How do I decode the contents of a UDP payload as CCSDS?

edit

select the UDP payload and then select "decode as", but CCSDS is not in the list

What did you do to get the list?

Unless you have a really old version, you need to:

• select the packet;
• select Analyze > Decode As...;
• click the + button;
• double-click the value in the "Current" column for the newly-added row (it probably says "(none)");
• clock the button on the right with "^" above "v".

That list shows CCSDS in the version of Wireshark I have.