====== Telecon 20171017 ======

Attending: Brian, Julian, Shaul, Karl, Qi, Roger, Kris, Jacques

__Agenda:__ 

  * optical system + noise model + focal plane options (Young, Wen)
    * {{:open_dragone_optics_20171017.pdf| 1.4 m Open Dragone Options }}
    * {{:crossdragone_d120cm_f2.5_fov4_10deg.pdf| 1.2 m Crossed Dragone}}
  * TM rates for large/small aperture systems (??)
  * {{::probe_scanning.pdf|Scan angles}}
  * Scan angles + full sky scan simulations + integration with systematics (Gorski, Delabrouille, + all)



__Notes:__

Open Dragone: optical system + noise model + focal plane options (Young)
  * Size of pixel defined on lowest or middle frequency band.
    * middle band means smaller pixel, higher sensitivity
    * 10 dB edge taper + middle band size, overall the best in terms of mapping speed
    * lowest band has 4.8 dB edge taper
    * edge taper is at 4K stop
    * Using 10 dB at middle of band moving forward.

  * For Open Dragone, the DLFOV is small. The outer area of the focal plane is not usable for high frequency, thus it’s hard to trade low -frequency detectors for more high-frequency detectors.
    * We don’t know what we need for low frequency, it depends on the synchrotron structures.
    * Plan is to optimize mirror shapes to increase ~150 GHZ DLFOV so trading low sensitivity for high sensitivity is an option.

  * Open Dragone Optics
    * V3.D: focal plane further from stop, linearly 10% more focal plane compared to baseline
     * looks good, has room for mechanical structure of focal plane
     * Karl is working on coma correction to this telescope, and hopefully we will have larger DLFOV **(AI)**
    * V4: 10% less DLFOV compared to baseline.  Overall smaller telescope, allows roughly 2-3 deg. increase in alpha.
    * sensitivity calculation uses edge taper defined as lowest band, can be done using middle band

Large-aperture Cross Dragone (Wen)
  * Follow-up to matrix from previous week.  Now we have a baffled, large cross dragone.
  * Reminder: Why 50cm? De-scoped to save cost, if imager + spectrometer is emplemented.
    * Still questions as to whether just 140cm --  50 cm saves cost.  
    * Idea here is to provide options to cost and be decided on by the EC.
  * Cross Dragone has large DLFOV if not limited by vignetting (blockage, mirror sizes etc)
    * current case is limited by vignetting and blockage, not image quality.
    * unlike Open Dragone case, we can trade detectors at low frequency for high-frequency detectors more easily
    * ~ 3K detectors (Open)  VS ~ 5K detectors (Cross)
    * F number: 1.5 (Open)  VS  2.5 (Cross)
    * more detectors + larger F#, means Cross Dragone has larger focal plane

  * We have filled the matrix of telescope categories
    * optics design is wrapping up.  Polishing will be done to improve sensitivities.
    * the large/small, open/cross options provide input to trade-off decisions.  

Scan (Kris)
  * Simulation
   * note WMAP Q/U map in V band; Probe with alpha = 22 deg, beta = 73 deg, is close to WMAP
   * fast spin + different precession (fast, slow, very slow)
     * for T spin 20s (3 rpm) is fast, Kris do 1 rpm **(AI)**
     * slowest precession, more non-smooth features, higher resolution needed
   * LiteBird & Core use same convention of alpha and beta, Kris will change his definition
  * The simulations are the average over 1 year
   * simulating over other different periods will be very useful, give more opportunities to look into the scanning.
     * Jacques: maps with no holes over week timescales are useful.
     * Kris will do two-week simulation **(AI)**

Scanning strategy
   * Julian: 6 + 1 parameters; precession angle alpha, spin angle beta, 3 rotation rates (spin, precession, HWP), radius of L2 orbit, + data (or sample) rate.
   * Jacques will lead to make table of scan drivers, wants, and evaluation metrics in wiki **(AI)**
     * Shaul to make table of hardware or engineering limits on 6 + 1 parameters **(AI)**
   * Brian: there may not be many options of the L2 orbits
     * there could be, we need more information input from project
     * Jacques: Planck had radius L2 = 300,000 km, small. Needed 380 kg fuel for insertion.
     * Brian and Amy to check details of L2 orbit **(AI)**
  * Amy told Shaul that we will probably have a steerable antenna for tele-communication; also fly wheels for pointing
  * Kris: demonstration of full scan + systematics + map making is also important
    * Julian: Agree, the machinery exists to do these sims.  They need to be in time domain.  They're computationally cheap.  Need limits on the input parameters and evaluation metrics.
  * Shaul’s comments on this scan parameters study: 1) optimization of parameters; 2) systematics given parameters
  * When mapping + noise correlation? Julian: As soon as we have the tables from Jacques, we will have a range of parameters.