" F R I N G E S "

S P A C E   I N T E R F E R O M E T R Y   M I S S I O N   N E W S L E T T E R

                        Number 23,  November 21, 2002


SIM COMPLETES ITS FINAL PHASE-A TECHNOLOGY MILESTONE

Previous Newsletters have reported on the completion of the first three out of
four SIM Phase A top-level technology milestones (beam launcher performance,
nanometer control performance, and micro-arcsecond narrow angle basic performance).

Now the SIM team has completed the last of these Phase A milestones on October
29, 2002.  This milestone demonstrates both wide-angle (global astrometry) and
narrow-angle 'basic' performance of the external metrology system needed to
relate SIM's guide interferometers to the science interferometers at the 10's of
picometer level.  This result comes from the 'Kite' Testbed - a combination of 6
laser metrology gauges arranged in a planar layout similar to the shape of a
child's classic four pointed kite.

The Kite team has worked long and hard achieve this milestone, overcoming many
challenges and difficulties along the way.  They are all to be commended for the
hard work and dedication to getting the job done.  This is a fantastic
achievement!  

Not only has the milestone been met, but the performance is well on the way to
meeting the more stringent 'goal' requirements, as explained in the table
(smaller is better!):

                                   Narrow Angle      Wide Angle
                                   [picometers]     [picometers]

Requirements as defined in the
   Kite milestone (see text below)     50              300

Current SIM error budget
   'basic' requirements                49              835

Kite Testbed actual demonstrated      
   performance (Nov 2002)              27              248

Current SIM error budget 
   'goal' requirements                 12              111

[Definitions:  SIM 'basic' requirements are 3 microarcsec narrow-angle, and 30
microarcsec for global astrometry; the Project designs to the 'goal'
requirements of 1 and 4 microarcsec, respectively.]

The full text of the completed milestone reads:

     "Demonstrate that multiple laser metrology gauges can be integrated 
     to achieve a 'metrology truss' like the SIM external metrology system 
     by achieving 300 pm wide angle and 50 pm narrow angle performance in 
     the 6-Gauge [aka Kite] experiment, a planar metrology truss 
     consisting of 6 laser gauges.

     This level of performance meets both narrow angle and global 
     astrometry Level-1 requirements of 3 micro-arcseconds and 30 
     micro-arcseconds respectively, and demonstrates, at the system-level, 
     that the external metrology will provide the performance required to 
     meet the scientific Mission goals for the Broad Survey and the 
     astrometric Grid.  It also demonstrates SIM's ability to meet the 
     global astrometry minimum science requirements.  Date [due] 7/02."


These results and the work that went into them have been peer reviewed by the
Navigator Program Independent Review Team (IRT) and the SIM Technical Advisory
Committee (SIMTAC); we are awaiting written confirmation of completion from them.

Again, congratulations to the Kite team!

   Jim Marr
   SIM Project Manager

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Steve Unwin, Editor                              stephen.unwin@jpl.nasa.gov

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