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Guide Star Discussion. August 27, 2007. Concerns Raised. Included in Email – Peter’s comments – Highlights below APT performance Recommend we build the basic computational capabilities to support the L4 requirements first (Plan to complete for Demo Release 10/1/09)

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guide star discussion

Guide Star Discussion

August 27, 2007

concerns raised
Concerns Raised
  • Included in Email – Peter’s comments – Highlights below
  • APT performance
    • Recommend we build the basic computational capabilities to support the L4 requirements first (Plan to complete for Demo Release 10/1/09)
    • Recommend we address any performance issues when we have enough of the system (APT &GSS) available to analyze specific performance issues. (Address for Preflight 10/1/10 and Flight release 7/12/11)
  • GSS Complexity
    • Will be C++, no Fortran
    • Will use a Relational DB for GSC-II data storage
    • Will reuse some existing C++ code in NGSS
  • Interface to 2MASS and SDSS
    • No GSS requirements to do this
    • Assuming GSC-II will be enhanced to include 2MASS/SDSS info
    • Assuming GSS doesn’t have to read GSC-II, 2MASS & SDSS and use data from the 3 catalogs to determine guide/reference stars
performance issues
Performance Issues
  • The existing NGSS for HST is fast for fixed targets. For 960 fixed targets scattered over the sky, it averaged about 6 seconds to perform the following on a SPARC 10:
    • Query observation input parameters from a Relational DB.
    • Access GSC II on an NFS mounted disk.
    • Convert GSC II magnitudes to HST FGS band.
    • Find potential guide stars for any roll angle in 3 “pickles”.
    • Compute roll ranges for each star – computed 0-360 all rolls.
    • Determine usable GS pairs.
    • Determine acquistion datasets.
    • Merge acquistion datasets.
    • Store Results in a Relational DB.
  • We expect performance of GSS will be similar or better.
  • Performance study of NGSS implemented with GSC II stored in a relational database is underway now.
who uses the guide star data
Who Uses The Guide Star Data
  • The PDT shall provide GS requests to the GSS. [PPS-1926]
  • The PDT shall obtain GS usability data from the GSS. [PPS-1929]
  • The PMT shall send GS requests to the GSS for the creation of GS usability data. [PPS-1092]
  • The PMT shall receive GS usability data from the GSS. [PPS-1145]
  • The VPS shall use a guide star acqusition metric as a planning preference. [PPS-1173]
  • For each prime visit on an STS timeline that requires guide stars, the VSS shall select the three candidates with the highest estimated quality (or as many as are available, if fewer than three). [PPS-569]
  • OPGS/OSS needs this info – Reqs elsewhere
  • The GSS shall respond to a GS request for a visit in an average time of no more than 60 seconds (TBR). [PPS-1316]
  • APT:LRP:STS/FOV, APT:LRP:STS/Schedulability, STS/Selection
gss architecture
GSS Architecture
  • Flexible architecture that supports either direct linking of the Guide Star library into an application program or use as a Web service.
  • GS_LIB is C++
  • GS_DB is a SQL server relational database holding the GSC-II catalog
  • GS_LIB & GS_DB will implement the L4 Requirements.
guide star request inputs
Guide Star Request Inputs
  • Not relevant to today’s meeting.
  • There are a lot of inputs parameters. Still reviewing which ones will be needed by JWST. Plan to complete by Feb, 08
  • Preliminary list available off of the PPS design web page
guide star request outputs
Guide Star Request Outputs
  • A list of stars and possibly other objects (guide or reference)
    • ID
    • RA,DEC with uncertainties
    • RA,DEC proper motionss
    • Annual parallax
    • Magnitudes and Magnitude uncertainties
    • Guider Magnitude/Counts ?
    • First and Second Closest Star Spoiler Radius & Magnitudes
  • A list of candidate guide stars
    • Pointer to star data
    • FGS aperture
    • Usable roll range
    • Time Range (moving targets only)
    • Quality Metric Value
guide star request outputs1
Guide Star Request Outputs
    • A Usability Function:
      • A sorted list of roll ranges, each containing:
        • Min Roll Angle
        • Max Roll Angle
        • Quality Metric
        • List of Pointers to Candidate Guide Stars
        • List of Pointers to Candidate Reference Stars
  • The roll ranges will be defined by sampling the roll angle space and creating a new roll range when the number of candidate guide stars changes.
  • The function may not be continuous -- there will be gaps in the span of roll ranges where there are no usable guide stars.
  • In crowded fields, user parameters will control the merging of roll ranges to avoid the creation of too many roll ranges.
guide star selection outputs
Guide Star Selection Outputs
    • A list of candidate guide stars for schedule roll angle
      • Pointer to star data
      • FGS aperture
      • Usable Roll Range (Should contain scheduled roll angle)
      • List of pointers to candidate reference stars
      • Time Range (moving targets only)
      • Quality Metric Value
      • Acquisition Attitude Info.
  • VSS will call GS_LIB to perform the Guide Star Selection.
  • VSS will be responsible for selecting “best 3” candidate guide star / reference star sets.
  • VSS User may override “best 3” candidates.
  • VSS Chosen guide stars/reference stars and Acq Attitudes will be passed to OPGS.