NASA Shuttle/ISS TV feed doctored?

I am sure many of you will have seen a documentary called 'Secret Space', made I believe by the late Jeff Chandler (maybe not and connection a bit slow to research right now!) who recorded many NASA transmissions before they were encrypted.

I am interested to know if any of the forum members have any technical expertise regarding TV transmissions from space?
In the programme, it is pointed out that whenever the TV feed from space went from being in daylight to night, it seemed like a 'snow' effect was deliberately added to the footage. If that is indeed the case, there may be more than one reason as to why but for the purposes of this post, lets just say it may have been to help hide things that NASA had no direct control over.

The evidence, on the face of it, seems compelling. There are numerous examples of perfectly good daytime footage that is suddenly marred by this 'snow' effect when the orbiting station or shuttle moves into the dark side of the earth. It does not seem to be a quality issue, because there are plenty of examples of when the night-time footage is fine for a while but then looks like the 'snow' effect is suddenly 'switched on'. There are also times when it looks like it is also switched off, only for it to return shortly. This affected footage is only when the camera shot is of the outside of the shuttle or ISS. Outside footage is interspersed with internal footage that is of good quality consistently.
Another tell-tale that this 'snow' effect is deliberate is that in the corner of the screen, there is a NASA logo that is affected with the snow also. The NASA logo would have to have been added after initial transmission from space, so it should really show the night-time footage and it's 'snow' but with the logo unaffected.
Is it really believable that such a high-tech agency such as NASA, in this age of satellite television, could consistently be obtaining such poor quality images - and images that are intended for education, study and posterity? I find it laughable that they would not have fixed such a problem as soon as it became apparent?
Bear in mind that it does not seem to be a lack of good technology because there exists footage that is crystal clear, shot at night, proving that there is nothing wrong with the cameras or the transmission of the signal.

It could be argued that for various genuine secrecy reasons that NASA should reserve the right to censor what is broadcast from the space program. All well and good, but considering there is a delay built into the system and they can just terminate broadcast anyway, anything deemed unfit for broadcast (such as the death of an astronaut or launching of a spy satellite) need not be shown.
It is almost as if they are required to show 'business as usual' but at night, where objects can be sometimes seen that NASA have no control over, objects that could be viewed as UFO's need to be masked somewhat, providing the get-out ? Maybe it has nothing to do with UFO's but it is still a very strange thing, NASA - WE CAN PUT A MAN ON THE MOON IN 1969 BUT WE CAN'T SHOW YOU LOW EARTH ORBIT IN 1999!

I would be interested to find out if anyone has any explanation for this?

gordon