1. Common Small Pedestal Motor and Bearing Requirements. Introduction
Common Small Pedestal Motor and Bearing Requirements Introduction System Operation Mass Balance Inertias Friction Environmental Requirements

2. Introduction
New Antenna Pedestal to support Antenna Reflector sizes up to 1.2m diameter.
An Preliminary design has been produced and is currently being refined.
Mass and Inertia analysis is currently in work.

3. Common Small Pedestal Preliminary Design

4. System Operation Antenna control loop model
For the Common Small Pedestal, requirements defining products are: -
1.2m, Ka: Rx 20.6GHz, Conscan radius: 

5. Mass Balance
The mass of the antenna will be balanced about all three axes of motion. The cant angle of the cross level axis will be 30° from horizontal. Estimated Masses are:
Azimuth Mass: 200 Kg (400mm above Brg CL)
Cross Level Mass: 100 Kg (200mm Fwd of Front Brg)
Elevation Mass: 80 Kg (Midway between El Brg CLs)

6. System Inertias (Estimated)
Elevation: 4.5kgm2
Cross-level: 5.7kgm2
Training: kgm2

7. System Friction (Existing Antenna)
To achieve system operation (worst case), the maximum allowable friction torque at each axis is: -
Elevation : Nm
Cross-level: Nm
Training: 12.0 Nm
Values include contribution from all sources,
i.e. all bearings, rotary joints, slip-rings etc., and including cable harness effects (it’s important that harnesses are free to move and tied loosely so as to minimise the torque imparted).

8. System Friction (Existing Antenna)
Azimuth static friction torque, summary:
Bearing 5.0 Nm max
Motor 2.2 Nm max
Rojo 0.5 Nm max
Slip-ring 1.0 Nm max
Resolver (0.35Nm X 528/22) = Nm
Total 8.71Nm
Margin 12.0 – 8.71 = 3.29 Nm (27%)
Since a slip-ring is used on the Az axis there are no friction contributions from cable harnesses.

9. System Friction (Existing Antenna)
Cross-Level static friction torque, summary:
XL Bearings 3.2 Nm
Motor Nm max
Rojo 0.5 Nm max
Resolver (0.35Nm X 99/22) = Nm
Total Nm
Margin 4.6 – 4.07 = 0.53 Nm (Not enough)
Since cable harnesses run across this gimbal they shall be positioned and tied to ensure they do not increase the torque requirement

10. Environmental Requirements
Platform Tilt
The Pedestal shall be capable of full operation as specified herein under the following conditions of ship's attitude:
Peak pitch angle:  10 degrees
Peak roll angle:  42 degrees
Maximum deck tilt will not exceed:  42 degrees.
The Antenna is to be capable of full hemispherical coverage of satellites between 0 and 90 degrees elevation with a deck tilt up to  35 degrees. Under conditions of  42 degree deck tilt hemispherical coverage may be limited to satellite elevations between 7 and 83 degrees.

11. Environmental Requirements
Ship Motion Forces
The Pedestal shall be designed for continuous operation with the following maximum static load cases.
Vertical Acceleration: 2.5g
Tranverse Acceleration: 2.5g

12. Environmental Requirements
Tracking Requirements
The Pedestal shall be capable of meeting the tracking requirements herein under the following conditions which are equivalent to MIL-STD-1399 Sea State 8 for vessels having beams less than 50 feet and lengths not less than 150 feet.
Roll:42 degrees amplitude, 10 second period
Pitch:10 degrees amplitude, 4 second period
Yaw:2.5 degrees amplitude, 4 second period
Pitch acceleration shall be taken as 1.5 times the sinusoidal equivalent.

13. Environmental Requirements
Shock – equivalent to MIL-STD-901D
The Pedestal shall be designed to withstand without degradation of performance a test equivalent to MIL-STD-901D.
The shock input is at the Pedestal Base/Ship interface.
The Pedestal is classified as Grade A, Type A, Class 1.
The Pedestal shall operate during the test and shall not sustain damage to the extent that operation within performance limits is prevented.
The shock test pulse is applied separately in 3 orientations.
In a vertical direction.
30 degrees to the vertical, when the equipment is rotated about it’s azimuth to two positions 90 degrees apart.

14. Environmental Requirements
Shock – equivalent to MIL-STD-901D Continued
The shock pulse levels below have been derived from the MIL-STD-901D ‘medium weight’ test carried out on a Pedestal in 1994, reference report as below.
For stress analysis of the Pedestal, the shock levels and durations will be as specified in below.
Acceleration of 120g, 1 cycle, 4ms duration, 250Hz sine wave.
Superimposed on a pulse of 37g Peak (30g Dynamic), 1 cycle, 40ms duration, 25Hz sine wave.

15. Environmental Requirements
Shock - MIL-STD-901D Continued
For the Elevation Gimbal mounted components the input shock levels will apply in all directions.
Because of assumed amplification of the shock pulse by the structure, the 37g pulse is multiplied by a factor of 2. This gives:
73g Peak (60g Dynamic) in X, Y and Z directions

16. Environmental Requirements
Vibration
The Pedestal shall operate within performance limits listed below, and shall not sustain damage to the extent that full operation is prevented, during and following a one off vibration test.
The test, derived from MIL-STD-167/1 (SHIPS), AD(15), comprises 3 sections as listed below.
This requirement shall be met in each of 3 orthogonal directions, vertical, athwartship (side-to-side), and fore/aft axes of the Pedestal in it’s fitted orientation.

17. Environmental Requirements
Vibration continued
Exploratory
Vibration frequency sweep from 4 – 33Hz at table single amplitude 0.25  0.05 mm (0.01  in), equivalent to 0.5  0.01 mm (0.02  in) peak to peak.
Change in frequency is made in 1 Hz discrete steps and each step is held for 15 seconds.

18. Environmental Requirements
Vibration continued
Variable Frequency
Vibration test from 4 – 33 Hz, at amplitudes defined below.
Change in frequency is made in 1 Hz discrete steps and each step is held for 5 minutes.

19. Environmental Requirements
Vibration continued
Endurance
The Pedestal shall be able to operate for periods up to 2 hours duration when subjected to an input amplitude of inches ±0.002 inches at a frequency of 33 Hz or, if one exists, at an equipment resonant frequency below 33 Hz with an input amplitude as specified in the Table above.

20. Environmental Requirements
Temperature
Combinations of materials, finishes and processes must be carefully chosen to withstand the following survival and operating temperature ranges, as defined in MIL-STD-810F, Methods 501.4, &
Equipment shall be capable of meeting all performance requirements during operation over the following temperature range:-
Operating: to +70C
Non-operating: to +70C
The antenna pedestal may also be required to operate down to -30C, with a degradation of performance agreed by the project.

21. Environmental Requirements
Salt Atmosphere
The Pedestal will be sheltered during operation, but during maintenance, it may be exposed to a salt atmosphere. Therefore equipment performance shall not be affected by a salt-laden atmosphere as defined in MIL-STD 810F, Method for a test duration of 24 hrs exposure followed by 24 hrs drying, repeated for a minimum of four 24-hour periods (two wet and two dry).

22. Environmental Requirements
Acidic Atmosphere
Combinations of materials, finishes and processes must be carefully chosen to reduce the possibility of corrosion when equipment is stored or operated in areas where an acidic atmosphere exist, such as industrial areas or near the exhausts of any fuel-burning device (e.g. ships’ funnel).
The Pedestal will be sheltered during operation, but during maintenance, it may be exposed to an acidic atmosphere. Therefore the equipment performance shall not be affected by occasional exposure to an acidic atmosphere, as defined in MIL-STD 810F, Method 518, for a test duration of three 2-hour spraying periods with 22 hours storage after each.

23. Environmental Requirements
Mould Growth
Combinations of materials, finishes and processes must be carefully chosen to reduce the possibility of mould growth.
The Pedestal will be sheltered during operation, but during maintenance, it may be exposed to the atmosphere. Therefore equipment shall be devoid of microbial growth, as defined in MIL-STD 810F, Method