Solar Sail Sun Satellites Could Intercept All Future Interstellar Objects

Earth orbiting satellites have the speed to counter the Earth’s gravity. The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (4.8 mi/s), which translates to 28,000 km/h (17,000 mph). However, this depends on the exact altitude of the orbit. A statite, or static satellite, would use a solar sail to cancel out the gravitational acceleration caused by the Sun by reflecting light to generate a propulsive force.

Materials exist today which can be used to make solar sails good enough to become solar sail sun satellites. Those solar sail satellites can be deployed to wait around the sun for interstellar objects. The solar sail satellites would then stop holding position and fall towards the sun. They would rapidly gain speed and we just need to adjust the fall to change direction and intercept the interstellar objects.

The gravitational force of the Sun and the propulsive force from the solar sail vary as 1/R^2. This allows the statite to exactly cancel the gravitational force hover at any distance from the sun, but it must have an area-to-mass ratio greater than a critical value. It turns out that the ability of the statite to cancel out the gravitational acceleration of the Sun is independent of the distance of the sail to the Sun. The key parameter to achieve a statite is the area-to-mass ratio.

The critical mass-to-area ratio is 1.6 g/m^2 and the area-to-mass ratio is 0.625 m2/g. To achieve statite-level performance, the payload and solar sail combination of mass m must provide these meet these specifications. This may be achievable with modern materials using aluminized, temperature-resistant material, also called CP-1. Since the solar sail is levitating or hovering, its inertial velocity is zero. When it is released from this state, it will fall into a Keplerian orbit.

A statite at 1 AU has a free-fall trajectory of about 64 days. This can be like slingshot effect, since the solar sail is used to store energy that is released when desired. Additionally, to achieve a flyby some Delta-V is required to adjust from the free-fall path to a flyby trajectory.

2 thoughts on “Solar Sail Sun Satellites Could Intercept All Future Interstellar Objects”

  1. Question
    Could we make a satellite that maintains it’s low earth orbit by unfurling a solar sail each orbit as it is travelling away from the sun until shadowed by the earth?

  2. Well … the calculations are correct in a theoretical sense. 1.53 g/m^2 at 1 AU is the maxMass of a statite WITH … 100% reflectivity, and 0% internal absorption, and 0% no-intercept opacity. Realistically, for ‘real’ metamaterials, one might get around 70% reflectivity and a substantial absorption. Under those criteria, the maxMass drops to less than 1.0 g/m^2.

    The maxMass also must include the payload of the statite distributed over its area. It’d take a fairly substantial statite (area wise) to even sport a 1 kg payload, which itself isn’t more than a DSLR camera. Well , just saying.

    I do remember writing this up in comments here at NBF a few years back. 5 or more. But the idea remains … a darn good one, to do interesting intercepts per what the article alludes to. Thank you again Brian.

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