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Sunday, 1 May 2016

SpaceX's Dragon 2 - opening up the solar system?


Elon Musk, founder of SpaceX, announced this week that he plans to launch aprivate (unmanned) mission to Mars. The core of the mission will be SpaceX's Dragon Two capsule, an upgrade on the Dragon One model currently flying missions to and from the ISS. Dragon Two - which is currently undergoing testing - will be capable of ferrying up to seven crew to ISS.
That's cool enough, but the design isn't limited to ISS flights: It's designed to land on any world with a solid or liquid surface.

Above: A mock up of dragon two, on display at a SpaceX facility.

In conjunction with SpaceX's planned Falcon Heavy rocket it could put four tonnes of equipment on Mars, land on the Moon, or even put a payload onto one of the Moons of Jupiter.

Above: SpaceX's recent landing of it's Falcon re-usable booster.

Musk, it seems, isn’t content with less than the whole inner solar system - and he aims to make Dragon Two the standard interplanetary delivery vehicle.

Above: Dragon Two tests it's propulsive landing engines.

In September we'll find out more details of the planned Mars mission. The internet is already alight with speculation on it, so instead I thought I’d try looking at some of the ideas being raised for using Dragon Two to explore the rest of the solar system.

First, some caveats: Putting humans onto another world -possible excepting the Moon or a small asteroid - with just a Dragon Two isn't really an option because many months in a capsule the size of a big shower cubicle isn't great for astronaut psychology.
Plus Dragon 2 is designed to land on these worlds, not take off again... which is also bad for astronaut psychology*.


The Moon:

Above: An Apollo astronaut . Will humans return to the Moon any time soon?

If you can do a rocket powered landing on the Martian surface you can certainly manage one on the Moon. Dragon Two could land large loads of sensors and instrumentation, heavy duty  rovers, multiple small rover, supplies and equipment for a lunar base, or robots to build one. There's a lot still that we don't understand about the Moon, and scientists are very eager to get exploring:



  • ISRU (In-Situ Resource Utilisation): This is one of the big enabling technologies we'll need to develop if dreams, like Elon Musk’s, of expanding into the solar system are ever to be realised. Experiments with using lunar resources for construction and science are also high on peoples list: It would take far less energy to build and launch a vessel from the Moon than it does from Earth.

Above: The strange 'Ina' formation, which seems to have erupted in the last million years.

Although Musk himself is focussed on Mars, a lot of folks who'd like to begin exploring the Moon again are paying close attention to the Dragon two.

Near Earth asteroid:

Above: An artists impression of an asteroid being transformed by 3D prinitng. Courtesy of NASA.

Dropping a major payload onto a near Earth asteroid with Dragon two would be even easier than landing it on the Moon. With missions like NEAR, Philae, and Hayabusa, we've learned a lot about landing on such teeny objects, and there’s lots of reasons to do so: The possibility of extracting resources from them, studying their geology (which would tell us about how the solar system formed), and even sending a manned expedition are all on the cards – not to mention learning how to move a dangerous one.

But one possibility being bought up  is that we could use a Dragon two to kidnap one: It's been known for a while that small space rock s - only a meter or less wide - can and do get caught in Earth's gravitational field, becoming 'quasi moons'. A heavily modified Dragon two capsule could track one of the smaller ones down and bring it back to Earth intact. Only tiny amounts of guaranteed uncontaminated  asteroid material have been returned to earth to face the full battery of scientific investigation.

Mars:

Above: Marathon valley, Mars.

You could write a book on the science that scientist want to do on Mars - and plenty of people have. Amongst the most exciting things a Dragon two could land on the Martian surface are :
  • Landing equipment and supplies for a manned mission: Any future 'boots on Mars' effort will have to include a long stay on the Martian surface - partly to make the time and money well spent, and partly because orbital mechanics dictate that there are better an d worse times to make the crossing. So dropping supplies onto the surface with Dragon 2, ahead of the main event, would make the whole thing more do-able.

  • An unmanned sample return mission: The large payload mass that Dragon 2 could put on the Martian surface means it might be able to deliver the mission that, in many space geek’s eyes, is the next best thing to a manned landing: A mission where carefully selected Martian rock and/or soil is collected by a rover, returned to the capsule, and then launched back to Earth. It's a huge technical challenge, but having a proven system that can land enough equipment on the Martian surface would clear the first big hurdle

  • Send a greenhouse: Dreams of terraforming Mars rest on the idea that, with some do-able modifications, the Martian environment could support plant life from earth. One mission being floated around the 'net is landing an inflatable greenhouse, and experimenting with growing living things on Martian soil. That might also give any manned missions the handy knowledge of how to grow their own supper while on the red planet.

  • ISRU experiments: Much like on the Moon, this means learning to use native resources of another world, such as ground ice, minerals in the soil and rock, and even the gasses in the air, to build, maintain, and power human activities.

Venus:

Above: the surface of Venus, as seen by a short lived Russian lander.

If you can go to Mars you can get to Venus - but the morning star planet has the most challenges of any world Dragon two could reach: The surface pressure is over ninety atmospheres, and the temperature is four hundred degrees Celsius plus. Probes have made it to the surface before, but haven't lasted long. However there's a lot of interesting science to be done at Venus, as Europe’sVenus Express spacecraft showed, and which Japan's Akatsuki is now following up on:




  • The atmosphere is a complex mystery of interacting chemical processes.

  • The atmosphere also contains a layer, at 70km altitude, which is actually the most Earth like environment in our solar system, and might one day be suitable for a manned visit by a balloon bourns space craft.

As well as the possibility of landing some kind of hardened probe on the Venusian surface, Dragon 2 could be used to drop a serious balloon mission into the atmosphere. Venus air is less like earth's atmosphere, and in many ways more like our oceans - there are plenty of mysteries, and even speculation of airborne bacteria, that could be explored without needing to go near the hellish surface.

The moons of Jupiter:

Above: An artists impression of Jupiter, seen below the plane of its moons.

In general outline Jupiter's system of moons resembles its own miniature solar system - and each of the four main moons (Io, Europa, Calisto, and Ganymede) has its own unique character. A Dragon two mission to any of them would be able to carry less than a Mars mission, and would need radiation shielding... but there’s a lot to do there:

Io:
The most volcanic world in the solar system, Io's surface is a complex and ever changing smorgasbord of lava lakes, gigantic volcanoes, and complexsulphur based chemistry. A lander mission to Io would open up a window onto one of the most fascinating and alien environments in the solar system, not to mention being an enormous technical achievement.

Europa:
The other world in Dragon 2's range which could easily have a whole book written on it, Europa has had astrobiologists practically drooling ever since it became clear that there's an ocean beneath the icy crust. Kept liquid by the heat from Io-like volcanoes, how far below the ice the ocean lies is upfor debate. Jumbled regions of ice called chaos terrain suggests that there are areas where it can break through to the surface. More evidence of the ocean reaching the surface emerged last year, when a plume of water vapour was seenshooting up above the surface by Hubble. A lander mission in then right spot could give us a chance to sample ice that was once water in the ocean - and if that ocean supports life the evidence for it could be right there to be picked up.

Callisto:
Although it doesn't receive the same amount of tidal heating as Europa, Callisto may well have its own internal ocean, albeit at over 150 km depth. it's surface is ancient, and something of a mystery - it's not clear exactly how old it is, or if it ever interacted with the internal liquid layers. Organic compounds have been detected on the surface, suggesting that there's scope for life-like chemistry to have gotten started if the surface did have contact with the ocean.

Ganymede:
Yet another world with an internal ocean, Ganymede is the largest Moon in the solar system, and like Io and Europa, has a hot core capable of driving geologic activity. The cores churning gives the moon a planet like, magnetic field, and it even has its own faint aurora's. Ganymede’s surface is broken into brighter and darker areas, possibly indicating that some areas were changed by cryovolcanism - which would mean that a lander on Ganymede might have a large selection of material from the internal ocean to study.

Above: An artists impression of the surface of Io, near a lava lake.

Being a jack of all trades will undoubtedly give the Dragon two capsule some disadvantages compared to a probe customised for a particular destination, but Musk's ambitions overall seem to be driving down the cost of space travel via standardisation and re-usability. And, if it works, it might help open a new age of exploration....

*Although, in all seriousness, a one-way manned mission has been suggested.

Thursday, 28 April 2016

SpaceX to Mars?

Above: An artists impression of the Red Dragon capsule landed on Mars. Courtesy of SpaceX.
SpaceX has announced plans to land a private unmanned mission on the Martian surface, launching as early as 2018. I've only got the time to put up a brief note on this at the moment, but I'll follow with something more detailed when I've had a chance to do the research - and listen to the reactions of various engineers and scientists I'm in contact with. For the moment, here're the highlights of the announcement:
  • Elon Musk, SpaceX's founder, has spoken in the past of hugely ambitious Mars missions.
  • His ultimate goal is private manned missions and a colony.
  • SpaceX have had a Mars adapted version of their Dragon spacecraft, called the Red Dragon, in planning for a while now.
  • Red Dragon will land a payload 5 to 10 times bigger than any previous mission, using  rocket motors to slow it's descent.
  • The science payload hasn't been described yet, but may include a sample return mission. 
  • Red Dragon will be a huge step towards the Dragon 2 craft, which will be able to land anywhere in the solar system. 
  • It will launch on SpaceX's Falcon heavy rocket.

Above: A dragon capsule conducts landing tests, using a similar 'propulsive landing' to that described for the Red Dragon variant.



Tuesday, 26 April 2016

Space: A blizzard of rocks?


When people think of the asteroids, they either think of this scene from Star Wars, with its cloud of close packed boulders...

Above: A Star Wars asteroid belt. Couyrtesy of Lucasarts. Or Disney. Or someone....

...or, if they've read a little bit more, they think of a doughnut shaped belt of a few thousand rocks going around the Sun.

OK, not that much like a doughnut shape. Mmmm, doughnut.

It's not like that. 

Take a hailstorm, and separate each of the hailstones by kilometres -  but keep the number of hailstones the same, so the storm is now huger than worlds. Scale it all up again, so the 'hailstones' can be up to hundreds of kilometres wide, and travelling at tens of thousands of kilometres an hour.

Now keep the storm running for billions of years and fly in circles through it. That's what you (and me, and all of us) are doing right now - planet Earth is zooming in circles through space, through a storm of flying rocks.
While the odds of getting hit by ones of the asteroid 'hailstones' at any given moment is small, over time it becomes pretty much certain we'll catch a few in the planetary windshield. When we do the results have ranged from spectacular fireworks...




Video above: The Leonid meteor shower - the Leonids are a stream of dust and debris left behind by comet Tempel-Tuttle, so what you're seeing here are pieces of comet raining out of the sky. That's fine, and beautiful. Whole comets raining out of the sky would be more of a problem... Video courtesy of Space.com.

... to an explosion that damages a city and injures thousands of people...


Above: A van-sized asteroid explodes over the city of Chelyabinsk, Russia.
 
....to the once in a hundred thousand years mega impact, or even bigger, that can kill off whole species. But asteroids aren't simple bad news: They also delivered the water and organic chemistry that enabled life to get a toehold on ancient Earth. They may even have warmed Mars enough to make it habitable, once.

Today they bring us a free way of exploring worlds billions of miles away, and even worlds that were destroyed long ago. And some people are hoping the could become a source of material we can use to expand our space economy.

Image above: A cut and polished nickel-iron meteorite, showing the strange Thomson structure that occurs when the metal has cooled very, very, slowly, under microgravity - which means in the dying core of a protoplanet. Bits of the iron cores of protoplanets just fall out of the sky! But it's too rare to justify always wearing a hard hat. And a hard hat wouldn't be much good against most of these things anyway. 
But, if you just like hard hats, feel free... Image courtesy of The National Museum of Wales
  
What does this hailstorm of asteroids look like? I ran across this video a long while ago, but it still shows it well: New discoveries in white, main belt asteroids in green, non-threatening Earth approachers in orange, potentially hazardous Earth crossers in red. Enjoy! Or possibly be afraid...



Video above: A map of the inner solar system, showing the discovery of asteroids from 1980 to the present day. That's a lot of rocks. What really strikes me, though, is that by the end of the animation all the terrestrial planets are embedded in a swirling disk of flying rocks! It's worth remembering:  These blips are the remnants of the Suns protoplanetary disk  that gave birth to all the planets... Video courtesy of Scott Manley 

Monday, 25 April 2016

Remote controlled asteroids?

3D printing is a technology that looks set to change lot of areas, and that includes space technology: It's already been tested to make ceramic components for spaceships, and people like DARPA are getting very excited about where it could lead. ESA has even begun planning a 3D printed Moon base:

Above: ESA's concept for a 3D printed Moonbase. Courtesy of ESA. 

But a new project, prompted by NASA and being carried out by Made In Space Inc,  seems to be veering slightly into supervillan territory: They're looking at sending 3D printers, to asteroids (link here), turning the asteroid material into crude mechanical parts, and slowly converting the asteroid into a huge (if basic) unmanned spacecraft. Once converted, an asteroid automaton would steer around the solar system under commands from Earth.

Above: Artists impression of an astroid beng converted.

That'll mean some major advances in 3D printing, but nothing unbelievable. Made In Space have already pushed the envelope, launching a 3D printer to the International Space Station and making tools with it there.

Above: 3D printing in space...

Although Made In Space are just doing a feasibility study, it could make things like asteroid mining far more realistic by allowing asteroids to be moved into accessible orbits near Earth. On top of that, any and all expedience we can gain modifying or moving asteroids could be vital in protecting Earth when - and it is a question of when, not if - we find discover an asteroid on a collision trajectory with Earth. It could allow previously unbuildable spacecraft designs to become reality, printing them from asteroid stuff, wherever they're needed.

Above: Very large antenna are just some of the structures that could be printed in space, but are too fragile to launch whole..Courtesy of Made In Space.
It's a study that could be very, very exciting... if it pans out. But - and I'll only raise this thought once - a steerable asteroid would also make one hell of a weapon of mass destruction...

Saturday, 23 April 2016

Eleven planets in our solar system?

If you've braced yourself for another rant on Pluto's demotion to the status of 'Dwarf planet' then you can unclench. Nor am I plugging a Tolkien fanfiction where we find out where Gimli really came from*.

 Would you want to tell him there's something wrong with being a dwarf? Image courtesy of Seraph777
I'm talking about the growing evidence that our solar system once had two extra planets, both bigger than earth.

So where are they
Lets start at the beginning: For millions of years the inner solar system was filled with hundreds of planetary embryo's, colliding and merging. These gradually grew from planetesimals to Cere's sized worlds, then to Moon size. 


Above: An artists impression of the growth of a protoplanetary disk. Courtesy of NASA

At the same time there was a cosmic demolition derby going onProtoworlds were tugging on each other with gravity, destabilising each others orbits. 
Eventually the inner solar system found some sort of stability. But, many other solar systems have worlds closer to their Suns than Mercury, and our solar system doesn't. In fact, the space between Mercury and the Sun is devoid of any kind of world, even asteroids - and that's also strange, since the missing matter makes our solar system lightweight compared to most.

Now Rebecca Martin and Mario Livio from the University of Nevada have found an explanation: There was a planet, bigger than Earth, inwards of Mercury, which absorbed all the asteroids and dwarf planets near its orbit.... then, in the outer solar system, Jupiter's orbit shifted inwards. All the inner planets were forced to move inwards too.... and the innermost world fell into the Sun.


Above: The Sun - a giver of life, but also a destroyer of worlds....

Why did Jupiter's orbit shift so disastrously?
Researchers trying to replicate the growth of the giant planets in computer simulations have found that it's hard to do so and end up with the four giants we have today. But making a solar system with five giant worlds is much more likely. 
So we're now missing two extra worlds - and it turns out they may have been victims of the same cosmic disaster: According to a team form the University of Toronto, the fifth giant planet was an ice giant in the outer region of the solar system. It wandered too close to Saturn, setting off a chain reaction: It was pulled inwards, simultaneously moving Saturn further out. Then it had a similar encounter with Jupiter, and the king of the giants threw the smaller giant entirely out of our solar system. That same encounter moved Jupiter closer to the Sun, dooming the young super-Earth. It was a planetary demolition derby - and it sent one world into fire, and doomed another to an icy exile.

What would these worlds have been like?  We can look at other solar systems for clues. The planet Janssen is a super-Earth orbiting the star 55 Cancri, at 1/25th the distance of Mercury, and it's an incredibly harsh place: Its surface temperature is 2000 kelvin, it's atmosphere is made of hydrogen, helium and hydrogen cyanide with lots of carbon. The surface is very black, and temperature variations may point to active volcanoes.

Above: An artists impression of Janssen (55 Canrcri e), a volcanic super earth closer to its Sun than Mercury is to ours.
The ice giant, if it's anything like the current ice giants Uranus and Neptune, would have been a huge blue or green orb with it's own system of rings and moons. But, unlike the long dead innermost world, the ice giant is almost certainly still out there somewhere, wandering the galaxy as a rouge planet.
If recent evidence of a ninth outer planet pans out then that means our solar system once had eleven planets - making the ancient solar system an even stranger place than we'd already thought.

*Don't go looking for that fanfic on the internet, nothing good ever came from such a googling.

Wednesday, 20 April 2016

Starship drives part 2: Faster than light engines!

In the last post we looked at the possibilities that exist for building an engine that could reach another star system. We were looking at things we could build, or at least realistically research, today. They're great - for unmanned probes, to the nearest star systems. 

Above: The nearest other solar system to our own - it's lonely out here! Space.com
But such engines are not great for much further jaunts, because they all have one thing in common: They're limited by the 'speed of light' rule. Breaking the speed of light isn't just a question of more power and better materials: Anything approaching lightspeed begins to experience seriously weird effects, like time slowing down, mass increasing, and distances distorting - all stopping any further attempts to increase forward speed. 

How quckly time moves, compared to how fast you travel- and if time slows down, so does whatever mechanism is running your engine, so your engines stop working.

But, when you get into their details, Einstein's theories point to certain loopholes - ways to reach your destination sooner than the lightspeed limit allows, without actually breaking the speed limit. We're into the realm of engines that distort space - although 'engines' might not be the right word. 'Bizzare phenomena we might one day tame' is a better way of describing them. 

None of these are anywhere near even a laboratory demonstration*, but as far as we know the theories are at least sound enough to be worth investigating 


Wormholes:

Above: The basic concept of a wormhole: If space is the sheet, and normally you'd need to travel all along the sheet to the destination, a wormhole lets you jump straight from one side to the other.
In many ways these are the grandaddy of FTL ideas, coming straight out of the equations of general relativity: Two distant points in the universe can be connected by a bridge/tunnel made of space/time itself - a wormhole - along which the distance is much shorter. 

If the two points are very far apart then a wormhole can simply provide a shortcut, like in the picture above. But that's not the only way such a bridge can shorten trip time: The ends of the bridge can be made to connect to different times. Connect the other end of the wormhole to  last Thursday and you could actually arrive before you set out. The trick is that light rays moving along the wormhole with you will still be moving faster than you - so the speed of light rule stays in one piece. But there are all sorts of problems with actually building, and maintaining, such a bridge:
  • It would be hugely unstable, prone to slamming shut and crushing a traveller - in fact the vibrations of just one photon could cause it to slam shut, making it useless even for communication. To counteract this it would need to be held open by cramming immense amounts of 'exotic matter', that has negative mass, into it.
  • Bringing the mouths of the wormhole close to each other, if it could be kept open, would cause an endless loop of regurgitated photons to build up between them, resulting in a gigantic radiation pulse.
  • Building it in the first place would mean tailoring black holes to have specific properties, no small feat considering we don't even understand what goes on inside one.
All that said, there is some hope: A recent study found that, while a truly stable wormhole might be impossible, very small wormholes might be persuaded to collapse very slowly - slowly enough for communications at FTL rates through it, at least. 


Alcubierre drive (Warp drive): 

I couldn't have an article on warp drive wihtout a Star Trek reference, could I?
This is a (slightly) less outlandish take on the trick wormholes pull. The Alcubierre engine is based on the observation that  the galaxies in our universe are not simply flying apart, the space between them is, of itself, actually expanding. If space can expand then, in theory, it can also  contract. 


Above: Space itself is expanding - courtesy of minutephysics, who do a lot of interesting videos!

So the Alcubierre drive applys huge amounts energy to the space behind the ship, making it rapidly expand, and huge amounts of negative energy to the space in front of the ship, forcing it to rapidly contract. The ship itself is caught in a calm bubble in between the two, and that bubble is dragged across the universe at FTL speeds by the expansion behind and contraction in front, along with anything inside it.  

Again, it works because a ray of light, in the calm bubble with the ship, would still be moving quicker than the ship, Hence the ship is not, technically, breaking the speed limit. 
To work the drive needs negative energy, which we can only make in minute amounts, and would build up a gigantic 'radiation shockwave' as it travelled, probably vapourising the destination world. Even so NASA has seriously looked at what would be needed to apply the theory, albeit as a simulation only. 


Natural variation in the speed of light:


In a completely different approach to the space/time engineering of wormholes and Alcubierre waves, one way of travelling faster than the current speed of light may simply be to wait for it to change. Going back to Einstein himself, various physicists and cosmologists have pointed out that some of the cosmos's great mysteries become a whole lot less mysterious is the speed of light was different in earlier eras - and hence might be different again in future ones. In fact the speed of light might have changed at least once in the history of Earth.

And, if lightspeed can change naturally, then perhaps one day we can change the speed of light ourselves.

Tachyons:
Above: A simulation of the Cerenkov radiation emission of an object exceeding lightspeed.

Here's a different technicality that has been exploited to try and show that FTL travel could happen: Relativity doesn't actually say that nothing in the universe can be travelling faster than light - just that nothing with mass can reach (or cross) the lightspeed limit.
But maths is a very, very strange poetry, and there're a whole bunch of numbers that don't obey the usual rules, called imaginary numbers**. What if a particle were given a mass that was defined by an imaginary number - imaginary mass? Such a particle could never slow down to less than lightspeed. Physicists call these theoretical objects tachyons.

While tachyons wouldn't be much use for actually travelling FTL, they would allow a very strange kind of signalling system to be set up - an FTL signalling system that could send a message backwards in time. That can cause paradoxes of the 'kill your on grandfather' type. For that reason most physicists think that either tachyons don't exist, or they can never interact with regular matter - but that isn't an actual rule, just some physicists gut feeling.

There are even more exotic avenues we might explore to bump a ship past the lightspeed barrier. Some processes - like the 'spooky entanglement'  effect in quantum mechanics - are actually confirmed to travel at FTL speeds. But they're always surrounded by rules to prevent them being used to outrun light. Entanglement, for example, can only send quantum information, which is literally destroyed by the act of reading it back - so in effect nothing usable can be sent.

 
Above: PhD comics taks us through entanglement.

Does that mean we should give up on FTL? If you ask me... no. We may never succeed, but every time we've tried we've learnt new and amazing things about the laws of physics. Maybe, one day, we'll learn enough...

*That would be a pretty astounding and terrifying lab, as it would need tame black holes and huge amounts of negative energy.
** Not negative numbers, no that'd be too easy: These are the square roots of negative numbers.

Sunday, 17 April 2016

Starship drives, part 1: Sublight engines.

If this post appears to be spaced strangely on your screen, I apologise - I'm having some formatting troubles I can't fix  at the moment, but I promise I'm working on it!

The recent announcement of a $100,000,000 'Breakthrough Starshot' effort, to solve the problems of sending a probe to the nearest star, has prompted a lot of on-line talking about what kind of engines a bona fide starship needs. There's even a 'breakthrough conference' taking place, covering everything from stardrives to SETI, so expect a few interesting ideas to be reaching the web over the next week or so.

I just like this picture.
There have been a lot of interstellar drive ideas proposed*, going back to designs from the 1950's. So here's a pick of some of my favourites, from the 'we could actually build this with enough money and time' type to designs that make people ask 'who's been feeding this physicist drugs?**'.
Let's start with sub-lightspeed drives. These tend to be based on more realistic, near term, technology. For unmanned spacecraft that don't mind spending decades travelling the void they're a perfectly serviceable option:
 

Orion drive:

Yes, nukes can be used for better things than genocide.
In the 1950's a bunch of the engineers, who worked on America's nuclear program, developed project Orion: A plan for spaceships propelled by throwing nukes out the back one at a time and setting them off. Because.. well... why not?
Thing is, as far as we can tell, it probably would have worked. Two things closed the project down: The nuclear test ban treaty, and one important piece of technology never happening - a fallout free nuke. Without that even starting these bad boys up in orbit would have increased cancers worldwide. There're still people interested in the general idea today -  as I said, it's very possible it could have been made to work. The original engineers even built a miniature Orion that used high explosive instead of nukes:


The biggest version of the Orion engine would have been a monstrous 100,000 ton nuke spitting behemoth capable of reaching 3% of lightspeed - a slow trip to the stars, and a fairly radioactive one... but the obstacles were ones of engineering, political will, and money, not plausibility.



 
Above: A really well made video on Daedelus, from Times Infinity, via youtube. Many thanks!

The British Interplanetary Society developed this idea n the 1970s, as a cleaner update of the Orion concept. Their engine used deuterium fusion explosions, heating pellets of deuterium fuel with an electron beam until they exploded, triggering fusion in the pellet's core - a process called 'inertial confinement fusion'.
The Daedalus team weren't ever aiming to build a working starship, it was simply a theoretical exercises. But it established ICF engines as a potential interstellar drive.
Interestingly, ground based inertial confinement fusion reactors have continued to be tested and developed, becoming the first fusion reactor design to generate more energy than they used in 2015 - so this is another idea that's already gone beyond the theory stage.


Bussard Ramscoop:

Above: The starship Red Dwarf, probably the smeggiest ramscoop starship ever, and the best known. Courtesy of the BBC.
In a previous post I mentioned how, although it seems empty, the space between the stars is actually filled with a very thin soup of ionised gas and dust. That gas is mostly hydrogen, the main fuel for a fusion reactor, and in the 1960's an engineer called Robert Bussard came up with a remarkably simple idea: Build a ship that could collect and concentrate that diffuse fuel source - a ramscoop. It would have a huge electromagnetic scoop, which would funnel hydrogen into the front of he ship, concentrate it, and use it as fuel.
It's a brilliant thought, but when engineers actually ran the maths they found that the interstellar medium is too thin in our part of the galaxy for the idea to work - though in other regions of the galaxy it might be more feasible. Several variations seeking to overcome the originals problems, like the RAIR drive, have been proposed since.


Laser boosted lightsail:

Above: JAXA's lightsail, the IKAROS.
This is the idea being (tentatively) put forward by the Breakthrough Starshot initiative. Lightsails are a technology that is fairly well understood, and have already been flown in space. Both JAXA's IKAROS space craft and the Planetary Society's Lightsail - A are propelled this way.
 
The idea is very simple: Although it's to subtle to influence much here on Earth, light produces a very tiny push on things it hits. In space, where there are no other forces (like friction or wind) a large mirror surfaced sail can collect enough of this push to slowly accelerate a spacecraft. Because it's 'wind' is travelling at lightspeed the sail can (in theory) keep accelerating up to just below lightspeed itself - it's the ultimate victory of fuel efficiency over raw thrust. 


Above: The Planetary society give a run-down on their (now launched and successful) lightsail mssion.

The downside is that light sources spread out, loosing intensity and reducing their push. So, to get a lightsail up to interstellar speeds, you'd need to replace the Sun with a laser beam - laser's don't spread out nearly as much
Like any idea it has it's own problems: An interstellar sail would need to be far higher quality reflector, not to mention more heatproof, than any sail flown to date. And the best sails we might build (in the near future at least) could only carry a few tens of grams at most. That means that sending a signal back to earth will be very difficult But, that said, this is probably the furthest developed potential starship engine.


Electromagnetic accelerator: 

Above: Jupiter's magnetic field is so powerful that, if you could seee it, this is how big it would look from Earth. Courtesy of www.thunderbolts.info.
If you're prepared to build your starship as a cloud of tiny 'chipsats', each no bigger than a thumb, then it's possible to get up to interstellar speeds using only natural resources: The planet Jupiter has a gigantic magnetic field, and a chipsat carrying a small electrical charge could use Lorentz forces (forces generated between electric charges and magnetic fields) to accelerate to a few percent of lightspeed. 


Above: A chipsat, the design which is being tested in earth orbit. courtesy of wikimedia commons.
The downside of this idea is that, while it's entirely plausible in terms of physics, the radiation environment of Jupiter is hellish, and the technique will only work for USB stick sized and smaller objects - so no room for much shielding. Sending a cloud, or swarm, of such tiny vehicles would help: If the probes functions were distributed across a large enough swarm it might reach its destination with enough functioning parts left to complete its mission. But the idea still suffers from the problem of how to communicate with Earth.



Antimatter rocket:

Above: The rings of Saturn, the most abundant source of natural antimatter in our solar system. Courtesy fo NASA/JPL.
Antimatter, made famous by Star Trek as the fuel of choice for starships, is very powerful stuff: Inert by itself, it reacts with regular matter to release astounding amounts of energy. A piece weighing only grams could produce a bigger explosion than the Hiroshima bomb. Various stardrive proposals over the years have designed ways to harness the power of Antimatter. Some are essentially a supercharged project Orion, others use the heat from an ongoing antimatter reaction to vapourise propellant, producing a continuous thrust like a regular rocket.
They all run up against the same basic problem: Antimatter is fantasticallyy rare, and so hard to make that it's price is estimated to run to the trillions of dollars per gram. But that may not be as much of a showstopper as once thought, for two reasons: 
  • There are a whole class of antimatter engines that use  antimatter to enhance conventional fusion or fission reactions, and so need much smaller amounts. 
  • There are small but significant sources of naturally occurring antimatter in our solar system, which it would be perfectly possible to mine. The biggest lies in the rings of the planet saturn, but there are small sources in near-Earth space too. An 'antimatter mine' could conceivable collect enough to make some of the lower end antimatter drives reality.  
There are other ideas - like the 'Cannae drive' still being investigated by NASA - that may or may not work, and the jury is still out. I've skipped those because it's hard to tell which will lead somewhere and which won't. But, if we're ever to go beyond tiny probes like the ones proposed by Starhot, we'll have to start investigating the more exotic options sooner or later - so in the next post we'll investigate the most realistic options for travelling faster than light.... 
 

Elsewhere in the Universe:

Private space station module installed on the International Space station.

In a big step towards realising their dream of building private 'space hotels' the Bigelow Aerospace company has installed one it's infalteable BEAM habitat module - essentially a small room - on the ISS. It's expected to be inflated to full size at some point in May. A succesful test would be a huge victory for the company

 


*The consensus, right now, seems to be that the more difficult problem would be establishing a communications link acoss such a vast distance. 

** A lot of them are on drugs to start with. No, seriously, you will never find a bigger collection of substance abuse time bombs than the inside of a physics lab.