GBT and 85-3 Weather Restrictions

Warning

High winds take priority over snow /ice conditions. Also, consider winds when operating with any Az/El motors inoperative. Please ensure personal safety through prompt notifications and aggressive monitoring of hazardous weather. Use caution and reduced speeds when tipping the antenna to snow dump position after any snow accumulation. 

Remember to consider 85-3 and stow it when prescribed below. High winds take priority. 

GBT  

Winds (During Routine Observing or Tests - All Az/El Motors Operative)

STEP

 ACTION
1 Winds > 20 MPH continuously for 5 seconds (any sensor) or any gust > 25 MPH:
  • Stop antenna and move in elevation to survival stow position (EL= 60.105 AZ= Based on wind direction).
  • Insert stow pin.
  • Move in azimuth to a position where the antenna is pointed away from the wind (winds > 40 MPH expected) or the closest parking position shown below (for winds expected to remain < 40 MPH).
  • Monitor winds. Resume operations when/if winds remain below the thresholds above for 30 minutes.
Antenna Facing Guide
Desired Pointing Direction

Azimuth Position to Use

N 359.15
NE 44.15
E 89.15
SE 119.15
S 179.15
SW 224.15
W 269.15
NM 314.15

 

Winds (During Outfitting/Maintenance)

STEP

 ACTION
1 Winds 20-25 MPH:
  • Cease any crane/hoist operations.
  • Continue to monitor winds and resume normal operations when possible.
2 Winds sustained at 25 MPH: 
  • Notify personnel working in open areas to leave the structure. Work in non-open areas may continue.
  • No Elevator use.
  • Advise personnel of potential for evacuation.
  • Continue to monitor winds and resume normal operations when possible.
3 Winds sustained at 30 MPH:
  • Notify all personnel to evacuate the antenna.
  • Move telescope in elevation to survival stow position (EL= 60.105).
  • Move in azimuth to a position where the antenna is pointed away from the wind (see antenna facing guide). 
  • Continue to monitor winds and resume normal operations when possible.

Wind Speed-Az/El Motor Decision Logic Table (Use if any Az/El motors are inoperative)

# El Motors Operating 8 6 4 2
# Az Motors Operating  
16 30MPH 30MPH STOW STOW
14 30MPH 30MPH STOW STOW
12 30MPH 30MPH STOW STOW
10 30MPH 30MPH STOW STOW
8 STOW STOW STOW STOW
6 STOW STOW STOW STOW
4 STOW STOW STOW STOW
2 STOW STOW STOW STOW

 

 

Electrical Storms

STEP

 ACTION
1 Notify all personnel to evacuate the structure. Continue to monitor conditions.
2 Advise personnel when access to the structure may resume. 
3 Notify GBT Supervisor if damage has occurred. Troubleshoot and notify additional personnel as needed. 

Snow and Ice

STEP

 ACTION
1 Monitor observed and forecast conditions. 
2 Restrict personal access if structure walkways/surfaces become slippery.   
3 Terminate observing/maintenance operations and move the telescope to the snow dump position (5.131 Deg. elevation) if surface accumulation is likely or forecast. Tip at a slow rate if accumulation has already occurred. Rotate the dish to face away from wind to reduce blown on accumulation.
4 Continue to monitor weather conditions and resume normal operations when possible.

85-3

Winds (> 30 MPH continuously for 5 seconds (any sensor) or any gust > 35 MPH)

STEP

 ACTION
1 Stop antenna and move to stow position.
  • Log into the 85-3 workstation (gbiops / flies-2)
  • In the T85_3 window set the Control Mode to Man unless already there
  • Using the menu selection bar above the red HALT button, select the STOW option (moves antenna to stow) 
  • Once the antenna is at stow (HA = 00:00:00 / Dec = +38:26:06) the brakes will automatically set
  • Re-lock the workstation screen
2 Enter comments in OpsLog and the 85-3 paper log noting the stow action.
3 Monitor winds. Resume operations when/if winds remain below the thresholds above for 30 minutes.

 

 

Snow and Ice

STEP

 ACTION
1 Move the antenna to snow position 1 or 2 depending on wind direction:
  • Snow 1: Winds blowing from NE - SW (45-225 degrees) (Faces dish towards SE)
  • Snow 2: Winds blowing from NW - SE (315-135 degrees) (Faces dish towards SW)
2 To move the antenna to Snow 1 or 2:
  • Log into the 85-3 workstation (gbiops / flies-2)
  • In the T85_3 window set the Control Mode to Man unless already there
  • Using the menu selection bar above the red HALT button, select either:

    SNOW 1 (HA = -05:36:00 / Dec = +2:00:00)

    SNOW 2 (HA = +05:36:00 / Dec = +2:00:00)

  • Once the antenna is in position the brakes will automatically set
  • Re-lock the workstation screen
3 Enter comments in OpsLog and the 85-3 paper log noting the stow action.
4 Continue to monitor weather conditions and resume normal operations when possible.

Prepared by: Dave Rose

Last modified: 8Nov02