How to Protect Astronauts from Space Radiation aboard space station?

Hi guys,

I continue to toil on my indie hard sci-fi video game concept. The game takes place in XXII century aboard the Daedalus Space Station orbiting Venus. I try to achieve the hard sci-fi realism in various spacecraft details for deeper immersion and to make space studies more popular among the audience.

My today’s set of questions is about Space Radiation:

How to Protect Astronauts from Space Radiation aboard space station?

RADIATION

As before, I’m putting what I dug and came to here at the beginning to save your time for answers. Please, correct me if I’m wrong in my facts and conclusions.

In general, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. It damages electronic, makes material radioactive, destroys cells and DNA.

Astronauts are exposed to approximately 200-400 mSv per year while aboard International Space Station (ISS) and around 11.5 mSv per day for Apollo space/moon missions. A maximum radiation doze for astronaut career approved by NASA is 1-4 Sv. For comparison: people on Earth receive 2-3 mSv per year; for people who works on uranium mines – 20 mSv per year. The risk of cancer caused by ionizing radiation is well documented at radiation doses beginning at 50 mSv and rises at 5.5% with every single Sv.

Radiation can be! either non-ionizing (low energy) or ionizing (high energy). Ionizing radiation consists of particles or photons that have enough energy to ionize an atom or molecule by completely removing an electron from its orbit, thus creating a more positively charged atom. Less energetic non-ionizing radiation does not have enough energy to remove electrons from the material it traverses. Examples of ionizing radiation include alpha particles (helium atom (He) nuclei moving at very high speeds),beta particles (high-speed electrons (-e) or *positrons (+e)), gamma rays, x-rays, and galactic cosmic radiation (GCR). Examples of non-ionizing radiation include radio frequencies, microwaves, infrared, visible light, and ultraviolet light.

So, for the spacecraft we usually face 2 issues about radiation:

• Van Allen Radiation Belts.

• Space Radiation.

TWO TYPES OF RADIATION SHIELDING CHALLENGES

1. Van Allen Radiation Belts.

A radiation belt is a layer of energetic charged particles (HZE): prevalent - electrons and protons; less - alpha particles (two protons and two neutrons bound together into a particle identical to a helium (He)nucleus) and neutrons. That belt is held them running around the Earth in place around a magnetized planet, such as the Earth, by the planet's magnetic field. That makes Van Allen Radiation Belt a natural CERN.

The Earth has two constant such belts! and sometimes others may be temporarily created (in 2013, NASA reported that the Van Allen Probes had discovered a transient, third radiation belt, which was observed for four weeks until destroyed by a powerful, interplanetary shock wave from the Sun).

The Outer Van Allen Belt consists mainly of high energy (0.1–10 MeV) electrons and various ions (most are in the form of energetic protons, but a certain percentage are alpha particles and O+ oxygen ions) trapped by the Earth's magnetosphere. It is almost toroidal in shape, extending from an altitude of about 3-10 Earth radii (RE) or 13,000-60,000 km above the Earth's surface. Its greatest intensity is usually around 4–5 RE.

Then the Safe Zone lies – a region between the Inner and Outer Van Allen belts lies at 2-4 RE or 6,000-13,000km.

The Inner Van Allen Belt contains high concentrations of electrons in the range of hundreds of keV and energetic protons with energies exceeding 100 MeV, trapped by the strong (relative to the outer belts) magnetic fields in the region. The Inner Van Allen Belt extends from an altitude of 0.2-2 RE or 1,000-6,000km above the Earth.

The ISS orbit lies on 280-460km above the Earth. Which is good because ISS lies (or “falls” to be correct) below the Inner Van Allen Belt and still has the strong protection of Earth’s magnetosphere from Solar Wind (term 2). On the dayside of Earth, the magnetic field is significantly compressed by the solar wind to a distance of approximately 11 RE or 65,000km. Earth's nightside, the magnetic field extends in the magnetotail, which lengthwise exceeds 1000 RE 6,300,000km.

The Daedalus Space Station which is primary on low Venus orbit about 560km above the Venus’ surface (geo stationary orbit around Venus is 1,536,647 km; Venusian SOI is 616,000km against 924,000km Earth SOI). Since Venus has no intrinsic magnetic field! to act as a shield against incoming charged particles, the solar wind sometimes interacts directly with the upper atmosphere. However, Venus is partially protected by an induced magnetic field!, albeit it does not have Van Allen Radiation Belts.

Q1: So aside from trespassing Earth Radiation belts there is no threat of them on Venus’ orbits, right?

2. Here we come to the Space Radiation which splits into two parts which compete and affect each other (still both are deadly dangerous):

• Galactic Cosmic Rays (GCR)

• Solar Energetic Particles (Solar Flare Particles)

A) Galactic Cosmic Rays (GCRs) come from outside the solar system but generally from within our Milky Way galaxy. 99% of GCRs are atomic nuclei (90% simple protons (p) like hydrogen nuclei (H), 9% are alpha particles identical to helium nuclei (He), and 1% are the nuclei of heavier elements, called HZE particles) from which all of the surrounding electrons have been stripped away during their high-speed passage through the galaxy. They have probably been accelerated within the last few million years, and have traveled many times across the galaxy, trapped by the galactic magnetic field. 1% of GCRs are solitary electrons similar to beta particles (a high-energy, high-speed electrons (-e) or positrons (+e)) and a very small fraction are stable particles of antimatter, such as positrons (+e) or antiprotons (**p-bar).

HZE ions are heavy ions having an atomic number greater than that of He and having high kinetic energy. Examples of HZE particles include carbon (C), iron (Fe), or nickel (Ni) nuclei (heavy ions). Though the HZE particles are less abundant, they possess significantly higher ionizing power, greater penetration power, and a greater potential for radiation-induced damage. I put HZE in a separated paragraph because despite they are less then 1% of GCR, the damage they inflict (especially to human DNA) is even more critical than those 90% simple protons it is proportional to the square of the electric charge (e.g. iron (Fe) nuclei inflicts 676-times more damage than hydrogen nuclei (H)).

GCRs have been accelerated to nearly the speed of light, probably by supernova remnants. As they travel through the very thin gas of interstellar space, some of the GCRs interact and emit gamma rays, which is how we know that they pass through the Milky Way and other galaxies.

B) The Sun emits all wavelengths in the electromagnetic spectrum. The majority is in the form of visible, infrared and ultraviolet radiation (UV). Occasionally, giant explosions called solar flares and Coronal Mass Ejections (CME) occur on the surface of the Sun and release massive amounts of energy out into space in the form of x-rays, gamma rays, and streams of protons (p) and electrons (-e) called Solar Particle Events (SPE).

The Sun is slightly brighter when there are many sunspots. During one of these periods, the Sun is more actively producing SPE and CME so the amount of radiation in the solar system is slightly increased. The number of CMEs varies with the solar cycle, going from about one per day at solar minimum, up to two or three per day at solar maximum. Although scientists can predict that the Sun can produce more SPE and CME during this period, they are unable to determine specifically when SPE and CME will occur.

The good thing that the majority of Sun radiation (visible/infrared/UV and streams of protons (p) with energy low enough) can almost all be physically shielded by the structure of the spacecraft.

Q2: The GCR are a dominant source of radiation that must be dealt with aboard current spacecraft and future space missions within our solar system, right?

Because these particles are affected by the Sun’s magnetic field, their average intensity is highest during the period of minimum sunspots when the Sun’s magnetic field is weakest and less able to deflect them. Also, because GCR is difficult to shield against and occurs on each space mission, it is often more hazardous than occasional solar particle events.

VENUS MISSION

Nowadays, with modern technologies for a six-month journey to Mars an astronaut would be exposed to roughly 300 mSv, or 1.6 mSv per day in solar system space. As well as Venus doesn’t have magnetosphere to protect it from GCR and Solar Flare we can estimate the dose of radiation (with modern technologies) the same as during the solar system travel. Albeit, I’m curious:

Q3: As the Venus is 2.5 times closer to Sun, shouldn’t the doses of radiation from GCR reduced by more intense compensation of Sun’s CME/SPE?

Q4: With modern technologies, if we put ISS on Venus low orbit (e.g. 500km), what will be the dose of radiation an astronaut aboard it receive (mSv per year)?

For the Daedalus Space Mission with your help I already calculated! optimal trajectory for the Earth-Venus-Earth round trip mission (flyby): LINK. Thus, for the crew we will have (2100+ AD): * 112 DAYS transfer E-V (solar system space: 179 mSv) * 365 DAYS Stay (on DSS: 584 mSv) * 272 DAYS transfer V-E (solar system space: 435 mSv).

That makes in 1,198 mSv per two-years-mission in total. Though that sounds acceptable even with modern technologies according to NASA’s standards, the half of that doze can damage 1/3 of human DNA. As a result, natural biological recovery mechanisms of the human body can not handle the load, and every tenth man to go into space and every sixth woman will die from cancer. In addition, heavy nuclei will cause cataracts and damage to the brain.

But we speak about the future of 2100+AD based on current modern research in spacecraft radiation protection...

ASTRONAUTS RADIATION PROTECTION

Q5: So, how to protect astronauts from Space Radiation?

As far as I remember, since 2003 there has been a program for protection from space radiation in NASA’s Marshall Space Flight Center in Alabama. But the issue has not been solved by nowadays, right?

As far as I get, all modern studies circle around three directions (from less to more perspective): * Electrostatic Shielding. * Shield by force field. * Shield by matter. * DNA repair drugs.

1. Electrostatic Shielding - utilizing electrostatic charges to direct the energetic particles to follow a designed path, thereby avoiding the spacecraft altogether. The mechanic is based on idea to make a spacecraft to get positive charge by emitting electrons [-e]. That charge, allegedly, should deflect positively charged protons. But that idea (if I am correct) was finally declined not just because it would require 2GW (average power plant) to charge the spacecraft, but because the space is not just a vacuum thus the spacecraft will attract other, negatively charged high energy particles instead positive ones. http://ift.tt/1UvFiUr

2. Shield by force field – using strong electromagnetic field to deflect all ways of high charged particles. It will require to create a magnetic field 600.000 times more strong than on Earth to deflect GCR particles of up to 2GW energy. Bad things are that concept does not provide axis shielding, as well as astronauts will have to live in a magnetic field of 20T induction (if you put your head in a magnetic field of 0,5T you’ll immediately see the flares and feel an acid flavor on your tong).

3. Shield by matter - there are two direction of this method: use a lot more mass of traditional spacecraft materials, or use more efficient shielding materials. The sheer volume of material surrounding a structure would absorb the energetic particles and their associated secondary particle radiation before they could reach the astronauts. However, using sheer bulk to protect astronauts would be prohibitively expensive, since more mass means more fuel required to launch. Most of people think that using lead [Pb] would be good idea, but that is wrong: being bombarded by radiation the lead will become radioactive itself as well as it will become the threat for the crew by that (I’m not even mentioning the mass => cost/maneuverability/fuel issue).

The best way to stop particle radiation is by running that energetic particle into something that’s a similar size. Because protons and neutrons are similar in size, one element blocks both extremely well – hydrogen (H), which most commonly exists as just a single proton and an electron. By bombardment it can be turned to Tritium (T or 3H, also known as hydrogen-3) or to Deuterium (D or 2H, also known as heavy hydrogen), thought these isotopes are unstable and hydrogen relatively swiftly come back to normal stage.

Conveniently, hydrogen is the most abundant element in the universe, and makes up substantial parts of some common compounds, such as water and plastics like polyethylene.

We could use water (H2O), which is already required for the crew, could be stored strategically to create a kind of radiation storm shelter in the spacecraft or habitat. A water shield of 5m will create the protection equivalent to 5km above the Earth. However, this strategy comes with some challenges - the crew would need to use the water and then replace it with recycled water from the advanced life support systems. As well as the mass issue again: e.g. for 5m water shield for ISS it will give extra 500 ton of mass.

Polyethylene (C2H4), the same plastic commonly found in water bottles and grocery bags, also has potential as a candidate for radiation shielding. It is very high in hydrogen and fairly cheap to produce - however, it’s not strong enough to build a large structure, especially a spacecraft, which goes through high heat and strong forces during launch. And adding polyethylene to a metal structure would add quite a bit of mass (for my example for ISS it will mean extra 400 tonne of mass).

Here we come to the best material for space craft protection from radiation: Hydrogenated boron nitride nanotubes (hydrogenated BNNTs). BNNTs – are tiny, nanotubes made of carbon (C), boron (B), and nitrogen (N), with hydrogen (H) interspersed throughout the empty spaces left in between the tubes. Boron is also an excellent absorber secondary neutrons, apparently, making hydrogenated BNNTs an ideal shielding material. This material is strong, even at high heat – that is good for structure construction. Beyond that, so it’s flexible enough to be woven into the fabric of space suits, providing astronauts with significant radiation protection even while they’re performing spacewalks. http://ift.tt/1XR7bc2

Q6: But I’m curious did NASA experiment on hydrogenated aerogel for radiation protection?

4. DNA repair drugs – are based on enhancing DNA repair mechanism. As far as I remember the was a fundamental discovery behind the 2015 Nobel Prizes in Chemistry, which were awarded on to three scientists for explaining how cells repair mistakes in DNA that occur when cells divide. Fortunately for us, cells have teams of repair enzymes that try to fix this damage and mistakes.

Q7: Is there any DNA-repair drug approved by NASA or under testing by it?

QUESTION SUMMARY

Wooof... I suppose that is all for today.

At the end I’d like to summarize my questions below for better navigation: * Q1: Aside from trespassing Earth Radiation belts there is no threat of them on Venus’ orbits, right? * Q2: The GCR are a dominant source of radiation that must be dealt with aboard current spacecraft and future space missions within our solar system, right? * Q3: As the Venus is 2.5 times closer to Sun, shouldn’t the doses of radiation from GCR reduced by more intense compensation of Sun’s CME/SPE? * Q4: With modern technologies, if we put ISS on Venus low orbit (e.g. 500km), what will be the dose of radiation an astronaut aboard it receive (mSv per year)? * Q5: So, how to protect astronauts from Space Radiation? * Q6: But I’m curious did NASA experiment on hydrogenated aerogel for radiation protection? * Q7: Is there any DNA-repair drug approved by NASA or under testing by it?

Thank you for your time and answers :)

Submitted June 01, 2016 at 11:19PM by MrNixonOnReddit http://ift.tt/22z3VCY