From: tarbell@tarbell.space.lockheed.com (Ted Tarbell)
Message-Id: <9708071751.ZM15319@tarbell.space.lockheed.com>
Date: Thu, 7 Aug 1997 17:51:04 -0700
X-Mailer: Z-Mail (3.2.3 08feb96 MediaMail)
To: mdiers@mdisas.nascom.nasa.gov, soitech@quake.stanford.edu
Subject: New Michelson tuning
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The new tunings were uplinked on Tuesday (ending 5-Aug-97 21:00) and
have taken effect.  They caused the average of the full disk raw
velocity image to change from about -580 m/s before to about +160 m/s
early on Aug 6.  These include an orbital velocity contribution of
about -200 m/s.  Using last year's orbit as a guide, this orbital
velocity will peak at about -550 m/s in mid-October and return to 0 m/s
at Christmas.  So neglecting Michelson drift, the observed average
velocity would drop to -190 m/s and increase to +360 m/s on these
dates.  By Christmas, we will do another tuning change (if necessary)
to prepare for the long continuous observing run which will start in
early January.

Over the past 5 months, one of the Michelsons (M2, the broader one) has
not drifted in wavelength; the other (M1) continues to drift at a
decreasing rate, causing an artifical blueshift of about 1.6
milli-Angstroms per month.  If this drift continues, it will add an
extra blueshift of about 120 m/s by mid-October and 240 m/s by
Christmas, resulting in observed average velocities of -310 m/s and
+120 m/s on these dates.  So unless the drift accelerates dramatically,
we can expect the present tuning to keep us nicely around 0 m/s until
the end of the year.

The new tunings are based on calibrations (detunes) taken July 18, 5
days after the continuous run ended.  At that time, the average
observed velocity was about -380 m/s, including orbital velocity of -20
m/s.  The best possible tuning on the date was (M1, M2) = (29, 42) for
the continuum position, with (30, 41) a close second.  The tuning in
use for the entire continuous run was (32, 42), which is the same
co-tuning as (30,41).  In other words, although there was some drift of
M1 during the run, the tuning at the end was still good though not
quite the best possible.  The new tuning uplinked yesterday uses (27,
41), a shift of (-2, -1) to compensate for the orbital velocity this fall.

Here is the table of tuning history.  The long version of this is
at http://www.space.lockheed.com/MDI/ops/dep_stuff/mdi_uobs.newest

Ted


#             Aug-97  Mar-97  22-Jul  16-May  10-Apr  21-Dec  Nov-95
#
Column  Label   Value
------- ------- -------
MTM1    F1      45      #50     #52     #56     #58     #62     #28
MTM1    F2      63      #68     #70     #74     #76     #80     #46
MTM1    F3      81      #86     #88     #92     #94     #98     #64
MTM1    F4      99      #104    #106    #110    #112    #116    #82
MTM1    FC      27      #32     #34     #38     #40     #44     #10
MTM1    LC      72      #77     #79     #83     #85     #89     #55

MTM2    F1      50      #51     #50     #52     #53     #58     #56
MTM2    F2      59      #60     #59     #61     #62     #67     #65
MTM2    F3      68      #69     #68     #70     #71     #76     #74
MTM2    F4      77      #78     #77     #79     #80     #85     #83
MTM2    FC      41      #42     #41     #43     #44     #49     #47
MTM2    LC      63      #64     #63     #65     #66     #71     #69