Artificial Air Glow

An Aerobee rocket soared up last week from Holloman Air Force Base, N. Mex. carrying an odd pay load. Inside its nose were two heavy steel cylinders containing thermite* and 2 lbs. each of metallic sodium. The rocket took off 20 minutes after sunset. When it reached 40 miles and had disappeared from sight, automatic instruments ignited the thermite in the cylinders. The sodium vaporized, jetting out of a hole in the rocket's nose, and a brilliant orange-colored trail appeared against the blue sky. This was the sodium; it picked up the light of the sun, still shining above the shadow of the earth, and reradiated it as brilliant "sodium light."

Orange "G." As the rocket rose to almost 70 miles, the high-altitude winds distorted the sodium-vapor trail into a gigantic "G" 20 miles across. It remained visible for 15 minutes, until the shadow of the earth reached it, and was seen in Amarillo, Texas, 300 miles away.

The sodium rocket was not merely a beautiful and expensive firework; it had a serious scientific purpose: to help the Air Force's long-range study of the upper atmosphere. Part of the "air glow" (the faint glow of the night sky) comes from sodium atoms that absorb solar energy during the day. At night they give off this energy as yellow sodium light. Scientists do not know how high the "sodium layer" is. Nor do they know how the sodium got into the top of the atmosphere. Some think it came from outer space; others suspect that it originated as fine particles of sea salt that were carried upward.

By putting a known amount of sodium vapor into the atmosphere at a known altitude, the sodium rocket will enable scientists to learn more about the natural sodium that is already there. They can compare the air glow coming from the two lots of sodium, and since the amount of one is known, the amount of the other may be calculated.

High-Wind Gauge. Probably more important for the Air Force's purposes is the possibility of measuring accurately the speed of the winds that blow on the boundaries of space, where guided missiles fly. There is some evidence that they may be extremely violent and that they may blow vertically as well as horizontally.

The sodium vapor that the Air Force put into the atmosphere will drift with the winds. If it increases the normal air glow, it can be followed, perhaps for considerable distances. A cloud of sodium of known origin picked up by astronomers' instruments in the Eastern states will be a fine way to measure wind velocity at levels that no weather balloon can reach.

From the observatory perched on nearby Sacramento Peak, Dr. Edward Manring of the Air Force Cambridge Research Center followed the sodium cloud all night. The light affected sensitive instruments so strongly that it drove them off-scale. It will be at least a month before Air Force scientists can analyze their data and decide what the experiment has taught them. If the results are promising, many other sodium rockets may be shot into the sky.

*Mixture of powdered iron oxide and aluminum, which, on ignition, gives great heat but no gas.

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