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====== Telecon 20180124 ======

Attending: 

Notes by : \\

=== Agenda===

  * {{::telescopei_t_v002_20171212_s.pdf|Telescope I+T}} (Tomo)
  * {{::bjohnson_01.24.17.pdf|GRASP status}} (Karl, Brad)
  * Attitude control requirements
 
^       ^ Pointing Knowledge  ^ Pointing Control  ^ Pointing Stability  ^
|       |  (arcsec)           |  (arcsec)         |  (arcsec/sec)       |
| EPIC  | <35 (3 sigma)       |  3600 (3 sigma)   |  45/0.05            |
| CORE  |  1 (1 sigma)        |  24               |  ?                  |
| PICO  |  6 (1 sigma)        |  3600 (3 sigma)   |  ?                  |


=== Notes:===

Notes:

Attitude control
  * Shaul: Pointing Control is how well spacecraft points at a direction; Pointing Knowledge is how well we know where it points at; Pointing stability is how stable pointing is in terms of changing rate.
  * Ben: thinking about map to understand definitions of pointing knowledge, control and stability; that's how engineers talk about them.
  * PICO rquires 6 arcsec pointing knowledge, which about 1/10 of the smallest beam.
  * Shaul thinks we do not need more than 1 degree of pointing control.
  * Bill: pointing stability is associated with spin; we may also think about how stable spin axis is aligned with star camera.
  * Bill: points out having 2 or more scan modes would have been very helpful for Planck. Break time constant and beam shape degeneracies. Shaul: right now we fix on having only 1 scan strategy, but it can be discussed.
  * Jacques: 3 star sensors garuntees 1'' pointing knowledge. This is the easiest and likely to be reasonable in cost.  Worth just using 3.
  * Jacques: Thoughts from CORE,
  * Pointing control is to eliminate gaps in map. 24'' ensures no gaps in single detector maps.
  * 24'' was technically doable for Core with reaction wheels.  Should check if that is true for PICO, if the engineers don't scream, then stop worrying about it.
  * Shaul: reaction wheels are current assumption for PICO
  * **A/I** Shaul to check with Amy about 24'' control with wheels.

  * Additional note from Brendan: Planck achieved 2 arcsecond rms pointing reconstruction [[https://wiki.cosmos.esa.int/planckpla2015/index.php/Detector_pointing|(see Planck Explanatory Supplement)]]


I + T, lessons from Planck, options for PICO. (Tomo)
  * Plank tested mirrors + baffles, then focal plane and feeds separately
  * example of parameters that need to be tested in presentation page 5 
  * tests at component and subsystem levels.
    * feed beam patterns not tested cold 
  * Jacques: Primary, secondary at different temperatures. difficult to test this on ground. Alignment may create issues.
  * Planck cold system test at CSR. Signal response test, but no beam mapping.
  * Photogrammetry of full structure to measure alignment, and align system.  Was costly for Planck, facility needed to be adapated.
  * 10 um interferometry of planck mirrors.
    * optics needed to be sufficiently polished for this test. may need to 'overbuild' mirrors.
    * also consider mirror material in cost, planck was CFRP.
  * focal plane testing at Saturne. criteria tested on page 13.
  * Comments for PICO:
    * page 16-17, cost drivers. 3 cyrostats (all large), plus full satellite sized chamber to test full system (cooling, etc.)
      * cold testing drives cost, dependent on availible facilities, dependent on what is characterized in flight vs on ground
    * page 19, calibrations done for Planck shown. 
      * spectral response not fully measured on ground, can't be sense 
    * Shaul: has Planck over tested or under tested any optics?
      * Bill: most valuable was cold photogrammetry of flight optics. Other tests were of interest, but not as critical.
      * Mirror material?  Bill: Silicon carbide, lower mass solution than aluminum. Jacques: Core proposal used silicon carbide, but now in doubt. carbide is expensive, machining challenge, large thermal contraction.  Aluminum is cheaper, easier.
        * Shaul: TeamX assumed aluminum mirrors. Silicon carbide may over run cost.  Aluminum below $10M.
  * Discussion on hold until next week due to time.
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