Micrometeoroids and Orbital Debris (MMOD)

    Millions of man-made debris and naturally occurring micrometeoroids orbit in and around Earth's space environment at hypervelocity speeds averaging 10 km/s (22,000 mph).

    This "space junk" collides with spacecraft and satellites. Collision with these particles can cause serious damage or catastrophic failure to spacecraft or satellites and is a life threatening risk to astronauts conducting extra-vehicular activities in space.

    EV Activities in space
    Astronaut conducting extra-vehicular activities in space.

    Debris hits spacecraft and satellites. To minimize the potential hazard of debris impacts, it is necessary to understand the current orbital debris environment.

    Impact Window
    STS-35 Space Shuttle window pit from orbital debris impact.

    Orbital debris in the near-Earth space environment is made up of micrometeoroids and man-made debris. The man-made debris or space junk consists mainly of fragmented rocket bodies and spacecraft parts created by 50 years of space exploration. These objects number in the millions and orbit the earth at hypervelocities averaging 10 km/s (22,000 mph).

    Low Earth Orbital
    Computer generated images of objects in low Earth orbit, the region of space within 2000 km of the Earth’s surface. Approximately 95% of the objects are orbital debris, not functional satellites.

    The orbital debris environment is growing. More satellites are being launched, and with non-functioning satellite explosions and fragmentation, the threat of debris impact damage on active satellites and spacecraft is a major concern. Orbital debris remains in orbit a long time, and high-speed collisions between existing particles can produce even more debris.

    Larger particles (objects greater than 10-cm in diameter) are being tracked and catalogued by USSPACECOM radar. Spacecraft and satellites can avoid collisions by maneuvering around the larger debris. For example, the USSPACECOM regularly examines the trajectories of orbital debris to identify possible close encounters with the International Space Station (ISS) or space shuttle. If a catalogued object is projected to come within a few kilometers of the spacecraft, it will normally maneuver away from the object.

    Micro-particle Comparison
    1. Gray human hair
    2. 200 micrometer Aluminum (~30 micrograms) Projectile
    3. 7.0 km/s Impact crater on copper from 0.2 micrometer Al projectile
    4. 200 micrometer drill bit


    Micro-particle Comparison

    Fortunately, small particles less than 1 cm pose less of a catastrophic threat, but they do cause surface abrasions and microscopic holes to spacecraft and satellites.

    The greatest challenge is medium size particles (objects with a diameter between 1 cm to 10 cm), because they are not easily tracked and are large enough to cause catastrophic damage to spacecraft and satellites.

    Spacecraft must be designed to withstand hypervelocity impacts by untrackable particles. Conducting hypervelocity impacts on spacecraft and satellite components assesses the risk of orbital debris impacting operating spacecraft and satellites. Developing new materials and designs from hypervelocity impact data provides a better understanding to protect spacecraft and satellites from the debris in the space environment.

    One type of spacecraft shielding, termed multishock, uses several layers of lightweight ceramic fabric to act as “bumpers,” which shocks a projectile to such high energy levels that it melts or vaporizes and absorbs debris before it can penetrate a spacecraft’s walls. Lightweight shields based on this concept are used on the ISS.

    Hypervelocity 1
    Spacecraft Shielding
    Spacecraft Shielding with Multi-shock Bumpers

    The ISS is the most heavily shielded spacecraft ever flown. Shielding is designed to protect critical components such as habitable compartments and high-pressure tanks from the nominal threat of an aluminum sphere approximately 1 cm in diameter. The ISS also has the capability of maneuvering to avoid tracked objects.

    For additional information, contact Karen Rodriguez at (575) 524-5279 or karen.m.rodriguez@nasa.gov.