In this video at the 2:40 minute mark there is a relatively clear image of the rear of a Blackbird. This is a new view - at least for me. Are those "ports" and, if so, what are they venting? IF not, what are they?
According to the SR-71 handbook section 6-11, these are fuel dump vents (outer) and fuel tank pressure relief vent (center).
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In some models these vents were relocated, because a camera system air conditioning appendage was added to the tail of the plane