Topic/Presenter: Additional Mechanisms / Jon Morse

Question/Comment: 

Impacts of additional mechanisms:
   (internal) focus mechanism
   pupil alignment mechanism
   shutter

Is it possible to add another (third) filter wheel without 
changing pupil relief/optics design significantly?

What is the cost impact of an additional wheel 
mechanism?

Submitted by: Jon Holtzman


NIC-FPS Response:

We add to the above list:
   calibration lamp unit
   ion pump
   

These additions will require a trade study.


1) Internal focus mechanism: At this time, we do not plan to include a
mechanical feedthrough for internal instrument focus.  Internal focus
will be achieved during instrument alignment. However, we will save
space on the forward bulkhead for such a feedthrough if we find the
adjustment is particularly sensitive.

2) Pupil mask alignment mechanism: At this time, we do not plan to
include a pupil mask alignment mechanism (either hand operated or
motorized). Other similar imaging instruments often do not have such an
adjustment capability, and we regard this alignment as sensitive but
not critical to the imaging performance because we do not penetrate
into the thermal IR.

3) Shutter mechanism: There is currently no plan to include a cryogenic
shutter in NIC-FPS. The flexible detector read-out modes appear to
mitigate the need for a shutter and a blocking slot will be included on
one of the filter wheels for obtaining detector dark exposures. (See
RFA opto-mechanical #1.)

4) Additional filter wheel: There are currently 3 filter wheels in the
NIC-FPS design, each with 7 slots. Each filter wheel must have a clear
slot and one of them needs to include a block for detector darks.
Thus, there are 17 slots available for science filters in the current
design.  Adding another wheel would permit an additional 6 filters.
Although  this additional is probably feasible, it adds cost that the
current budget will not support.  Furthermore, 65 mm filters can cost
$10-13K a piece, thus an additional $60-75k is required to populate the
additional wheel.

5) Internal calibration lamp(s): Although this would permit some
calibration of the etalon even while NIC-FPS is off the telescope, one
would generally not rely on internal calibrations for flat fields.  At
this time, we plan to obtain calibration exposures using lamps mounted
on the secondary support structure that illuminate the primary mirror
covers. Wavelength calibration of the etalon is generally not an
excessive overhead.

6) Ion pump: At this time, we are not planning to use an ion pump.  For
more details, see RFA Dewar #3.


Status: 1-4 Closed. 
Options to include an internal calibration lamp (5) and ion pump (6) 
are present in the baseline design. They can be added at any time 
during the lifetime of the instrument should the need arise.