Can a ghost travel through space

Radiation exposure in space: "The limit value is clearly exceeded"

Correct. The radiation exposure on the ISS is only around a third of that further out in free space. In addition, a mission to Mars will probably take up to three years.

What would that mean for the health of the astronauts?

Presumably this would increase the additional cancer risk by more than three percent. From the perspective of the space agencies, these three percent are the limit for the radiation dose accumulated in the course of an astronaut's career. If the mission lasted three years, it would probably not be possible. Model calculations - which are fraught with great uncertainties - tend to assume 4 to 25 percent.

“A flight to Mars has always felt 30 years away in the past few decades. Lately, however, it looks like things are getting moving «

That sounds like a lot.

Space mission planners actually agree that such radiation doses are unacceptable. However, that does not mean that such a mission cannot be carried out anyway, provided that the appropriate volunteers are available. For a single astronaut who wants to fly to Mars, the risk of cancer is initially only an abstract consequence that may not even occur. The organizers of the missions would of course have to educate them in detail about the potential risks. And they would have to keep the mission duration as short as possible - that is the best way to minimize the radiation dose and significantly reduce the risk of long-term effects.

SpaceX has specific goals and is reportedly planning a manned mission to Mars in the 2020s. The flight should therefore only last around five months. Would that be a reasonable duration?

The less time in free space, the better. On a five-month Mars mission, the radiation exposure will be in the range of two six-month stays on the ISS, provided that there is sufficient shielding. In this respect, at least one of the central requirements of radiation protection - reducing the exposure time - would be implemented very well.

How could the still great uncertainties in risk assessment be reduced?

Ten to hundreds of thousands of people who have been exposed to space radiation would be needed to make precise predictions. This database does not yet exist - and it will not exist in the near future either. So far, we have relied heavily on the findings from the atomic bombs dropped on Japan in 1945. A lot of knowledge about the long-term effects of radiation exposure is based on this. For example, there is a relationship between the formation of various tumors and cancer mortality due to increased radiation doses.

And do you try to transfer this knowledge to the situation in space?

Yes, but we are dealing with different types of radiation in space than with the atomic bombs. In addition, those affected in Japan received a very high dose in a very short time - a few hours. In space, however, the radiation acts over a long period of time. We therefore make do with correction factors, which of course are again fraught with uncertainties.

So you don't really know anything concrete?

Scientists have done many biological experiments on heavy ion accelerators. There, atomic nuclei, which are also found in space radiation, are accelerated and shot at biological tissue. We have thus developed a relatively good idea of ​​how the cells react to a hit with a heavy ion and what damage occurs in tissues and organs. The uncertainties are more related to the effects of a complex radiation field, the transferability of short-term to long-term exposure and the risks for certain organs, such as the brain. We are trying to further reduce these existing uncertainties.

How?

For example, we conduct experiments with many different cell types and look at the damage and how the cells deal with it, for example whether they inform other cells about it. It could be that surviving cells do not "forget" a hit by a heavy ion and thus the first step towards a disease process has been taken.

Can't you just shield space travelers better from cosmic rays?

It is probably going a little better than before - but by far not completely. The cosmic radiation from the depths of our galaxy consists partly of particles with very high energy that can penetrate the outer walls of the spaceships.

And making it thicker doesn't help?

Space engineers are limited by the weight they can shoot into space with the rockets. However, one could, for example, shield a small sleeping area of ​​the spaceship better than the rest. Or one can place water supplies in such a way that they also serve to shield radiation. But a complete shielding is not possible in the spaceship. Simply because the particles of cosmic rays interact with the shielding material, which can create fragments with lower energy. These then simply fly on - and are often even more harmful to the body than the original particle. A bit of shielding can even be worse than none at all.

If astronauts land on Mars, for example, is the radiation dose still harmful there?

Yes, the dose rate on Mars is roughly a third of that in free space - and thus as high as on the ISS. This is because Mars has a very thin atmosphere compared to Earth and no magnetic field. So you also need a very well-protected habitat there, in which the astronauts spend most of the time. They would only get relatively high doses when they were deployed outside. Solar flares that only occur sporadically can also be dangerous. Large amounts of particles are accelerated enormously and then fly through space in a large gush.

Can such eruptions be life-threatening for astronauts?

The dose rates can actually reach levels that would be fatal to a person if they were outside in a spacesuit, for example. But with a shelter in the spaceship or in a habitat, this type of radiation could be shielded relatively well.

Is it possible to predict events with some time lag and warn astronauts?

Let me put it this way: The weather forecast for the sun is very, very difficult. But there is a lot of research going on and the astronauts can still be warned in good time with the right technology. Satellites close to the Sun would then warn of a sharp increase in the particle rate. And as a rule it would not be the case that an astronaut would receive a fatal dose within a few minutes, it would take hours or even days. The warning systems could therefore prevent the crew from being exposed to a lethal dose.

What do you think: will the first humans actually land on Mars in a few years?

A flight to Mars has always felt 30 years away in the past few decades. Lately, though, it looks like things are getting moving. Perhaps the way to Mars actually leads over the moon, where we can learn a lot about suitable habitats, shielding and warning systems. The manned and manned mission to Mars becomes more "science" than "fiction".