UMN to develop focal plane loading model including load from mirror(s) and cold stop as a function of temperature
JPL to develop scaling of cooling cost depending on what mass we cool to which temperature
Need input on feasibility and cost model of deployable shields
Need input on cooling and trade-off with mass of stop and secondary mirror
Roger to work on ASIC solutions to TDM, FDM
discuss with Matt
do wiring load trade-off between the two options
Telecon Notes
Optics
UMN reviews tradeoff study between open and cross Dragon. For fixed aperture and f# Open Dragone has 3/4 the DLFOV of the crossed system. Largely agrees with the result from the comparison shown a week before when they had different f#.
How large is the stop in the current Open Dragone design?
Not clear. To be checked. Qi checked: It’s ~130 cm.
Loading needs to be calculated
How cold does the stop need to be?
It’s easily calculable; to be done by UMN. this is part of the focal plane model that UMN is developing.
Different temperatures for the stop and optics box (e.g. 4K, 30K) require different cooling technologies, and they could probably lead to different costs. Thermal modeling and testing are needed to estimate the cost
The additional power/cost required to cool the stop and secondary to 4 K may not be significant relative to cooling just the focal plane.
Let's calculate the temperature we need, and in parallel develop a cost model.
Cross Dragone VS Open Dragone
Open Dragone has no significant side lobes
Version with cold stop improves density of detectors on the focal plane
Brad discusses the sidelobe analysis that was done for epic. Analysis was done by Mark Dragovan, but can probably be repeated. For every pixel, rotate the beam with respect to fixed sky coordinates. Assume uniform coverage (within some resolution). Main beam was masked out. Assess the leakage from T to P due to the galaxy. Compare to the target B. Results: just barely good enough for B of 10 years ago.
UMN finds that for both cross and open dragon there is a 7 deg gain in alpha for 20 cm reduction in aperture diameter without deployable shields.
Need input on deployable shields.
What are 'good' scan angles? Kris said with high confidence that he would give a report next week on scanning strategy.
Focal Plane Technology
Roger and Jeff post their answers to the questions Shaul posed on last week on last week’s minutes page.
Q1: what is the plan for detector technology for the high frequency bands of the imager?
monochroic PSBs above 600 GHz because of Nb band gap. Not suitable for Nb-based antenna coupling.
Q2: are the distribution of colors for pixels as described by the worksheet reasonable?
Yes. 2-3 colors per pixel is OK. Perhaps could fit more bands in lower frequency bands.
Q3: are the bandwidths assumed reasonable?
Yes. Currently assuming 25% bandwidth
Q4: what should we assume about beam sizes as a function of frequency, specifically for the high frequency bands? Is it reasonable to assume single mode coupling all the way to the highest frequencies?
Yes. Single mode all the way to 900 GHz. “Technologies are there.”
Roger points out that power consumption is poised to be an issue. He is looking to have a discussion with Matt. Charles (and Shaul) advocate assuming custom-made ASICs for which the power consumption could be significantly lower. How much lower? Need to check
Roger says that with current technologies he projects 400 and 1.1 kW for 10,000 detectors for the TDM, FDM, respectively.
Jamie says that for EPIC-IM a JPL engineer found ways to reduce the power consumption of the TDM by a factor of 3(?) even without ASICs.