The potential impact of meteoroids on the debris population

One of the principal challenges associated with predicting the future debris population is modelling hypervelocity collisions accurately. We assume that higher closing velocities result in more fragments with smaller sizes; but how many more?

One of the principal challenges associated with predicting the future debris population is modelling hypervelocity collisions accurately. We assume that higher closing velocities result in more fragments with smaller sizes; but how many more?

Two objects in low Earth orbit, (LEO), at an altitude of 500 km, colliding head-on have a closing velocity of about 15.2 km/s. This isn’t the worst that man-made objects can do, however. Satellites in highly elliptical orbits, (Geostationary transfer orbit and Molniya) have perigee velocities close to 10 km/s. A head-on collision between two such objects, albeit unlikely, would involve 75% more kinetic energy than a LEO-LEO collision.

But the Earth’s orbital population is not a closed system. The occasional passing meteorite could, if we are unfortunate, collide with one of the debris objects in Earth orbit. Since meteorites can have velocities of 30 km/s, the energies involved in such collisions could be significantly greater than a LEO-LEO collision.

The scenario that results depends on the size, composition and trajectory of the meteorite, but in the case of the unfortunate piece of space debris, the word “smithereens” is likely to be appropriate.

Initially, this sort of intervention from the Solar System might seem extremely unhelpful to the debris population, but surprisingly, this may not be the case.

The lifetime of satellite-sized objects in LEO is typically many decades, but for mm-sized fragments, the time spent in Earth orbit is much shorter, perhaps as little as weeks. The process at work here is that solar radiation pressure can make the orbits of small fragments significantly eccentric, allowing atmospheric drag at the perigee to shorten the lifetime.

What we need to know, therefore, is the flux of meteoritic material and its collision probability. Answers to these questions may be provided by space-based IR sensors which can observe thermal events in the Earth’s upper atmosphere as the incoming objects burn up.

Obviously, objects that are not in Earth orbit will spend far less time in the densely populated bands between 700 km and 1000 km, but there can on occasion be many, many such objects, as this woodcut of the 1833 Leonid meteor shower shows.

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