Solar Sail Asteroid Deflection: Slow-Push Radiation Pressure

Mission Setup

Sail area 2000 m²

Sail reflectivity 90%

Asteroid diameter 140 m

Steering (cone) angle 35°

Warning time before encounter 8.0 yr

Time acceleration 6.0 yr/s

Live Readouts

Mission elapsed

0.00 yr

Time to encounter

8.00 yr

Tangential thrust

— µN

Cumulative Δv

0.00 mm/s

Semi-major axis drift

0.00 km

Projected miss shift

0 km

How it works

A sail bonded to (or towed alongside) the asteroid tilts its normal by a cone angle δ from the Sun line. Reflected sunlight pushes it with a force whose magnitude follows the standard flat solar-sail law:

F(δ) = (S₀ / d²) · A · (1 + r) · cos(δ) / c
radial component:     F_r = F(δ)·cos(δ)
tangential component:  F_t = F(δ)·sin(δ)

S₀ = 1361 W/m² (solar constant at 1 AU), d = Sun distance in AU, A = sail area, r = reflectivity (0 = black absorber, 1 = perfect mirror), c = speed of light. Only the tangential component — along or against the asteroid's orbital velocity — does useful work reshaping the orbit.

For a near-circular orbit, a small sustained tangential acceleration a_t secularly changes the semi-major axis (Gauss's planetary equation, circular-orbit limit):

da/dt = 2·a_t / n,   n = √(μ☉/a³)   (mean motion)

Each slice of thrust applied a time Δt before the encounter nudges the asteroid's along-track position at closest approach by roughly the planetary-defense "3× rule" used for kinetic impactors, generalised to continuous low thrust by integrating over the whole push:

miss shift ≈ ∫ 3 · a_t(t) · (L − t) dt

where L is the warning time and t runs from mission start to now. Posigrade (along-velocity) pushing raises the orbit and makes the asteroid arrive late; retrograde pushing lowers it and makes it arrive early — both grow the miss distance. This slow-push strategy needs years of warning, unlike a kinetic impactor's single instantaneous Δv, but needs no rendezvous propellant beyond attaching the sail.

Sun Asteroid orbit (deflected) Original orbit Earth (1 AU reference)

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