BAMFORD, BINGHAM, HAPGOOD: SHIELDING SPACECRAFT BAMFORD, BINGHAM, HAPGOOD: SHIELDING SPACECRAFT Shields for the starship Enterprise Ruth Bamford, Robert Bingham and Mike Hapgood discuss Downloaded from https://academic.oup.com/astrogeo/article-abstract/48/6/6.18/233155 by University of Strathclyde user on 25 April 2019 the physics behind shielding spacecraft from solar and cosmic radiation with mini- magnetospheres. ABSTRACT A renewed interest in human space exploration demands renewed care for the safety of astronauts venturing far from Earth’s protective magnetosphere. Here we assess possible mechanisms for the active shielding of a spacecraft, with consideration of scale, effectiveness and power use. Although nothing yet exists to match the apparent simplicity and effectiveness of the shields shown on Star Trek, the physics of plasmas 1: The Earth’s magnetic field extends out into space to form the magnetosphere, which deflects the demonstrates that some useful form of hazardous energetic plasma of the solar wind, leaving our planet sitting like a pebble in a stream. shielding should be possible in the next few decades. space activity has been close to the Earth, at less So why not bring a portable magnetosphere than 600 km altitude. This means that it is still along with you into the solar system? It seems a within the Earth’s ionosphere and within a tenu- pretty obvious solution. Future spacecraft and/ fter more than three decades, space ous atmosphere. So how is going to the Moon or or Moon bases could perhaps have portable exploration is again on the agenda, with Mars any different from spending 18 months on “mini-magnetospheres” of their own to pro- Athe distinct possibility of manned mis- the International Space Station? Space is space, tect the inhabitants and electronics from the sions to the Moon and Mars within a few years. right? Wrong. “Space” between astronomical potentially lethal energetic particles from the And this is where the trouble starts: space is a bodies is mostly empty vacuum by terrestrial Sun and outer cosmos. We need to determine really dangerous place for humans to explore. standards, but it is the very lack of matter that the physics of a magnetospheric shield: Does a There are the obvious dangers of blasting off the means that energetic particles can be accelerated magnetosphere have to be the size of a planet Earth on tons of liquid explosives in a tin can further and travel unattenuated. The energies in order to work? Could it work in miniature? carrying all your own air, food and water. Cou- the particles reach are so high that the atoms are And is it technologically practical to even con- pled with this is the essential ability to know mostly stripped of their electrons and travel as a sider on a spacecraft? This may all sound too exactly where you are in three dimensions, over quasi-neutral collective of negatively and posi- like science fiction, but then again so did mobile vast distances, through complex manoeuvres, tively charged particles connected together by phones 30 years ago. before you even attempt the delicate business of electric and magnetic forces – a state of matter re-entry. However, we have become quite adept defined as a plasma. The particles are electrons More than one solution at solving those problems over the past 50 years, and protons, predominately, though there are a The obvious and simple-sounding solution is to and are confident enough to go to the Moon to few heavier elements. Although there are rela- shield the occupants and electronics of a space- stay and then move on to Mars. The problems tively few particles, their energies can be so high craft behind thick absorbing walls. A planetary in going further and staying longer are logistical that they blast through DNA like a cannon ball body offers the possibility of underground bases, and demand optimized engineering capabili- – bringing radiation sickness and even death though risks during EVAs remain – and there is ties, but solutions can be envisioned, given the to astronauts. They don’t do instrumentation little point establishing a planetary base just funds. But there is a potential show stopper – a much good either. to stay indoors all the time. But it is during the hazard that has not been addressed since the Close to the Earth we have additional protec- journey in free space, fully exposed to the solar Apollo Moon missions. This is the effects of tion from radiation in the form of the Earth’s energetic particles, that the protection is most solar and cosmic radiation. Space may appear to atmosphere and magnetosphere (figure 1). It is needed. It is here that the material solutions have be a calm empty void, but in reality it is teeming the presence of this “shield” that has enabled a problem with extra weight, although that may with energetic particles and cosmic rays that manned space programmes to avoid dealing have to be considered a necessity. But material have devastating effects on human tissue, and with this problem so far. But they have to tackle shields have to be carefully designed if they are on DNA in particular. it now if we are to venture to the Moon and not to make matters worse. Energetic particles With the exception of Apollo, all manned Mars, outside the magnetospheric protection. hitting a material shield can generate secondary 6.18 A&G • December 2007 • Vol. 48 BAMFORD, BINGHAM, HAPGOOD: SHIELDING SPACECRAFT BAMFORD, BINGHAM, HAPGOOD: SHIELDING SPACECRAFT Shields for the starship Enterprise a “collective” of free positive ions and electrons. All “empty” space, be it interplanetary, inter- stellar or intergalactic, has to contain plasma. Downloaded from https://academic.oup.com/astrogeo/article-abstract/48/6/6.18/233155 by University of Strathclyde user on 25 April 2019 It is just at very low density. Stars, nebulae and pretty much everything else out in the universe is also a plasma, with a bit of dust here and there, and the odd black hole, so it is pretty important stuff to understand. The defining characteristic of a plasma turns out to be its collective nature. What this means is, because of the linkage between the electric fields of the charges of the plasma, if you per- turb one part of the plasma the whole of it can respond, a bit like slapping a jelly. Another defining characteristic of most plasma states is its truly “super” conductivity. There are excep- tions, but most plasmas have virtually no elec- trical resistance. As a plasma consists of free positive and negative charges, if you try to inject an electric field, electrical current or magnetic field into a plasma it will very quickly set up 2: A conceptual illustration of a spacecraft, in this case the SS Enterprise, protected from a coronal currents and electric fields to try to keep the mass ejection from the Sun by a deflector shield, thus keeping the human crew within safe. impinging fields outside. Plasmas really, really radiation as they lose energy by colliding with to 20 Earth radii (RE) in the direction facing the do not like to have electric fields or magnetic nuclei in the material shield. This secondary Sun and can extend up to 1000 RE in the shadow fields imposed upon them and they have the radiation is potentially very dangerous as its or magnetotail due to the drawing out effect super high conductivity to back that up. lower energy particles have a great propensity to of the flowing solar wind. The Moon’s average Magnetospheric plasma barrier deposit their energy in human tissue. The shield orbital radius is 60 RE, which means it goes in must be thick enough to reduce secondaries to and out of the Earth’s magnetosphere, although Here is where the importance of the Earth’s an acceptable level. it has no magnetosphere of its own. Astronauts magnetic field comes in. Empty space is filled Medical solutions are another approach, and en route to the Moon have to consider flight with plasma of one density or another and so is one with potentially far-reaching contributions paths that ensure only a limited exposure to the Earth’s magnetosphere. In fact it is critical to the to human health on Earth. NASA takes them boundary region or the tail, making the most of action of the magnetosphere as a shield that the very seriously. Frank Cucinotta, chief scientist the Earth’s magnetosphere. The Apollo astro- Earth’s magnetic field does come with plasma. for NASA’s Radiation Research Program at the nauts were lucky – Mike Lockwood discusses The solar wind consists of energetic parti- Johnson Space Center, recently said to Physics just how lucky on pages 6.11–17. They missed cles racing out of the Sun in a fast flowing (say World: “We should be able to develop biological being exposed to any major solar proton events ~400 km/s) plasma. When this hazardous, high- countermeasures such as antioxidants, pharma- that would have lead to either short-term radia- speed plasma encounters Earth’s dipole mag- ceuticals and gene therapy.” tion sickness (no joke on a spacecraft) or even netic field, the solar-wind plasma “sees”, from However, in this article we will consider issues lethal radiation exposure. its perspective, a region of space with a different relating to the possibility of being able to create The energetic particles from cosmic radiation, magnetic field and plasma density than it is car- some kind of “active shield”. How can we bor- in particular protons and electrons from the rying itself. It “sees” a magnetically confined row from nature’s solution by taking a portable Sun, possess a charge and are thus affected by plasma “wall” or barrier.