so ullage motors are pretty cool & the wikipedia page does a better job of explaining than i could on my phone, BUT this part totally surprised me:
Russian Proton rockets use ullage motors called SOZ motors. These have a bad tendency of exploding years after end of operations, contributing to space debries. So far, 54 such SOZ motors have exploded in orbit.
first, wow that’s impressively bad! i haven’t read the background on any of this but at first glance it’s a bit of a struggle to imagine how they managed this; hat tip to whoever was ultimately responsible for it.
second, the reason i was so surprised is that whenever i think of Soviet/Russian spaceflight i tend to do so with respect to Soyuz:
see that bit where the second and third stages meet up? that bit with the truss structure?
yeah, Soyuz doesn’t combat ullage with dedicated motors.
the Soviets took the “simpler” (and extraordinarily characteristic) engineering approach of lighting the third stage while the second stage is still attached.
hence the truss, because all that exhaust has gotta go somewhere; which, i mean, okay yeah that’s a little horrifying but honestly way better than exploding after decades in orbit.
