Object high in upper atmosphere producing pale green pulsating cloud as it slowly spiraled downward, then disappeared.

Former Navy military adviser,Viet Nam; Army Reserve Helicopter Gunship armament artificer, Electrical project manager / engineer.
In the summer of 1972 I went to LaCoste, Texas, to hunt coyotes with a friend on his grandfather's property.  After several cups of coffee, I went outside to relieve myself, when I noticed a round or oblong object high in the upper atmosphere. What drew my attention to it was the extremely wide vapor trail or cloud that emanated from the object as it slowly spiraled downward in a long, wide, and very slow spiral. 
Aside from appearing unusual, what really fascinated me was that the vapor trail or cloud the object produced, was a pale green color and was pulsating. 
I watched the object for approximately 10-15 minutes, when it finally just stopped.  The cloud continued to pulsate and then slowly faded from pale green to white and looked then like any other cloud in the sky. It was a full moon night and very clear. I watched the cloud then fade to nothing.  I thought it may be a satellite falling to earth after losing it's orbit, but then I feel it would have been traveling at a much greater speed once it entered earth's atmosphere.  This object was moving VERY slowly and the spiral was gradual and very wide.  
I have never shared this with anyone as I was the only one to witness the object and was afraid I'd be ridiculed.
Witness indicates that the date of the incident is approximate.  PD