To the history of the discovery of the Earth's radiation belts

As you know, already the first launches into space gave us a discovery that changed our idea of ​​the world around us. It's about the Earth’s radiation belts. According to a common theory, this discovery was made exclusively thanks to the first American satellite Explorer-I.

There is some truth in this, but the story itself, as often happens, is much more complicated. In this article I will try to reveal it in a little more detail. This is a revised fragment of my book about the Moon, which I hope will be published.



So Explorer-I. Launched February 1, 1958. Total weight (together with the last stage) 14 kg. They were not divided. Orbit 358 for 2550 km.

It is believed that it was during the study of his signals that a very interesting fact was discovered for the first time: at a certain height, the registration of charged particles completely ceased, the device "did not see" even cosmic rays always present. What was so strange that initially, James Van Allen (the director of the experiment) was told that his equipment was corny refused. But he did not give up and put forward his hypothesis: the radiation level at those altitudes where the satellite climbs is so high that this leads to a glut of the sensor.


Explorer-I before assembly.

Subsequently, this hypothesis was confirmed. This was precisely the discovery of the Earth’s radiation belts.

Actually in this formulation, everything is correct. But there is a slight nuance. If you open any articles, then most likely you will not find there scientific data transmitted by this particular satellite. Link will be to later devices.

What is the matter? To assess how difficult it was to make this assumption, which turned out to be a scientific discovery, we need to understand what data were available to a group of scientists involved in the calculations.

Explorer-I was very small. Of course, that was then all that the United States could take into space, but it also meant that it had a very, very weak transmitter. If radio amateurs could easily receive signals from the first Soviet satellite, in the USA it was necessary to build stationary posts of the Minitrack system to receive signals.


Appearance of stations. Several antenna fields are visible.


Control room


Antenna fragment close-up


Location of Minitrack stations. In addition to them, there was another station in Australia.

Minitrack was developed for the Vanguard, but was used to receive data from both the Explorer and Soviet artificial Earth satellites.

Despite the very high gain, it was difficult to obtain a signal from the satellite. There was no tape recorder on the first Explorer, and this meant that reception could only be carried out on a small section of turns.

To obtain a high-quality signal, it is desirable that, at the time of passage of such sections, the ground receiving station be relatively close, and the satellite itself should be successfully oriented. In itself, such a coincidence of all conditions at the right time is a rarity, and besides, most of the signals drowned in extraneous noise. A 1960 article explicitly states that most of the signals from the Explorer-1 are not processed and it is unclear when it will be, and whether it will be processed.
Half of all telemetry records had a rating of F. Completely unreadable data. The rest were no better.

But what is good if there is a proven design - you can run more.

The launch of Explorer 2 was scheduled for March 5, 1958, but it failed - the satellite did not enter orbit. On March 26, the Escplorer-3 was sent into space, and this was an important step forward, even though it entered an unintended orbit. Scientists removed the equipment for the study of micrometeors, and instead installed a miniature storage device for recording data during the entire turn. And the Geiger counters were covered with a metal sheet to reduce their sensitivity.


Explorer III. If you compare with the first device, you can easily notice the shielding sheet



Explorer-III miniature tape recorder

Now it was possible to obtain information about the entire orbit as the satellite passed perigee, under optimal conditions. It was this that led to a qualitative breakthrough, and after studying these data, a landmark discovery was made.

This happened on April 2, 1958. On this day, Van Alenn found out that the first data from Explorer 3 came to the NRL processing center. Taking a taxi to the center, he took printouts of the data there, then looked at the pharmacy to buy graph paper and a ruler. Then he locked himself in a hotel.

“At 3 o’clock in the morning, I packed the calculations and graphs and went home with the conviction that our tools on both Explorers I and III worked properly, but that we had a new mysterious physical effect .” - after Van Allen recalled

He did not yet know that on the same day, in his laboratory, an audio recording of the data he traveled had come. His staff, McIlvane, Ray, and graduate student Joe Casper, immediately began to analyze them. And when he returned, he saw on his chair a note: "The cosmos is radioactive!"


The same note.

Of course, Allen later referred to the data from Explorer-III in his scientific works. And he formed the first description of radiation belts. At that time, in the scientific literature, Explorer-1 and Explorer-3 were mentioned side by side, now they often talk only about the first apparatus, although the main work in this tandem was performed by the second. Perhaps this is done for simplicity, and perhaps for a better effect: the first American satellite made the first discovery that turned our view of space upside down. That sounds!


The first record of the Geiger counter readings along the orbit of the Explorer-3 satellite. The decrease in the counting rate of charged particles from zero to tenth minute is due to a change in the intensity of cosmic rays with latitude, and its constancy from the 15th to the 20th and from the 37th to the 80th minute is due to the saturation of the registration scheme of its signals. A decrease in readings to zero from the 20th to the 37th minute indicates that the meter was overloaded with intense flows of charged particles


May 1, 1958 Van Allen spoke at a joint meeting of the National Academy of Sciences and the Physical Society of the United States, where he voiced his theory. And soon she received strong evidence.



May 15, 1958 - TASS reported that Sputnik-3 weighing 1327 kg entered the Earth’s orbit. But he was impressive already. A large mass - more advanced appliances. The data of Sputnik-3 confidently confirmed the correctness of Van Alen and gave a lot of new information about radiation belts. But even then the formation of the myth about the success of the American Explorer and the failure of the Soviet Sputniks began. Here is what the Times magazine editor wrote:

"" ... not one of the three heavy Russian satellites transmitted reports of Van Allen radiation. One of the explanations is that the Russians outwitted themselves by refusing to tell the outside world how to interpret signals from their satellites. Because only the lower parts of the satellite’s orbits passed over Soviet territory, Russian scientists never received data from high altitudes.If some of the Soviet satellites had a storage device, then it did not work.Another assumption is that Geiger counters do not They were loaded near the apogee by Van Allen radiation and the Russian scientists did not know how to explain this unusual behavior.The dog, launched on the second satellite, died about a week later, but the Russians did not report whether it was caused by radiation. "".
But, after reading this remark, Van Allen demanded to add the following lines:

“I strongly disagree with the section of the article regarding the failures of Soviet researchers in detecting trapped radiation. In my opinion, our work with the Explorer-1 satellite really provided the main discovery, and I made the first public announcement at the joint session of the American Physical Society and the US National Academy of Sciences on May 1, 1958. Two weeks later, the Soviet Satellite-was successfully launched 3 ", and he provided substantial confirmation of our early results."

It would seem that you can put an end to this. But not so simple. To do this, it is enough to recall that a couple of months before the first “Explorer” Sputnik-2 was launched, and it already had all the necessary equipment for fixing radiation. Why didn’t his data lead to this epoch-making discovery? Didn’t he fix anything? As is now known, fixed. So what's the deal?


The SP-65 device on Sputnik-2 had a very complex design and was originally intended to study solar activity. He had three input devices located at an angle of 120 degrees relative to each other. This was done so that when the apparatus rotates, the Sun can fall into at least one receiver. Moreover, information from all receivers in telemetry was summarized. Why not? When the Sun enters one of the receivers, it cannot get into the others in any way, which means that their data are close to zero and do not affect the overall picture. Moreover, due to the rotation of the station (the satellite was non-oriented, after all), the data was expected to be received in the form of small bursts at those moments when the Sun fell into the field of action of one of the receivers.

The device turned on automatically when passing through Soviet telemetry stations. A total of nine telemetry fragments were received. Their decoding has puzzled scientists. Yes, sometimes a signal from the satellite came close to what was expected. But most of the information signaled a certain uniform (and very strong) background surrounding the device. This background increased or decreased very smoothly, and there were no correlations with the rotation of the station, as if the Sun was shining from all sides. Device failure? Control data testified to its serviceability. Here someone would exclaim: “Space is radioactive!”, As it was done in Van Alen’s team a few months later. Alas, such a daredevil was not found.

However, it should also be noted here that these were only the first steps. The discovery of radiation belts meant the appearance before scientists of a new, truly gigantic field of activity, its features scientists still had little idea.