Launch of two more TROPICS cubesats as viewed (maybe!) by GOES-18
The TROPICS constellation of satellites was augmented by a final launch of two cubesats from the Mahia Rocket Launch site at the south end of the Mahia Peninsula on the east coast of New Zealand’s North Island on 26 May 2023. GOES-18 visible imagery, above, stepping from 0320 to 0350 UTC on 26 March, shows a smudge in the 0340 UTC imagery (highlighted below). What facts argue for this feature being associated with the launch? The smudge is there at the correct time: launch was at 1046 PM CDT or 0346 UTC on 26 May. The timestamp of the image, 0340 UTC, is when ABI starts scanning at the North Pole; the Mode 6 Scanning timeline (here) suggests scanning at 39oS, the latitude of the Mahia Launch facility, occurred between 0347 and 0348 UTC. Thus, the plume would be at considerable height in the image. The cubesats do travel west to east (see the figure at this page) so you should not expect the plume to be west of the launch site. However, Mahia, at 39.3° S, 177.9° E is far from the GOES-18 sub-satellite point (0oN, 137o W), so the westward displacement of the (possible) plume is likely an artifact of parallax (link) which for that location and a 50000′ height is close to 40km/25 miles southwestward of its true location.
Note: the reflectance range for GOES-18 visible imagery above has been altered for this post, from the default (0-130) to 1-20 to better highlight the possible plume.