Observed Space Shuttle Endeavour STS-118 amidst flying clouds
The first pass in deep twilight at 20:03 UTC was indeed lost. An unbroken cloud cover, and no hopes for the next and final pass, 21:37 UTC.
But Lo Behold....at 21:15 UTC I noted gaps in the cloud cover. I could see Vega and Arcturus. The situation was very dynamic, with parts of the sky opening and then filling up again in a matter of tens of seconds, the cloud cover moving very fast...but breaking up a little.
At 21:30 I was ready at the courtyard. At 21:34 I spotted the ISS, passing through the zenith very close to Vega. Three minutes to go for the Shuttle, and the zenith was filling up with clouds again.
21:36....I looked west, hoping to see it near Arcturus. Brief glimpse of the latter, but no luck regarding the Shuttle. Clouds occupied the west. Then moved my watch to the zenith. It was breaking open again. I could see Vega.
21:37....YES!!!!!! For maybe 20 seconds I see it, passing a bit south of Vega, fast and about magnitude 0, similar to Vega!
20 seconds and then it was gone in clouds again. Did not even attempt to photograph, it was futile.
But I saw it! :-)