>>14301166It's the S-IVB stage of Apollo 7, being used as a rendezvous (but not docking) target to simulate LM docking and extraction which would occur once the LM---still in production delay at this point---would become available. Notice especially that one of the pieces of fairing did not open completely (later designs would have these blown away with small charges, to get them completely out of the way of the docking operation). This prevented a closer rendezvous attempt.
>>14301284 You are correct that the attached panels are payload fairing, and incorrect that the object (fairing plus stage) is (a component of) the Saturn V rocket. Launching only the command module spacecraft without the LM for an Earth orbital prove-out flight, Apollo 7 launced as the two-stage Saturn IB, not the complete three-stage Saturn V carrying the additional payload of the LM. The S-IVB stage served as the second stage of the Saturn IB configuration, and the third stage of the Saturn V configuration. Moreover, two slightly different versions of the S-IVB itself were used for each rocket configuration. The 200-series S-IVB had three smaller thruster rockets to be used during staging, whereas the 500-series S-IVB had just two. Compare the famous staging stock footage in the link below, which is manifestly a 200-series stage and sometimes falsely attributed to Apollo 11 due to its frequent use as documentary stock footage.
https://www.youtube.com/watch?v=xMr_AGJprrg[spoiler:lit]NERD! NEEEEEERD!!!!![/spoiler:lit]
