JWST Science Instrument Payload Update

The JWST science instrument payload is designed as a highly integrated module in which many systems are shared among the science instruments in order to reduce mass, power, and volume resources. This Integrated Science Instrument Module (ISIM) system is a 1.4 metric ton element of the JWST space vehicle that consists of four science instruments, a fine guidance sensor (FGS), 7 other shared hardware systems and two shared software systems. It completed its system-level critical design review during 2009 and is currently in integration and test (I&T) at Goddard Space Flight Center in Greenbelt MD. A description of the ISIM is available at: Greenhouse, M.A., et al., 2010, Proc SPIE, 7731 and references therein. Its science instruments include: a Near-Infrared Camera (NIRCam), a multi-object Near-Infrared Spectrometer (NIRSpec), a Mid-Infrared camera and spectrometer (MIRI), and a Near-Infrared Imaging Slitless Spectrometer (NIRISS). Functional capability of the instruments is described at: www.jwst.nasa.gov.

Two science instruments (MIRI and NIRISS), the FGS, and 5 support systems (optical metering structure, ISIM electronics compartment, ISIM remote services unit, ISIM command & data handling system) have been completed through flight qualification testing and have been delivered to ISIM-level I&T. Delivery of the remaining hardware systems (cryogenic thermal control system and harness radiator system) is expected during January 2013.

MIRI, NIRISS, and FGS are currently undergoing electrical tests with the above flight systems, which were represented by simulators during instrument-level qualification. Each science instrument shares a common computer system with instrument specific software applications and a real time process control script system residing on a common ISIM flight software system. MIRI, NIRISS, and FGS applications and scripts are currently undergoing test with the ISIM flight software system.

The NIRCam instrument is currently in its second of three planned instrument-level cryo-vacuum test cycles at Lockheed Martin Advanced Technology Center in Palo Alto California. The NIRSpec instrument will begin its second instrument-level cryo-vacuum test at EADS Astrium GmbH in Ottobrunn Germany during December 2012. Delivery of both instruments to ISIM I&T is expected during summer 2013.

Completion of ISIM ground support equipment is on track to support ISIM-level cryo-vacuum testing. The ISIM will be tested in the Space Environment Simulator (SES) using a high fidelity cryogenic optical simulator of the JWST telescope (OSIM). The SES helium shroud system has completed performance testing, and the OSIM has completed 1 of 2 planned cryogenic performance tests in the SES.

The ISIM cryo-vacuum test is among the most complex space environmental tests ever conducted. This testing will begin during Spring 2013 with a risk reduction test cycle that will include MIRI, and NIRISS science instruments, FGS, and all of ISIM’s other systems. Two subsequent comprehensive performance test cycles containing all of the science instruments will occur during 2014 and 2015. The ISIM will be delivered to observatory-level I&T during Autumn 2015.

Re-manufacture of ISIM’s near-infrared detectors was initiated during 2010 after discovery of degradation in pixel operability with prolonged ambient storage (Rauscher, B. J., et al. 2012, AIP Advances, 2(2), 021901). Root cause of the degradation was identified; prototypes of a new design were manufactured and flight qualified during 2011. Flight manufacture is on schedule, and the first flight units have been delivered to the NIRCam for detailed characterization. Installation of the new detectors will occur during 201