ACA Spec and Reqs differences from ALMA Antenna Spec & Reqs Section 4.3.2 The antenna shall be a symmetrical paraboloidal reflector of 7m diameter with a Cassegrain geometry F/D = 0.37 For the smaller antenna, the receiver package has stayed the same. The center of gravity in the smaller antenna, to fit the rx package, must be raised, moving the rx closer to the subreflector. But the collision zone size, and the mechanism for tilting the subreflector's size, require it not to move outward in a commensurate fashion. The solution has been that the F/D ratio must be slightly decreased. A science penalty has not been identified. Section 5.2.1 Velocity and Acceleration: ALMA Melco 12m Melco 7m Az > 18 deg/s2 Az > 10 deg/s2 Az > 9 deg/s2 El > 9 deg/s2 El > 9 deg/s2 El > 4.5 deg/s2 Needs discussion. ACA will not fast switch. In the AWS mode, the 7m antennas will always be last ones to get to the source, decreasing observing efficiency. However AWS is not yet approved. Scientific cost as of this moment is minimal or non-existent but because of this relaxation of spec there will be a science penalty when AWS is approved. Section 5.4.1 Fast switching phase calibration ALMA Melco 12m Melco 7m Steps 1.5 deg on sky Steps 1.5 deg on sky Steps 1.5 deg on sky settle to within 3" settle to within 3" settle to within 3" peak pnting error peak pnting error peak pnting error all in 1.5s of time. all in 1.8s of time. all in 1.9s of time. 7m antennas do not fast switch, so no science penalty has been identified. 5.4.2 On the Fly TP Mapping ALMA Melco 12m Melco 7m settle within 0.8" settle within 0.8" settle within 1.0" 7m antennas do not contribute to OTF TP mapping; settling seems OK. No science impact identified. 5.4.4 Step response ALMA Melco 12m Melco 7m 3" within 1.5s and 3" within 1.8s and 3" within 1.9s and 0.6" within 2.0s (total) 0.6" within 2.3s (total) 0.6" within 2.4s (total) No science impact identified. Spectral line OTF impact? 5.5 Antenna surface accuracy ALMA Melco 12m Melco 7m <25 microns <25 microns <20 microns Good science impact. 5.5 Antenna surface accuracy ALMA Melco 12m Melco 7m Error budget allocates Error budget allocates Error budget allocates 10 microns rms for holo 10 microns rms for holo 8 microns rms for holo accuracy accuracy accuracy To enable above. 5.8 Low Noise ALMA Melco 12m Melco 7m Total unweighted Total unweighted Total unweighted geometrical blockage geometrical blockage geometrical blockage less than three per cent less than three per cent less than three per cent (<3%) (<3%) (<5%) Three is not five. Five is the correct number. 6.3.4 Thermal requirements ALMA Melco 12m Melco 7m It shall be possible Same, except secondary Same as Melco 12m locally at the antenna restrictions limited to and remotely via the ACU T<20 C to set the temp inside the cabin inside the range of 16-22 C during any of the primary and secondary operating conditions. Needs FE group discussion I think. No science impact identified. One more on OPT. No science impact identified.