Plastic models of polystyrene beads are produced to within 0.02 cm accuracy, in various diameters designed to meet exact requirements of particular radar system frequency spectrum. They are inexpensive and do not require special handling imposed on metal spheres

Holdren, R. H.

English

NASA Technical Reports Server

June 1971	 Brief 71-10190 
NASA TECH BRIEF 
Wallops Station, 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield; Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Inexpensive, Large-Diameter, Radar Tracking and Calibration Spheres 
Firm, lightweight, large diameter, conductive-
coated plastic spheres can be used to replace expen-
sive, small diameter, metal spheres as radar tracking 
and calibration targets. The plastic models can be 
produced to within 0.02 cm (0.01 in.) accuracy, 
in various diameters designed to meet the exact 
requirements of the particular radar system fre-
quency spectrum. They are inexpensive and do 
not require the special handling imposed on metal 
spheres, especially with regard to FAA flight re-
strictions. 
Various plastics were evaluated, and expandable 
polystyrene beads were chosen as the most appro-
priate for this application. The beads are preheated 
to ten times their original size and allowed to cool. 
Final expansion occurs when the beads are placed 
in a special hemispheric mold where they are sub-
jected to high steam temperature and pressure. 
Two hemispheres, each designed with interlocking lips, 
are fastened together with an epoxy cement. The re-
sult is a rigid sphere of exact diameter, with a 1.11 
cm (7/16 in.) thick wall. Special coatings are used to 
seal and cover the sphere, giving it the desirable 
conductivity and reflectivity of a consistent cross-
section calibration target. 
Experiments have proven the feasibility of 
using a silver-conductive coating which would meet 
the requirement that a sound, uniform reflective 
surface have no more than a 5 Q resistance across 
the sphere. 
The sphere is assembled for launch by inserting 
an aluminum rod through its center and attaching
the looped end of the rod to a gas-filled balloon, 
using a nylon cord. Assembled, a plastic sphere 
weighs approximately 0.45 kg (1 lb) and costs 
only $10.00 to produce. The only known spheres of 
equal diameter, 56.4 cm (22.21 in.), are made from 
aluminum, weigh 6.4 kg (14 lbs), and are more than 
30 times as expensive. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Wallops Station 
Code AMD-SP 
Wallops Island, Virginia 23337 
Reference: TSP71-10190 
Patent status: 
This invention is owned by NASA and a patent 
application has been filed. Royalty-free nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should 
be made to: 
Patent Counsel 
Mail Code 173 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365 
Source: Robert H. Holdren

Wallops Station

(X LA- 1 1154) 
Category 01,08 
This documefc't was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately ownedrights.
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Inexpensive, large-diameter, radar tracking and calibration spheres

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