Total force resulting from the attractive gravitational field of the Sun and the Earth, and the repulsive force from the solar radiation. The sail is assumed to have a mass of m = 1 g, a radiative coupling constant of κ_rad = 1, and a mass per cross section area ratio of σ = 3.6 × 10⁻⁴ kg m⁻², about a factor of two below the critical value of σ_⊙ = 7.6946 × 10⁻⁴ kg m⁻² to enable interstellar escape from interplanetary space. For a 1 g aerographite hollow sphere (σ = 4ρϵ = m/S) with a shell thickness of ϵ = 500 μm this corresponds to a cross section area of 2.78 m² and a radius of 94 cm. Panel a: throughout this 1D cut through the solar system, F_tot >  0 because σ/κ_rad <  σ_⊙, except in the vicinity of the Earth at 1 AU. Units along the ordinate are μN. Panel b: within a fraction of an AU around the Earth, the Earth’s gravitational well is too deep for this sail to escape and F_tot <  0. Units along the ordinate are mN.