observing the ‘train’ of 21 Starshield satellites

On May 22, 2024, at 08:00:20 UTC, SpaceX launched a Falcon 9 from Vandenberg SLC-4 as NROL-146, carrying 21 classified payloads for the NRO. It is the first operational launch of a ‘proliferated architecture’ (meaning: launching a lot of the same payloads, creating redundancy and with that less vulnerability to failure or countermeasures). The mission motto was: ‘Strength in Numbers’.Based on previous SDA Tranche 0 launches, I initially guessed that they would go in a ~900 km orbit. But on May 22 near 23:08 UTC, Spanish meteor cameras operated by the SPMN recorded a Starlink ‘train’ like phenomena low in the northern sky, with the ‘train’ entering Earth shadow around 23:08:10 UTC. I identified it as likely NROL-146, as the orbital plane would indeed pass over southern Europe around the time of observation. Time of observation and shadow entry itself however suggested a much lower orbital altitude, near 300 km, than my initial estimate.The next two days I was clouded out, but yesterday evening (25-26 May), the sky finally cleared. Just after local midnight, I observed the ‘train’ from Leiden, counting 21 objects that passed over a 4-5 minute timespan. The 4-minute video above shows all 21 objects. They were very bright (magnitude +2 to +3).If you get a ‘Starlink’-vibe from the video, that is because they basically are. Built by SpaceX and Northrop Grumman, “Starshield” is a military version of Starlink, likely built on the same type of bus. Observations so far suggest they were launched into a ~310 km, 69.7 degree inclined orbit. Over the coming days and weeks they will disperse along their orbital plane, and likely also raise their orbital altitude.click to enlargeBelow is a very cautious elset for the leading object:NROL-146 obj A                                           310 x 311 km1 70006U 24999A   24146.90436495 0.00000000  00000-0  00000+0 0    052 70006  69.7199  66.3577 0000678 155.5007 204.6228 15.87074186    05