lockheed Martin Advanced Technology of Palo Alto, Calif.
It is expected to arrive later this month after NASA determined the need to electrically ground a mirror on the instrument, a hardware change that required the contractor to attach a small wire to the edge of the mirror, with the other end attached to the metal of the support mechanism holding it, says Lockheed Martin spokesman Buddy Nelson.
Another challenge JWST must address is reducing mass on the spacecraft bus, the mission’s least-mature subsystem and one that can still accommodate design changes to account for the mass of its electrical wiring harnesses, which turned out to be more than expected. Mass constraints have been allocated for each subsystem, including the spacecraft, which is limited to 1,754 kg. As of September 2012, however, its estimated mass was 1,960 kg, a 12% overage.
NASA spokesman J.D. Harrington says design changes were insignificant, and included the use of lighter-weight components and finding low-mass means for meeting spacecraft requirements. “We also received additional mass margin from the launch provider,” he said, referring to Arianespace, which manages Ariane 5 launches. “All of this is completely normal as the observatory design matures.”
Conceived in the late 1990s as a follow-on to the Hubble Space Telescope, JWST was projected to cost just $1 billion. By 2011, however, the program had been plagued by almost a decade of cost overruns and schedule delays, prompting NASA to rebaseline the program with a revised cost estimate of $8.8 billion, a new launch date of October 2018, and a healthy amount of schedule margin to maintain both.