" 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 22,  October 4, 2002


SIM MICROARCSECOND METROLOGY TESTBED MEETS MAJOR MILESTONE

There is excellent news from the MAM Testbed.  The following announcement from
Jim Marr, Project Manager, describes the result and its significance for SIM:


As all of you know, the SIM Micro Arcsecond Metrology (MAM) team has been
working for several years to demonstrate the system-level capability for a
single interferometer to meet the "basic" narrow-angle performance requirement
of 3 uas over a 1 degree narrow-angle field of regard. This milestone is one of
four technology "gates" that are needed to be met prior to entry into Phase B,
the preliminary design phase of SIM's development.  Back in March of 2001, we
scheduled this milestone to complete in July 2002 and have just completed it
September 30, 2002.

The actual statement of the technology demonstration milestone is: "Demonstrate
Microarcsecond Metrology (MAM-1) Testbed performance of 150 picometers, over its
narrow angle field of regard.  This level of performance is consistent with the
narrow angle astrometry Level-1 requirement of 3 microarcseconds.  It
demonstrates, at the system level, SIM's ability to meet its Level-1
requirements for planet finding.  This level of performance is required to
perform the scientific Broad Survey.  Date: 7/02."

To demonstrate this milestone, the definitive test is what is called a "three
star test" that involves chopping between two reference stars and one target
star between them.  Chopping goes as: Target - Ref1 - Target - Ref2 - Target -
etc.  One T-R-T sequence is called a chop and represents how SIM makes its
narrow angle observations.  The objective was to achieve less than 150 pm within
10 chops.  Achieving 150 pm means that the white-light fringe position agrees
with the predicted position of the fringe derived from the internal 
metrology from both the test article interferometer and the inverse
interferometer pseudo star (IIPS) within 150*sqrt(2) pm.  The sqrt(2) accounts
for the fact that essentially the same errors occur in both the test article
interferometer and the IIPS, since they are essentially identical.  Dividing the
total result by sqrt(2) yields the fraction of the error attributable to the
test article interferometer.

The first successful data was taken on Monday, September 30th, and then
confirmed on Tuesday and Wednesday, October 1st and 2nd, respectively.
A plot (in JPEG format, see link below) that shows white-light (WL) vs.
internal-metrology (SAVV) data taken on October 1st that shows the performance
achieved versus the chop number that demonstrates meeting the milestone.  Note
that in the plot, the definition of a chop is T-R1-T-R2-T, so five of these
'chops' is equivalent to ten SIM chops of T-R-T.

http://planetquest.jpl.nasa.gov/images/10-02.jpg 

All data supporting the claim of meeting this milestone has been reviewed by the
SIM Project Scientist, Mike Shao, the SIM Project Engineer/Architect, Jeff Yu,
and the Flight System Manager, Bob Laskin, all of whom confirm meeting the
milestone.  The detailed evidence for completion of this milestone will be
further reviewed by the SIM Technical Advisory Committee (SIMTAC) and the
Navigator Program Independent Review Team (IRT) at the November SIMTAC meeting.

Congratulations to the entire MAM team for achievement of this enormously
challenging and very significant demonstration! --Jim
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James (Jim) C Marr -IV
Project Manager, Space Interferometry Mission (SIM)
NASA/Jet Propulsion Laboratory
4800 Oak Grove Drive, MS 301-486
Pasadena, CA 91109
Ph: (818) 393-1528    FAX: (818) 393-5239     email: jim.marr@jpl.nasa.gov


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

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