Van Allen belt and how Apollo overcame this challenge to the Moon (Part 2)

The last part of the two-part series on NASA's process prepares Apollo astronauts to cross to the moon.

The series is mainly from the prestigious 150-year-old popular Science magazine of US history and NASA documents.

Summary of Part 1: A brief overview of Van Allen's radiation belt and NASA's search for a solution to bring Apollo over this deadly belt to the moon in 1961. Space physicist James Van Allen proposed "cleaning" the belt with a nuclear bomb. NASA did not intend to do this, the Atomic Energy Commission tested a bomb to study nuclear war.

Part 2: Nuclear testing and radiation measurement results after reaching the Moon

US nuclear tests have been kept private for more than 50 years. Until recently, documents about them were declassified and widely published.

Nuclear testing

According to Popular Science, the US nuclear testing program in the early 1960s called Operation Dominic was a group of atmospheric tests designed to help researchers understand how nuclear weapons dust interacts with Earth's magnetic field if there is a nuclear war. The pinnacle of these Fishbowl tests was Starfish Prime , a 1.4-megaton bomb (equivalent to 1.4 million tons of TNT, 100 times larger than the bombs dropped by Hiroshima and Nagasaki in Japan). War 2) was dropped into the Pacific Ocean from a height of 400km.

The result of the nuclear explosion was the bomb Starfish, which caused the radiation around the earth to be more heavy, rather than erasing small (inner belt) as expected. By 1969, the number of high-energy electrons that had been pumped by Starfish Prim into the small Van Allen belt was reduced to 1/12 of the highest intensity after the explosion.

Starfish Prime after exploding 45-90 seconds.(Photo: Los Alamos National Laboratory).

Go to the moon and the radiation measurement results

In February 1964, NASA was confident that the Apollo crew could pass the belts fast enough so that the spacecraft shells and shipboard tools were adequately protected. It seems that NASA was somewhat reckless to take the risk of taking people through the deadly radiation belt without any extra protection. But in the framework of Apollo missions, it was just a small risk, said Amy Shira Teitel of Popular Science.

Launch the shuttle.

To monitor radiation exposure during flights, Apollo crews carry radioactive meters on board and on individuals. The results confirm that NASA made the right decision. At the end of the program, the world's largest space agency insisted that its astronauts had avoided a large amount of radioactivity that many feared would land on the moon.

The lethal amount of radiation recommended by the American Occupational Safety and Health Association is 300 Rads per hour. Radiological diseases only occur when you are exposed to radiation at 200-1000 rads in a few hours. The Atomic Energy Commission's regulations on radiation exposure for workers who regularly work with radioactive material are 5 rem or 5 rad / year (rem and rad are all units of measure Radiation, rem absorption is used to measure the extent of radioactive absorption in human tissues.

According to Space Center UK, the Apollo dates to the moon are the times when the intensity of the Van Allen belt is the lowest (this intensity is calculated by the oscillation of the sun's activity).

James Van Allen (1914-2006).

In an e-mail replying to a reader of a mysterious cosmic forum in 2005, who discovered Van Allen's belt, researcher James Van Allen (1914-2006) explained the radiation effects of this belt as down here:

"The most dangerous and difficult area is very high energy protons (tens to hundreds of millions of electron volts).

(MeV-mega electron-volt is the unit indicating the energy obtained by an electron moving through a 1 million volt voltage in a vacuum).

In particular, to avoid significant radiation exposure, long flights (eg for many months) of humans and other animals in earth orbit must be carried out at altitudes lower than 400 km. .

At 1,600km, a person in a space shuttle cabin in a circular equatorial trajectory in the strongest area of ​​the inner belt belt will infect the lethal dose of radiation. about a week.

However, the inner and outer trajectories of Apollo will cut the outer parts of the inner belt, and because of the high speed Apollo takes only 15 minutes to cross the area, and less than 2 hours to tape through much less radioactive area is the outer belt (the speed of Apollo according to NASA documents is 25 thousand km / h).

As a result, the radiation exposure of a round trip (trip) is still less than 1% of the lethal level - a very small risk between the much greater risks of such flights. I made these estimates in the early 1960s and informed NASA engineers in charge of planning Apollo flights. These estimates are still reliable ".

Thus, the total time Apollo passed through the Van Allen belts was about two hours. Apollo 11's trajectory was also calculated to avoid the strongest radiation areas, according to journalist Amy.

Apollo 11's trajectory was calculated to avoid the strongest radiation areas.(Photo: NASA).

Below is the average table of radioactivity that Apollo crews absorbed, from Apollo 7-Apollo 17 in 1972 (trips to the moon are Apollo 11-17). Data source is NASA's technical report on radiation.

The average amount of radiation absorbed by Apollo 7-Apollo 17 Apollo crews.

According to the table above, the average radiation exposure of the first voyage crew to the moon, Apollo 11, is 0.18 rads (equivalent to 0.18 rem or radiation from a chest X-ray). . The average radiation exposure of all Apollo missions to the moon is only from 0.18 to 0.55 rads, far below the safety regulations mentioned above.

According to Popular Science, no astronaut has any physiological or medical weakness. In addition, Apollo astronauts have ever been tested in trainings to prepare for the first moon flight in human history. Journalist Amy said that flying to the moon and radiation exposure to Apollo astronauts is like a day in the office and it is still safer to test military aircraft in the air at Edwards air base.

(*) Edwards Base in Southern California is one of America's most important military bases. This is also the headquarters of NASA's Armstrong Flight Research Center.