From the signboard:

British Aerospace Spacelab Pallet F003/MD004

The use of pallets for transport is not restricted to rail trucks.  During the 1980s, British Aerospace produced a series of pallets for carrying experiments and cargo on the American space shuttle as part of the European Spacelab programme.

To utilise the available space as efficiently as possible, the Spacelab Pallet is U-shaped like an aircraft container.  The aluminium structure incorporates cooling panels, connected to a Freon circuit.  Up to 5 pallets can be joined together, each with its own electricity and data connections.  A special version of the normally fixed pallet can even be unloaded in space.