Strange UFO similar to Sputnik satellite seen in Alfena Portugal 1990

CITY:
REGION:
COUNTRY:
DATE:

Alfena
Valongo
PRT
September 10, 1990

UFO Sightings report: The UFO was sighted by about 50 people over 50 minutes, during which the object will have traveled 500 meters, David Silva came to see a ring with a sort of Windows, there were those who saw shadows.
The NASA consultant. Richard Haines, was one of the foreign experts that analyzed photos of the UFO. Until today, no one knows what flew over Alfena.
Can sighting be explained as any conventional man-made or natural object?
 

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