Micrometeoroids and Space Debris
Astronauts on spacewalks are likely to encounter fast-moving particles called meteoroids. A meteoroid is usually a fragment of an asteroid consisting of rock and/or metal. It can be very large with a mass of several hundred metric tons, or it can be very small- a micrometeoroid which is a particle smaller than a grain of sand. Micrometeoroids are usually fragments from comets. Every day Earths atmosphere is struck by millions of meteoroids and micrometeoroids. Most never reach the surface because they are vaporized by the intense heat generated by the friction of passing through the atmosphere. It is rare for a meteoroid to be large enough to survive the descent through the atmosphere and reach solid Earth. If it does, it is called a meteorite.
In space there is no blanket of atmosphere to protect spacecraft from the full force of meteoroids. It was once believed that meteoroids traveling at velocities up to 80 kilometers per second would prove a great hazard to spacecraft. However, scientific satellites with meteoroid detection devices proved that the hazard was minimal. It was learned that the majority of meteoroids are too small to penetrate the hull of spacecraft. Their impacts primarily cause pitting and "sandblasting" of the covering surface.
Recently spacecraft debris is of great concern to spacecraft engineers. Thousands of space launches have left many fragments of launch vehicles, paint chips, and other "space trash" in orbit. Most particles are small, but they travel at speeds of nearly 8,000 meters per second. These space-age particles have become a significant hazard to spacecraft and to astronauts on extravehicular activities.
Engineers have protected spacecraft from micrometeoroids and space trash in a number of ways, including thick-wall construction and multi-layer shields consisting of foil and hydrocarbon materials. A micrometeoroid striking multi-layer shields disintegrates into harmless gas that disperses on inner walls. Spacesuits provide impact protection through various fabric-layer combinations and strategically placed rigid materials.
Although effective for particles of small mass, these protective strategies do little if the particle is large. It is especially important for spacewalking astronauts to be careful when they repair satellites or do assembly jobs on the International Space Station. A lost bolt or nut could damage a future space mission through an accidental collision. (Note: Low orbit tends to be clearer of particles than higher orbits because low orbit particles tend to decay and burn up in the atmosphere.)
Pea Shooter Meteoroids
The effects of high-speed micrometeoroid impacts can also be simulated
with a "pea shooter." The shooter is actually a plastic milkshake straw.
The projectile can be dried peas, popcorn, dried lentils, etc. The object
of the activity is to penetrate tissue paper with the projectile. As with
the Potato Astronaut activity, the velocity of the impactor determines
Potato Astronaut-Part One
The effects of high-speed micrometeoroid impacts are simulated with a potato and a straw. Students hold the potato in one hand and stab it with the other using a plastic milkshake straw. The penetration depth into the potato relates to the speed of the stabbing action. A straw slowly pushed into the potato collapses. The plastic isn't strong enough to support the force exerted at the opposite ends of the straw. However, when the straw is thrust rapidly into the potato, the straw easily penetrates and passes through. The straw enters the potato before it has a chance to collapse. As it enters, the surrounding potato helps support the straw by shoring up its sides.
The kinetic energy output of an impact, given in Joules, is calculated with the following equation:
KE = 1/2mv2
m = mass of impacting object
Note: The mass in this activity is actually the combined mass of the straw and the hand and forearm driving it.
Potato Astronaut-Part Two
In part one of Potato Astronaut, students found that "high speed" impacts
enabled the plastic straw to penetrate the potato without collapsing.
Challenge the students to design a way to protect the potato from damage
caused by impacts using just the materials they brought to the classroom.
Their solutions to the challenge should be flexible and light in weight.
Compare technologies for protecting astronauts from micrometeoroid and space debris impacts to other protective technologies such as bullet-proof vests, suits of armor, shields on power tools, and windshields on vehicles. How does the function determine the form? (e.g. Motorcycle helmet--provide protection during crash . . . be streamlined . . . comfortable to wear . . . protect face from bug and rock impacts, etc.)
Experiment with different fabrics and fabric combinations for protective garments