Telecon 20180124

Attending:

Notes by :

• Telescope I+T (.pdf) (Tomo)
• GRASP status (.pdf) (Karl, Brad)
• Attitude control requirements

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 (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.