Dear _____,

I will be the Uplink Support Interface (USINT) contact for your
LETGS/HRC-S observation of ____  (Sequence ######) throughout
the "uplink cycle", i.e., until your photons are collected by Chandra. 
I am contacting you now to request that you confirm your observation
set-up by DD-MMM-YYYY.

Your confirmation ensures that your observation set-up will be ready when 
the satellite command loads are built.  It is important to note that after 
the above date it will not be possible to change any of the observation 
parameters (unless your observation is a TOO and updates are inherently 
unavoidable).  The scheduling process becomes more complicated each year 
because of the increasing number of thermal control issues, and Mission 
Planning needs all observation configurations confirmed early in the Cycle.

If you have any questions concerning your observation or its set-up, please 
do not hesitate to contact me. Correspondence via email is preferred (cc to 
"cus@head-cfa.harvard.edu"), but you may also contact me by phone or FAX 
(see below).  If the set-up is correct as it is, I still require your 
confirmation.

Your observation is currently scheduled for the week of DD-MMM-YYYY.

You can check your observation parameters in the on-line OBSCAT by going to
http://cxc.harvard.edu, clicking on "Target Search Page," and then using 
the search facility to find your "Summary of Sequence Number" page, or by 
following these links:

    http://cxc.harvard.edu/cgi-gen/mp/target.cgi?#####
    http://cxc.harvard.edu/cgi-gen/target_param.cgi?####

Please check that page for accuracy of the following in particular:
        * the target name,
        * the target coordinates (in decimal degrees),
        * the exposure time (in kilo-seconds),
        * the target offset (in arcminutes),
        * the defocus (in mm),
        * the SIM-Z (detector translation, in mm),
        * the roll constraint (in degrees),
        * the time constraint
        * the HRC configuration

You can view the orientation of the detector on the sky in the optical
and X-ray bands by clicking on the "DSS" (Digital Sky Survey),
"ROSAT" (pointed observation, if any), and "RASS" (ROSAT All-Sky
Survey) buttons at the bottom of the page.  Please note that if your
observation is a TOO, the roll angle will of course be unknown; the
DSS, ROSAT, and RASS images are shown assuming a roll angle of 0
degrees.  The range of permitted roll angles vs date is illustrated
via the "Roll/Visibility" button.

Please be advised that the following changes in your observing program are
not generally permitted: 
        * adding any constraints, 
        * changing exposure time or target, 
        * adding or removing a grating, or 
        * switching between ACIS and HRC or LETG and HETG so that 
          the target and instrument configuration end up being the same 
          as in someone else's observing proposal.

If you request changes, I will confirm these with you by e-mail (or
telephone), and after about two days you should see these updated 
parameters in the on-line OBSCAT database.

In considering your observation set-up, I draw your attention to
aspects of the current in-flight performance of the LETG/HRC-S
that you might need to consider when deciding your final set-up.
These issues are discussed in detail in the Chandra Proposer's 
Observatory Guide.  Links to the relevant chapters are listed on 
the LETGS Observer Information page (http://cxc.harvard.edu/cal/Letg/).

As a reminder:
1) In order to avoid telemetry saturation, the HRC-S is running with 
      a cross-dispersion width of 6 coarse taps (slightly less than 10mm, 
      corresponding to about 3.2 arcmin, or half of its active area); 
      this could be relevant if you are observing an extended source.  A 
      different readout area can be specified if necessary.
2) Telemetry saturation may be a concern if you are observing a bright
      source with > 40 counts per second total and if accurate
      absolute or relative photometry as a function of time is of
      interest.
3) If timing resolution of better than a few milliseconds is required, 
      the HRC-S must be used in a special configuration.  Please contact 
      me for more information after reading "Instrument Anomalies" at
      http://asc.harvard.edu/proposer/POG/html/HRC.html#tth_sEc7.11

Again, if you have any questions at all about the set-up and execution
of your LETGS observation please do not hesitate to contact me. 

Best wishes,

_________