Parting is such sweet sorrow, according to the quotation from Shakespeare.
But at least when Endeavour comes back from its trip into orbit this time, it will be back for good.
The US space shuttle is due to blast off on its last mission from Florida’s Kennedy Space Centre just before 9am local time.
Support teams have been busy with last-minute preparations.
The crew will be led by Mark Kelly, the husband of US politician Gabrielle Giffords who is recovering from a gunshot to the head after an assassination attempt in January.
The final flight of the US Space Shuttle programme, by Atlantis, is scheduled for July.