  Space launches produce ionospheric disturbances which can be observed through
measurements such as Global Navigation Satellite System signal delays. Here we
report observations and numerical simulations of the ionospheric depletion due
to a Small-Lift Launch Vehicle. The case examined was the launch of a Rocket
Lab Electron at 22:30 UTC on March 22, 2021. Despite the very small launch
vehicle, ground stations in the Chatham Islands measured decreases in
line-of-sight total electron content for navigation satellite signals following
the launch. General Circulation Model results indicated ionospheric depletions
which were comparable with these measurements. Line-of-sight measurements
showed a maximum decrease of $2.7$~TECU in vertical total electron content,
compared with a simulated decrease of $2.6$~TECU. Advection of the exhaust
plume due to its initial velocity and subsequent effects of neutral winds are
identified as some remaining challenges for this form of modelling.
