[robin_reala]

I haven’t watched it, but probably sounding rockets to measure the blast wave? https://en.wikipedia.org/wiki/Sounding_rocket

[quicklime]

Looks like it, except that the rocket itself isn't taking measurements, it's just there to create a smoke trail which can be analyzed later?

http://www.atomcentral.com/atomic-smoke-trails.aspx http://nuclearweaponarchive.org/Usa/Tests/SmokeTrails.html

[robin_reala]

Yes, exactly. Immediately before detonation you send up rockets in a grid pattern, then film it with high speed cameras. You can then look at the grid deformation over time to get an idea of the shape of blast wave.