Meteors and Spaceflight

EVERY HOUR OF every day, thousands of intruders from interplanetary space enter the atmosphere of the EARTH. Only the largest and these are very few in number, ever manage to penetrate the atmosphere and reach the surface of the Earth. This sounds like the beginning of a science fiction story, but, if it is said that these intruders are meteorites, then this statement is perfectly true.

Meteorites are important from the point of view of interplanetary flight because their presence in space forms one of the most obvious potential hazards to a vessel leaving the protection of the Earth’s atmosphere. The danger lies in the possibility of collisions between the rocket ship and the meteor particles, both of which would be travelling at high speeds. Such a high speed collision might involve the penetration of the hull of the spaceship with subsequent loss of air, damage to the interior of the vessel and maybe even injury to members of the crew. Although this danger is very real, it is often exaggerated and it is certainly not great enough to make interplanetary flight impossible, as is sometimes stated. It is necessary then to discuss this potential danger and to obtain some idea of the probability of a damaging collision occurring, and also to describe a method of protecting the rocket ship or artificial satellite against such collisions. To appreciate more fully the danger, the nature of meteor particles and the speeds and numbers of them near the Earth must be considered.

In the year 1833 a large number of people, amongst others, were convinced that the world was about to end. On the night of the November 11 the sky was filled with brilliant falling stars; over 20,000 fell each hour for most of the night. This phenomenon is now known to have been caused by a swarm of meteors called the Leonids. It is this phenomenon of ‘falling’ or ‘shooting’ stars which first acquaints most of us with meteors, although their cause was not known until the last century. There are records of falling stars going back about 2,600 years, but even before this time, no doubt, mankind was familiar with the sight. It is thought that prehistoric man obtained some of his iron from fallen particles picked up on the Earth’s surface, and no doubt regarded this as a gift from the gods in the skies.

Falling stars were usually regarded with superstitious dread. In many parts of the world meteors were worshiped and built into walls of temples as sacred stones. In fact the word ‘meteor’ comes from the ancient Greeks and means ‘things in the air’. The Chinese catalogued falling stars in 616 B.C., whilst Livy mentioned a shower of stones falling Mount Alban, near Rome, in about 654 B.C. The ancients thought that falling stars were generated in the atmosphere, as the word meteor implies, and the ancient Greeks regarded them as projectiles pelted at erring humanity by irritated gods, although the number of direct hits obtained speaks very poorly of their accuracy. It was not until the great shower of 1833 that scientists became convinced that the origin of meteors was outside the atmosphere and only recently was it realized that they nearly all come from within the solar system and not from outer space. In fact, it was as late as 1803 that the work of the French physicist, Biot, convinced scientists that bodies falling from the sky really did exist, and were not a figment of popular imagination. Nowadays million’s of these bodies have been observed and tracked both visually and by radio astronomy.