You are a large nation. A superpower. You have enemies in the world. It is a time when countries are in possession of incredibly destructive weapons. Some of these are your enemies. Some you just think are your enemies. Some don't really care what you think. To discourage them from attacking you, you also have such weapons. You have lots of them.
But you are not satisfied with this. You, the large nation with the ability to destroy the world's population before breakfast, must have more such weapons, and they must be better. They must blow up more stuff. You must be able to destroy the world's population several times over in case, y'know, your enemies are hiding standing armies underground or something.
To make better weapons, you have to develop new ideas in weapons design. This means hiring lots of clever people to think of ways to blow up more stuff. Their designs must of course be tested to aid their development. Since you can't yet test weapons without firing them, you literally have to try them out to see how well they blow stuff up.
You do so.
Way back when you were developing your first nuclear weapons, you of course didn't fully understand how they worked. You didn't expect to be knocked over by the blast of the first atomic test while you were watching its fireball from miles away. You thought the two were one and the same.
One of the many things you had to measure when you were developing new nuclear weapons was the speed and strength of the blast wave they gave off when they exploded. If you couldn't find a way to measure this you'd be throwing money at the problem without being able to gauge the success of the results.
Your scientists find that for the first few milliseconds of a nuclear explosion, the fireball and the shock front do propagate together. Evidently they separated eventually, when the shock front became too weak to heat the air by compression. The shock front is invisible in the air afterwards, but you still needed some way to monitor its progress.
Then some of your clever people, while they were going through frame by frame video of the first milliseconds of the Trinity burst, noticed something interesting about a cable from a barrage balloon in the background. Actually what they were looking at was smoke from the cable as it got vaporised.
Anyhow, your clever people saw what appeared to be a break in the cable; they eventually realised that it was actually refraction of light caused by the high-pressure air of the shock front meeting the low-pressure air in front of it. The effect was similar to a how a drinking straw in a glass of water appears to be cut by the surface of the water, when viewed from the side.
Since this clearly showed where the blast wave was, your testing teams devised their own version of this fluke for future tests. Several years had passed by this point and nuclear testing had continued, testing things like weapon designs, the effect of atomic explosions on objects and what changing various bomb design parameters did to yields. Anyway, your clever people sorted it.
Ever seen the movie Thirteen Days? All those small rockets being fired during the opening credits, amongst the nuclear test footage? They were the most common means of tracking the progression of a nuclear explosion's shock front (you can actually see the distortion of the smoke trails occurring on one of the burst clips). Smoke rockets would be fired behind the testing area before the burst and when the detonation occurred, the light from their smoke trails would be distorted by the shock front as it passed. With filming, this would record where it was at any particular time and make it possible to calculate its speed.
Note that smoke trails being moved by the blast is not an issue; hence the rockets are launched opposite the monitoring camera, 'behind' the burst. One nuclear test (Teapot HA - High Altitude) attempted to measure the shock front by measuring the movement of the smoke trails but evidently this didn't work very well, as it was not attempted again.
A final thing to note is that when vertical smoke trails were used (test archive photographs show that a mixture of horizontal, vertical and crisscrossing smoke trails were used) the rockets had to be launched at an angle according to the curvature of the camera lens, so that they would appear to be vertical to the camera. Basically they were angled to fire slightly away from the camera in a fan pattern:
x = rocket launch point
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x x x x x
Rather rough and exaggerated but hopefully you get the idea. The first recorded example of the use of rockets to collect blast data is the Tumbler-Snapper Able test in 1952. The first of the sources has images of various employments of smoke trails in nuclear tests.
I want to note here that these things are probably not actually called 'streamers', nor could I, in the considerable Googling for this subject, find the correct name if there even is one. If anyone knows what it is or finds out, please let me know or file a title edit request. Thanks.
- Orbwar (email@example.com); (Untitled);
- Sublette, Carey; "Smoke Trails and Nuclear Tests";
- vce.com (author not specified); "Atomic Smoke Trails";
- Various usenet posts. Prefix all following sources with http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=