Effects of ionizing radiation in spaceflight facts for kids
Astronauts traveling in space are exposed to a type of energy called radiation. This radiation can be harmful to their bodies. For example, on a six-month trip to the International Space Station (ISS), astronauts are exposed to about 72 millisieverts (mSv) of radiation. To give you an idea, 100 mSv is the point where the risk of getting cancer from radiation starts to become clear.
Longer trips, like a three-year mission to Mars, could expose astronauts to much higher levels, possibly over 1,000 mSv. On Earth, our planet's magnetic field acts like a shield, protecting us from most of this harmful radiation. But in space, astronauts don't have that protection, so they get much more radiation.
Scientists have studied people who were exposed to radiation on Earth, like survivors of the atomic bombs in Hiroshima and Nagasaki, or patients who had radiation treatments. These studies help us understand how radiation affects the human body.
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What is Space Radiation Made Of?
In space, astronauts are hit by different kinds of radiation. Most of it comes from very energetic particles like protons, helium nuclei (also called alpha particles), and heavy atoms called HZE ions. Sometimes, radiation can also come from nuclear reactions happening within the spacecraft itself or even in the astronauts' bodies.
This space radiation is different from the X-rays or gamma rays we usually encounter on Earth. It affects molecules, cells, and tissues in unique ways. Much of this radiation comes from outside our Milky Way galaxy and is called Galactic cosmic rays (GCRs). GCRs are mostly made of super-fast protons, but they also include some HZE ions.
Some important HZE ions are:
These particles carry a lot of energy, which contributes to the total radiation dose astronauts receive.
Why is it Hard to Predict Cancer Risk?
One of the biggest challenges for sending humans on long trips to other planets, like Mars, is the risk of cancer from radiation. It's hard to know exactly how much risk there is because:
- We aren't sure how much radiation causes cancer in space.
- We don't have simple ways to protect astronauts.
- It's hard to tell if the protection methods we try actually work.
To help reduce these risks, scientists need to figure out the best ways to plan missions. This includes thinking about:
- How long the space missions will be.
- The age of the crew members.
- Whether the crew members are male or female.
- What kind of shielding to use.
- If there are any special medicines or treatments that can help.
Do Astronauts Get More Cancer?
Scientists have studied many U.S. and Russian astronauts and cosmonauts. So far, these studies haven't found a clear increase in cancer deaths among astronauts compared to people on Earth. This is good news, but it's important to remember that not many people have been astronauts, so it's hard to get a lot of data.
How Do We Decide What's a Safe Radiation Level?
Scientists and space agencies like NASA have different ideas about how to set safe radiation levels for astronauts.
- No Limit? Allowing unlimited radiation risk is not an option because it would be too dangerous for astronauts.
- Comparing to Risky Jobs: Some compare it to other dangerous jobs on Earth. But safety on Earth has improved a lot, so this comparison might be too strict for space.
- Comparing to General Population: Another idea is to compare it to cancer rates in the general population. However, radiation-induced cancers can happen earlier in life than most cancers, which usually appear when people are older.
- Earth Worker Limits: Using the same radiation limits as workers on Earth is a starting point. But space radiation is different and harder to predict.
A group called the NCRP has looked at all the information about radiation risks. They have made recommendations for how to protect astronauts, especially for missions beyond low Earth orbit.
Current Radiation Limits for Astronauts
Career Cancer Risk Limits
NASA has a rule that an astronaut's risk of dying from cancer due to radiation exposure over their entire career should not be more than 3%. NASA wants to be 95% sure that this limit is not crossed. These rules apply to all missions in low Earth orbit (LEO) and lunar missions shorter than 180 days. For comparison, on Earth, the legal limit for adult workers is 50 mSv per year.
ALARA: As Low As Reasonably Achievable
There's a very important safety rule called ALARA, which stands for "As Low As Reasonably Achievable." This means that even if astronauts are within the set limits, space agencies must always try to reduce radiation exposure as much as possible. It's a way to make sure that the limits are not seen as "okay to reach," but rather as a maximum that should be avoided if possible. ALARA is especially important because there are still many unknowns about how space radiation affects the body.
How Can We Protect Astronauts?
Finding good ways to protect astronauts from radiation is a big goal for space scientists. While these protections might not be needed for shorter trips around the Moon, they will be very important for longer missions to Mars and beyond. In 2013, NASA scientists reported that a trip to Mars would involve a lot of radiation, based on measurements from a spacecraft traveling to Mars.
There are three main ways to reduce radiation exposure:
- Distance: Stay as far away from the radiation source as possible.
- Time: Spend as little time as possible near the radiation source.
- Shielding: Use a physical barrier to block the radiation.
Shielding sounds like a good idea, but it's very expensive to send heavy materials into space. Also, because we don't fully understand the risks, it's hard to know exactly how much shielding is needed. Scientists are also looking into other ideas, like special medicines or dietary supplements that could reduce the effects of radiation. Choosing crew members who might be less sensitive to radiation is another option.
Shielding works well against solar particle events (SPEs), which are bursts of radiation from the Sun. But for GCRs, which are very powerful, the type of shielding material matters a lot.
Antioxidants are substances that can help prevent damage from radiation. However, they might not protect against all types of cell damage that could lead to cancer.
Spacecraft Shielding
Using materials to shield a spacecraft can help against GCRs. However, thin shielding might actually make the problem worse for some very high-energy rays. This is because the shielding can cause new, harmful particles (called secondary radiation) to be created. For example, the aluminum walls of the ISS help reduce radiation, but in deep space, thin aluminum might actually increase exposure. Thicker shielding would be needed to block the secondary radiation.
Scientists are studying different materials for shielding, like plastics rich in hydrogen instead of aluminum.
- Liquid hydrogen, often used as fuel, is good for shielding and doesn't create many secondary particles. So, fuel tanks could be placed around the crew area for protection. But as fuel is used, the shielding decreases.
- Fresh or waste water can also be used for shielding.
- Even asteroids could provide natural shielding if a base were built inside one.
Scientists are also looking into more advanced ideas:
- Active radiation shields that use electrically charged materials like graphene to block gamma rays.
- Magnetic or electrostatic shields that use powerful fields to push away charged radiation particles. These are still theoretical and very complex to build.
Special protection is also needed for solar proton events (SPEs), which can be deadly in hours or days. Astronauts might move to a small, heavily shielded area, perhaps behind the spacecraft's water supply. During the Apollo missions, astronauts moved to the Command Module, which had thicker walls, and then returned to Earth if an SPE happened. Measurements later showed this shielding was enough.
However, current shielding methods are often too heavy and expensive to launch into space. For example, a design for a large space station needed hundreds of tons of shielding to reduce radiation to safe levels. This would only be practical if we could launch materials much more cheaply, or even get them from the Moon or asteroids.
Active shielding methods, like magnetic fields, are being explored because they might be lighter. But they also have challenges, like needing huge amounts of power or creating very strong magnetic fields that could affect astronauts' health. The NASA Space Radiation Laboratory is studying these effects.
Wearable Radiation Shielding
Besides shielding the whole spacecraft, scientists are also interested in designing special protective suits for astronauts. Adding a lot of shielding to the spacecraft makes it very heavy and expensive to launch. Active shielding is still a new technology.
Wearable suits could be helpful, especially for SPEs, which have less penetrating power than GCRs. Materials like polyethylene (a type of plastic) or water could be used. The challenge is making these suits comfortable and easy to move in. The Italian Space Agency, for example, suggested a garment that could be filled with recycled water when an SPE is detected.
A product called Astrorad, developed by the Israel Space Agency, StemRad, and Lockheed Martin, was tested on the ISS. It's a protective vest designed to shield the most sensitive organs, like the stomach, lungs, and bone marrow. This helps reduce the overall radiation dose without adding too much weight to the mission. It can also slightly reduce GCR exposure if worn often, like during sleep.
Timing of Missions
The Sun's activity changes over an 11-year cycle. When the Sun is very active (solar maximum), it creates a "bubble" that pushes away some of the GCRs. So, planning long space missions during solar maximum could help reduce the average radiation dose for astronauts.
Sometimes, large solar events called coronal mass ejections (CMEs) can temporarily lower GCRs. But this effect only lasts a few days, and CMEs can also cause dangerous solar proton events, so timing missions with CMEs is risky.
Choosing the Right Orbit
When spacecraft orbit Earth, they usually avoid or quickly pass through Earth's radiation belts. For example, a low Earth orbit (LEO) is generally below the inner radiation belt.
However, if a spacecraft goes to the Lagrange points between the Earth and the Moon, it will be outside Earth's protective magnetosphere for about two-thirds of the time. Lagrange points between the Earth and the Sun are always outside Earth's magnetosphere.
See also
- Central nervous system effects from radiation exposure during spaceflight
- Dosimetry
- Health threat from cosmic rays
- Radiation protection
