\begin{table}%t2
   \caption {\label{tab:summary_flight_testing_conditions}Summary of main thermal conditions.
      }
        %\centerline
 { \begin{tabular}{lccc}
         \hline\hline
          \noalign{\smallskip}
          Temperatures            &  Flight & Receiver    & Instr.\\
         \hline
         Sky &  $\sim$3~K & $\gtrsim$8~K & $\gtrsim$18.5~K \\
         Ref. & $\sim$4.5~K & $\gtrsim$8~K & $\gtrsim$18.5~K \\
         Front-end& $\sim$20~K & $\sim$20~K & $\sim$26~K  \\
         Back-end & $\sim$300~K & $\sim$300~K & $\sim$300~K \\
         \hline
      \end{tabular}}
\par
\tablefoot {The table reports thermal conditions achieved in-flight and in the various testing facilities.}
\par
\end{table}