National Geographic : 1964 Mar
the earth by our own planet's magnetic field. Basically there is only one belt, but it in cludes two dissimilar regions. One consists of high-energy protons caught in a layer that arches some 2,000 miles above earth at the magnetic equator. The other, containing high energy electrons, girdles the magnetic equator about 10,000 miles from earth. In schematic drawings these regions curve around the globe like horns or crescent moons. The sec ond, in particular, is quite deep, extending outward some 20,000 miles. Manned space flights to date have been too low to get into this radiation, but Apollo crew men will have to slash through it going out and coming back. Fortunately they will be exposed for a total of only a few hours, and the estimated 20 roentgens of radiation they will absorb will not be serious from a health standpoint. Their spacecraft, of course, gives only limited protection; it cannot be sheathed in thick lead. Solar Flares a Threat to Astronauts Beyond the Van Allen belt lies another ra diation hazard from intermittent solar erup tions, or flares. Actually the sun is never really quiet, since it ejects about 400,000 tons of matter a second in all directions. But these sub-atomic particles, called the solar wind, are very sparse in the vastness of space and limited in velocity. They would not pierce a sheet of tissue paper. Flares, however, pro duce concentrated streams of far more en ergetic proton particles, some traveling at nearly the speed of light. Fortunately an outburst of radio noise coincides with these eruptions, and they can also be viewed by astronomers as they occur. Apollo crewmen will have at least four hours' warning before the major part of the proton stream reaches them. They may have to shield themselves with special garments and goggles, but their equipment and double-hulled space craft are designed to keep the radiation dos age safe during one large flare. In the event of a second flare during the outward journey, they might have to scurry home. Actually the prospects are not as serious as they seem. We know the kinds of solar activity-particularly sunspots-that tend to forecast eruptions, and a safe period can be predicted with a reasonable degree of accu racy. Even when danger indicators are pres ent on the sun, large flares do not occur in most cases. If one should happen, the chances are favorable that it will be minor or be di rected away from the earth-moon system. 382 NASA is pushing a determined program to improve the reliability of flare forecasts and to find ways for making long-range predic tions. Such knowledge will be particularly important during periods when the 11-year sunspot cycle reaches a peak, as it will in late 1968 and early 1969. Space contains a lot of rubbish-the meteors we often see streaking down the night sky but most of this celestial debris is extremely minute and no danger to Apollo. Pieces as large as a sand grain are believed rare. Statistics indicate only one chance in 10,000 that Apollo would encounter a me teor big enough to pierce the hull, yet we have planned for that possibility. If a half-inch hole were blasted, permitting the spacecraft's atmosphere to escape, the life-support system would automatically gush out enough oxygen to sustain the men for five minutes. In that period they could get back into their space suits and plug the hole. However, Apollo may have to avoid me teor streams that intersect the orbits of earth and moon. Astronomers count about 30 of these periodic streams or showers, but only four are considered of major importance: the Quadrantids in January, the Perseids in Au gust, the Giacobinids in October, and the Leonids in November. Extremes of Heat and Cold Grip Moon Perhaps the greatest hazards will be found on the moon itself. For example, we know little about the composition of the lunar sur face. Some authorities believe it may be covered by a dust layer from four inches to three feet in depth. Others think the dust in some areas may be far deeper, enough to engulf any spaceship. A third group holds to the theory that porous rock covers much of the surface. Obviously we cannot risk landing men until these uncertainties are resolved by un manned lunar probes, such as our forthcom ing Rangers and Surveyors.* Their intelli gence will determine the final design of LEM's landing gear. On the airless moon, a man's best friend will be his pressure suit. If it fails, or if he should fall and tear it open on some jagged rock, the vacuum would claim him. We have good experience in building tough, dependa ble pressure suits, but the Apollo garment must be a super one, able to withstand micro meteorites, easily flexible at the body joints, *See "NASA's Robots to the Moon," by Frank Sart well, NATIONAL GEOGRAPHIC, October, 1962.