\begin{table}%t1
\caption{\label{table:1}Internal structures and material properties used in the simulations. }
%\centerline
 {\small \begin{tabular}{c c c c}
\hline\hline  
Simulation & Structure & Microporosity &Strength \\
\hline
1 & Monolithic & $25\%$ & low \\ 
2 & Monolithic & $25\%$ & high \\
3 & Monolithic & $0\%$& high \\
4 & Rubble-pile & $25\%$ & low \\
5 & Rubble-pile & $25\%$ & high \\
6 & Rubble-pile & $0\%$ & high \\
\hline
\end{tabular}}
\medskip
Targets with a rubble-pile structure have a fraction of macroscopic voids of~15\%. See Table~\ref{table:2} for definitions of low and high  tensile strengths.
\end{table}