Plot of the data latency T_L in yr vs. the logarithm of the total data volume ﹩{ \mathcal V }﹩ in bits for different values of the mass ratio ζ (the curves are labeled with ζ). For example, ﹩{\mathrm{log}}_{10}{ \mathcal V }=9﹩ corresponds to 10⁹ bits or 1 Gb. The dashed line is, for each value of ﹩{ \mathcal V }﹩, the minimum T_L achievable by the optimum choice of ζ. It is assumed that for ζ = 1 (the lowest-mass probe) the speed is u₀ (1) = 0.2c, and the initial transmit data rate is ﹩{{ \mathcal R }}_{0}(1)=1\,{\rm{b}}\,{{\rm{s}}}^{-1}﹩. The Voyager (V) and New Horizons (NH) points are obtained from Table 5.