Chicago-2016: Red Team
From CMB-S4 wiki
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?