\begin{table}%t1
\caption{\label{tabrefreq}Design requirements of the \textit{Planck} telescope reflectors.} 
\par
%\centering
\par
\begin{tabular}{lcc}
\hline \hline \noalign{\smallskip}
Requirement & Primary reflector & Secondary reflector\\
\hline
Contour shape & off-axis ellipsoid & off-axis ellipsoid\\
Size (mm) & 1555.98 $\times$ 1886.79 & 1050.96 $\times$ 1104.39\\
Radius of  &  & \\
Curvature (mm) & 1440 $\pm$ 0.25 & $-$643.972 $\pm$ 0.2\\
Conic constant & $-$0.86940 $\pm$ 0.0003 & $-$0.215424 $\pm$ 0.0003\\
\hline
\multicolumn{3}{l}{Stability of best fit ellipsoid}\\
along each axis & \multicolumn{2}{c}{$\pm$0.1 mm}\\
around each axis & \multicolumn{2}{c}{$\pm$0.1 mrad}\\
\hline \noalign{\smallskip}
\multicolumn{3}{l}{Mechanical surface errors rms spec (goal)\tablefootmark{a}}\\
ring 1 & \multicolumn{2}{c}{7.5 $\mu$m (5 $\mu$m)}\\
ring 2 & \multicolumn{2}{c}{12 $\mu$m (8 $\mu$m)}\\
ring 3 & \multicolumn{2}{c}{20 $\mu$m (13 $\mu$m)}\\
ring 4 & \multicolumn{2}{c}{33 $\mu$m (22 $\mu$m)}\\
ring 5 & \multicolumn{2}{c}{50 $\mu$m (33 $\mu$m)}\\
\hline
{Surface roughness} & \multicolumn{2}{c}{$R_{\rm q}<0.2~\mu$m on scales $<$0.8~mm}\\
\hline \noalign{\smallskip}
{Surface dimpling}\tablefootmark{b} & \multicolumn{2}{c}{${\pm}2~\mu$m PTV}\\
\hline
{Reflector thickness} & 80 mm & 65 mm\\
\hline
\multicolumn{3}{l}{Reflectivity (25$-$1000~GHz)}\\
Beginning of life & \multicolumn{2}{c}{$>$99.5 per cent} \\
End of life & \multicolumn{2}{c}{$>$98.5 (goal 99.0)\tablefootmark{c}}\\
\hline
{Mass} & 30.6 kg & 14.5 kg\\
\hline
{First eigenfrequency} & \multicolumn{2}{c}{$>$120 Hz}\\
\hline
\multicolumn{3}{l}{Temperatures}\\
Operational & \multicolumn{2}{c}{45 K}\\
Qualification & \multicolumn{2}{c}{30$-$325 K}\\
\hline
\end{tabular}
\tablefoot {\tablefoottext{a}{Each ring is a concentric ellipse with the same ellipticity as the rim of the reflector, dividing the major axis in 5~equal pieces. Ring~1 is the innermost ring and ring~6 the outermost~one.} \\
\tablefoottext{b}{Defined in Sect.~3.1.} \\
\tablefoottext{c}{At telescope level, the total emissivity is specified to be $<$6\% ($<$3\%~goal), including also the effect of dust deposited on the~\mbox{reflectors}.}}
\end{table}