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Monday 27 June 2016

I'm off on my holidays...

Hi everyone, I'm off on summer holidays with my family, so I'm afraid there'll be no new posts for about ten days.

I guarantee you everything will happen over the next ten days. Oh well.

I'll be back with more space related awesomeness soon, until then please do browse the posts already up, and I hope you enjoy the site!

All the best,

John Freeman

Sunday 26 June 2016

All eyes are on our galaxy's biggest black hole....

This week has seen the start of turbulent times in the British Isles. The future, especially for science is looking uncertain.
 What can I write about to distract myself? 

How about the biggest black hole in our galaxy ? What if I throw ina whole star that’s about to skim the surface at 1/40th of lightspeed.  

‘Cause that’s what’s about to happen. 

For those of you that aren’t up to speed with galactic geography: In the centre of our galaxy is a monstrous black hole, that astronomers call ‘Sagittarius A*’. It weighs more than a million solar systems, is bigger than the orbit of Neptune, and probably grows by eating other black holes. It’s so powerful that, when it really chows down on something, the radiation produced as a by product can influence the evolution of life on Earth, 26,000 light years away. 

Above: The region of the giant black hole, and an X-ray close of of the area closest to it.

As far as extreme paces go, you literally won’t find better in this galaxy. It’s a naturally occurring lab for testing the theories of physics in the most intense ways imaginable: The Swift X-ray telescope monitors the hole daily, and right now a consortium of radio telescopes are being connected across the world to form the Event Horizon telescope, which will (hopefully) be able to get a direct image of it for the first time

Above: A quick run-down on the Event Horizon telescope.

Orbiting this monster is a collection of stars, gas clouds, and (presumably) smaller objects down from brown dwarfs to space dust. Recently the star ‘S2’ has been imaged by the new GRAVITY interferometer, which will be able to track it more accurately than ever before. That’s important, because S2 is in an orbit around the black hole that takes it to within spitting distance (alright… 17 light hours) of it’s point-of-no-return, the event horizon . 

As it falls towards the black hole it picks up speed, until it is travelling at more than 200 times the speed of our fastest space probe. It will tear around the black hole, close enough to have the hole loom large in the sky of any planets along for the ride (there almost certainly aren’t any, but that gives me an excuse to throw this picture up). 
Above: An artists impression of a world orbiting close to a titanic black hole.

There aren’t many tests of our theories of physics – especially the theory of general relativity – more extreme than close observation of an event like this. Watch this patch of (extremely hazardous) space, there could be some serious discoveries coming out of it.

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Tuesday 21 June 2016

How many moons does Earth have now?

The original, and still the champ.
A newly discovered space rock, which rejoices in the name 2016 HO3*, has been confirmed to be a long term ‘quasimoon’ of Earth. That means lots of ‘Earth has two Moons!’ headlines. Which is kind of fun, but this is probably something people are getting fed up with ("those crazy astronomers thinking they've found another new Moon that isn't one"), and tuning out.

It also gives me a perfect excuse to insert this QI clip...

And that would be a shame: If you take away the over the top headlines, this is a nice bit of science. 
The definition of a moon is "... a celestial body that orbits another celestial body of greater mass (e.g. a planet, star, or dwarf planet), called its primary". It doesn’t even have to be round. Earth definitely only has one that fully fits that definition. But, as well as the Moon, Earth has a loose family of tiny worlds that keep it company…

Tag along (co-orbital) asteroids: 

Above: The weird path of a co-orbital asteroid, relative to Earth.

The best known of this group is an asteroid called 3753 Cruithne. Cruithne has an orbit which crosses ours and takes one year like ours, so it’s always in a predictable position relative to us and is influenced by Earth’s gravity… but doesn’t orbit us (it seems asteroids can have comet-ment problems … geddit?*). From our perspective it follows a funny little horseshoe path, and so do a handful of other asteroids… 

Quasi Moons: 

Above: 2016HO3's quasi-orbit of Earth.

These have been known about for a while, and the new find fits into this category. The last one before this drifted away about ten years ago...  Which is why they get called ‘quasi’ moons: Although they are connected to Earth gravitationally, and follow an orbit of sorts about the planet, they’re not permanently bound to Earth. Over time they wander away, and new ones replace them. 2015 HO3  is one of the more stable ones, having been looping around Earth for over a century and set to stay for the foreseeable ffuture.  

Trojan asteroids: 

Above: A map of Jupiter's mysterious Trojan asteroids.
Earth has only on of these: It’s a 300 meter wide place called 2010TK7. 2010TK7 sits in a ‘Lagrange point’, a spot in space where Earth’s gravity and the Sun’s gravity cancel out. Things caught in such a cosmic sweet spot can lurk there for millennia, and the giant planets each have respectable collection of Trojans – which are some of the most mysterious objects in the solar system
Because the planets move about the Sun the Lagrange points do to, dragging their asteroid occupants with them. So 2010TK7 is under the influence of Earth’s gravity, and has a stable relationship with Earth, but also isn’t in an orbit around us. 

Future Moons: 

Above: Triton, Neptune's weirdest moon - one which was once a planet in its own right.

There are other worlds that have captured a moon - Neptune and Mars have both done it - when a wandering world happened to stumble into that planet's gravity at the right angle and speed to enter a stable orbit. And, with plenty of objects out there it’s easy to imagine that one day Earth could pick up a second Moon in this way. 

So,  how many moons do we have? 

One… but Earth also has an entourage of other hangers on, and ‘one’ is only the situation today…. 

* Seriously Science, I'm getting you a book of baby names or something.

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Friday 17 June 2016

LIGO, black holes, and cosmic mysteries...

Above: The gigantic LIGO  gravitational wave detector, seen from the air.

The LIGO detector has found another gravitational wave signal – evidence of two black holes colliding about 1.5 billion years ago. Because space is really huge, and the waves are only so fast, the signal only just reached us. Translated into sound, here’s what LIGO heard… 

…. But it’s not sound. What we’re detecting is a moving warp in space-time itself. It’s kind of awesome to live in a time when we can (as a species) sense something so bizarre – and by doing so we’re spying on the most extreme kinds of physics, only found in conditions we could never reproduce here on Earth. Now LIGO has proved that there are gravitational wave sources out there, we’re faced with a new question: What kinds of extreme things could we sensing with them, as our detectors improve? 

Black holes: 
The stellar beast that needs no introductions: Squeeze the core of a dying star hard enough and gravity becomes strong enough to override every other force. It shrinks the core down until the surface gravity is so intense that not even light could escape. Time essentially comes to a halt at the point of no return – called the event horizon – so, to an outside observer, every object that ever fell into the hole appears to be frozen on its edge
Both the gravitational wave signals detected so far by LIGO have (we think) been due to black holes spiralling around each other then colliding. Gravitational waves are produced by very heavy things moving very fast, so we hear a rising ‘chirp’ as the holes spiral quickly around each other, then collide and stop. 

Neutron stars / Quark stars / Magnetars: 
All these exotic, supermassive, objects (see ‘Major Tom visits a magnetar) are heavy enough to produce the same kinds of gravitationl wave signatures black holes do as they collide, albeit less intensely. 

Supernova are huge stars, tens or hundreds of times bigger than the Sun, that explode. Although, ‘explode’ is underselling it: First the giant star runs out of fuel. Then the outer layers collapse inwards, crushing and heating the core. The collapsing layers superheat and explode, temporarily outshining an entire galaxy. In the core, at the moment of collapse, black holes, neutron stars, and other weird denizens of the interstellar zoo can be forged. 
All of this involves massive amounts of matter moving at very, very high speeds, which should produce a gravitational wave signature – especially if the explosion is lopsided. Some are thought to be, as some neutron stars are flying through space a high speed, like they were shot out of an insanely big cannon. 

Fall of stars into supermassive black holes: 
In the centre of our galaxy – and, we suspect, most galaxies - lies a supermassive black hole weighing more than millions of Suns. When a star falls into one of these it accelerates to huge speeds just before it passes over the event horizon and into darkness – and huge masses moving at high speed equals gravitational waves.

Quakes on neutrons stars and magnetars: 
Neutron stars (and their close relatives magnetars) are both very dense, very heavy, and in many cases spin very very fast. They don’t produce gravitational waves as long as they spin on axis, but if something throws one off axis it would give a signal as it wobbled. And one of the things that could make a neutron star wobble is a ‘glitch’ or starquake in its mantle. Magnetars are prone to even more extreme events, driven by their magnetic fields, which are amongst the strongest in the universe. 

The Big Bang: 
The beginning of the Universe, understandably, involved very high concentrations of matter and energy moving about very, very, fast. That will have left behind a sort of ‘noise’ (in sciencese it’s a ‘Stochastic’ source). These waves could have been amplified by interaction with the background curvature of space-time, amplifying tiny variations in it. That could tell us things about the distribution of matter and energy in the very early universe.

These are just a few possibilities - things we know should be picked up. Other things we LIGO might detect include dark matter, and cosmic strings...

Above: An artists impression of a solar system being dragged into a supermassive black hole.
So stay tuned: Now the 'Einstein window' on the universe has been well and truly opened we could be finding a lot of weird new things....

Tuesday 14 June 2016

Homes in space part 3: Ringworlds, O'Neil cylinders, and bigger ideas...

We’ve looked at the kind of off-Earth living places - both on a planets surface and floating in space - that we might well build in the foreseeable future. A lot of them are based upon technologies tested in the last ten years on the ISS, like the inflatable BEAM module which astronauts entered for the first time recently...

But those are small fry. There are much more extreme habitats that, although we probably won't be building them anytime in the future, might be built by future generations. To keep thing manageable I’ve divided them into three broad category's:

Space bases we could build today - if we had the money:

In many ways this is the most interesting category, because the engineering and maths for these ideas checks out… it's just the maths associated with construction costs that don't close. And by ‘don’t close’ I mean you'd probably have to mortgage Earth itself to pay for just one. 

I'm not sure who you'd mortgage it to, either...

As such they make a cool look at the kind of in-space megastructures we might build if we really do expand into our solar system in a big way - to make them work monetarily we’d have to have a thriving off world economy, and the means to transport many thousands of residents off Earth and onto the new colony. As we’d need to get tons of building material, and power from in-space sources, to make these ideas work some of the concepts that companies like Planetary Resources and SpaceX are working on (asteroid mining, space based solar power, and mass space transportation) may one day feed into these concepts...

Bernal Sphere:

A steel and concrete globe about a third of a mile in diameter, floating in space, the Bernal sphere wold be a teeny, inside out, planet. Residents would live inside and it would rotate once every thirty seconds to provide Earth like gravity along its equator. Since this artificial gravity would peter out near the poles, and the poleward surfaces would appear to be sloped, it would be like living near the bottom of a really weird valley, wrapped around itself. A valley wit one added bonus: If you climbed the walls high enough you could fly!

10,000 people could live in one, their buildings lining the curve and appearing overhead. Although it’s a perfectly good design, I like to look at the stars at night, so the Bernal Sphere’s not my personal favourite – although I could always just dig ‘down’ until I found them…

Stanford Torus:

Above: The Stanford Torus from the movie Elysium.

Have you sen the movie ‘Elysium’? That space station is a Stanford Torus: A donut-shaped tube 130 meters thick with a diameter just over a mile. It also spins to produce its gravity, but unlike the Bernal Sphere the inner portion of the tube is open – the artificial gravity alone holds the atmosphere in place.

The torus would house a similar number of residents to the sphere. I prefer the torus as, looking up, you’d see both the far side of the torus, and the stars beyond. Spokes could connect the habitat ring to a central hub where spacecraft can dock, so when you visit your first sight will be the whole ring stretching around you. Weighing in at 10 million tons, you’d need an asteroid mining industry already in place to build this beast, but it could certainly done using materials like steel and concrete.

The O'Neill Cylinder:

Above: The Babylon 5 space station, the adventures of which crew I watched on a Sunday as a kid.

If you’re old like me* you probably remember a Sci Fi show called Babylon 5. If you don’t: The show was about the crew of an O'Neill cylinder, christened Babylon 5. As the name suggests, it’s a cylinder the main body of which is about 5 miles wide and 20 miles long. Once again, a gentle spin of one revolution every minute and a half would be enough for terrestrial gravity. O'Neill’s original design had two cylinders built in counter-rotating pairs to offset destabilising, gyroscopic effects that would cause the cylinders to stray from their intended, Sun-facing angles.

While any of these space colonies would be far more vast than the International Space Station, their engineering challenges could be met. "From an engineering standpoint, the structure is very easy—the engineering calculations are totally valid," says Anders Sandberg, a research fellow at Oxford University who has studied megastructure concepts. 

Ideas we might build using the strongest conceivable materials:

These are space habitat concepts where the engineering numbers close... just barely, and only if you use things like carbon nanotubes, or mass manufactured diamond. To build these structures you’d need massive amounts of such super-strong building materials – and, since these materials are usually only available in tiny quantities, these ideas will almost certainly stay fictional for a long time. But, that said, the numbers do close in theory...

Bishop ring:

Above: An artists impression of a Bishop ring

A Bishop Ring, originally proposed in 1997 by Forrest Bishop, is the Staford Torus’s big brother. Like Stanford's design, the Bishop Ring would spin to produce artificial gravity, but differs that it would use carbon nanotubes instead of steel. That would allow it to be approximately 1,000 km in radius and 500 km in width, containing 3 million square kilometers of living space – about the same size as India.

The habitat could either have an arrangement of mirrors to reflect sunlight onto the inner rim or an artificial light source in the middle, powered by a combination of solar panels on the outer rim and solar power satellites.

Mckendree cylinder:

Above: Artists impression of the inside of a McKendree cylinder, courtesy of Eburacum 45.

The Stanford Torus has a big brother, and the O’neill cylinder has one too: A McKendree cylinder is a space habitat originally proposed at 'NASA's Turning Goals into Reality' conference by NASA engineer Tom McKendree. As with other space habitat designs, the cylinder would spin to produce artificial gravity by way of centrifugal force. It differs from the classical designs by using carbon nanotubes instead of steel, allowing the habitat to be built much, much, larger. In the original proposal, the habitat would be 460 km in radius and 4600 km in length, containing 13 million square kilometers of living space… nearly as much land area as Russia.

McKendree proposed dedicating half of the surface of the colony to windows, allowing direct illumination of the interior. The habitat would be composed of a pair of counter-rotating cylinders which would function like momentum wheels to control the habitat's orientation. But why stop at ideas we might be able to build with a limitless supply of our most advanced materials?

Ideas we might never be able to build... but which are really, really cool:

Now we're definitely into science fiction territory: The ideas below are things we couldn't build, not even with infinite resources and all the exotic building materials we could eat**. That said... today's super strong materials were impossibly strong a hundred years ago: Maybe in another thousand years some engineer will be looking at plans for one of the ideas below and going "Yep... we can do that...".

This field is a as vast as a sci-fi writers imagination - so I'll just give you a taste, with two of the most mind bending...


Above: An artists impression of a ringworld.

Not just an even bigger brother to the other rings – a ringworld is an artificial ring approximately the diameter of Earth's orbit (which makes it about 1,000,000,000 meters in circumference), encircling a sunlike star. It rotates, providing artificial gravity, and has a habitable inner surface equivalent to, oh… about three million Earth-sized planets. Night is provided by an inner ring of shadow squares.

The idea for this first showed up the the Larry Niven novel 'Ringworld' and caught a lot of peoples imagination. In the novel the titular ringworld is made from a material that has a tensile strength nearly equal in magnitude to the strong nuclear force. In science circles we call such amazing miracle materials ‘unobtainium’… but history teaches us not to be so sure we understand the bounds of what’s possible.

Which brings me onto a really batshit crazy idea…

Ship stars:

Image: The Shipstar. Artwork by Don Davis.
If you're gonna build a titanic world all around a star, why not make use of all that caged power and turn the whole insane structure into a mind buggeringly huge starship? Because that’s utterly insane, of course.

Which has done nothing to deter authors Gregory Benford and Larry Niven from conceiving just such a thing. For a bit more description here’s the afterword for their novel 'Shipstar':

"Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a “ship” that is the shell, the Bowl. On the shell’s inner face, a sprawling civilisation dwells. The novel’s structure doesn’t resemble Larry’s Ringworld much because the big problem is dealing with the natives.

The virtue of any Big Object, whether Dumb or Smart, is energy and space. The collected solar energy is immense, and the living space lies beyond comprehension except in numerical terms. While we were planning this, my friend Freeman Dyson remarked, “I like to use a figure of demerit for habitats, namely the ratio R of total mass to the supply of available energy. The bigger R is, the poorer the habitat. If we calculate R for the Earth, using total incident sunlight as the available energy, the result is about 12 000 tons per Watt. If we calculate R for a cometary object with optical concentrators, travelling anywhere in the galaxy where a 0 magnitude star is visible, the result is 100 tons per Watt. A cometary object, almost anywhere in the galaxy, is 120 times better than planet Earth as a home for life. The basic problem with planets is that they have too little area and too much mass. Life needs area, not only to collect incident energy but also to dispose of waste heat. In the long run, life will spread to the places where mass can be used most efficiently, far away from planets, to comet clouds or to dust clouds not too far from a friendly star. If the friendly star happens to be our Sun, we have a chance to detect any wandering life-form that may have settled here.”

A complete flight of sci-fi gibberish, yes? But then, what would the people of the Roman empire thought of the geostationary satellite ring that encircles our planet, 36,000 km wide? Or the Three Gorges dam?


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Monday 13 June 2016


My sincerest sympathies to the families of those killed in the Orlando shootings over the weekend. My heart goes out to the survivors also,

John Freeman

Friday 10 June 2016

Fire in space...

Above: Some footage of the FLEX 2 experiments, part of a series of experiments to better understand fire in space. Oddly beautiful, isn't it?

To understate things hugely: Being stuck in a burning building is not fun. That’s why we have a heroic body of people called the fire service who do the ‘save you from a burning building’ thing.

In a space there’s no fire brigade, and outside is only slightly less deadly than the fire - which means an astronaut crew has nowhere to run, and no-one to help them in a major fire. And it's not like they never happen: In 1994, on the Russian Mir space station, a cosmonaut thought he’d beaten a small fire out with a jumpsuit (I assume a spare, unless naked firefighting in space is the best way to do it). Moments later he was horrified to find the the fire had just jumped into the jumpsuit, and was cheerily burning its way back out through it.
Jerry Linenger, an American astronaut aboard Mir, described fighting a larger fire in 1997: 

"As the fire spewed with angry intensity, sparks – resembling an entire box of sparklers ignited simultaneously – extended a foot or so beyond the flame’s furthest edge. Beyond the sparks, I saw what appeared to be melting wax splattering on the bulkhead opposite the blaze. But it was not melting max. It was molten metal. The fire was so hot that it was melting metal." 

Above: The Mir space station. One day someone will made a movie about it. That movie will include fires, the station getting rammed by a space freighter, and lots of cross-lingual swearing.
People began realising that fire in space has different rules, and space agencies spent a lot of time studying it. And it’s much, much worse than we thought:

Fire is generally hard to fight in space, partly because it can become freaking invisible: On Earth hot air rises, pulling the waste products and the flame itself into a relatively well confined (and hence easy to spot) cone. In space the flame has no such guide, so it spreads in a diffuse fashion that spreads out the light it emits – so much that it becomes almost undetectable. For the same reasons, fire is also less predictable in space: On Earth it will tend to spread upward faster than it does any other direction, but in space it spreads in all directions. 

Above: On the left is a normal flame, and on the left is a flame in space. Courtesy of the Discovery channel.
Oh but it gets worse: In space a fire will change how it operates to fit its circumstances, reacting to its environment. Fire wit limited oxygen in space will, rather than simply going out, split itself into many tiny ‘flamelets’. The flamelets use much less oxygen than a single flame front, move quickly and independently, will each then go it’s own way until one finds a new source of fuel and oxygen, and will cover more ground by dividing and multiplying where they can. The effect has been reproduced on Earth by keeping a fire sandwiched between glass and metal sheets, suggesting that the effect is linked to the different way air moves under microgravity.

To make the job of a space firefighter even harder, fire in space also needs less oxygen, and can stay burning at a lower temperature, making it much less likely to burn itself out. In experiments, fires have even been seen to carry on burning in an 'impossible' fashion: Still combusting after they’ve been apparently extinguished, via some unknown mechanism.

So how do you put a space fire out for good?

The Fire Industry Association put this question to astronaut Time Peake (link to their article here). He said: 

“We have procedures that deal with each case depending on the severity of the situation. In the most serious cases, we would don breathing apparatus and fight the fire using either CO2, water mist or foam fire extinguishers. We would also try and locate the power source and remove electrical power (electricity is most likely to be the cause of a fire on board). The smoke detectors trigger an automatic response from the ISS to shut down all ventilation systems, so as not to feed oxygen to the fire and to reduce the spread of smoke throughout the station."
Here's Chris Hadfield demonstrating some of their fire safety equipment... if by demonstrating you mean 'playing with it, and using it as a musical instrument':


If all else fails, the ISS always has at least one man rated spacecraft docked to act as a life raft. However the crew operate on a very, very strict ‘prevention is better than cure’ policy*: Anything going up to the ISS is tested to make sure it's completely non flammable - that's done by pressing a heated filament against it in a ventilated, sealed, box. When an experiment or mission absolutely must carry something flammable up there the crew do everything humanly possible to keep it away from any sources of ignition.

Until there's a real space fire service it will stay the nightmare enemy for astronauts - but we're getting better at understanding and controlling it, and it's turning out to be an amazing thing to study (even aside from the terrible danger)...

* Because you don't want to tell your boss you broke the ISS and left it to explode now, do you? Unless you're Sandra Bullock.

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Tuesday 7 June 2016

Fighting in space....

A bit of Kung Fu action is a staple of most sci-fi, but there’s little or nothing about how to fight barehanded in microgravity. That’s mainly because (for reasons we’ll examine below) it’s a very bad place to have a fight… but I’ve honestly never found a good place to have one, and this makes an interesting start point for looking at how people move in microgravity.

That's actual microgravity, not wires, guys...
Oh, by the way, while I have little experience with martial arts and self defence I'm no instructor. None of what follows is intended as serious self defence advice - it's a bit of amusement, which I've based on my own very limited knowledge and experience! If you're looking for real information on that then I'd recommend starting here (link).

So, to set up our scenario: We’re trying to disable an insane / alien controlled astronaut with only our hands and feet. Or we're bored, and they're passing by. Either way, as a first guess, we can look at how astronauts move in micro gravity, and apply some (very) basic martial principles*.

First we need to be clear about the difference between inertia, weight, and friction: 
  • Weight is the downwards force a mass feels in a gravity field, it’s what sticks things to the floor. 
  • Inertia is a mass’s inherent resistance to being moved, or having it’s direction of movement changed. 
  • Friction is the force you feel resisting movement because of two things (like your feet and the ground) rubbing against each other. 

In microgravity objects have no weight holding them to the floor, so the main source of friction is also removed. They still have the same inertia, so a person will still take effort to move about, or move other people about - but it will be significantly less than on Earth. In fact, even a fairly slight shove could send something flying into the opposite wall. This astronaut can literally move herself with a hair's force… 
So, yeah, where gravity is less you're effectively stronger. But there’s a downside: With no ground friction to brace yourself against Newton’s third law - every action has an equal and opposite reaction - will make you it’s bitch. Heavy things move at a slight push, but you go spinning backwards at the same time. That's why astronauts quickly learn to anchor themselves to something before using their over powered Earth muscles in any way. 

Above: An astronaut shows us around the ISS. Watch how he moves: He is able to move his whole body with only a fingertip's pressure, or gentle shove, and is constantly bracing himself against the walls.

So what does this mean if one of your crew mates is an alien agent on a bloodlust powered mission to kill everyone on board? The bad news is that, in effect, he's superstrong.
The good news is, so are you...
We’ll avoid the use of guns in space. In part this is because I have nearly zero experience of them. But mainly it's because if you had to fight in space you'd really, really, want to avoid putting a hole in the hull, or the oxygen generator, or the power cables.

Spotting the crazed astronaut:  

If one of them looks like this, that's a clue.
People who are about to get violent often display physical and behavioural signs, different than those who are merely angry. Their faces will go pale instead of red, their speech will tend towards shorter sentences. Their body language will change, perhaps to include an unconscious ‘stancing up’, often turning slightly sideways. Microgravity may well change some of these signals, for example: The redistribution of fluids and blood in microgravity makes a persons swollen and redder, which may make the face paling harder (but not impossible) to spot. But those signals are based in very basic human instincts, so they’ll be there in some form. A skilled fighter can read these signals, and use them to spot an attack tens of seconds to minutes before it occurs. More generally, having to operate in a world of 3D instead of 2D movement will make paying attention to your surroundings extra important, as you could also face danger from above and below. On the other hand if you’re ambushing someone this works in your favour.


How to hit in microgravity:

So you’ve spotted your crazed astronaut, and are either confronting them (possibly using some sort of fence position and distraction) or possibly ambushing them**. 

Above: Geoff Thompson, one of my favourite self defence authors, demonstrates 'the fence'. I have no idea how that would apply in microgravity, and I doubt I'll ever get the chance to try it out...

But, physically, mechanically, what’s the best way to attack them? 
  • Any blow you landed would send you ricocheting backwards, which also means…
  • Half the power of any punch is wasted in moving yourself, and….
  • Most of the energy going into the target will move them** rather than go into them, reducing the damage done by the initial impact - but greatly increasing the likelihood of damage from a collision with the walls.
So, looking at the physics of it, getting hands or feet attached to a solid wall is a must: It will make your blows/grapples much more effective, and stop you from being bounced off the walls like a football. Where one fighter has anchored themselves, and the other hasn't, things would probably be over fast: An astronaut who grabbed a hand rail and kicked out at an unsecured opponent would send them smashing into a wall with immense force, spinning them around wildly and disorienting them as well as injuring them. 

That said, it wouldn't do any important equipment they struck any favours either...
Once you've incapacitated your blood crazed attacker you need to contain them. Locking them up, zip-tied hand and foot, sounds like a plan. But, if there isn’t time, you can just strand them out of touching distance of anything: Although astronauts can wiggle about easily enough, actually moving forwards or backward without anything to touch is very difficult in  microgravity – although blowing hard in one direction for a long while should eventually cause some movement (Newton’s third again).
Of course, the best defence against a fight is not to have one – use your words! But that doesn’t make for a very exciting article…

*I have a little experience in martial arts, but as far as I know astronauts have never even tried play wrestling in space. So, if you disagree with any of this, feel free to post a comment:  Your take on it is just as likely to be valid as mine!

** Yes, I game that way too. No, no one will play with me anymore.


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