Word of the Day -- Whipple Shield

The Whipple shield or Whipple bumper, invented by Fred Whipple, is a type of hypervelocity impact shield used to protect manned and unmanned spacecraft from collisions with micrometeoroids and orbital debris whose velocities generally range between 3 and 18 kilometres per second (1.9 and 11.2 mi/s).

As opposed to monolithic shielding of early spacecraft, Whipple shields consist of a relatively thin outer bumper placed a certain distance off the wall of the spacecraft. 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 a bumper placed at a standoff over a single thick shield is that the bumper wall can shock the incoming particle and cause it to disintegrate. This spreads out the impulse particle over a larger area of the inner wall of the spacecraft.

There are several variations on the simple Whipple shield. Multi-shock shields, like the one used on the Stardust spacecraft, use multiple bumpers spaced apart to increase the shield's ability to protect the spacecraft. Whipple shields that have a filling in between the rigid layers of the shield are called stuffed Whipple shields. The filling in these shields is usually a high strength material like Kevlar or Nextel aluminium oxide fiber. The type of shield along with the material, thickness and distance between layers are varied to produce a shield with minimal mass that will also minimize the probability of penetration. There are over 100 shield configurations on the International Space Station alone, with higher risk areas having better shielding.