MMA ANTENNA REQUIREMENTS



Summary Description To Allow Antenna Vendors to Provide Budgetary Cost Estimate

P.Napier, 4 February, 1997.

1. WORK PACKAGE DEFINITION

NRAO would appreciate budgetary cost estimates for the two MMA antenna work packages defined below . For the purposes of this estimate assume that the antenna consists of a complete structure including mount, reflector, receiver cabin and quadrupod and a control and drive system. Do not include a subreflector or subreflector movement mechanism, any RF equipment, an antenna foundation or antenna transporter. The antennas will be used for radioastronomical observations using both single dish and interferometer observing techniques.

1.1 Work Package 1- Design and First Item Delivery

The vendor will design and deliver two antennas that meet the performance requirements. The vendor can use a conceptual design prepared by NRAO, which NRAO's analysis shows should meet the requirements, or he can use his own design. In either case the vendor must accept full responsibility for the adequacy of the design and must provide a complete engineering analysis and a complete set of reproducible, as-built, fabrication drawings. Tooling will be suitable for the production run of antennas and will also be a deliverable under the contract. The antennas will be assembled and acceptance tested by the vendor at the Test Array location which will be at an existing radioastronomy observatory in the US.

Approximate schedule: RFP - October 1997

Contract start - January 1998

Deliver Antenna 01 - June 1999

Deliver Antenna 02 - June 2000

Deliver as-built fabrication drawings - June 2000

1.2 Work Package 2 - Fabrication of 38 Antennas

The vendor will fabricate antennas according to the fabrication drawings provided from Work Package 1. Antennas will be fabricated at a rate of about 8 per year. Antennas after the first 8 will be contracted as unilateral options which will be exercised by NRAO on a year-by-year basis. The first production antenna, Antenna 03, will be shipped to the Test Array site and assembled by NRAO. Antennas after Antenna 03 will be partially assembled in the vendor's factory and shipped in a few large pieces to the port of Antofagasta, Chile. For the purposes of this estimate assume that the antenna pieces are sized to fit on a two-wide flat rack and are FOB Antofagasta. NRAO will be responsible for final assembly of the antennas on the MMA site.

Approximate schedule: RFP - December 2000

Contract start - February 2001

Antenna 03 delivery to Test Array site - October 2001

Antenna 04 delivery to Antofagasta - December 2001

Antenna 40 delivery to Antofagasta - June 2006

2. ANTENNA SPECIFICATIONS

The requirements for the MMA antennas are listed below. This is not intended to be a complete antenna specification, but should provide sufficient information to allow preparation of a budgetary cost estimate.

2.1 Environment

The antennas will be located on a volcanic plateau in Northern Chile at an altitude of 5000 m (16400 ft). The air density at this elevation is 56% of its sea-level value. The antennas will not be protected by any type of enclosure but, because the site has exceptionally low precipitation, there are no requirements for unusually heavy snow or ice loading or for reflector surface deicing. A survival wind specification of 65 m/s (130 mph) will be required. The expected temperature range for the site is -30 to +30 C with operation of the antenna being required for temperatures above -20 C.

The precision performance requirements listed in 2.2 below must be met for winds up to 6 m/s (14 mph) and for the full range of thermal environments from nighttime, including any kind of partial solar illumination, to full solar illumination during observations of the Sun. For winds in the range 6 m/s to 20 m/s (45 mph) the antennas will be used with whatever degraded pointing, surface accuracy and phase stability performance is available. The antennas will be stowed in winds above 20 m/s.

2.2 Performance

Diameter: 8 m (26.2 ft)

Focal Ratio: 0.38

Operating Frequency Range: 30 GHz to 850 GHz

Reflector Surface Accuracy: 25 micrometers (0.001 in) rms. Subreflector focusing as a function of elevation angle is allowed.

Sky Coverage: Elevation 0 to 95 deg, Azimuth -270 to +270 deg

Pointing Accuracy: Non-repeatable pointing errors less than 1 arcsec. rms. Astronomical calibration is allowed every 30 minutes of time.

Fast Position Switching: The antenna must move 1.5 deg on the sky and settle, all in 1 second of time. Settling must be sufficient so that the surface accuracy requirement is met and pointing is within 3 arcsec. rms.

Phase Stability: Changes in electrical pathlength as they affect the incoming wavefront must be less than 10 micrometers (0.0004 in) rms. This specification applies to pathlength changes caused by thermal or wind effects and to mechanical changes that are not reproducible functions of azimuth and elevation. Astronomical calibration is allowed every 3 minutes of time.

Transportability: The antennas will be picked up and moved from one foundation to another using a transporter vehicle which runs on rubber tires. The transporter will travel on inclines of up to 15%.

Close Packing: In the most compact array configuration adjacent antennas will be located so that their azimuth axis are separated by only 10.3 m (33.8 ft). With this separation, for antenna elevation angles greater than 20 degrees and for all possible relative orientations between the two antennas, it must be impossible for two antennas to hit each other. The focal ratio of 0.38 has been chosen to make this possible.

Antenna Configuration: Elevation over azimuth mount. Circularly symmetric reflector with minimum blockage quadrupod supported at the edge of the primary aperture. A large receiver cabin at the Cassegrain focus is required, as shown in Figure 1 and Table 1. Note that Figure 1 shows only that part of the antenna which moves in elevation.

2.3 Materials

The following materials are preferred for the various parts of the antenna.

Az/El mount: Steel

Reflector Surface: Machined aluminum panels

Reflector Backup Structure: Provide budgetary estimates for both CFRP and Steel

Receiver Cabin: Steel

Quadrupod: CFRP



MMA Antenna Optics Design

Figure 1:MMA Optical Configuration, Version 1.

  Table 1: Dimensions of MMA Optical Configuration, Version 1.

D Primary Aperture 8,000 mm 315.0 inches
fp Focal length of primary 3,040.38 mm 119.7 inches
fp/D of primary 0.38 0.38
d Secondary aperture 530.86 mm 20.90 inches
Final f/D 8.39 8.39
Magnification factor 22.08 22.08
theta p Primary angle of illumination 133.36 deg 133.36 deg
theta s Secondary angle of illumination 6.83 deg 6.83 deg
2c Distance between primary and secondary foci 4,564.0 mm 179.7 inches
H Depth of primary 1,316.0 mm 51.8 inches
r1 Tipping structure apex radius (1" clearance) [close packing 1.36 D] 5,433.0 mm 213.9 inches
r2 Tipping structure dish radius (1" clearance) [closepacking 1.28 D] 5,114.0 mm 201.3 inches
h Distance from vertex to secondary focus 1,524.0 mm 60.00 inches
a Distance from elevation axis to focus 304.8 mm 12.00 inches
b Distance from elevation axis to base of center cone 152.4 mm 6.00 inches
g Distance from primary focus to top of quadrapod 533.4 mm 21.0 inches
x Clear aperture at receiver cabin window 480.06 mm 18.9 inches
Center cone base inside diameter 2,844.80 mm 112 inches
u Center cone height 1,506.22 mm 59.3 inches
v Center cone and primary surface inside diameter 530.86 mm 20.90 inches
j Receiver cabin inside width and depth (square) 2,794.0 mm 110 inches
k Receiver cabin inside height 2,006.60 mm 79.0 inches
m Receiver cabin door width 1,016.0 mm 40.0 inches
n Receiver cabin door height 1,676.4 mm 66.0 inches
R Receiver cabin door fillet 101.6 mm 4.0 inches
w Distance from primary focus to edge of secondary mirror 114.414 mm 4.5045 inches
y Distance from primary focus to front face of secondary mirror 197.772 mm 7.7863 inches

Table 1: Dimensions of MMA Optical Configuration, Version 1.

Last modified 7 Feb 97

mma@nrao.edu