NATIONAL RADIO ASTRONOMY OBSERVATORY
Charlottesville, Virginia

August 30, 1989

MEMORANDUM:

TO:	Active Surface Group

FROM:     J. Payne

SUBJECT:  Actuators



We now have a starting point for the surface controlling actuators.
The surface will be arranged in rafts of panels; the largest raft
contains 12 panels, the smallest 4 panels.  When wind loading (60 mph)
is considered, each actuator should meet the following rough
specifications.  These can be refined as we go along.

		Number of actuators          1,152

		Range of movement            ± 1 cm

		Force required               2,000 lbs.

		Time for full travel         10 seconds

I've attached a data sheet from a suitable manufacturer.  The
estimated price for 1,000 actuators would be about $1,000 each.

My feelings are that each actuator should form part of a closed-loop
servo system consisting of a position transducer, an amplifier, and
the actuator.  Position input commands could be analog or, more
likely, digital with each actuator having a unique address.  The
commands could then be distributed on a fiber optic network (or maybe
even over the power lines to the actuators).  The actuator/readout
package should have built-in travel limits.

So that we don't duplicate efforts, please note that I have written to
the manufacturers on the attached list.

Would everyone please think about the actuator problem so that we can
discuss it at our next meeting (Thursday, September 7, 10:00 a.m.).





Distribution: 	F. Crews
		L. King
		R. Lacasse
		R. Maddalena

cc:  M. Balister
     D. Schiebel
     A. R. Thompson
     G. Seielstad