Chicago-2016: Red Team

From CMB-S4 wiki
Jump to navigationJump to search

RED TEAM: Homogeneous array of medium (~5m) monolithic dishes

Powerpoint Notes: File:S4 Telescope Array Red Team Notes 2016-09-20.pdf


Discuss pros, cons, and outstanding questions for a homogeneous array of medium aperture (~5 m) monolithic primary telescopes


  • Can dedicate all resources to one instrument design
    • Same analysis pipeline
    • Only need to solve systematics mitigation for one type of telescope
    • Apply debugging/improvements learned from one telescope to all telescopes.
  • Fabrication costs – economy of scale
  • Big advantages to interchangeable parts
    • Operation costs cheaper
    • Same parts/operations software
  • Flexible instrument
    • Robust to telescope down time for servicing.
    • Can change survey strategy mid-course based on detection or changing science goals
  • Could be monolithic mirrors
  • Could be a more exotic costly design


  • Telescopes expensive compared to small aperture telescopes
  • Expensive/difficult to implement forebaffles and boresight rotation.
  • Homogeneous array does not have built in systematics check of comparing data between different telescope types.
  • Not as capable as 10-m class telescopes for addressing high-ell science.
  • Low-ell performance not proven/known
    • May be harder to convince a review committee that design is conservative enough since not proven on-sky like current small/large telescopes.


  • What is relative power consumption of few 5-m telesopes vs many small telescopes?
  • How expensive will implementing forebaffles be?
  • Noted that we could build and test one before building N.
  • Can 5-m telescope achieve low enough ell sensitivity? Need to convince ourselves this is achievable.
    • Can we scan fast enough?
    • Do we need HWP? Where in system?
  • What are pros/cons of having ~5 Niemack telescopes vs N times more lower-throughput telescopes?
  • What costing model should we use to optimize design vs fab vs operations vs risks?
  • Homogeneous array will have variable angular resolution vs frequency.
    • 1.6’ res at 150 GHz
    • 8’ res at 30 GHz
  • How important is it to have a monolithic mirror?
    • Can we fabricate a 5 m monolithic mirror?
    • Can we transport a 5 m monolithic mirror to the South Pole? (Will not fit on a C-130.)
    • Curvature of xD is small, will affect segmented mirror diffraction pattern – may be better.
    • Forebaffle would eliminate far sidelobes of a segmented mirror.
  • Would homogeneous array be more flexible for altering scan strategy for changing science goals?
    • How well do we understand the relative depths we need vs ell before deciding on mix of small/large apertures for heterogeneous array?
  • Will it be harder to have confidence that systematics will be low enough?
    • Forebaffles implemented on small telescopes but not yet on large telescope
  • Can we achieve necessary fast time constants to enable fast scanning/pol modulation?
  • Will one design be able to serve both a moderate latitude site (Chile) and a polar site (South Pole)?
    • Cross-linking/pol mod is different
    • Weatherization needs are different
  • Could we use one receiver or optics tube design to serve both the 5-m telescope and a small ~0.5-m telescope?
  • For the 5-m telescope – what are pros/cons of one large receiver/cryostat vs many small receivers/optics tubes?
    • Smaller receivers or modular optics tubes would have lower focal plane filling factor but are potentially more serviceable.
  • Sociologically, can the community get behind one design?