Compact Array vs Large Single Dish Telescope - which is more cost-effective -

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1 Compact Array vs Large Single Dish Telescope - which is more cost-effective - Satoru Iguchi National Astronomical Observatory of Japan SOKENDAI [The Graduate University for Advanced Studies] 2015/7/29 NRO-ALMA Science Develop Workshop 1

2 State-of-Art Radio Telescope ALMA Atacama Large Millimeter/submillimeter Array m antennas 4 12-m antennas 12 7-m antennas In total 66 antennas. Aperture area 6600 m 2 91-m diameter Last 66th antenna arrived at AOS on Jun 13, /7/29 NRO-ALMA Science Develop Workshop 2

3 Compact Array - ACA Atacama Compact Array (ACA) ALMA Four 12-m diameter antennas Twelve 7-m diameter antennas Aperture Area: 452 m 2 Aperture Area: 462 m /7/29 NRO-ALMA Science Develop Workshop 3

4 Large Single Dish Telescope Cerro Chajnantor Atacama Telescope (CCAT) Submillimeter Astronomy 25-m diameter antenna Aperture Area: 491 m /7/29 NRO-ALMA Science Develop Workshop 4

5 7-m Array vs CCAT 7-m Array CCAT Diameter 7-m Dish x m Dish Aperture 462 m m 2 Surface Accuracy 20 µm rms (worst) 10 µm rms (EL>30 deg) 4 µm rms (best) 10 µm rms (spec) Offset Pointing Accuracy 0.6 rms 0.35" x (λ/350 µm) rms Angular Resolution 1.7"x (λ/350 µm) 3.5"x (λ/350 µm) Field of View for one-beam 12"x (λ/350 µm) 3.5"x (λ/350 µm) at multi-beam 24"x (λ/350 µm) at 50 pixels 24 = 3.5 * sqrt(50) Quit comparable at camera specifications Of between course, 7-m not applicable! Array and CCAT at heterodyne x 128 pixels receivers at 350 µm! x 54 pixels at 850 µm See CCAT science requirements 2015/7/29 NRO-ALMA Science Develop Workshop 5

6 How do we compare them? Field of View θ FoV ~ 1.2 λ D where λ = observing wavelength [m] D = antenna diameter [m] N bbbb = number of beams in receiver N bbbb rrr Diameter of antenna for Compact Array θ FoV ~ 1.2 λ D N aaa N bbbb N aaa where N aaa = number of antenna for Compact Array rrr 2015/7/29 NRO-ALMA Science Develop Workshop 6

7 How do we compare them? Aperture Area π D 2 2 = N aaa π D/ N aaa 2 where D = antenna diameter [m] N aaa = number of antenna for Compact Array Assumption Sixteen 7-m antennas (sixteen is maximum number of antennas stations in ACA) Estimating the Aperture area of 616 m 2 Then deriving Equivalent diameter of 28 m. These parameters will be used to compare between Compact Array (CA) and Large Single Dish Telescope (SD) /7/29 NRO-ALMA Science Develop Workshop 7

8 Configuration - Assumption Compact Array Diameter (D) 7-m Dish 28-m Dish Number of antenna (N ant ) 16=(D SD /D CA ) 2 1 Aperture 616 m m 2 Surface Accuracy 10 µm rms (EL>30 deg) 10 µm rms Large Single Dish Offset Pointing Accuracy 0.35" (improved as needed) 0.35" x (λ/350 µm) rms Angular Resolution 1.7"x (λ/350 µm) 3.1"x (λ/350 µm) Field of View for one-beam 12.4"x (λ/350 µm) 3.1"x (λ/350 µm) Num. of multi-beam 4 pixels 64 pixels at multi-beam 24.8"x (λ/350 µm) 24.8 = 12.4 * sqrt(4) 24.8"x (λ/350 µm) at 64 pixels 24.8 = 3.1 * sqrt(64) Note: Angular resolution - Compact array is better than Single Dish. That difference is 1.8 times. 2015/7/29 NRO-ALMA Science Develop Workshop 8

9 Instruments - Requirements Compact Array Large Single Dish Number of Bands (N band ) N band N band Number of antenna (N ant ) 16 1 Number of Beams (N beam ) 4 64 Number of IFs (N IF ) 64 = N ant *N beam 64 = N ant *N beam Auto-correlations (dual pol.) 192 = (2pol+1Xpol)*N ant *N beam 192 = 3*N ant *N beam Cross-correlations (dual pol.) 1920= 4*N ant *(N ant -1)/2*N beam Not applicable. Cryo- and Warm- IF Analog and IF Digital processors: required number is the same. Cryogenics system and First cryo-mixer units including the device: number may depend on the N ant. In that case, SD has an advantage in number but may have a challenging in technology to meet the multi-beams. Correlator: CA must have much more materials as compared with SD. 2015/7/29 NRO-ALMA Science Develop Workshop 9

10 Summary Based on Number Compact Array Antennas 16= N ant 1 Cryogenics system and First cryo-mixer units including the device Cryo- & Warm- IF Analog and IF Digital processors Correlator and or Spectrometer 16= N ant 1 Large Single Dish 64 = N ant *N beam 64 = N ant *N beam 2112 = =3*N ant *N beam + 4*N ant *(N ant -1)/2*N beam 192 = 3*N ant *N beam We will extend these numbers to estimate the cost of telescope from next slides. 2015/7/29 NRO-ALMA Science Develop Workshop 10

11 Costs CA and SD Antennas Cryogenics system and First cryo-mixer units including the device Cryo- & Warm- IF Analog and IF Digital processors Correlator and or Spectrometer Compact Array (CA) 16*P CAant = N ant * P CAant =(D SD /D CA ) 2 *P CAant Large Single Dish (LSD) P SDant 16*P CAant vs P SDant Depending on the diameter of antennas! 16= N ant 1 May be balanced, including initial studies. 64 = N ant *N beam 64 = N ant *N beam Well balanced = =3*N ant *N beam + 4*N ant *(N ant -1)/2*N beam 192 = 3*N ant *N beam Correlator cost increases by N 2 ant =(D SD /D CA ) 4 CA needs10 times more than SD, but this cost is too much lower than that of antenna! 2015/7/29 NRO-ALMA Science Develop Workshop 11

12 Antenna - Cost How do we estimate the cost of antennas? Design cost Material costs (may be proportional to Weight) Pre-assembly cost, including the rental cost of area for the temporary assembly before shipping. Transportation cost Assembly, Integration and Verification (AIV) cost Documentation cost 2015/7/29 NRO-ALMA Science Develop Workshop 12

13 Antenna Total Cost CA (7-m D) LSD (28-m D) N ant =(D SD /D CA ) 2 Design cost P dgn F dgn *P dgn F dgn depends on the difficulty level. Material costs P mtrl *N ant P mtrl *(D SD /D CA ) 3 Weight is proportional (maybe, weight) =16*P mtrl = 64*P mtrl to (D SD /D CA ) 3~4. Component costs 16*P cmp F cmp *P cmp Depend on the number. F cmp depends on the difficulty level. Pre-assembly cost P pre-ass P pre-ass *(D SD /D CA ) 2 Depend on the size. = 16*P pre-ass Enough for one antenna. Transportation cost 16*P trans ~64*P trans Depend on the weight and size. AIV cost P AIV *N ant =16*P AIV P AIV *(D SD /D CA ) 2 = Depend on the size and 16*P AIV number of antenna. Documentation cost P doc P doc Same ratio. Construction cost 1 2~4 (=D SD /D CA ) At 7-m CA vs 28-m SD

14 Conclusion Which is more cost-effective? At this moment, Compact Array is more cost-effective, in case that D SD /D CA is not large. Issues In science use cases with heterodyne receivers, the large single-dish telescope has no big advantage as anticipated. However, camera science capabilities in the large single-dish telescope will be very unique in the ALMA era. How do we realize the large single-dish telescopes with low cost and good ideas or new technology? I hope that we will have good discussion tomorrow. 2015/7/29 NRO-ALMA Science Develop Workshop 14

ALMA Overview. Leonardo Testi (European Southern Observatory)

ALMA Overview. Leonardo Testi (European Southern Observatory) ALMA Overview Leonardo Testi (European Southern Observatory) The ALMA Project Status Timeline towards Early and Full Science Operations Future Developments Atacama Large Millimeter Array At least 50x12m