Early March observations and pulsing (?) brightness of the STSS Demo-1

I am well behind on reporting on my March observations so far. I observed on the evenings of 1, 2, 3, 6, 7, 9 and 16 March. Observed objects include:

The Lacrosses 2, 3 and 5; NOSS 3-1; USA 200; USA 129; The USA 144 decoy; STSS demo 1 and demo 2; and a number of strays.

The KH-12 KeyHole USA 129 (96-072A) is a favourite target, now it has come out of it's winter hiding. I observed a number of flares from this satellite again (alas all while the camera was closed). Below are two trail images from 7 and 16 March, showing it rising (16 March) and decsending (7 March):

click image to enlarge

The STSS Demo 1 & 2 objects (09-052A & B) were also frequently targetted. On March 16, I captured a shortlived pulsating brightness behaviour for STSS Demo 1 that is very similar to the shortlived pulsating behaviour I captured for the other STSS Demo object (demo 2) on February 20. Liek on that occasion, the behaviour is present in the first 2 seconds of one single trail image (out of a series of several). below is the image showing the pulses in the early part of the trail (top), and below that are the brightness diagram, and a diagram of the delta T between the pulses (read and compare also the report for February 20). The period for the early part is a flat 0.16s.

I do not want to exclude, even though I cannot explain it, that it is some instrumental effect. This because it is again in the first 2 seconds of a trail.