Mount / Platform

Introduct

The Array for Microwave Background Anisotropy (AMiBA) is a radio interferometric array of 19 small receiver+dish elements. These elements are mounted on a platform which is controlled and pointed by the AMiBA mount. There will be two sizes of dishes: 1.2m diameter and 0.31 m diameter. The platform will be roughly 6-8 m in maximum size.

Design Progress

We have considered both a single platform array and multiple, platforms for the AMiBA instrument. The multiple platforms would allow higher resolution observations which are useful for some AMiBA science follow up investigations. However, the cost and complexity of such an instrument has led us to stay with the single platform array. A platform of 6-10 m in diameter will serve the primary science goals of the AMiBA project .We are currently doing a detailed cost comparison and preliminary design analysis for the mount and platform. This analysis will set the final platform size and the mount configuration. Both a hexapod mount and a more traditional mount are being considered. Current analysis indicated that the hexapod mount is a favorable choice for the AMiBA project. This evaluation will be completed in May 2001. Construction of a mount will begin soon after that. We expect the mount and platform to be complete by June 2002.

fig.1: Possible Mount Styles

Platform Concept Layout

AMiBA Platform Specifications

Platform type -Single cfrp structure -Constructed in 7 pieces of 3   different unique types bolted together at the site
- Must be broken apart in parts fitting in standard -Optical telescope attached to one of the open platform   cell
- Dishes are not attached to platform but directly to   receivers
- Space must be provided for standard 19¡¨ racks for   electronics
Mechanical resonant frequencies >10 Hz
Dimensions Diameter 6 m
Weight 500 kg
Load 3,200 kg
Interface with receivers -Receivers will be bolted at the top of the platform
-Receivers extend into platform cell
-Cabling is through the back of the platform
Diameter of the 6 screw holes for receiver interface 350 mm
Location of receiver mounting positions <0.5 mm
Stability in z (over time scales of months) 30 µm r.m.s.
Repeatability of mounting positions for 1.2 m dishes at 1 mm wavelength 20 arcsec
Receivers spacing 0.35 m
Receiver connection in length 0.5 mm
Interface with mount Attached to the 3 upper universal joints of hexapod mount with invar steel pads to minimize thermal deformations
Operating Conditions Wind <10 m/s
Altitude 3,300 m
Temperature -10 to +300C
Humidity 40 %
Survival Conditions Wind (mount in stow position) 65 m/s
Earthquake (vertical and horizontal acceleration) in any position 0.3g
Temperature (mount in stow position) -300C

fig.2: Platform Concept Layout

Mount Specifications

AMiBA Mount Specifications

Mount type Hexapod, 6 actuators, 6 degrees of freedom Rear access to platform necessary Must be broken apart in parts fitting in container for shipping
Dimensions Diameter at base 3.7 m
Diameter at upper joints 3.1 m
Height in neutral position (base to upper joints) 7.02 m
Operating Conditions Wind <10 m/s
Altitude 3,300 m
Temperature -10 to +300C
Humidity 40 %
Survival Conditions Wind (stow position) 65 m/s
  Earthquake (vertical and horizontal acceleration) with mount in any position 0.3g
  Temperature (stow position) -30°C
Pointing Performance 3 mm wavelength operation 12 arcsec r.m.s
  Upgrade at 1 mm operation 4 arcsec r.m.s.
Pointing monitor optical telescope
Travel Ranges Azimuth >3600 without interruption
  Elevation 30 to 150° without interruption (reduced performance: 20~30°)
  Polarization +/- 30°
Drive Velocity Slew 40 deg/m
  Track 0.00417 to 0.01667 deg/sec
Power 208/120 V 3 phase 60 Hz
Environmental Protection EMI/RFI protection Lightning protection and grounding incorporated
Safety Codes US National Electrical Code US OSHA (Occupational Safety and Health Administration) US National Fire Protection Association Underwriter Laboratory Requirements 1950

fig.3: Existing Hexapod Optical Telescope by Vertex Antennentechnik, GmbH