The Whipple shield, invented by Fred Whipple, is a type of hypervelocity impact shield used to protect manned and unmanned spacecraft from collisions with small particles whose velocities are measured in kilometers per second. As opposed to monolithic shielding of early spacecraft, Whipple shields place spacings between several layers of shielding. This improves the shielding to mass ratio, critical for spaceflight components, but also increases the thickness of the spacecraft walls, which is not ideal for fitting spacecraft into launch vehicle fairings. The advantage of spacing out thinner shields over a single thick shield is that the initial wall shock can melt the incoming particle (depending on its speed) and molten bits of the particle strike a wider area of the subsequent walls reducing the pressure. Some Whipple shields have a filling in between the layers of a lower density material, such as a high-strength fabric and plastics. There are many different configurations of thickness of walls, number of walls, materials, and filling on the International Space Station alone. Higher risk areas are given better shielding.
