William P. Blair

Planning JWST NIRSpec MSA spectroscopy using NIRCam pre-images

The Near-Infrared Spectrograph (NIRSpec) is the work-horse spectrograph at 1-5microns for the James Webb Space Telescope (JWST). A showcase observing mode of NIRSpec is the multi-object spectroscopy with the Micro-Shutter Arrays (MSAs), which consist of a quarter million tiny configurable shutters that are 0. ′′20×0. ′′46 in size. The NIRSpec MSA shutters can be opened in adjacent rows to create flexible and positionable spectroscopy slits on prime science targets of interest. Because of the very small shutter width, the NIRSpec MSA spectral data quality will benefit significantly from accurate astrometric knowledge of the positions of planned science sources. Images acquired with the Hubble Space Telescope (HST) have the optimal relative astrometric accuracy for planning NIRSpec observations of 5-10 milli-arcseconds (mas). However, some science fields of interest might have no HST images, galactic fields can have moderate proper motions at the 5mas level or greater, and extragalactic images with HST may have inadequate source information at NIRSpec wavelengths beyond 2 microns. Thus, optimal NIRSpec spectroscopy planning may require pre-imaging observations with the Near-Infrared Camera (NIRCam) on JWST to accurately establish source positions for alignment with the NIRSpec MSAs. We describe operational philosophies and programmatic considerations for acquiring JWST NIRCam pre-image observations for NIRSpec MSA spectroscopic planning within the same JWST observing Cycle.

Optimizing the observing efficiency of the James Webb Space Telescope

One of the goals of the operations system being developed at the Space Telescope Science Institute for the James Webb Space Telescope (JWST) is to produce the most efficient use of the observatory that is scientifically justified. To first order, this means maximizing the amount of time spent collecting photons on science targets while ensuring the health and safety of the observatory and obtaining the necessary calibration data. We present recent efforts by the JWST EfficiencyWorking Group at STScI to quantify the expected observing efficiency based on current plans for the operations system. These include collecting the expected observatory and instrument overheads and updating a set of prototypical observing programs that will approximate over one full year of JWST observations. The combination of these two efforts is being used to investigate the expected observing efficiency and determine revised strategies to minimize overheads and maximize this efficiency.

The Evolution of the FUSE Mission Planning System and Operations

The Far Ultraviolet Spectroscopic Explorer ( FUSE ) is a low-Earth orbit NASA astrophysics satellite requiring 3-axis stabilized pointing control to perform high resolution spectroscopy in the far ultraviolet regime (905-1187 A). FUSE was launched in 1999 and designed for a three year prime mission with the goal of operating for five years. During its eight years of operations (1999-2007), the FUSE mission encountered numerous unforeseen operational challenges; in particular, the successive failures of the four reaction wheels and four of the six gyroscopes required multiple innovative solutions to restore spacecraft control and meet mission requirements. As each new operations constraint was encountered, the FUSE Project successfully adapted to the new operations environment after modifying the ground system planning models and software, and the spacecraft on-board attitude control system software, albeit in some cases with changes in sky coverage, pointing performance and science scheduling efficiency. In this paper, we describe the evolution of the FUSE Mission Planning system and operations scheme, given the pre-launch mission assumptions, on-orbit realities, and the operational challenges due to attitude control system problems. We discuss the workarounds adopted in order to satisfy the unexpected operational constraints and share the lessons-learned from the FUSE experience, drawing conclusions pertinent to future missions in the areas of mission planning and operations design.