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
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State-of-Art Radio Telescope
• ALMA
– Atacama Large Millimeter/submillimeter Array
• 50 12-m antennas
• 4 12-m antennas
• 12 7-m antennas
In total 66 antennas.
Last 66th antenna arrived at AOS
on Jun 13, 2014
– Aperture area
• 6600 m2
 91-m diameter
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Compact Array - ACA
• Atacama Compact Array (ACA) – ALMA
– Four 12-m diameter antennas Aperture Area: 452 m2
– Twelve 7-m diameter antennas Aperture Area: 462 m2
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Large Single Dish Telescope
• Cerro Chajnantor Atacama Telescope (CCAT)
– Submillimeter Astronomy
– 25-m diameter antenna
Aperture Area: 491 m2
http://www.ccatobservatory.org/
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7-m Array vs CCAT
7-m Array
CCAT
Diameter
7-m Dish x 12
25-m Dish
Aperture
462 m2
491 m2
Surface Accuracy
20 µm rms (worst)
10 µm rms (spec)
10 µm rms (EL>30 deg)
4 µm rms (best)
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)
24"x (λ/350 µm) at 50 pixels
24 = 3.5 * sqrt(50)
at multi-beam
course,7-m
not applicable!
at camera
6.5’ 128
x 128 pixels
at 350 µm
Quit comparable
specificationsOfbetween
Array and CCAT
at heterodyne
receivers
!
15’ 54 x 54 pixels at 850 µm
See CCAT science requirements
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How do we compare them?
• Field of View
◦
𝜆
𝜃FoV ~ 1.2 ∙ 𝑁𝑏𝑏𝑏𝑏 𝑟𝑟𝑟
𝐷
where
 𝜆 = observing wavelength [m]
 D = antenna diameter [m]
 𝑁𝑏𝑏𝑏𝑏 = number of beams in receiver
– Diameter of antenna for Compact Array
2015/7/29
𝑁𝑏𝑏𝑏𝑏
𝜆
𝜃FoV ~ 1.2
∙
𝐷
𝑁𝑎𝑎𝑎
𝑁𝑎𝑎𝑎
◦ where
 𝑁𝑎𝑎𝑎 = number of antenna for Compact Array
NRO-ALMA Science Develop Workshop
𝑟𝑟𝑟
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How do we compare them?
• Aperture Area
𝐷
𝜋
2
2
𝐷/ 𝑁𝑎𝑎𝑎
= 𝑁𝑎𝑎𝑎 ∙ 𝜋
2
2
◦ where
 D = antenna diameter [m]
 𝑁𝑎𝑎𝑎 = 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 m2
 Then deriving Equivalent diameter of 28 m.
– These parameters will be used to compare between Compact
Array (CA) and Large Single Dish Telescope (SD).
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Configuration - Assumption
Compact Array
Large Single Dish
Diameter (D)
7-m Dish
28-m Dish
Number of antenna (Nant)
16=(DSD/DCA)2
1
Aperture
616 m2
616 m2
Surface Accuracy
10 µm rms (EL>30 deg)
10 µm rms
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)
4 pixels
64 pixels
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)
Num. of multi-beam
at multi-beam
• Note: Angular resolution - Compact array is better than Single Dish.
That difference is 1.8 times.
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Instruments - Requirements
Compact Array
Large Single Dish
Number of Bands (Nband )
Nband
Nband
Number of antenna (Nant)
16
1
Number of Beams (Nbeam)
4
64
Number of IFs (NIF)
64 = Nant*Nbeam
64 = Nant*Nbeam
Auto-correlations (dual pol.)
192 = (2pol+1Xpol)*Nant*Nbeam
192 = 3*Nant*Nbeam
Cross-correlations (dual pol.)
1920= 4*Nant*(Nant-1)/2*Nbeam
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 Nant. 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.
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Summary – Based on Number
Compact Array
Large Single Dish
Antennas
16= Nant
1
Cryogenics system and
First cryo-mixer units
including the device
16= Nant
1
Cryo- & Warm- IF Analog
and IF Digital processors
64 = Nant*Nbeam
64 = Nant*Nbeam
Correlator and or
Spectrometer
2112 = 192 + 1920 =3*Nant*Nbeam+
4*Nant*(Nant-1)/2*Nbeam
192 = 3*Nant*Nbeam
• We will extend these numbers to estimate the
cost of telescope from next slides.
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Costs – CA and SD
Antennas
Compact Array
(CA)
Large Single
Dish (LSD)
16*PCAant
= Nant* PCAant
PSDant
Depending on the
diameter of
antennas!
16*P
vs PSDant
=(D /DCAant
) *P
SD
CA
2
CAant
Cryogenics system and
First cryo-mixer units
including the device
16= Nant
1
May be balanced,
including initial
studies.
Cryo- & Warm- IF
Analog and IF Digital
processors
64 = Nant*Nbeam
64 = Nant*Nbeam
Well balanced.
Correlator and or
Spectrometer
2112 = 192 + 1920
192 =
=3*Nant*Nbeam+
3*Nant*Nbeam
4*Nant*(Nant-1)/2*Nbeam
Correlator cost increases by N2ant =(DSD/DCA)4
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CA needs10 times
more than SD, but
this cost is too much
lower than that of
antenna!
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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
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Antenna – Total Cost
CA (7-m D)
LSD (28-m D) Nant=(DSD/DCA)2
Design cost
Pdgn
Fdgn*Pdgn
Fdgn depends on the
difficulty level.
Material costs
(maybe, ∝ weight)
Pmtrl*Nant
=16*Pmtrl
Pmtrl*(DSD/DCA)3
= 64*Pmtrl
Weight is proportional
to (DSD/DCA)3~4.
Component costs
16*Pcmp
Fcmp*Pcmp
Depend on the number.
Fcmp depends on the
difficulty level.
Pre-assembly cost
Ppre-ass
Ppre-ass*(DSD/DCA)2 Depend on the size.
Enough for one antenna.
= 16*Ppre-ass
Transportation cost
16*Ptrans
~64*Ptrans
Depend on the weight
and size.
AIV cost
PAIV*Nant=16*PAIV
PAIV*(DSD/DCA)2=
16*PAIV
Depend on the size and
number of antenna.
Documentation cost
Pdoc
Pdoc
Same ratio.
Construction cost
1
2~4 (=DSD/DCA)
At 7-m CA vs 28-m SD
Conclusion
• Which is more cost-effective?
– At this moment, Compact Array is more cost-effective,
in case that DSD/DCA is not large.
• 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.
• Issues
– 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.
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