Telecon 20180221
Attending: Tom, Tomo, Toki, Brian, Kris, Shaul, Karl, Qi
Notes by : Qi
Agenda
- Attitude Control and Reconstruction Requirements (Wrap up)
- Tentative baseline: control = 1' (3 sigma) over 1 spin period; reconstruction = 1“ (3 sigma)
- Last week's presentation from Jacques: Attitude control requirements (Jacques)
- Last week's images from Kris: |
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- Telescope I+T (Tomo and Bill)
- Instrument I+T (Bill J.)
Notes
- Attitude Control and Reconstruction Requirements (Wrap up)
- The discussion was from last week: based on cross scan sampling, Jacques argued that increasing precession period T_prec is an potential solution, in order to achieve better sky coverage
- Kris did not agree
- Kris's updates:
- figures show the high-resolution (highest frequency beam) hits number of sky coverage, assuming precession angle 30 deg and spin spin angle 65 deg.
- Two cases were studied, fast (48 hrs) and slow (7 hrs)
- it's shown that hits are dense on the edge of “donuts”, and coarse in the middle
- for slow precession, the distinction between edges and inner parts is more obvious
- color is in log scale, red is much more dense than blue
- color scales in slow and fast are not same; the maxium in 48 hrs is a factor of ~4 compared to 7 hrs
- Kris's conclusion: short (fast) precession is better
- Shaul: 1 arcmin in 3 sigma in single spin rate is based on fast precession
- Kris: many motions of PICO are much faster than Planck, we need to be careful. Someone studing WMAP pagers is a good thing to do.
- Shaul: we need to be careful, star tracker; In optical astronomy, they don’t scan fast, so it’s trivial for them.
- Telescope I+T (Tomo）
- pg24
- reminder, introduction about what Tomo talks today
- fully integrated test when it’s cold
- optics only; tests one can possibly imagine
- pg28
- purpose: mirror shape
- two spacial scales: large ,small scales
- Large scals: you cannot probe smaller than the space between markers
- Short scales: very small scales
- A combination of both scales; blue table
- “Cold” means some cold temperature, not necessary the mission temp
- Minimal tests for PICO: Photogrammetry and Interferometry; certainly can be done
- CMM: surface, not sure if there is facility big enough for PICO mirror
- Shaul: mirror vendor, whatever lab who puts the instrument together; whoever provides mirrors, they would CMM warm; CMM is part of the cost buying the mirror; I & T is beyond vendor level.
- Tomo: for space mission, it’s common you repeat measurements even vendors have done so.
- Brian: normally, vendors verify, we would not check again.
- Tomo: different models, e.g. ground model, flight model; you can do tests in first few models, then you trust (vendors).
- pg29
- Tomo: partly a comment, partly a question
- after the characterization, what information are we using?
- pre-flight: sub and full level tests; outputs: performance verification and mirror shapes
- inflight: beam calibration; slide shows beam profile from Planck
- post-flight: if with precise beam, with pre-flight information, systematics; if beam not precise, we need GRASP model, and correct for it.
- What did Planck use to get beam? What are the key information?
- Kris: LFI used Grasp model; HFI used planet measurements; signal-to-noise is the reason. LFI is much more noisy. Absolute size of beam matters. pre-flight + inflight consideration.
- Beam size is important because couple to focal plane; in part of scanning. Sometimes more reliable on GRASP model.
- Tomo: future mission should have tighter requirement for signal-to-noise; does this mean they will be like LFI case?
- Kris: Any test before flight is valuable.
- Shaul: not clear what Planck did was used and useful in terms of tests.
- Kris: not sure if there is a short path compared to Planck.
- Pg30
- Tomo: it’s very important to characterize feed beam. For Planck, corrugated horns are classic and thus did not need more attention; PICO could use something else.